7 Cornea / External Disease

Anatomy / Physiology

Precorneal Tear Film

Layers

Lipid: outer layer; reduces evaporation; cholesterol and lipids; produced by meibomian, Zeis’, and Moll’s glands

Aqueous: middle layer; provides oxygen to epithelium; 98% water, 2% protein, pH = 7.2; osmolarity ~ 302 mOsm/L; produced by lacrimal and accessory lacrimal glands (Krause’s and Wolfring’s), basal secretion rate = 2 µL/min; lysozyme (antibacterial enzyme) constitutes 30% of total protein in tear film; also, lactoferrin, IgA and IgG (not IgD), electrolytes, oxygen

Mucin: inner layer; reduces surface tension and allows aqueous tear film to be spread evenly; helps structure the tear film; glycoproteins; 3 types: secreted mucins (MUC4 and MUC7) produced by lacrimal gland, gel-forming mucins (MUC5-AC) produced by conjunctival goblet cells (glands of Manz and crypts of Henle, primarily in fornix), and membrane associated mucins (MUC1 and MUC16) that protect the ocular surface; 2–3 mL/day

Cornea (Figure 7-1)

(From Yanoff M, Fine BS: Ocular Pathology, 5th edn, St Louis, Mosby, 2002.)

Figure 7-3 PAS stain demonstrating guttata as wart-like excrescences of Descemet’s membrane.

(From Yanoff M, Fine BS: Ocular Pathology, 5th edn, St Louis, Mosby, 2002.)

Endothelium

4–6 µm thick

Monolayer of interdigitating hexagonal cells joined by tight junctions

Transports nutrients into cornea, pumps fluid out of cornea

Rich in mitochondria; metabolizes carbohydrates at 5–6 times the rate of epithelium

Functions:

1 Barrier between stroma and anterior chamber

2 Keeps cornea dehydrated and clear 1 million cells at birth (∼3800 endothelial cells/mm²); loss of approximately 50% with aging; adjacent cells stretch to fill gaps (no regeneration), insufficient pump when <500 cells/mm²

Morphology: at least 60% of cells should be hexagonal; less than this represents unhealthy cornea

Innervation

Innervation to cornea occurs via CN V₁

Approximately 70–80 branches of long posterior ciliary nerves enter peripheral cornea after myelin sheath is lost 1–2 mm before limbus

Special techniques

Pachymetry: measures corneal thickness

Keratometry: measures corneal curvature (only 2 points 3 mm apart in paracentral region)

Topography: measures curvature of entire cornea

Limbus

Area 1–2 mm wide at which cornea and sclera meet; contains corneal epithelial stem cells, goblet cells, lymphoid cells, Langerhans’ cells, mast cells (see Ch. 10, Anterior Segment)

Conjunctival Disorders

Inflammation

Follicles

Gray-white round elevations with avascular center and vessels at periphery

Well-circumscribed focus of lymphoid hypertrophy (lymphocytes with a germinal center) due to reactive hyperplasia

Generally most prominent in inferior fornix (except in trachoma)

Chemosis

Conjunctival edema; may be caused by allergy or infection, can occur after eyelid surgery or be idiopathic

Symblepharon

Adhesion between conjunctival surfaces (palpebral and bulbar)

Due to inflammation, trauma, or surgery

Bilateral in ocular cicatricial pemphigoid and Stevens-Johnson syndrome

Degenerations

Amyloidosis

Yellow-salmon, subepithelial, interpalpebral plaque in primary localized disease

Systemic amyloidosis is not associated with conjunctival amyloid but is associated with amyloid of lid

Pathology

acellular eosinophilic material that stains with Congo red, thioflavin T, metachromatic with crystal violet, apple-green birefringence and dichroism with polarization microscopy

Concretions (Lithiasis)

Small, round, yellow-white deposits in palpebral conjunctiva

May contain calcium

May erode through conjunctiva and abrade ocular surface causing foreign body sensation

Treatment: remove with needle if erodes through conjunctiva

Conjunctival Telangiectasia

Associated with Louis-Barr syndrome (ataxia telangiectasia), Osler-Weber-Rendu (hereditary telangiectasia), Sturge-Weber syndrome, diabetes, sickle cell disease, Fabry’s disease, increased orbital pressure (C-C fistula), blood-filled lymphatic tissue, irradiation

Allergy

Type I hypersensitivity reaction

airborne allergens (pollen, mold, dander) cross link IgE receptors on mast cells causing degranulation with release of histamine, eosinophil chemotactic factors, platelet-activating factor, major basic protein, and prostaglandin D₂

Symptoms

itching (H₁ receptors), hyperemia (H₂ receptors)

Conjunctival scraping

abundant eosinophils (normally, there are very few)

Treatment

topical antihistamine (emedastine [Emadine], levocabastine [Livostin]), mast cell stabilizer (pemirolast [Alamast], nedocromil [Alocril], lodoxamide [Alomide], cromolyn sodium [Crolom]), antihistamine / mast cell stabilizer combination (azelastine [Optivar], olopatadine [Patanol, Pataday], ketotifen [Zaditor, Alaway], epinastine [Elestat], bepotastine [Bepreve], alcaftadine [Lastacaft]), NSAID (ketorolac [Acular]), steroid, artificial tears, cold compresses

Atopic Keratoconjunctivitis (AKC)

Atopy

hereditary allergic hypersensitivity (10–20% of population)

Types I < IV hypersensitivity reactions

Onset usually between ages 30 and 50 years

Clinical diagnosis (atopic skin disease [eczema], hay fever, asthma)

Eczema (atopic dermatitis)

3% of population; AKC in 15–40% of those with atopic dermatitis

Symptoms

itching, burning, photophobia, tearing, blurred vision

Findings

atopic dermatitis of eyelids (may have blepharitis, madarosis [loss of lashes], punctal ectropion), papillary conjunctivitis (small or medium-sized papillae in inferior fornix); may develop symblepharon, corneal vascularization, and scarring

Associated with keratoconus (10%), subcapsular cataracts (Maltese cross pattern), bilateral HSV keratitis, pellucid marginal degeneration

Pathology

mast cell infiltration of conjunctival epithelium

Treatment

topical allergy medication; consider systemic antihistamine, cyclosporine (up to 5 mg/kg/day)

Vernal Keratoconjunctivitis (VKC)

(See Ch. 5, Pediatrics / Strabismus)

Toxic Keratoconjunctivitis

Etiology

direct contact of medication or chemical substance with ocular surface

Findings

conjunctival injection, follicles, papillae, keratitis (SPK, occasionally pseudodendrite)

Superior Limbic Keratoconjunctivitis (SLK)

Recurrent inflammation of superior bulbar and palpebral conjunctiva; unknown etiology

Associated with CL wear and thyroid dysfunction (50%)

Female preponderance (70%), onset usually between ages 30 and 55 years

Recurrent episodes; lasts 1–10 years, eventually resolves permanently

70% bilateral; symptoms worse than signs

Symptoms

foreign body sensation, burning, photophobia, blurred vision

Findings

conjunctival injection, thickening, redundancy of superior bulbar conjunctiva with fine punctate staining (rose bengal), velvety papillary hypertrophy of upper palpebral conjunctiva, micropannus, filamentary keratitis (50%), decreased Schirmer’s test (25%)

Pathology

thickening and keratinization of superior bulbar conjunctiva with loss of goblet cells

Conjunctival scraping

neutrophils, lymphocytes, plasma cells

Conjunctivitis Associated with Systemic Diseases

Mucocutaneous disorders

Stevens-Johnson syndrome, ocular cicatricial pemphigoid (OCP), bullous pemphigoid, pemphigus, epidermolysis bullosa, dermatitis herpetiformis, arthropathies (Reiter’s syndrome, psoriatic arthritis), infections (Parinaud’s oculoglandular syndrome, Kawasaki’s disease), Wegener’s granulomatosis

Infectious Conjunctivitis

May be hyperacute, acute, or chronic

Usually viral in adults and bacterial in children

Findings

papillae, follicles, conjunctival injection, chemosis, discharge; may have preauricular lymphadenopathy, lid swelling, membranes, keratitis, corneal infiltrates, AC reaction

Subconjunctival hemorrhages: hemorrhagic conjunctivitis

ETIOLOGY: coxsackie A24, Picorna (enterovirus 70), EKC (adenovirus types 8 and 19)

True membrane: fibrin exudation, inflammatory cells, and invasion by vessels; firmly adherent to epithelium, bleeding occurs when peeled (diphtheria, gonococcus, β-hemolytic streptococcus, Stevens-Johnson syndrome)

Pseudomembrane: less adherent fibrin exudate (HSV, EKC, pharyngoconjunctival fever [PCF], bacterial, chlamydial, VKC, chemical burn, OCP, foreign body, ligneous, Kawasaki’s disease, GVH disease)

DDx of conjunctivitis with preauricular lymphadenopathy

EKC, HSV, Gonococcus, Chlamydia, Parinaud’s oculoglandular syndrome, Newcastle’s disease

DDx of acute follicular conjunctivitis

EKC, PCF, chlamydial, primary HSV, medicamentosa (antivirals, atropine, Propine, apraclonidine [Iopidine], brimonidine [Alphagan], neomycin), viral lid infections (verruca, molluscum), Newcastle’s disease, acute hemorrhagic (enteroviral) conjunctivitis

DDx of chronic follicular conjunctivitis (>4 weeks)

chlamydial, medicamentosa, viral lid lesion, HSV, psittacosis, Lyme disease, Parinaud’s oculoglandular syndrome, chronic fiber granuloma (nylon in fornix), type I hypersensitivity (atopic), molluscum, trachoma

Viral

Adenovirus

Most common; double-stranded DNA; primary infection provides lifelong immunity; 51 stereotypes, 1/3 associated with ocular infection

Findings

initially diffuse epithelial keratitis with normal vision; later, focal epithelial keratitis, coalescence of fine spots that become subepithelial infiltrates

Epidemic keratoconjunctivitis (EKC)

adenovirus types 8, 19 and 37; bilateral in 75% to 90%

Findings: preauricular lymphadenopathy, follicular conjunctivitis, lid swelling, watery discharge, pseudomembrane, subconjunctival hemorrhage, conjunctival scarring (symblepharon), SEIs; rarely, corneal edema, AC reaction, hypopyon; pharyngitis and rhinitis in 50%; can cause corneal ulceration

Treatment: steroids are useful primarily with a true membrane or vision worse than 20/40 from SEIs

Pharyngoconjunctival fever (PCF)

adenovirus types 3, 4, 5 and 7; young children; spread by respiratory secretions

Findings: fever, pharyngitis, folliclular conjunctivitis; may have punctate keratitis, rarely SEIs

Newcastle’s Disease

Unilateral follicular conjunctivitis, pneumonitis, preauricular lymphadenopathy

Occurs in poultry handlers; self-limited, lasts 1 week

Etiology

RNA virus; causes fatal disease in turkeys and other birds

Measles

Conjunctivitis, epithelial keratitis (associated with vitamin A xerosis)

Molluscum Contagiosum

Chronic follicular conjunctivitis associated with elevated umbilicated lid lesions

Due to release of toxic viral products

Treatment

excision of lesions or cryosurgery

Bacterial

Acute (hours to days)

Purulent discharge, not as severe as hyperacute

Streptococcus pneumoniae, Staphylococcus, Haemophilus influenzae, Pseudomonas

Treatment

topical antibiotic (Polytrim, tobramycin, azithromycin, or fluoroquinolone); add systemic antibiotic for H. influenzae

Chronic

Staphylococcus, Moraxella (chronic angular blepharoconjunctivitis), occasionally Gram-negative rods

Diagnosis

culture

Treatment

topical antibiotic (Polytrim)

Chlamydial

Trachoma

Bilateral keratoconjunctivitis; leading cause of preventable blindness

Chlamydia trachomatis serovars A to C

Findings (progressive)

bilateral infection of upper tarsal and superior bulbar conjunctiva, papillary reaction, conjunctival follicles, repeated infections, conjunctival scarring (Arlt’s line), tarsal shortening, entropion, trichiasis, corneal abrasion, superior corneal pannus, corneal scarring, cicatrized limbal follicles (Herbert’s pits)

Pathology

epithelial cells contain initial bodies (basophilic intracytoplasmic inclusions of Halberstaedter and Prowazek); Leber’s cells (macrophages in conjunctival stroma with phagocytosed debris)

Treatment

3 weeks of systemic and several months of topical antibiotics (tetracycline) during active disease; management of dry eyes; removal of misdirected lashes

Other Conjunctivitis

Ligneous

(See Ch. 5, Pediatrics / Strabismus)

Reiter’s Syndrome

Triad of urethritis, uveitis, and arthritis; mucopurulent discharge, conjunctivitis in 30%; may have keratoderma blenorrhagicum

Etiology

non-gonocococcal urethritis, Chlamydia, Shigella and Salmonella bowel infection; 85% HLA-B27 positive

Staphylococcal Disease

Blepharitis, conjunctivitis, keratitis (SPK, marginal infiltrates), phlyctenule

Tumors

Hamartoma

growth arising from tissue normally found at that site (e.g. nevus, neurofibroma, neurilemmoma, schwannomma, glioma, hemangioma, hemangiopericytoma, lymphangioma, trichoepithelioma)

Choristoma

growth arising from tissue not normally found at that site (e.g. dermoid cyst, dermatolipoma, ectopic lacrimal gland)

Congenital Tumors

(See Ch. 5, Pediatrics / Strabismus)

Squamous Tumors

Conjunctival Intraepithelial Neoplasia (CIN)

Premalignant lesion

Replacement of conjunctival epithelium by atypical dysplastic squamous cells

Usually transluscent or gelatinous appearance; <10% exhibit leukoplakia (keratinization)

Carcinoma in situ

total replacement of epithelium by malignant cells; BM intact; no invasion into substantia propria; characterized by leukoplakia, thickened epithelium, and abnormal vascularization

Usually begins at limbus and spreads onto cornea

Associated with HPV subtype 16 and 18 (check HIV in young patient), and actinic exposure

Men > women; occurs in older, fair-skinned individuals

Pathology

dysplastic epithelium spreads anterior to Bowman’s membrane, fine vascularity with hairpin configuration (similar to papilloma), anaplastic cells, dyspolarity (Figure 7-5)

Figure 7-5 CIN demonstrating full-thickness atypia and loss of polarity.

(From Yanoff M, Fine BS: Ocular Pathology, 5th edn, St Louis, Mosby, 2002.)

Treatment

wide local excision with cryotherapy; remove involved corneal epithelium (use fluorescein or rose bengal to delimit); excise until margins are clear. Consider topical or intralesional mitomycin C or interferon alpha-2b

Melanocytic Tumors

Racial Melanosis

Light brown, flat, perilimbal pigmentation; increased melanin in basal epithelium

Most common in pigmented individuals

No malignant potential

Freckle

Congenital; increased melanin in basal epithelium; normal number of melanocytes

Nevus

Congenital nests of benign nevus cells along basal epithelial and / or substantia propria

20–30% amelanotic

Freely movable over globe

50% have epithelial inclusion cysts

Often enlarges or becomes more pigmented during puberty or pregnancy

Primary Acquired Melanosis (PAM, Acquired Melanosis Oculi)

Unilateral, flat, diffuse, patchy, brown pigmentation; waxes and wanes

Proliferation of intraepithelial melanocytes; no cysts (Figure 7-8)

Figure 7-8 PAM with pigmentation throughout the epithelium.

(From Yanoff M, Fine BS: Ocular Pathology, 5th edn, St Louis, Mosby, 2002.)

Most frequently on bulbar conjunctiva or in fornices, but can occur on palpebral (tarsal) conjunctiva

Analogous to lentigo maligna of skin

Occurs in middle-aged to elderly whites

20–30% risk of malignant transformation, nodular thickening is indication for excisional biopsy

PAM without atypia

very low risk for melanoma

PAM with atypia

high risk for melanoma (overall 46%)

20% if atypical melanocytes confined to basal epithelium

75% if epithelioid cells present

90% if intraepithelioid pagetoid spread present

Treatment

observe with photographs; biopsy thickened areas (does not increase risk of metastasis); complete excision if malignant

Congenital Ocular Melanosis

(See Ch. 5, Pediatrics / Strabismus)

Secondary Acquired Conjunctival Melanosis

Addison’s disease, radiation, pregnancy, topical epinephrine

Malignant Melanoma

Rare, variably pigmented, elevated mass most commonly on bulbar conjunctiva

May see feeder vessel

Arises from PAM (67%) or preexisting nevi (25%), or de novo

Pathology

intraepithelial pagetoid spread; need to bleach specimen to determine amount of atypia (Figure 7-9), stain with S-100 and HMB-45

Figure 7-9 Malignant melanoma appears as pigmented tumor with loss of polarity.

(From Yanoff M, Fine BS: Ocular Pathology, 5th edn, St Louis, Mosby, 2002.)

Treatment

document with photos; complete excision (no touch technique) with clear margins, partial lamellar sclerectomy, and cryotherapy

Recurrence is usually amelanotic

Prognosis

20% mortality; 25% risk of metastases (regional lymph nodes and brain); more likely to invade sclera than SCC

If more than 2 mm thick, increased risk of metastasis and mortality

Involvement of caruncle, fornices, palpebral conjunctiva has worst prognosis

Better prognosis than cutaneous melanoma

Exenteration does not improve survival

Vascular Tumors

Cavernous Hemangioma

Red patch; may bleed

Associated with other ocular hemangiomas or systemic disease

Pathology

endothelial lined canals with RBCs

Lymphangioma

Cluster of clear cysts; may have areas of hemorrhage

Pathology

dilated lymphatic vessels

Treatment

excision if small

Metastatic Tumors

Very rare to conjunctiva

Fleshy yellow-pink mass

Breast, lung, cutaneous melanoma (usually pigmented)

Other Tumors

Fibrous Histiocytoma

Yellow-white mass composed of fibroblasts and histiocytes

Extends from limbus to peripheral cornea

Pathology

storiform pattern

Treatment

local excision

Corneal Disorders

Congenital

(See Ch. 5, Pediatrics / Strabismus)

Trauma

Foreign Body (FB)

May be superficial or deep

Often metal (usually associated with adjacent rust ring), glass, or organic material

Treatment

removal of FB, topical antibiotic; old deep inert material may be observed

Laceration

Partial- or full-thickness cut in cornea

Requires surgical repair and topical antibiotic and steroid

Complications include scarring and irregular astigmatism, which if affect vision, may be treated with rigid contact lens or keratoplasty

Recurrent Erosion

Spontaneous epithelial defect

Associated with anterior basement membrane dystrophy (ABMD) in 50% or previous corneal abrasion; also occurs in other corneal dystrophies

Abnormal adhesion of epithelium to Bowman’s membrane allows spontaneous sloughing

Symptoms usually occur in morning upon awakening (epithelium swells 4% overnight, and mechanical force of lids rubbing across corneal surface when open eyes or blink can dislodge epithelium)

Duration of symptoms depends on size of erosion

Findings

epithelial defect (may be partially healed), conjunctival injection; may have mild AC reaction and signs of corneal dystrophy (i.e. ABMD with irregular epithelium, areas of negative stain)

Treatment

lubrication, hypertonic saline (Muro 128 5% ointment qhs × 3-12 months); if recurs, consider bandage contact lens, epithelial débridement, anterior stromal puncture / reinforcement, diamond burr (débride and polish Bowman’s membrane), laser (phototherapeutic keratectomy [PTK] with excimer laser, or micropuncture with Nd : YAG laser (1 mJ, aim just below epithelium)); also, consider treatment with matrix metalloproteinase-9 inhibitors (doxycycline 50 mg PO bid × 2 months and topical steroids tid × 2-3 weeks); débridement for subepithelial scarring

Burns

Radiation

thermal burn (similar to acid burn)

UV light (snow blindness, arc-welding): punctate epithelial keratitis 8–12 hours after exposure; completely resolves

Ionizing radiation: superficial keratitis; then stromal disruption from keratocyte damage; corneal drying secondary to keratinization of conjunctiva

Treatment

Copious irrigation; débridement of necrotic conjunctiva and particulate matter; check pH level

Topical (10%) and oral sodium ascorbate (aids collagen synthesis and scavenges superoxide radicals)

Collagenase inhibitors (acetyl cysteine or EDTA)

Steroids for first 5–10 days only (reduce corneal and intraocular inflammation, help prevent symblepharon but can enhance collagenase-induced corneal melting, which often begins 1–2 weeks after injury)

Topical antibiotic

Ocular hypotensive medication for elevated IOP

Cycloplegic

Citrate (chelates calcium)

Complications

cataract, glaucoma, uveitis, symblepharon, entropion, xerosis, retrocorneal membrane, neurotrophic keratitis, corneal ulceration, anterior segment ischemia, and neovascularization

Ocular Surface Disease

Causes tear film disturbance and dry eye

Due to deficiency in tear film component(s)

Aqueous Deficiency

Lacrimal gland dysfunction (aplasia, surgical removal), infiltration (sarcoidosis, thyroid disease, lymphoma, amyloidosis, TB), inflammation (mumps, Sjögren’s syndrome), denervation (Riley-Day [familial dysautonomia], Shy-Drager [adult dysautonomia, idiopathic autonomic dysfunction], Möbius’ syndrome), drugs that decrease lacrimal secretion (antihistamines, diuretics, anticholinergics, psychotropics)

Keratoconjunctivitis Sicca

Adult women (95%), often associated with Sjögren’s syndrome

Symptoms

burning, dryness, foreign body sensation, tearing; worse later in day, with prolonged use of eye, and in dry or windy environments

Findings

decreased tear meniscus height (normal = 0.5 mm), decreased tear breakup time (<10 seconds), increased mucus, filaments in severe cases, interpalpebral corneal and conjunctival staining with rose bengal / lissamine green or fluorescein, Schirmer’s test (<10 mm/5 min), increased tear osmolarity (>311 mOsm), Phenol red thread test (<9 mm/15 seconds)

Pathology

lymphocytic infiltration of lacrimal gland

Treatment

lubrication with artificial tears and ointments, punctal occlusion, humidifier, moisture chamber goggles; consider acetylcysteine (Mucomyst) or bandage contact lens for filaments; topical cyclosporine (Restasis)

Mikulicz’s syndrome

lacrimal and parotid gland swelling and keratoconjunctivitis sicca due to sarcoidosis, TB, lymphoma, leukemia

Mucin Deficiency

Goblet cell dysfunction due to conjunctival scarring and keratinization (vitamin A deficiency, OCP, Stevens-Johnson syndrome, alkali burns, trachoma, GVH disease); impression cytology measures number of goblet cells

Xerophthalmia

Epithelial keratinization due to vitamin A deficiency

Vitamin A required for conjunctival goblet cell mucin production, corneal stromal metabolism, retinal photoreceptor metabolism, normal iron metabolism, normal growth, resistance to measles

Incidence 5 million new cases / year; affects 20-40 million children worldwide

Usually in developing countries (50% in India); in developed countries, due to lipid malabsorption (short bowel syndrome, chronic liver dysfunction, cystic fibrosis) and poor diet (chronic alcoholism)

Findings

night blindness (nyctalopia), conjunctival xerosis (leathery appearance) and Bitot’s spots (gray foamy plaques), corneal xerosis with keratomalacia, ulceration, and scarring, xerophthalmic fundus (fine white mottling)

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Tags: Review of Ophthalmology Expert Consult

Jun 4, 2016 | Posted by admin in OPHTHALMOLOGY | Comments Off

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Cornea / External Disease

Cornea (Figure 7-1)