- •
Wavefront aberrometry is the measurement of the wavefront that emerges from an eye as a result of light reflecting from a focused light spot on the fovea. Application of Zernike polynomials allows characterization of a reconstructed estimated wavefront.
- •
Videokeratography is the computerized measurement of variation in curvature and dioptric power across the corneal surface that is typically based on the corneal reflection of the Placido pattern.
- •
Pachymetry is the measurement of corneal thickness.
Key Features
- •
Preoperative evaluation for refractive surgery should involve documentation of refractive stability, review of both systemic and ophthalmic contraindications, manifest refraction, cycloplegic refraction, pupil measurements, pachymetry, wavefront analysis, corneal topography, slit-lamp examination, and dilated fundus examination.
- •
Care should be taken to identify patients at risk for postoperative corneal ectasia.
- •
Patient counseling is an important part of preoperative testing before refractive surgery.
Introduction
Comprehensive preoperative evaluation of patients considering refractive surgery is often preceded by a brief screening examination to eliminate patients who are clearly not candidates for refractive surgery. Although it can help identify patients who would not benefit from refractive surgery, it also helps the surgeon plan the operative technique and further recommendations for a patient.
General Considerations
Age
Laser corrective surgery is approved for those over 18 years of age who have had a stable refractive error over the previous 1–2 years. Although laser corrective surgery may be indicated in younger patients who are otherwise intolerant of traditional therapy, care must be taken because refractive error at this age often is unstable. A stable refractive error generally is defined as a ±0.5 diopter (D) change in refraction over the past 1–2 years. Every patient presenting to a screening examination should be asked to discontinue all contact lens wear (1 week for soft nontoric lenses, 2 weeks for toric lenses, and at least 3 weeks for rigid lenses) and asked to bring their previous spectacles for assessment of refractive stability.
Degree of Correction
Although different laser platforms are approved for various thresholds of refractive correction, most surgeons opt to limit myopic correction to −10 D and hyperopic and astigmatic correction to +4 D to prevent postoperative corneal ectasia and haze and to avoid the unpredictability of correction at these higher refractions.
Patient Expectations
Perhaps the most important aspect of refractive surgery is appropriate counseling to set realistic expectations. Patients who are risk averse, who expect better vision than with glasses or contacts, or who have unrealistic expectations are likely not good candidates for refractive surgery. Appropriate counseling becomes even more important in patients between 40 and 50 years of age as presbyopia sets in and monovision may need to be a consideration. Another aspect to consider is a patient’s occupation and hobbies. Those who perform activities that may put them at risk for flap dislocations should not be offered laser-assisted in situ keratomileusis (LASIK).
Systemic Contraindications to Keratorefractive Surgery
A thorough medical history should be obtained from all patients considering refractive surgery. In particular, patients with a history of diabetes mellitus, pregnancy, autoimmune disease, collagen vascular disorders, thyroid disease, or abnormal wound healing may be at risk for poor outcomes postoperatively and should be identified before proceeding with surgery ( Box 3.2.1 ).
Immunological Disease
- •
Autoimmune
- •
Collagen vascular
- •
Immunodeficiency
Pregnancy or Nursing (not absolute contraindication)
Abnormal Wound Healing
- •
Keloids (contraindicated for PRK only)
- •
Abnormal scars
Diabetes Mellitus (if corneal sensation is not intact)
Interference from Systemic Medications
- •
Isotretinoin
- •
Amiodarone hydrochloride
Diabetes Mellitus
Uncontrolled diabetes not only leads to unstable refractions but also causes poor wound healing, persistent epithelial defects, and neurotrophic changes after laser surgery. A high risk of complications has been reported in the literature, including poor healing, worse refractive outcomes, and epithelial ingrowth. Other studies did not show a significant complication rate in diabetes patients with well-controlled blood glucose. Therefore it is recommend that refractive surgery be performed only in diabetes patients with tight blood glucose control (Hb A 1c <7.9%) over the previous year, normal corneal sensation, and no signs of diabetic retinopathy.
Pregnancy and Lactation
Refractive surgery during pregnancy is contraindicated because pregnancy can lead to transient changes in refractive error and cornea curvature and changes in tear quality. In addition, there are risks of fetal or infantile exposure to topical and systemic medications. There are multiple case reports of pregnancy-induced keratectasia following LASIK; it is important to counsel young female patients regarding this possibility. Sharif reported a greater risk for corneal haze and myopic regression in women who became pregnant within 5 months of photorefractive keratectomy (PRK). Starr also reported the case of a pregnant patient in whom overcorrection was induced and haze formation occurred. It is recommended that patients wait 3 to 6 months after pregnancy and cessation of lactation before undergoing refractive surgery.
Autoimmune Diseases
Uncontrolled collagen vascular disease is an absolute contraindication to undergoing laser refractive surgery, as it can lead to corneal melts and irregular healing. Patients with Sjögren’s disease and thyroid-associated eye disease are predisposed to tear film irregularities and dry eyes. Although most surgeons would agree that PRK will lead to poor healing in these patients, the debate is still ongoing whether patients with inactive or well-controlled collagen vascular disease can safely undergo LASIK. Multiple studies have shown no additional complications with LASIK in patients with inactive disease and a normal ocular surface. Case reports of severe complications also exist, however. Appropriate counseling must be done in any patient with a collagen vascular disease interested in pursuing laser refractive surgery.
Dermatological Keloid
Although dermatological keloid is listed as a precaution for LASIK and PRK, several studies have demonstrated good results without any additional complications after both PRK and LASIK. Most surgeons at this point do not consider this a concern with laser surgery.
Human Immunodeficiency Virus
A theoretical risk exists of transmission of human immunodeficiency virus (HIV) through laser plumes, but no reported cases have occurred to date that have shown such transmission. Nevertheless, adequate precautions must be taken while operating on patients with HIV. Hagen et al. used culture plates, and an excimer laser was used to ablate infected tissue. None was culture positive. These patients also have a theoretical higher risk of infectious complications. Therefore only those on appropriate therapy and with adequate CD4 cell counts should be considered for refractive surgery.
Medications
Multiple medications delay or inhibit wound healing after laser refractive surgery. Of these, amiodarone and isotretinoin need to be carefully considered before refractive surgery. Amiodarone is used to treat arrhythmias and can lead to multiple ocular side effects, including optic neuropathy, corneal and lenticular deposits, and halos around lights. Although there are reports of no increased complications, patients must be appropriately screened. Isotretinoin is used to treat acne and can lead to dry eyes, blepharoconjunctivitis, and photosensitivity, all of which can complicate recovery. Sumatriptan was previously considered to delay wound healing. However, recent reports do not show any significant adverse effects. Various other systemic medications can exacerbate dry eye symptoms, and therefore patients on these should be appropriately counseled and treated.
Ophthalmic Diseases
Multiple ophthalmic conditions necessitate special attention. Of note are disorders that lead to tear film deficiency, corneal dystrophies and ectasias, glaucoma, and other retinal and intraocular disorders ( Table 3.2.1 ).
| Relative Contraindications | Absolute Contraindications | |
|---|---|---|
| Ocular surface disease | Mild dry eye Lid disorders that affect the tear layer | Severe dry eye
Neurotrophic keratitis |
| Disorders that may be exacerbated by photorefractive keratectomy | Herpes zoster ophthalmicus/herpetic keratitis (if inactive for >1 year—unproved) | Herpes zoster ophthalmicus/herpetic keratitis (especially if active during the previous 6 months) Uncontrolled glaucoma |
| Abnormalities of corneal shape | Shape changes induced by contact lens Mild irregular astigmatism | Corneal ectasia
High, irregular astigmatism |
| Other ophthalmic disorders | Posterior corneal dystrophies | Uveitis Diabetic retinopathy Progressive retinal disease |
Corneal Dystrophy
Any form of anterior corneal dystrophy is a contraindication for excimer laser use because this may lead to increased deposits. Patients with epithelial basement membrane disease may benefit from PRK, as this can treat both the refractive error and the underlying pathology. LASIK is contraindicated in patients with Fuchs’ dystrophy because of the risk of corneal decompensation and potential for overestimation of corneal thickness in subclinical edema. There are case reports of safe performance of LASIK and PRK for posterior polymorphous corneal dystrophy. Family history should be especially noted to ensure that any subtle changes of familial dystrophies are not missed.
Corneal Curvature
Corneal curvature must be carefully examined because corneal ectasia after refractive surgery is a feared complication that can lead to severe loss of vision. Any signs or symptoms of corneal ectasia like keratoconus or pellucid marginal degeneration are a contraindication for laser refractive surgery. There are multiple criteria to evaluate and identify eyes at risk for postrefractive ectasias, but the key factors include abnormal topography, percent of tissue altered, thin corneal thickness, thin residual stromal bed, young age, and high myopia. Key elements of history such as rapidly changing refraction or a family history of ectasia can be helpful. Imaging using Placido-slit topography or Scheimpflug tomography can often identify suspicious changes in the anterior and posterior cornea.
Ocular Surface Disease
Dry eyes are the most commonly experienced side effect after LASIK. Preoperative dry eye symptoms are at risk for worsening after laser surgery. It is important to optimize the ocular surface before refractive surgery. Although artificial tears are the mainstay of treatment, punctal plug placement during the LASIK procedure can decrease dry eye symptoms after LASIK. Use of medications such as cyclosporine A after LASIK, while not significantly changing patient symptoms, may improve refractive predictability. Similarly, uncontrolled ocular allergy symptoms can lead to increased risk of perioperative complications; systemic treatment can decrease the risk of complications.
Herpes Reactivation
Excimer laser treatment can lead to reactivation of herpes keratitis in both animal models and humans. Therefore refractive surgery was considered a contraindication. Recently however, de Rojas et al. presented a study in 48 patients who had inactive herpes keratitis for at least 1 year and in whom LASIK was performed while they were on oral and topical antiviral prophylaxis without any reactivation postoperatively. The authors suggest careful patient selection, with inactive disease for at least 1 year, normal corneal sensitivities, and normal corneal parameters before proceeding. Given the risk of potentially devastating scarring if reactivation does occur, caution must be used while considering refractive surgery in this population.
Glaucoma
Laser refractive surgery poses multiple complexities in patients with glaucoma. Although uncontrolled intraocular pressure is a contraindication for refractive surgery, patients with well-controlled glaucoma may be candidates. However, these patients often have ocular surface diseases that can complicate healing for LASIK or PRK. In addition, a change in corneal thickness can falsely change intraocular pressure measurements. Case reports exist of visual field, optic nerve, and nerve fiber layer changes occurring during the acute intraocular pressure elevation involved in LASIK flap creation, and surface ablation procedures may be better suited in these patients. Another aspect to consider is the prolonged use of corticosteroids in patients undergoing PRK, which may lead to corticosteroid-induced intraocular pressure elevation, which occurs more commonly in patients predisposed to glaucoma.
Other Considerations
Patients with visually significant or incipient cataracts must not undergo laser refractive surgery. Similarly, patients with significant retinal disease, latent strabismus, and monocular patients should not undergo laser refractive surgery.
General Considerations
Age
Laser corrective surgery is approved for those over 18 years of age who have had a stable refractive error over the previous 1–2 years. Although laser corrective surgery may be indicated in younger patients who are otherwise intolerant of traditional therapy, care must be taken because refractive error at this age often is unstable. A stable refractive error generally is defined as a ±0.5 diopter (D) change in refraction over the past 1–2 years. Every patient presenting to a screening examination should be asked to discontinue all contact lens wear (1 week for soft nontoric lenses, 2 weeks for toric lenses, and at least 3 weeks for rigid lenses) and asked to bring their previous spectacles for assessment of refractive stability.
Degree of Correction
Although different laser platforms are approved for various thresholds of refractive correction, most surgeons opt to limit myopic correction to −10 D and hyperopic and astigmatic correction to +4 D to prevent postoperative corneal ectasia and haze and to avoid the unpredictability of correction at these higher refractions.
Patient Expectations
Perhaps the most important aspect of refractive surgery is appropriate counseling to set realistic expectations. Patients who are risk averse, who expect better vision than with glasses or contacts, or who have unrealistic expectations are likely not good candidates for refractive surgery. Appropriate counseling becomes even more important in patients between 40 and 50 years of age as presbyopia sets in and monovision may need to be a consideration. Another aspect to consider is a patient’s occupation and hobbies. Those who perform activities that may put them at risk for flap dislocations should not be offered laser-assisted in situ keratomileusis (LASIK).
Age
Laser corrective surgery is approved for those over 18 years of age who have had a stable refractive error over the previous 1–2 years. Although laser corrective surgery may be indicated in younger patients who are otherwise intolerant of traditional therapy, care must be taken because refractive error at this age often is unstable. A stable refractive error generally is defined as a ±0.5 diopter (D) change in refraction over the past 1–2 years. Every patient presenting to a screening examination should be asked to discontinue all contact lens wear (1 week for soft nontoric lenses, 2 weeks for toric lenses, and at least 3 weeks for rigid lenses) and asked to bring their previous spectacles for assessment of refractive stability.
Degree of Correction
Although different laser platforms are approved for various thresholds of refractive correction, most surgeons opt to limit myopic correction to −10 D and hyperopic and astigmatic correction to +4 D to prevent postoperative corneal ectasia and haze and to avoid the unpredictability of correction at these higher refractions.
Patient Expectations
Perhaps the most important aspect of refractive surgery is appropriate counseling to set realistic expectations. Patients who are risk averse, who expect better vision than with glasses or contacts, or who have unrealistic expectations are likely not good candidates for refractive surgery. Appropriate counseling becomes even more important in patients between 40 and 50 years of age as presbyopia sets in and monovision may need to be a consideration. Another aspect to consider is a patient’s occupation and hobbies. Those who perform activities that may put them at risk for flap dislocations should not be offered laser-assisted in situ keratomileusis (LASIK).
Systemic Contraindications to Keratorefractive Surgery
A thorough medical history should be obtained from all patients considering refractive surgery. In particular, patients with a history of diabetes mellitus, pregnancy, autoimmune disease, collagen vascular disorders, thyroid disease, or abnormal wound healing may be at risk for poor outcomes postoperatively and should be identified before proceeding with surgery ( Box 3.2.1 ).
Immunological Disease
- •
Autoimmune
- •
Collagen vascular
- •
Immunodeficiency
Pregnancy or Nursing (not absolute contraindication)
Abnormal Wound Healing
- •
Keloids (contraindicated for PRK only)
- •
Abnormal scars
Diabetes Mellitus (if corneal sensation is not intact)
Interference from Systemic Medications
- •
Isotretinoin
- •
Amiodarone hydrochloride
Diabetes Mellitus
Uncontrolled diabetes not only leads to unstable refractions but also causes poor wound healing, persistent epithelial defects, and neurotrophic changes after laser surgery. A high risk of complications has been reported in the literature, including poor healing, worse refractive outcomes, and epithelial ingrowth. Other studies did not show a significant complication rate in diabetes patients with well-controlled blood glucose. Therefore it is recommend that refractive surgery be performed only in diabetes patients with tight blood glucose control (Hb A 1c <7.9%) over the previous year, normal corneal sensation, and no signs of diabetic retinopathy.
Pregnancy and Lactation
Refractive surgery during pregnancy is contraindicated because pregnancy can lead to transient changes in refractive error and cornea curvature and changes in tear quality. In addition, there are risks of fetal or infantile exposure to topical and systemic medications. There are multiple case reports of pregnancy-induced keratectasia following LASIK; it is important to counsel young female patients regarding this possibility. Sharif reported a greater risk for corneal haze and myopic regression in women who became pregnant within 5 months of photorefractive keratectomy (PRK). Starr also reported the case of a pregnant patient in whom overcorrection was induced and haze formation occurred. It is recommended that patients wait 3 to 6 months after pregnancy and cessation of lactation before undergoing refractive surgery.
Autoimmune Diseases
Uncontrolled collagen vascular disease is an absolute contraindication to undergoing laser refractive surgery, as it can lead to corneal melts and irregular healing. Patients with Sjögren’s disease and thyroid-associated eye disease are predisposed to tear film irregularities and dry eyes. Although most surgeons would agree that PRK will lead to poor healing in these patients, the debate is still ongoing whether patients with inactive or well-controlled collagen vascular disease can safely undergo LASIK. Multiple studies have shown no additional complications with LASIK in patients with inactive disease and a normal ocular surface. Case reports of severe complications also exist, however. Appropriate counseling must be done in any patient with a collagen vascular disease interested in pursuing laser refractive surgery.
Dermatological Keloid
Although dermatological keloid is listed as a precaution for LASIK and PRK, several studies have demonstrated good results without any additional complications after both PRK and LASIK. Most surgeons at this point do not consider this a concern with laser surgery.
Human Immunodeficiency Virus
A theoretical risk exists of transmission of human immunodeficiency virus (HIV) through laser plumes, but no reported cases have occurred to date that have shown such transmission. Nevertheless, adequate precautions must be taken while operating on patients with HIV. Hagen et al. used culture plates, and an excimer laser was used to ablate infected tissue. None was culture positive. These patients also have a theoretical higher risk of infectious complications. Therefore only those on appropriate therapy and with adequate CD4 cell counts should be considered for refractive surgery.
Medications
Multiple medications delay or inhibit wound healing after laser refractive surgery. Of these, amiodarone and isotretinoin need to be carefully considered before refractive surgery. Amiodarone is used to treat arrhythmias and can lead to multiple ocular side effects, including optic neuropathy, corneal and lenticular deposits, and halos around lights. Although there are reports of no increased complications, patients must be appropriately screened. Isotretinoin is used to treat acne and can lead to dry eyes, blepharoconjunctivitis, and photosensitivity, all of which can complicate recovery. Sumatriptan was previously considered to delay wound healing. However, recent reports do not show any significant adverse effects. Various other systemic medications can exacerbate dry eye symptoms, and therefore patients on these should be appropriately counseled and treated.
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