Ocular Diseases of Importance to the Refractive Surgeon





Introduction


This chapter discusses the pathogenesis and management of ocular diseases that are frequently encountered in the preoperative evaluation and course of management of the refractive surgery patient. Many of these conditions should be identified and treated preoperatively, while others are contraindications for refractive surgery. The chapter reviews these conditions, beginning with ocular surface diseases: inflammatory eyelid disease followed by conjunctivitis and keratitis, tear film abnormalities, atopic and allergic diseases, peripheral corneal ulceration, keratoconus, and corneal dystrophies and degenerations. This is followed by a brief review of those disorders, both systemic and ocular, that have been clearly associated with either myopia or hyperopia and that are of day-to-day relevance to the practicing ophthalmologist. The relationship of these conditions to keratorefractive surgical procedures will be emphasized.




Blepharitis and Meibomitis


An examination of the skin of the eyelid as part of the external ophthalmologic examination should include a search for any signs of active inflammation or infection. Acute infectious blepharitis—such as staphylococcal blepharitis, herpes simplex, or zoster virus blepharitis—represents an absolute contraindication for keratorefractive surgery as long as the infection has not been eradicated. One must probe carefully and specifically for any history of herpetic dermatoblepharitis because recurrent corneal or conjunctival disease, or associated corneal hypesthesia, are factors that would impact adversely the suitability of these patients for refractive surgical procedures ( Fig. 10.1 ).




Fig. 10.1


(A) Patient with herpes zoster dermatoblepharitis localized to the left side of the face. (B) Associated corneal subepithelial scarring is a relative contraindication for laser refractive surgery.




Chronic eyelid inflammation is frequently underestimated and could alter the visual and refractive outcome of patients undergoing corneal refractive surgery. Careful examination of the eyelid margins is therefore essential in evaluating keratorefractive surgery patients.


Anterior Blepharitis


Staphylococcal blepharitis can be manifested as acute blepharitis or, more commonly, as chronic blepharitis or blepharoconjunctivitis. In acute ulcerative blepharitis, there is evidence of erythema and ulceration of the anterior lid margin. These findings can be unilateral or bilateral. Generally, conjunctival involvement is not prominent. All corneal refractive procedures should be postponed to avoid transmitting the infection to the cornea.


The entity that general ophthalmologists confront frequently is chronic staphylococcal blepharitis; it may be associated at various degrees with meibomitis. The patients often report symptoms of burning, foreign-body sensation, and crusting of the eyelashes, especially in the morning. On examination, there is evidence of debris adhering to the eyelashes (classic sign of the fibrin collarette ) and anterior lid margin; there also may be some thickening of the lid margin itself. There may be evidence of hyperemia of palpebral and bulbar conjunctiva, and papillae involving the limbus. Phlyctenulosis can also accompany this condition as a type IV hypersensitivity reaction to microbial antigens. Chronic staphylococcal blepharitis can involve the cornea with a superficial coarse epitheliopathy and punctate corneal erosions. More serious corneal involvement, such as acute marginal infiltration and ulceration, is less common. Proper management of staphylococcal blepharitis and associated corneal conditions should increase the likelihood of successful refractive surgery.


Meibomitis and Meibomian Gland Dysfunction


Dysfunction of the meibomian glands is thought to result in a form of blepharitis that has a wide range of severity. The symptoms are burning, foreign-body sensation, and fluctuation of vision that changes with blinking. These patients often give a history of recurrent chalazion. The classic signs of meibomian gland dysfunction are inspissated meibomian glands, lipid or foam in the tear film, thickening of the lid margin, and hyperemia of the lid margin and conjunctiva. The cornea may be secondarily involved with epithelial erosion, pannus formation, peripheral neovascularization, marginal catarrhal infiltration or ulceration, or phlyctenular disease. Sebaceous gland dysfunction may accompany meibomian gland dysfunction with associated acne vulgaris, acne rosacea, and seborrheic dermatitis. Acne rosacea is a chronic condition that is characterized by facial flushes, telangiectasias, and pustules along the nose and cheeks ( Fig. 10.2 ). An eyelid hygiene regimen that includes warm compresses is valuable in keratorefractive surgery patients preoperatively but should be avoided postoperatively. A course of preoperative systemic tetracycline, doxycycline, or erythromycin also can be useful postoperatively because of the possible association of meibomian secretions and diffuse lamellar keratitis following laser in situ keratomileusis (LASIK).




Fig. 10.2


Rosacea blepharoconjunctivitis. Note extensive telangectasia of the nose.




Anterior Blepharitis


Staphylococcal blepharitis can be manifested as acute blepharitis or, more commonly, as chronic blepharitis or blepharoconjunctivitis. In acute ulcerative blepharitis, there is evidence of erythema and ulceration of the anterior lid margin. These findings can be unilateral or bilateral. Generally, conjunctival involvement is not prominent. All corneal refractive procedures should be postponed to avoid transmitting the infection to the cornea.


The entity that general ophthalmologists confront frequently is chronic staphylococcal blepharitis; it may be associated at various degrees with meibomitis. The patients often report symptoms of burning, foreign-body sensation, and crusting of the eyelashes, especially in the morning. On examination, there is evidence of debris adhering to the eyelashes (classic sign of the fibrin collarette ) and anterior lid margin; there also may be some thickening of the lid margin itself. There may be evidence of hyperemia of palpebral and bulbar conjunctiva, and papillae involving the limbus. Phlyctenulosis can also accompany this condition as a type IV hypersensitivity reaction to microbial antigens. Chronic staphylococcal blepharitis can involve the cornea with a superficial coarse epitheliopathy and punctate corneal erosions. More serious corneal involvement, such as acute marginal infiltration and ulceration, is less common. Proper management of staphylococcal blepharitis and associated corneal conditions should increase the likelihood of successful refractive surgery.




Meibomitis and Meibomian Gland Dysfunction


Dysfunction of the meibomian glands is thought to result in a form of blepharitis that has a wide range of severity. The symptoms are burning, foreign-body sensation, and fluctuation of vision that changes with blinking. These patients often give a history of recurrent chalazion. The classic signs of meibomian gland dysfunction are inspissated meibomian glands, lipid or foam in the tear film, thickening of the lid margin, and hyperemia of the lid margin and conjunctiva. The cornea may be secondarily involved with epithelial erosion, pannus formation, peripheral neovascularization, marginal catarrhal infiltration or ulceration, or phlyctenular disease. Sebaceous gland dysfunction may accompany meibomian gland dysfunction with associated acne vulgaris, acne rosacea, and seborrheic dermatitis. Acne rosacea is a chronic condition that is characterized by facial flushes, telangiectasias, and pustules along the nose and cheeks ( Fig. 10.2 ). An eyelid hygiene regimen that includes warm compresses is valuable in keratorefractive surgery patients preoperatively but should be avoided postoperatively. A course of preoperative systemic tetracycline, doxycycline, or erythromycin also can be useful postoperatively because of the possible association of meibomian secretions and diffuse lamellar keratitis following laser in situ keratomileusis (LASIK).




Fig. 10.2


Rosacea blepharoconjunctivitis. Note extensive telangectasia of the nose.




Bacterial Conjunctivitis and Keratitis


Chronic Bacterial Conjunctivitis and Keratitis


Chronic bacterial conjunctivitis, which is defined by a duration of longer than 3 weeks, is most commonly caused by infection with Staphylococcus aureus . The eyelids are often involved as well, a condition thought to be related to the toxins and lipases elaborated by this class of bacteria. This entity is discussed in full in the earlier section on blepharitis and meibomitis . Other causes of chronic bacterial conjunctivitis are the Gram-negative bacteria, such as Moraxella lacunata , Serratia marcescens , Escherichia coli , Klebsiella pneumoniae , and Proteus species. Appropriate cultures should be obtained and directed antimicrobial therapy with erythromycin and bacitracin ointments should be administered in order to minimize the morbidity of this condition.


Adult inclusion conjunctivitis is secondary to infection with Chlamydia trachomatis immunotypes D, E, F, G, H, I, J, and K and is an important cause of chronic conjunctivitis in the adult, an entity distinct from trachoma. Transmission is through contact of the eye with infected secretions. The history is often one of chronic ocular limitation and redness, which may be accompanied by mucopurulent discharge. The most helpful sign in diagnosis is a prominent lymphoid reaction, that is, conjunctival follicles that may involve the bulbar or limbal conjunctiva and preauricular lymphadenopathy. There may be micropannus formation in the cornea, superficial epitheliopathy on the superior cornea, and even subepithelial infiltrate formation. Patients with chronic follicular conjunctivitis seeking keratorefractive surgical procedures complain of chronic redness and ocular irritation with or without contact lenses. Treatment can ameliorate symptoms and increase their contact lens tolerance. It is advisable to treat these patients preoperatively with oral tetracycline 1.0 to 1.5 g daily or oral doxycycline 100 mg b.i.d for 2 weeks, or a single 1-g dose of azithromycin. If untreated, this infection can lead to persistent keratitis and/or conjunctivitis, resulting in corneal and conjunctival scarring.


Viral Conjunctivitis and Keratitis


The major etiologic agents of acute viral conjunctivitis are herpes simplex, adenovirus, and varicella zoster. There are 41 antigenically distinct serotypes of adenovirus, a nonenveloped DNA virus that is probably the most common cause of viral conjunctivitis in the adult. There are three clinical presentations of infection with adenovirus: pharyngoconjunctival fever (PCF), epidemic keratoconjunctivitis (EKC), and acute nonspecific follicular conjunctivitis (NFC). PCF is most commonly caused by adenovirus serotypes 3, 4, and 7, but it can also be caused by other serotypes. In this instance, the follicular conjunctivitis is accompanied by fever, pharyngitis, and regional lymphadenopathy. Constitutional symptoms frequently are encountered. The conjunctivitis is generally bilateral but not severe, and secondary corneal involvement is usually restricted to mild epithelial keratitis. In contrast, EKC is more serious and can have significant ocular morbidity. EKC is caused most commonly by adenovirus serotypes 8, 19, and 37. This highly contagious condition produces symptoms of watery discharge, redness, irritation, and itching. The corneal signs, which occur in 80% of patients, consist of diffuse punctate epithelial keratitis for 2 to 5 days and the formation of classic subepithelial infiltrates ( Fig. 10.3 ) as a late complication. The use of topical corticosteroids is not recommended, even for severe conjunctival or corneal involvement, because it prolongs viral shedding and may worsen the final visual outcome. A history of acute adenoviral infection should not be a contraindication for keratorefractive surgery except in some cases when chronic subepithelial infiltrates are noted.




Fig. 10.3


Classic subepithelial infiltrates that persist for several months following the initial epidemic keratoconjunctivitis episode.


Herpes simplex keratitis can accompany both primary and recurrent infections. It may range in severity from a diffuse punctate epithelial keratitis to typical dendritic keratitis. It can be associated with preauricular adenopathy, a mild follicular or papillary conjunctivitis. Recurrent ocular herpes can present as isolated conjunctivitis, epithelial and stromal keratitis, or uveitis. Dendritic epithelial keratitis is a sign of active viral replication ( Fig. 10.4 ). Punctate keratitis can accompany the conjunctivitis seen with primary herpes simplex infection or can occur without the conjunctivitis before dendrite formation or as a manifestation of drug toxicity. Geographic epithelial keratitis should be distinguished from trophic ulceration caused by chronic disease.




Fig. 10.4


Epithelial keratitis, as evidenced by rose bengal staining, is a sign of active herpes simplex viral replication.


Most keratorefractive surgeons believe that patients with past history of herpetic keratitis should not undergo corneal laser surgery because dormant viral disease may be reactivated. However, perioperative prophylactic treatment with oral 400 mg acyclovir twice daily could prevent the onset of herpetic recurrence following refractive photoablation.


The varicella zoster virus causes two clinically distinct entities: chickenpox and herpes zoster (shingles). Herpes zoster keratitis (HZK) can be associated with severe late corneal complications, such as recurrent stromal keratitis, scarring, neovascularization, lipidic infiltrates, and neurotrophic keratitis, all of which are absolute contraindications for keratorefractive surgery. When HZK during the acute phase is limited to punctate superficial keratitis and microdendrites that resolve and leave a clear and compact cornea with no corneal hypesthesia, keratorefractive surgery can be considered.


Chronic follicular conjunctivitis can occur as a toxic response secondary to infection with the poxvirus, molluscum contagiosum. A pearly white, umbilicated lesion may hide among cilia along the lid margin and elaborate toxins onto the conjunctival surface, leading to chronic follicular conjunctivitis. A superficial epitheliopathy may also be seen in addition to micropannus formation. These lesions respond to excision and cryotherapy, which should be performed before surgery. Patients should be educated about the risks of combining keratorefractive surgery with the excision of molluscum lesions.




Chronic Bacterial Conjunctivitis and Keratitis


Chronic bacterial conjunctivitis, which is defined by a duration of longer than 3 weeks, is most commonly caused by infection with Staphylococcus aureus . The eyelids are often involved as well, a condition thought to be related to the toxins and lipases elaborated by this class of bacteria. This entity is discussed in full in the earlier section on blepharitis and meibomitis . Other causes of chronic bacterial conjunctivitis are the Gram-negative bacteria, such as Moraxella lacunata , Serratia marcescens , Escherichia coli , Klebsiella pneumoniae , and Proteus species. Appropriate cultures should be obtained and directed antimicrobial therapy with erythromycin and bacitracin ointments should be administered in order to minimize the morbidity of this condition.


Adult inclusion conjunctivitis is secondary to infection with Chlamydia trachomatis immunotypes D, E, F, G, H, I, J, and K and is an important cause of chronic conjunctivitis in the adult, an entity distinct from trachoma. Transmission is through contact of the eye with infected secretions. The history is often one of chronic ocular limitation and redness, which may be accompanied by mucopurulent discharge. The most helpful sign in diagnosis is a prominent lymphoid reaction, that is, conjunctival follicles that may involve the bulbar or limbal conjunctiva and preauricular lymphadenopathy. There may be micropannus formation in the cornea, superficial epitheliopathy on the superior cornea, and even subepithelial infiltrate formation. Patients with chronic follicular conjunctivitis seeking keratorefractive surgical procedures complain of chronic redness and ocular irritation with or without contact lenses. Treatment can ameliorate symptoms and increase their contact lens tolerance. It is advisable to treat these patients preoperatively with oral tetracycline 1.0 to 1.5 g daily or oral doxycycline 100 mg b.i.d for 2 weeks, or a single 1-g dose of azithromycin. If untreated, this infection can lead to persistent keratitis and/or conjunctivitis, resulting in corneal and conjunctival scarring.




Viral Conjunctivitis and Keratitis


The major etiologic agents of acute viral conjunctivitis are herpes simplex, adenovirus, and varicella zoster. There are 41 antigenically distinct serotypes of adenovirus, a nonenveloped DNA virus that is probably the most common cause of viral conjunctivitis in the adult. There are three clinical presentations of infection with adenovirus: pharyngoconjunctival fever (PCF), epidemic keratoconjunctivitis (EKC), and acute nonspecific follicular conjunctivitis (NFC). PCF is most commonly caused by adenovirus serotypes 3, 4, and 7, but it can also be caused by other serotypes. In this instance, the follicular conjunctivitis is accompanied by fever, pharyngitis, and regional lymphadenopathy. Constitutional symptoms frequently are encountered. The conjunctivitis is generally bilateral but not severe, and secondary corneal involvement is usually restricted to mild epithelial keratitis. In contrast, EKC is more serious and can have significant ocular morbidity. EKC is caused most commonly by adenovirus serotypes 8, 19, and 37. This highly contagious condition produces symptoms of watery discharge, redness, irritation, and itching. The corneal signs, which occur in 80% of patients, consist of diffuse punctate epithelial keratitis for 2 to 5 days and the formation of classic subepithelial infiltrates ( Fig. 10.3 ) as a late complication. The use of topical corticosteroids is not recommended, even for severe conjunctival or corneal involvement, because it prolongs viral shedding and may worsen the final visual outcome. A history of acute adenoviral infection should not be a contraindication for keratorefractive surgery except in some cases when chronic subepithelial infiltrates are noted.




Fig. 10.3


Classic subepithelial infiltrates that persist for several months following the initial epidemic keratoconjunctivitis episode.


Herpes simplex keratitis can accompany both primary and recurrent infections. It may range in severity from a diffuse punctate epithelial keratitis to typical dendritic keratitis. It can be associated with preauricular adenopathy, a mild follicular or papillary conjunctivitis. Recurrent ocular herpes can present as isolated conjunctivitis, epithelial and stromal keratitis, or uveitis. Dendritic epithelial keratitis is a sign of active viral replication ( Fig. 10.4 ). Punctate keratitis can accompany the conjunctivitis seen with primary herpes simplex infection or can occur without the conjunctivitis before dendrite formation or as a manifestation of drug toxicity. Geographic epithelial keratitis should be distinguished from trophic ulceration caused by chronic disease.




Fig. 10.4


Epithelial keratitis, as evidenced by rose bengal staining, is a sign of active herpes simplex viral replication.


Most keratorefractive surgeons believe that patients with past history of herpetic keratitis should not undergo corneal laser surgery because dormant viral disease may be reactivated. However, perioperative prophylactic treatment with oral 400 mg acyclovir twice daily could prevent the onset of herpetic recurrence following refractive photoablation.


The varicella zoster virus causes two clinically distinct entities: chickenpox and herpes zoster (shingles). Herpes zoster keratitis (HZK) can be associated with severe late corneal complications, such as recurrent stromal keratitis, scarring, neovascularization, lipidic infiltrates, and neurotrophic keratitis, all of which are absolute contraindications for keratorefractive surgery. When HZK during the acute phase is limited to punctate superficial keratitis and microdendrites that resolve and leave a clear and compact cornea with no corneal hypesthesia, keratorefractive surgery can be considered.


Chronic follicular conjunctivitis can occur as a toxic response secondary to infection with the poxvirus, molluscum contagiosum. A pearly white, umbilicated lesion may hide among cilia along the lid margin and elaborate toxins onto the conjunctival surface, leading to chronic follicular conjunctivitis. A superficial epitheliopathy may also be seen in addition to micropannus formation. These lesions respond to excision and cryotherapy, which should be performed before surgery. Patients should be educated about the risks of combining keratorefractive surgery with the excision of molluscum lesions.




Tear Abnormalities and Exposure Keratitis


Tear Film Abnormalities


Because dry-eye symptoms are the most frequent complaints of patients following LASIK, it is fundamental to assess the tear film function of all candidates for this surgery. Performing a flap with a mechanical microkeratome or with a femtosecond (FS) laser cuts the corneal nerves that all penetrate into the cornea from the periphery to the center. It is well known that corneal nerves play a significant role in tear film homeostasis.


Aqueous tear deficiency may be caused by inadequate tear production or excessive tear evaporation. Many tests exist to assess tear film function. The most frequently utilized measure of tear production is the Schirmer test. In 83% of patients with dry eyes, the Schirmer test without topical anesthetic will be positive, showing a value of paper strip wetting over 5 minutes of less than 5.5 mm (vs. 15 mm or more in normal individuals). The marginal tear film strip or tear meniscus present on the lower eyelid can also be an indicator of the amount of tear produced. The height of the tear meniscus should be 0.5 to 1.0 mm. The most specific diagnostic tests for keratoconjunctivitis sicca (KCS) are the rose bengal staining and Schirmer test with topical anesthetic. The detection of increased tear lactoferrin concentration and tear osmolarity are the most sensitive indicators of dry-eye syndrome. The recovery time following refractive surgery may be prolonged in patients with dry eyes, generally because of superficial epithelial keratitis and persistent epithelial defects ( Fig. 10.5 ).




Fig. 10.5


Dry-eye syndrome. The recovery time following refractive surgery is prolonged in patients with dry eyes, generally because of superficial epithelial keratitis.


All diseases that are associated with severe tear production deficiency are contraindications for LASIK surgery. A nonexhaustive list of these diseases includes multiple congenital ocular diseases, such as Riley–Day (familial dysautonomia), anhidrotic ectodermal dysplasia, multiple endocrine neoplasia, and congenital hypoplasia or aplasia of the lacrimal gland. Idiopathic aqueous deficiency frequently develops in middle-aged women but can also occur secondary to systemic autoimmune diseases, infiltrative disorders, and neurologic conditions that affect the autonomic nervous system and thereby lacrimal gland innervation. Conditions that are characterized by infiltration of the lacrimal gland itself—such as lymphoma, amyloidosis, pulmonary fibrosis, graft-versus-host-disease, hemochromatosis, and some hematopoietic disorders—can result in replacement of normal gland tissue, thereby causing dry eyes. Disorders more likely to be encountered in the relatively healthy potential refractive surgery patient include autoimmune thyroiditis, sarcoidosis, and systemic lupus erythematosus (SLE). There are several infectious causes of dry eye, including hepatitis B and C, syphilis, trachoma, tuberculosis, and human immunodeficiency virus (HIV)–related diffuse infiltrative lymphadenopathy syndrome, in which CD+ cells infiltrate the lacrimal gland and lymphatic tissues.


Keratoconjunctivitis sicca in conjunction with xerostomia comprises Sjögren syndrome. This is characterized by focal lymphoid infiltrates in the lacrimal and salivary gland and circulating autoantibodies (ANA, SS-A, and SS-B). Primary Sjögren syndrome is characterized by the absence of associated autoimmune diseases, such as rheumatoid arthritis, progressive systemic sclerosis, primary biliary cirrhosis, dermatomyositis, and SLE.


Mucus deficiency occurs whenever the conjunctival goblet cells are affected and can result in inadequate wetting of the ocular surface. As a result, tear film stability is compromised, with a decreased tear break-up time (TBUT; less than 10 seconds’ duration between the blink and the appearance of the first dry area after instillation of 2% fluorescein solution and examination with oblique illumination using a cobalt blue filter). Diseases associated with inadequate mucus production include chemical burn, ocular cicatricial pemphigoid, Stevens–Johnson syndrome, and vitamin A deficiency.


Complete lipid deficiency is primarily seen in ectodermal dysplasia, which is a rare disease secondary to the congenital absence of meibomian glands. Defective tear film lipid secretion also is a permanent finding in conditions such as meibomitis and blepharitis. It results in meibomian gland inspissation and increased tear evaporation.


Many medications can decrease tear production; these often can be obtained over the counter and are not even considered to be medicine by patients. Antihistamines are probably most commonly taken by young patients, and they clearly reduce tear production, as do nasal decongestants, antitussives, and some analgesics that contain antimuscarinic compounds. Any agent with anticholinergic properties—such as antidepressants, antihypertensives, antiulcer medications, and some antiarrhythmics—will inhibit tear production. Some of the beta-adrenergic antagonists, specifically timolol, have been shown to decrease tear production as measured by the Schirmer test.


A careful history searching specifically for symptoms of dry eye is indicated in the evaluation of the refractive surgery patient. These symptoms include foreign-body sensation, burning, and heaviness of the eyelids. They typically are exacerbated by activities in which the frequency of blinking is reduced because of the effort required to concentrate, such as with reading. Severe dryness can manifest as photophobia, whereas minimal dryness may be asymptomatic.


Neurotrophic Keratitis


Lesions of the fifth cranial nerve from the trigeminal nucleus to the cornea may lead to interruption of the normal sensation and trophic stimulation of the cornea and result in neurotrophic ulceration. Corneal anesthesia results, leading to decreased tear production. The blink rate can also be decreased while the tear film osmolarity is increased. The trigeminal nerve provides trophic factors that are necessary for the maintenance of healthy corneal epithelium. The trophic ulceration results from abnormal repair of the corneal epithelium secondary to abnormal epithelial cell turnover and reduced reflex tearing. In addition, corneal epithelial mitosis appears to be damaged when corneal innervation is disrupted, reportedly secondary to reduction in glycolytic and respiratory cell activity. An epithelial defect with heaped-up edges is a characteristic finding ( Fig. 10.6A ). This can occur either in varicella zoster and herpetic viral infections, in which the virus travels via retrograde axoplasmic flow to the trigeminal ganglion, where it can become dormant, or in response to space-occupying lesions, such as aneurysms or tumors, which compromise trigeminal nerve function. Vascularization of the cornea can follow repeated episodes of epithelial defects ( Fig. 10.6B ). Clearly, these patients should not undergo keratorefractive surgery.




Fig. 10.6


(A) Epithelial defect with heaped-up edges in a patient with neurotrophic keratitis. (B) Vascularization of the cornea can follow repeated episodes of neurotrophic epithelial defects.




Exposure Keratopathy


Exposure keratopathy may result from a variety of causes: thyroid disease, lagophthalmos secondary to neuroparalytic disease, and cicatricial ocular diseases. Any exposed corneal epithelium quickly becomes desiccated, causing cell membrane damage and death. There is loss of corneal epithelial cells and thinning of the entire corneal epithelium ( Fig. 10.7 ).




Fig. 10.7


The inferior one-third of the cornea undergoes epithelial breakdown when there is significant lagophthalmos (A). Lateral tarsorrhaphy is used to limit the ocular surface exposure (B).






Tear Film Abnormalities


Because dry-eye symptoms are the most frequent complaints of patients following LASIK, it is fundamental to assess the tear film function of all candidates for this surgery. Performing a flap with a mechanical microkeratome or with a femtosecond (FS) laser cuts the corneal nerves that all penetrate into the cornea from the periphery to the center. It is well known that corneal nerves play a significant role in tear film homeostasis.


Aqueous tear deficiency may be caused by inadequate tear production or excessive tear evaporation. Many tests exist to assess tear film function. The most frequently utilized measure of tear production is the Schirmer test. In 83% of patients with dry eyes, the Schirmer test without topical anesthetic will be positive, showing a value of paper strip wetting over 5 minutes of less than 5.5 mm (vs. 15 mm or more in normal individuals). The marginal tear film strip or tear meniscus present on the lower eyelid can also be an indicator of the amount of tear produced. The height of the tear meniscus should be 0.5 to 1.0 mm. The most specific diagnostic tests for keratoconjunctivitis sicca (KCS) are the rose bengal staining and Schirmer test with topical anesthetic. The detection of increased tear lactoferrin concentration and tear osmolarity are the most sensitive indicators of dry-eye syndrome. The recovery time following refractive surgery may be prolonged in patients with dry eyes, generally because of superficial epithelial keratitis and persistent epithelial defects ( Fig. 10.5 ).




Fig. 10.5


Dry-eye syndrome. The recovery time following refractive surgery is prolonged in patients with dry eyes, generally because of superficial epithelial keratitis.


All diseases that are associated with severe tear production deficiency are contraindications for LASIK surgery. A nonexhaustive list of these diseases includes multiple congenital ocular diseases, such as Riley–Day (familial dysautonomia), anhidrotic ectodermal dysplasia, multiple endocrine neoplasia, and congenital hypoplasia or aplasia of the lacrimal gland. Idiopathic aqueous deficiency frequently develops in middle-aged women but can also occur secondary to systemic autoimmune diseases, infiltrative disorders, and neurologic conditions that affect the autonomic nervous system and thereby lacrimal gland innervation. Conditions that are characterized by infiltration of the lacrimal gland itself—such as lymphoma, amyloidosis, pulmonary fibrosis, graft-versus-host-disease, hemochromatosis, and some hematopoietic disorders—can result in replacement of normal gland tissue, thereby causing dry eyes. Disorders more likely to be encountered in the relatively healthy potential refractive surgery patient include autoimmune thyroiditis, sarcoidosis, and systemic lupus erythematosus (SLE). There are several infectious causes of dry eye, including hepatitis B and C, syphilis, trachoma, tuberculosis, and human immunodeficiency virus (HIV)–related diffuse infiltrative lymphadenopathy syndrome, in which CD+ cells infiltrate the lacrimal gland and lymphatic tissues.


Keratoconjunctivitis sicca in conjunction with xerostomia comprises Sjögren syndrome. This is characterized by focal lymphoid infiltrates in the lacrimal and salivary gland and circulating autoantibodies (ANA, SS-A, and SS-B). Primary Sjögren syndrome is characterized by the absence of associated autoimmune diseases, such as rheumatoid arthritis, progressive systemic sclerosis, primary biliary cirrhosis, dermatomyositis, and SLE.


Mucus deficiency occurs whenever the conjunctival goblet cells are affected and can result in inadequate wetting of the ocular surface. As a result, tear film stability is compromised, with a decreased tear break-up time (TBUT; less than 10 seconds’ duration between the blink and the appearance of the first dry area after instillation of 2% fluorescein solution and examination with oblique illumination using a cobalt blue filter). Diseases associated with inadequate mucus production include chemical burn, ocular cicatricial pemphigoid, Stevens–Johnson syndrome, and vitamin A deficiency.


Complete lipid deficiency is primarily seen in ectodermal dysplasia, which is a rare disease secondary to the congenital absence of meibomian glands. Defective tear film lipid secretion also is a permanent finding in conditions such as meibomitis and blepharitis. It results in meibomian gland inspissation and increased tear evaporation.


Many medications can decrease tear production; these often can be obtained over the counter and are not even considered to be medicine by patients. Antihistamines are probably most commonly taken by young patients, and they clearly reduce tear production, as do nasal decongestants, antitussives, and some analgesics that contain antimuscarinic compounds. Any agent with anticholinergic properties—such as antidepressants, antihypertensives, antiulcer medications, and some antiarrhythmics—will inhibit tear production. Some of the beta-adrenergic antagonists, specifically timolol, have been shown to decrease tear production as measured by the Schirmer test.


A careful history searching specifically for symptoms of dry eye is indicated in the evaluation of the refractive surgery patient. These symptoms include foreign-body sensation, burning, and heaviness of the eyelids. They typically are exacerbated by activities in which the frequency of blinking is reduced because of the effort required to concentrate, such as with reading. Severe dryness can manifest as photophobia, whereas minimal dryness may be asymptomatic.




Neurotrophic Keratitis


Lesions of the fifth cranial nerve from the trigeminal nucleus to the cornea may lead to interruption of the normal sensation and trophic stimulation of the cornea and result in neurotrophic ulceration. Corneal anesthesia results, leading to decreased tear production. The blink rate can also be decreased while the tear film osmolarity is increased. The trigeminal nerve provides trophic factors that are necessary for the maintenance of healthy corneal epithelium. The trophic ulceration results from abnormal repair of the corneal epithelium secondary to abnormal epithelial cell turnover and reduced reflex tearing. In addition, corneal epithelial mitosis appears to be damaged when corneal innervation is disrupted, reportedly secondary to reduction in glycolytic and respiratory cell activity. An epithelial defect with heaped-up edges is a characteristic finding ( Fig. 10.6A ). This can occur either in varicella zoster and herpetic viral infections, in which the virus travels via retrograde axoplasmic flow to the trigeminal ganglion, where it can become dormant, or in response to space-occupying lesions, such as aneurysms or tumors, which compromise trigeminal nerve function. Vascularization of the cornea can follow repeated episodes of epithelial defects ( Fig. 10.6B ). Clearly, these patients should not undergo keratorefractive surgery.




Fig. 10.6


(A) Epithelial defect with heaped-up edges in a patient with neurotrophic keratitis. (B) Vascularization of the cornea can follow repeated episodes of neurotrophic epithelial defects.






Exposure Keratopathy


Exposure keratopathy may result from a variety of causes: thyroid disease, lagophthalmos secondary to neuroparalytic disease, and cicatricial ocular diseases. Any exposed corneal epithelium quickly becomes desiccated, causing cell membrane damage and death. There is loss of corneal epithelial cells and thinning of the entire corneal epithelium ( Fig. 10.7 ).




Fig. 10.7


The inferior one-third of the cornea undergoes epithelial breakdown when there is significant lagophthalmos (A). Lateral tarsorrhaphy is used to limit the ocular surface exposure (B).






Immunologic Diseases of the Conjunctiva and Cornea


Ocular Allergic Diseases


Allergic Conjunctivitis


The most common ocular allergic disease is allergic conjunctivitis, the result of a type I hypersensitivity response to seasonal or perennial allergens such as pollen, molds, mite dust, and cat danders. The allergens crosslink immunoglobulin E (IgE) molecules fixated on mast cells, which then degranulate and release vasoactive amines such as histamine, eosinophil chemotactic factor (ECF), and platelet-activating factor (PAF); eosinophil granule major basic protein (EMBP); and prostaglandin D2. Histamine results in conjunctival hyperemia, via H2 receptors, and itching, via H1 receptors, quite characteristic of this condition. Ocular signs include various degrees of conjunctival redness, chemosis, and tarsal conjunctival papillae. Patients with seasonal or perennial allergic conjunctivitis are good candidates for keratorefractive surgery, but they should be instructed to refrain from eye rubbing during the early postoperative period following LASIK.


Atopic Keratoconjunctivitis


Atopic keratoconjunctivitis (AKC) is the most severe ocular allergic disease. It involves young adults and is associated with atopic dermatitis. Other atopic manifestations, including bronchial asthma and hay fever, can be present. Itching, burning, photophobia, and blurred vision are frequent complaints. This may be one reason to discourage atopic patients from undergoing keratorefractive surgery. Atopic blepharitis is typically characterized by tylosis, a thickening of the eyelid margins, and eyelid swelling associated with a scaly, indurated, and wrinkled appearance of the periocular skin ( Fig. 10.8A ). Marginal blepharitis caused by staphylococcal infection, maceration of the canthal skin, and excoriation of the periorbital region are common and are exacerbated by scratching ( Fig. 10.8B ). A hallmark of AKC is chronic ocular surface inflammation. The conjunctiva becomes hyperemic and edematous. Tarsal conjunctival papillary hypertrophy is a common finding. This chronic condition can result in conjunctival cicatrization and symblepharon.




Fig. 10.8


(A) Atopic keratoconjunctivitis associated with atopic dermatitits of the eyelids. (B) Mild atopic disease. Maceration of the canthal skin and excoriation of the periorbital region is exacerbated by scratching.




Corneal involvement may include punctuate erosions and keratitis. Patients with AKC are at risk for developing infectious and noninfectious corneal ulcers. Peripheral micropannus is common in chronic AKC. Neovascularization and scarring can extend to the central cornea. A subcapsular anterior cataract and posterior subcapsular opacity can develop, mainly due to long-term corticosteroid use. As a result, many patients with atopic disease may seek refractive surgery procedures. A strong relation between atopy and keratoconus has been described; 25% of patients with atopic dermatitis and 16% of patients with AKC demonstrate classic signs of keratoconus. Accordingly, atopic patients are not good candidates for refractive surgery.


Giant Papillary Conjunctivitis


Because many refractive surgery prospective patients are long-term contact lens wearers, a thorough examination of the palpebral conjunctiva is indicated. Giant papillary conjunctivitis (GPC) has been found in conjunction with contact lens wear, protruding suture material, presence of irregularities in the ocular surface, and the use of ocular prostheses ( Fig. 10.9 ). Investigators have estimated that between 1% and 5% of wearers of rigid gas permeable contact lenses and between 10% and 15% of those wearing hydrogel contact lenses have GPC. The origin of GPC appears to be a combination of mechanical irritation and allergic factors. It has been postulated that mechanical trauma induced by contact lenses on the conjunctiva, intolerance to accumulated lens deposits, hypoxia, and bacterial colonization of the lenses are all involved in the pathogenesis of this condition. Keratorefractive surgery is thus a viable alternative for many patients with GPC.




Fig. 10.9


Giant papillary conjunctivitis of the upper palpebral conjunctiva.


GPC is characterized by the presence of abnormally large papillae on the upper tarsal conjunctiva, conjunctival hyperemia and thickening, excess mucus secretion, foreign-body sensation, or pruritus and intolerance to contact lens wearing.


Ocular Mucous Membrane Pemphigoid


The ocular surface may be the site of autoimmune mucocutaneous blistering diseases, such as ocular mucous membrane pemphigoid. It is important to diagnose these conditions in order to avoid exacerbation of the disease process following ocular surgery.


Mucous membrane pemphigoid, previously known as cicatricial pemphigoid, is an immune-mediated disease characterized by autoantibodies to the basement membrane zone at the epithelial–subepithelial junction of mucous membranes and occasionally skin. Mucosal surfaces affected include eyes, nose, mouth, respiratory tract, and gastrointestinal tract. Ocular mucous membrane pemphigoid is seen as a progressive cicatrizing conjunctivitis, which, if left untreated, results in scarring and obliteration of the conjunctival fornices (symblepharon). Additionally, the goblet cells are affected and lacrimal gland ducts sclerosed, resulting in both mucus and aqueous tear deficiency. These each can cause devastating effects on the cornea, which may be further compromised by trichiatic lashes, exposure, and secondary conjunctival cicatrization.


Connective Tissue Disease and Systemic Vasculitides


Systemic rheumatologic disease can be manifest initially in the eye, which makes the ophthalmologist very important in the evaluation of these patients. The systemic vasculitis most likely to involve the eye is rheumatoid arthritis. In this condition, the diagnosis is usually made before the ocular manifestations occur, of which keratoconjunctivitis sicca is the most common. Sjögren syndrome in 24% to 31% of rheumatoid arthritis patients has been demonstrated by lacrimal gland biopsy. This syndrome can cause corneal disease, which may be a mild epitheliopathy or may progress to furrowing, peripheral ulcerative keratitis, keratolysis, and perforation ( Fig. 10.10 ). Some 15% of patients with rheumatoid arthritis show corneal involvement. It is very often accompanied by episcleritis and/or scleritis, which can be necrotizing with or without inflammation (scleromalacia perforans). One of the severe manifestations is sclerosing keratitis, in which peripheral stromal opacification progresses accompanied by stromal vascularization and associated scleritis. The proposed etiology of these findings is type III (immune complex) hypersensitivity; circulating immune complexes have been isolated from the serum and synovial fluid of these patients. With appropriate treatment, including immunosuppressive therapy, the disease process may be halted. Significant astigmatism and surface irregularity may bring the patient to the attention of the refractive surgeon. Keratorefractive surgery may worsen the ocular condition and is contraindicated.




Fig. 10.10


Rheumatoid melting of the corneal periphery.


Keratorefractive surgery also is contraindicated in SLE. In particular, LASIK worsens the dry-eye syndrome that is a consistent feature of SLE and that can be associated with a superficial epitheliopathy and, rarely, peripheral ulcerative keratitis.


Systemic vasculitides, which can potentially be associated with corneal complications, also are contraindications for keratorefractive surgery. Corneal thinning may rarely occur centrally, requiring patch grafting. The corneal manifestations of polyarteritis nodosa tend to be severe, consisting of peripheral ulceration that can accelerate to involve the entire limbal region. There is loss of tissue secondary to the enzymes produced by the phagocytic white blood cells attracted to the region by immune complex formation. Peripheral ulcerative keratitis can also be seen in Wegener granulomatosis, even as the presenting sign of disease. The lesion starts at one region of the limbus and can progress to involve the entire limbus, even moving centrally. Relapsing polychondritis is characterized by inflammation of the cartilage of the ears, nose, and trachea. This serious disorder can be accompanied by peripheral ulcerative keratitis thought to be secondary to the formation of antibodies against type II collagen. Progressive systemic sclerosis can have the following ocular manifestations: keratoconjunctivitis sicca, foreshortening of the inferior fornix, and blepharophimosis.




Ocular Allergic Diseases


Allergic Conjunctivitis


The most common ocular allergic disease is allergic conjunctivitis, the result of a type I hypersensitivity response to seasonal or perennial allergens such as pollen, molds, mite dust, and cat danders. The allergens crosslink immunoglobulin E (IgE) molecules fixated on mast cells, which then degranulate and release vasoactive amines such as histamine, eosinophil chemotactic factor (ECF), and platelet-activating factor (PAF); eosinophil granule major basic protein (EMBP); and prostaglandin D2. Histamine results in conjunctival hyperemia, via H2 receptors, and itching, via H1 receptors, quite characteristic of this condition. Ocular signs include various degrees of conjunctival redness, chemosis, and tarsal conjunctival papillae. Patients with seasonal or perennial allergic conjunctivitis are good candidates for keratorefractive surgery, but they should be instructed to refrain from eye rubbing during the early postoperative period following LASIK.


Atopic Keratoconjunctivitis


Atopic keratoconjunctivitis (AKC) is the most severe ocular allergic disease. It involves young adults and is associated with atopic dermatitis. Other atopic manifestations, including bronchial asthma and hay fever, can be present. Itching, burning, photophobia, and blurred vision are frequent complaints. This may be one reason to discourage atopic patients from undergoing keratorefractive surgery. Atopic blepharitis is typically characterized by tylosis, a thickening of the eyelid margins, and eyelid swelling associated with a scaly, indurated, and wrinkled appearance of the periocular skin ( Fig. 10.8A ). Marginal blepharitis caused by staphylococcal infection, maceration of the canthal skin, and excoriation of the periorbital region are common and are exacerbated by scratching ( Fig. 10.8B ). A hallmark of AKC is chronic ocular surface inflammation. The conjunctiva becomes hyperemic and edematous. Tarsal conjunctival papillary hypertrophy is a common finding. This chronic condition can result in conjunctival cicatrization and symblepharon.




Fig. 10.8


(A) Atopic keratoconjunctivitis associated with atopic dermatitits of the eyelids. (B) Mild atopic disease. Maceration of the canthal skin and excoriation of the periorbital region is exacerbated by scratching.




Corneal involvement may include punctuate erosions and keratitis. Patients with AKC are at risk for developing infectious and noninfectious corneal ulcers. Peripheral micropannus is common in chronic AKC. Neovascularization and scarring can extend to the central cornea. A subcapsular anterior cataract and posterior subcapsular opacity can develop, mainly due to long-term corticosteroid use. As a result, many patients with atopic disease may seek refractive surgery procedures. A strong relation between atopy and keratoconus has been described; 25% of patients with atopic dermatitis and 16% of patients with AKC demonstrate classic signs of keratoconus. Accordingly, atopic patients are not good candidates for refractive surgery.


Giant Papillary Conjunctivitis


Because many refractive surgery prospective patients are long-term contact lens wearers, a thorough examination of the palpebral conjunctiva is indicated. Giant papillary conjunctivitis (GPC) has been found in conjunction with contact lens wear, protruding suture material, presence of irregularities in the ocular surface, and the use of ocular prostheses ( Fig. 10.9 ). Investigators have estimated that between 1% and 5% of wearers of rigid gas permeable contact lenses and between 10% and 15% of those wearing hydrogel contact lenses have GPC. The origin of GPC appears to be a combination of mechanical irritation and allergic factors. It has been postulated that mechanical trauma induced by contact lenses on the conjunctiva, intolerance to accumulated lens deposits, hypoxia, and bacterial colonization of the lenses are all involved in the pathogenesis of this condition. Keratorefractive surgery is thus a viable alternative for many patients with GPC.




Fig. 10.9


Giant papillary conjunctivitis of the upper palpebral conjunctiva.


GPC is characterized by the presence of abnormally large papillae on the upper tarsal conjunctiva, conjunctival hyperemia and thickening, excess mucus secretion, foreign-body sensation, or pruritus and intolerance to contact lens wearing.




Allergic Conjunctivitis


The most common ocular allergic disease is allergic conjunctivitis, the result of a type I hypersensitivity response to seasonal or perennial allergens such as pollen, molds, mite dust, and cat danders. The allergens crosslink immunoglobulin E (IgE) molecules fixated on mast cells, which then degranulate and release vasoactive amines such as histamine, eosinophil chemotactic factor (ECF), and platelet-activating factor (PAF); eosinophil granule major basic protein (EMBP); and prostaglandin D2. Histamine results in conjunctival hyperemia, via H2 receptors, and itching, via H1 receptors, quite characteristic of this condition. Ocular signs include various degrees of conjunctival redness, chemosis, and tarsal conjunctival papillae. Patients with seasonal or perennial allergic conjunctivitis are good candidates for keratorefractive surgery, but they should be instructed to refrain from eye rubbing during the early postoperative period following LASIK.




Atopic Keratoconjunctivitis


Atopic keratoconjunctivitis (AKC) is the most severe ocular allergic disease. It involves young adults and is associated with atopic dermatitis. Other atopic manifestations, including bronchial asthma and hay fever, can be present. Itching, burning, photophobia, and blurred vision are frequent complaints. This may be one reason to discourage atopic patients from undergoing keratorefractive surgery. Atopic blepharitis is typically characterized by tylosis, a thickening of the eyelid margins, and eyelid swelling associated with a scaly, indurated, and wrinkled appearance of the periocular skin ( Fig. 10.8A ). Marginal blepharitis caused by staphylococcal infection, maceration of the canthal skin, and excoriation of the periorbital region are common and are exacerbated by scratching ( Fig. 10.8B ). A hallmark of AKC is chronic ocular surface inflammation. The conjunctiva becomes hyperemic and edematous. Tarsal conjunctival papillary hypertrophy is a common finding. This chronic condition can result in conjunctival cicatrization and symblepharon.




Fig. 10.8


(A) Atopic keratoconjunctivitis associated with atopic dermatitits of the eyelids. (B) Mild atopic disease. Maceration of the canthal skin and excoriation of the periorbital region is exacerbated by scratching.




Corneal involvement may include punctuate erosions and keratitis. Patients with AKC are at risk for developing infectious and noninfectious corneal ulcers. Peripheral micropannus is common in chronic AKC. Neovascularization and scarring can extend to the central cornea. A subcapsular anterior cataract and posterior subcapsular opacity can develop, mainly due to long-term corticosteroid use. As a result, many patients with atopic disease may seek refractive surgery procedures. A strong relation between atopy and keratoconus has been described; 25% of patients with atopic dermatitis and 16% of patients with AKC demonstrate classic signs of keratoconus. Accordingly, atopic patients are not good candidates for refractive surgery.




Giant Papillary Conjunctivitis


Because many refractive surgery prospective patients are long-term contact lens wearers, a thorough examination of the palpebral conjunctiva is indicated. Giant papillary conjunctivitis (GPC) has been found in conjunction with contact lens wear, protruding suture material, presence of irregularities in the ocular surface, and the use of ocular prostheses ( Fig. 10.9 ). Investigators have estimated that between 1% and 5% of wearers of rigid gas permeable contact lenses and between 10% and 15% of those wearing hydrogel contact lenses have GPC. The origin of GPC appears to be a combination of mechanical irritation and allergic factors. It has been postulated that mechanical trauma induced by contact lenses on the conjunctiva, intolerance to accumulated lens deposits, hypoxia, and bacterial colonization of the lenses are all involved in the pathogenesis of this condition. Keratorefractive surgery is thus a viable alternative for many patients with GPC.




Fig. 10.9


Giant papillary conjunctivitis of the upper palpebral conjunctiva.


GPC is characterized by the presence of abnormally large papillae on the upper tarsal conjunctiva, conjunctival hyperemia and thickening, excess mucus secretion, foreign-body sensation, or pruritus and intolerance to contact lens wearing.




Ocular Mucous Membrane Pemphigoid


The ocular surface may be the site of autoimmune mucocutaneous blistering diseases, such as ocular mucous membrane pemphigoid. It is important to diagnose these conditions in order to avoid exacerbation of the disease process following ocular surgery.


Mucous membrane pemphigoid, previously known as cicatricial pemphigoid, is an immune-mediated disease characterized by autoantibodies to the basement membrane zone at the epithelial–subepithelial junction of mucous membranes and occasionally skin. Mucosal surfaces affected include eyes, nose, mouth, respiratory tract, and gastrointestinal tract. Ocular mucous membrane pemphigoid is seen as a progressive cicatrizing conjunctivitis, which, if left untreated, results in scarring and obliteration of the conjunctival fornices (symblepharon). Additionally, the goblet cells are affected and lacrimal gland ducts sclerosed, resulting in both mucus and aqueous tear deficiency. These each can cause devastating effects on the cornea, which may be further compromised by trichiatic lashes, exposure, and secondary conjunctival cicatrization.




Connective Tissue Disease and Systemic Vasculitides


Systemic rheumatologic disease can be manifest initially in the eye, which makes the ophthalmologist very important in the evaluation of these patients. The systemic vasculitis most likely to involve the eye is rheumatoid arthritis. In this condition, the diagnosis is usually made before the ocular manifestations occur, of which keratoconjunctivitis sicca is the most common. Sjögren syndrome in 24% to 31% of rheumatoid arthritis patients has been demonstrated by lacrimal gland biopsy. This syndrome can cause corneal disease, which may be a mild epitheliopathy or may progress to furrowing, peripheral ulcerative keratitis, keratolysis, and perforation ( Fig. 10.10 ). Some 15% of patients with rheumatoid arthritis show corneal involvement. It is very often accompanied by episcleritis and/or scleritis, which can be necrotizing with or without inflammation (scleromalacia perforans). One of the severe manifestations is sclerosing keratitis, in which peripheral stromal opacification progresses accompanied by stromal vascularization and associated scleritis. The proposed etiology of these findings is type III (immune complex) hypersensitivity; circulating immune complexes have been isolated from the serum and synovial fluid of these patients. With appropriate treatment, including immunosuppressive therapy, the disease process may be halted. Significant astigmatism and surface irregularity may bring the patient to the attention of the refractive surgeon. Keratorefractive surgery may worsen the ocular condition and is contraindicated.




Fig. 10.10


Rheumatoid melting of the corneal periphery.


Keratorefractive surgery also is contraindicated in SLE. In particular, LASIK worsens the dry-eye syndrome that is a consistent feature of SLE and that can be associated with a superficial epitheliopathy and, rarely, peripheral ulcerative keratitis.


Systemic vasculitides, which can potentially be associated with corneal complications, also are contraindications for keratorefractive surgery. Corneal thinning may rarely occur centrally, requiring patch grafting. The corneal manifestations of polyarteritis nodosa tend to be severe, consisting of peripheral ulceration that can accelerate to involve the entire limbal region. There is loss of tissue secondary to the enzymes produced by the phagocytic white blood cells attracted to the region by immune complex formation. Peripheral ulcerative keratitis can also be seen in Wegener granulomatosis, even as the presenting sign of disease. The lesion starts at one region of the limbus and can progress to involve the entire limbus, even moving centrally. Relapsing polychondritis is characterized by inflammation of the cartilage of the ears, nose, and trachea. This serious disorder can be accompanied by peripheral ulcerative keratitis thought to be secondary to the formation of antibodies against type II collagen. Progressive systemic sclerosis can have the following ocular manifestations: keratoconjunctivitis sicca, foreshortening of the inferior fornix, and blepharophimosis.




Developmental Abnormalities of the Cornea


Although rarely encountered routinely, developmental corneal abnormalities are important to recognize in the newborn or during early childhood. Recognition can inform the clinician concerning the natural history of the condition, indicate the necessary medical or surgical treatment, and alert the physician to the various ocular and systemic complications that may accompany the disorder and warrant additional investigation. In addition, accurate identification and analysis of the disease help parents deal with the prognosis and guide them in seeking the proper genetic counseling when indicated.


Anomalies of corneal size include megalocornea and microcornea, whereas anomalies of corneal shape include oval cornea (horizontal or vertical cornea), sclerocornea, posterior keratoconus, and keratoglobus.


Megalocornea


The normal newborn cornea measures approximately 10 mm horizontally, reaching the adult size by 2 years of age when the horizontal diameter is approximately 12 mm. The measured horizontal diameter usually exceeds the vertical diameter by 1 mm. Megalocornea refers to an enlarged cornea with a horizontal diameter greater than or equal to 13 mm. It is a nonprogressive, bilateral, and symmetrical condition. Because of its predominant transmission as an X-linked recessive trait, 90% of cases are found in the male population. Clinically, it is an enlarged but clear cornea of normal thickness and curvature, with normal endothelial cell density. The steeper cornea usually results in a myopic eye with with-the-rule astigmatism. Ocular associated findings include phacodonesis, iridodonesis, and ectopia lentis owing to zonular stretching caused by the widened ciliary ring and enlarged anterior segment (anterior megalophthalmos). The differential diagnosis is mainly buphthalmos from congenital glaucoma.


Microcornea


Microcornea is defined as a cornea having a horizontal diameter less than or equal to 10 mm in an otherwise normal-sized globe. Not to be confused with microphthalmos (the entire eye is small and disorganized) or nanophthalmos (the entire eye is small but otherwise normal), it is a nonprogressive condition and may be unilateral or bilateral. The small cornea is clear, with normal thickness, but usually flatter than the normal cornea, giving rise to hyperopia, although any refractive error can exist depending on axial length. Unlike megalocornea, microcornea is rarely an isolated condition and can have many ocular and systemic anomalies associated with it. The crowded anterior chamber contributes to the development of glaucoma.


Oval Cornea


Although the normal cornea is horizontally oval, the term horizontal oval cornea is reserved for extreme cases of this proportion and indicates some degree of sclerocornea. Vertical oval cornea exists when the vertical diameter exceeds the horizontal diameter. When associated with other ocular abnormalities, oval cornea can present some ametropia.


Sclerocornea


In sclerocornea, the cornea is flat with a curvature commonly ranging from 30 to 35 diopters (D) (in some cases, as low as 20 D). This ocular abnormality is usually associated with cornea plana and hyperopia ( Fig. 10.11 ). It is a nonprogressive, bilateral, and asymmetric condition. Most cases are sporadic; the autosomal-recessive cases exhibit a more severe manifestation of total sclerocornea and autosomal-dominant cases present with a more benign form of peripheral sclerocornea. Similarly, autosomal-dominant transmission in cornea plana is related to less corneal flattening, compared to autosomal-recessive transmission.




Fig. 10.11


(A) A 22-year-old woman with sclerocornea and cornea plana. (B) Corneal topography showing severe corneal flattening under 30 D in both eyes. (C) Ultrasound biomicroscopy showing shallowing of the anterior chamber with 0.995 mm of depth.


Posterior Keratoconus


Posterior keratoconus is considered to be a rare developmental condition that bears no relationship to anterior keratoconus. It is usually unilateral, nonprogressive, noninflammatory, and it rarely affects visual acuity. However, it may cause a myopic astigmatism that should be corrected with spectacles to prevent amblyopia. The condition may occur in a generalized or circumscribed form. Generalized posterior keratoconus exists when the entire posterior corneal surface has an increased curvature with a shorter radius of curvature and a normal anterior corneal surface. This pattern of posterior keratoconus is less common. The more common circumscribed form of posterior keratoconus is characterized by one or more localized, crater-like lesions in the central or eccentric posterior cornea. Corneal clouding with variable corneal thinning is frequently encountered overlying the posterior corneal defect. The majority of cases are sporadic. It is also thought to be a mild variant of Peters anomaly, thereby implying intrauterine inflammation or some other anterior segment dysgenesis as an etiologic factor.


Keratoglobus


Keratoglobus is more frequently present at birth and is considered to be a developmental anomaly. It is a bilateral, noninflammatory, ectatic disorder in which the entire cornea becomes thinned (to approximately one-third to one-fifth of the normal corneal thickness) and takes on a globular shape, with keratometry readings as high as 50 to 60 D, generating high myopia. The anterior chamber is very deep with otherwise normal anterior segment structures and a normal-sized globe ( Fig. 10.12 ). Corneal hydrops can occur from spontaneous breaks in the Desçemet membrane. Corneal rupture is a potential complication and may occur spontaneously or following minimal trauma. The differential diagnosis includes keratoconus, pellucid marginal degeneration, megalocornea, and buphthalmos. Treatment is centered on correcting the accompanying high myopia with spectacles to prevent amblyopia. Lamellar/penetrating keratoplasty and epikeratoplasty are technically challenging procedures in this setting and should be attempted only when absolutely necessary.




Fig. 10.12


Side view of keratoglobus revealing the globular shape of the cornea and deep anterior chamber.

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Oct 10, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on Ocular Diseases of Importance to the Refractive Surgeon
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