Anterior Segment

Published on 10/03/2015 by admin

Filed under Opthalmology

Last modified 22/04/2025

Print this page

This article have been viewed 1997 times

10 Anterior Segment

IRIS, CILIARY BODY, AND ANTERIOR CHAMBER (AC) ANGLE

Iris, ciliary body, and anterior chamber (AC) angle

Anatomy

Limbus

Transition zone between cornea and sclera; 1–2 mm wide

Conjunctiva and Tenon’s capsule are fused over this area; contains corneal epithelial stem cells, goblet cells, lymphoid cells, Langerhans’ cells, mast cells

Definitions

Anatomist’s: termination of Descemet’s and Bowman’s membranes

Pathologist’s: anterior limbus corresponds to termination of Bowman’s and Descemet’s membranes, and posterior limbus corresponds to line between iris root and Schlemm’s canal

Surgeon’s: anterior blue zone (1 mm) and posterior white zone (1 mm); a perpendicular incision through the conjunctival insertion enters the AC through Descemet’s membrane; a perpendicular incision through the posterior aspect of the limbus will enter the AC through the trabecular meshwork (Figure 10-1)

Figure 10-1 Anatomy of the surgical limbus.

Ciliary Body and Angle Structures

(See Ch. 9, Glaucoma)

Disorders

Trauma

Hyphema

Blood in anterior chamber

Etiology

trauma, surgery (incisional or laser), spontaneous (neovascularization, Fuchs’ heterochromic iridocyclitis, intraocular tumors, juvenile xanthogranuloma), clotting abnormalities (leukemia, hemophilia, anemia, coumadin, aspirin, ethanol)

Findings

layer of blood and/or clot with suspended RBCs in AC; called microhyphema if only suspended cells; damage to other structures may be seen

Diagnosis

sickle prep, consider hemoglobin electrophoresis, rule out ruptured globe, gonioscopy (wait 4–6 weeks in traumatic cases)

Treatment

cycloplegic, topical steroid, control IOP (avoid miotics); consider Amicar (aminocaproic acid), protective shield; elevate head, bed rest, no aspirin-containing products, control systemic BP, antiemetics (if needed); may require surgery (AC washout)

Indications for surgical intervention: large hyphema that persists for longer than 10 days, total hyphema that persists for longer than 5 days, corneal blood staining, uncontrolled IOP, 8-ball hyphema; best to perform washout 4–7 days after injury (clot has time to solidify, reducing rate of rebleed)

Complications

8-Ball hyphema: hyphema that has clotted and taken on a black or purple color because of impaired aqueous circulation and deoxygenated blood, which prevents resorption; total hyphema is differentiated from 8-ball hyphema by retention of bright red color, which indicates aqueous circulation

Corneal blood staining: passage of erythrocyte breakdown products into stroma, creates yellow-brown discoloration; occurs in about 5%, especially with recurrent hemorrhage, compromised endothelial cell function, large hyphemas that remain for extended periods, elevated IOP

Recurrent hemorrhage: usually larger than initial hyphema; incidence 5–35% with greatest risk at 2–5 days

Secondary glaucoma:

EARLY: due to TM obstruction, pupillary block by clot, hemolytic, steroid-induced

LATE: due to angle recession, ghost cell, PAS formation, posterior synechiae with iris bombe

Central retinal artery occlusion

Sickle cell and hyphema

higher elevation in IOP (sickled RBCs cannot pass through TM), and higher risk of central retinal artery occlusion and optic nerve infarction due to vascular sludging

Factors that increase sickling: acidosis, hypoxia, hemoconcentration

Ocular hypotensive medications in sickle cell: β-blockers are safe; avoid CAIs (increases concentration of ascorbic acid in aqueous, decreasing pH and leading to sickling), epinephrine and α-agonists (cause vasoconstriction with subsequent deoxygenation and sickling); hyperosmotics (lead to hemoconcentration with vascular sludging and sickling)

Iris and Angle Trauma (Figure 10-2)

Iris sphincter tear

small tear at pupillary margin; asymptomatic

Figure 10-2 Seven areas of traumatic ocular tears (shown in yellow) with the resultant findings.

(Adapted with permission from Campbell DG: Traumatic glaucoma. In Shingleton BJ, Hersh PS, Kenyon KR [eds]: Eye Trauma. St Louis, Mosby, 1991.)

Traumatic mydriasis

dilated, poorly reactive pupil; may cause glare or photophobia; consider cosmetic contact lens or surgical repair

Iridodialysis

tear in iris root; consider cosmetic contact lens or surgical repair if large or symptomatic

Angle recession

tear in anterior face of ciliary body between the longitudinal and circular ciliary muscles; most common source of hemorrhage in blunt trauma, occurs in more than 60% of hyphemas; 10% of patients with greater than 180° of angle recession will develop chronic glaucoma

Cyclodialysis

separation of ciliary body from scleral spur; allows free passage of aqueous into suprachoroidal space; can result in hypotony; treat with atropine, laser, and/or surgical repair

Open Globe/Intraocular Foreign Body

Full-thickness defect in cornea or sclera

Usually due to trauma (penetrating or blunt), may also occur from melt (chemical injury, autoimmune disorder, infection)

Penetration

entrance wound only

Perforation

entrance and exit wounds (double penetrating injury)

Risk of infectious endophthalmitis (3–7%) increases if retained foreign body, delayed surgery (>24 hours), rural setting (soil contamination), and lens disruption

S. aureus is the most common organism to cause post-traumatic endophthalmitis; Bacillus cereus is also common and causes severe damage

Findings

wound with positive Seidel test, hemorrhage (conjunctiva, hyphema, vitreous, retina), decreased IOP, shallow or flat AC, peaked pupil (toward wound), cataract, retinal tear//detachment, prolapsed intraocular contents (uvea, vitreous), foreign body (small high-velocity FB may cause self-sealing wound or intermittently positive Seidel; iris transillumination defect, capsule/lens disruption)

Types of foreign bodies

Inert: glass, plastic, sand, stone, ceramic, gold, platinum, silver, aluminum

COPPER: severity of inflammation is directly proportionate to amount of copper in foreign body (≥85% copper causes severe endophthalmitis; <85% causes chalcosis; <70% is relatively inert)

CHALCOSIS: mild intraocular inflammation, deposition of copper in anterior lens capsule (sunflower cataract) and Descemet’s membrane (Kayser-Fleisher ring), retinal degeneration, iris may become green and sluggishly reactive to light

ERG: decreased amplitude (suppressed by copper ions)

IRON (siderosis): iris heterochromia (hyperchromatic on involved side), mid-dilated minimally reactive pupil, lens discoloration (brown-orange dots from iron deposition in lens epithelium, generalized yellowing from involvement of cortex), vitritis, pigmentary RPE degeneration with sclerosis of vessels, retinal thinning, and atrophy

ERG: initial a wave increased, may eventually become flat

WOOD: significant inflammation; plant matter has higher risk of endophthalmitis

Treatment

rule out FB with CT or MRI (contraindicated for metallic FB); surgical exploration and repair, remove reactive material as soon as possible

Prophylactic antibiotics: IV (aminoglycoside plus cephalosporin or vancomycin; consider clindamycin) and intravitreal (vancomycin [1 mg/0.1 mL], amikacin [0.4 mg/0.1 mL], or ceftazidime [2.25 mg/0.1 mL]) reduces risk of endophthalmitis; consider intravitreal dexamethasone 0.4 mg/0.1 mL

Prognosis

variable; poor if endophthalmitis or PVR develops (7–21 days later)

Congenital Abnormalities

(See Ch. 5, Pediatrics/Strabismus)

Mesodermal Dysgenesis Syndromes

(See Ch. 5, Pediatrics/Strabismus)

Other Disorders

Corectopia

Displacement of pupil

Isolated or associated with Axenfeld-Rieger syndrome, ICE syndrome, uveitis, trauma, or ectopia lentis et pupillae

Rubeosis Iridis

Neovascularization of the iris

Etiology

ischemia (usually proliferative diabetic retinopathy [PDR], CRVO, carotid occlusive disease; also CRAO, sickle cell retinopathy, anterior segment ischemia), tumor, uveitis, chronic RD.

Findings

abnormal iris vessels; perform gonioscopy to assess presence of angle neovascularization; may have elevated IOP (neovascular glaucoma [NVG])

Treatment

often requires panretinal photocoagulation (PRP) for ischemia; NVG often needs glaucoma drainage implant for IOP control

Pigment Dispersion Syndrome

Pigment liberation from posterior iris surface (due to contact with zonules)

More common in young Caucasian males

Associated with myopia and lattice degeneration (20%)

Findings

pigment deposits on lens capsule, anterior iris, angle structures, and corneal endothelium (Krukenberg spindle); midperipheral, radial, iris transillumination defects; pigmentary glaucoma may develop

Iridocorneal Endothelial (ICE) Syndrome

Nonhereditary, progressive abnormality of corneal endothelium

Abnormal corneal endothelium grows across angle and iris, producing membrane that obstructs trabecular meshwork, distorts iris, and may contract around iris stroma to form nodules

Unilateral, mostly women, occurs during middle age

Findings

fine, beaten metal appearance of endothelium; secondary angle-closure glaucoma may develop due to angle endothelialization and PAS

Syndromes

common features of iris distortion, corneal edema, secondary angle-closure glaucoma

Iris nevus (Cogan-Reese) syndrome: flattening and effacement of iris stroma, pigmented iris nodules (pseudonevi) composed of normal iris cells that are bunched up from the overlying membrane, corectopia, ectropion uveae

Chandler’s syndrome: corneal edema often with normal IOP, mild or no iris changes (minimal corectopia, iris atrophy, peripheral anterior synechiae)

Essential iris atrophy: proliferating endothelium produces broad PAS, corectopia, ectropion uveae, and iris holes (stretch holes [area away from maximal pull of endothelial membrane is stretched so thin that holes develop] and melting holes [holes in areas without iris thinning due to iris ischemia])

Pathology

growth of endothelium and Descemet’s membrane over trabecular meshwork and onto iris

DDx

posterior polymorphous dystrophy, mesodermal dysgenesis syndromes

Iridoschisis

Separation of iris stroma due to senile changes

Bilateral; onset in 6th-7th decade of life

Glaucoma in 50%

Iris Nevus Syndrome (Cogan-Reese)

Iris Tumors

Perform transillumination to differentiate cyst from solid tumor

Freckle

No distortion of iris architecture

Nevus

Localized or diffuse variably pigmented lesion of stroma; obscures crypts

Pathology

usually low-grade spindle cells

Small risk of transformation into melanoma (∼5% of suspicious iris lesions grow during first 5 years after detection)

Melanocytosis

Congenital ocular: usually unilateral with diffuse iris nevus causing iris heterochromia

Oculodermal (nevus of Ota)

ocular plus periorbital skin involvement

Melanocytoma

Form of nevus; darkly pigmented, very discohesive (like black, wet sand)

May have necrotic center

5% risk of melanoma

Tumors of Iris Pigment Epithelium

Adenoma (benign) or adenocarcinoma (malignant)

Rare compared with melanomas

Deeply pigmented, circumscribed or multinodular mass; can cause secondary glaucoma by involvement of angle

Treatment

chemotherapy, radiation, or excision

Lisch Nodules

Benign, tan, iris hamartomas; associated with neurofibromatosis type 1

Metastasis

Most commonly, breast, lung, lymphoma

Findings

fluffy, friable iris mass; may have pseudohypoyon, anterior uveitis, hyphema, rubeosis, and glaucoma

Leiomyoma

Well localized or pedunculated, often diffuse and flat

Pathology

very similar to amelonotic spindle cell melanoma

Leukemia

Rare nodular or diffuse milky lesions with intense hyperemia

Findings

iris thickening with loss of normal architecture; iris heterochromia and pseudohypopyon

Cystic Lesions

IPE: can be AD; flocculi around pupillary margin; associated in certain families with aortic dissection; midperipheral cysts, peripheral cysts (usually clear; can push iris forward)

Stroma

congenital or acquired (after trauma or surgery)

Ciliary Body Tumors

Melanoma

May be very large before detection, producing lenticular astigmatism, cataract, or shallow AC; may have classic sentinel vessel or nodule of extrascleral extension

Pathology

spindle, epithelioid, or mixed cells

Treatment

local resection, XRT, enucleation

Ciliary Body Leiomyoma

Similar to fibroid; myogenic origin

Schwannoma

Looks like amelanotic melanoma

Ciliary Body Adenoma or Adenocarcinoma

Arises from neuroepithelial cells

Occurs during adulthood

May metastasize

Fuchs’ Adenoma (Fuchs’ Reactive Hyperplasia, Benign Ciliary Epithelioma)

Proliferation of basement membrane material (type IV collagen and laminin) and nonpigmented ciliary body epithelial cells located at ciliary crest

Occurs in 25% of older patients

Rarely causes localized occlusion of anterior chamber angle

Medulloepithelioma

(See Ch. 5, Pediatrics/Strabismus)

Lens

Anatomy/Physiology (Figures 10-3 and 10-4)

Lens capsule

basement membrane secreted by epithelium; thickest peripherally near the equator, thinnest posteriorly. Thickening of lens capsule can occur with anterior chamber inflammation or pathologic proliferation of lens epithelium

Figure 10-3 Typical photographic procedure.

(From Mandava N, Reichel E, Guyer D, et al: Fluorescein and IGC angiography. In Yanoff M, Duker JS [eds]: Ophthalmology, London, Mosby, 1999.)

Figure 10-4 Thickness of the lens capsule.

(From Saxby LA: Anatomy. In Yanoff M, Duker JS [eds]: Ophthalmology, London, Mosby, London, 1999.)

Epithelium

present anteriorly, ending just posterior to the lens equator. Derived from cells of original lens vesicle. In the germinative zone, just anterior to equator, lens epithelial cells divide, elongate, and differentiate into lens fibers. During this transformation, epithelial cells lose their nuclei and most organelles. Lens fibers do not contain nuclei except in rubella, Lowe’s syndrome, and trisomy 13. The embryonal nucleus develops by proliferation and migration of epithelial cells from the equator. Acute IOP elevation may cause patches of epithelium degeneration and necrosis beneath the capsule, which appear as white flecks (glaukomflecken). Chronic iritis may cause liquefaction of the nucleus, peripheral cortical changes, and degeneration and necrosis, as well as proliferation of anterior lens epithelium

Sutures

upright Y suture anteriorly and inverted Y suture posteriorly represent the ends of lens fibers; sutures appear during the 2nd month of gestation because of unequal growth of new lens fibers

Zonules

attach from pars plicata to anterior and posterior lens capsule in midperiphery (inserting more centrally on anterior capsule). During the 5th month of gestation, nonpigmented ciliary epithelium of ciliary body secretes collagen fibers that become zonules. Equatorial zonules are lost with aging

Tunica vasculosa lentis

vascular network that surrounds lens during embryogenesis; derived from hyaloid and long ciliary arteries. Remnants of tunica vasculosa lentis include Mittendorf’s dot, epicapsular star, persistent pupillary membrane, and capsular whorls

Properties of the crystalline lens

Potassium-rich tissue: due to Na⁺/K⁺ pumps found on lens epithelial cells, which pump Na⁺ out and K⁺ in; concentrations of Na⁺ and K⁺ in aqueous are inverse to those in lens (10× as much Na⁺ in aqueous as in lens)

Grows throughout life: weight at maturity is 3× that at birth, anterior-posterior diameter increases from 3.5 mm at birth to 5 mm at maturity, equatorial length increases from 6.4 mm at birth to 9.0 mm at maturity; also increase in curvature with greater refractive power

Refractive index: increase in lens curvature and thickness with age is offset by change in gradient of refractive index due to increased concentration of main intrinsic polypeptide; associated with increased brunescence, resulting in greater absorption of blue and violet wavelengths, as well as UV light (aiding in retinal protection)

Metabolism: anaerobic; 80% of glucose metabolized by glycolysis, 10% metabolized by pentose phosphate pathway, 5% reduced to sorbitol, and 5% converted to glucuronic acid; highest metabolic rate is in cortex; energy is required for ion transport and glutathione production

Lens fiber structure: fibers contain few intracellular organelles and no nuclei; appear hexagonal in cross section

Average lens power: at birth = 37 diopters (D), at age 2 years = 23 D, at adulthood = 20 D

Protective mechanisms against free radical damage and oxidation: glutathione peroxidase, superoxide dismutase, catalase, and vitamins C and E

Accommodation: parasympathetic fibers of CN 3

Generally accepted theory is that of von Helmholtz: ciliary muscle contraction causes zonules to relax, allowing the lens to become more spherical and increasing its focusing power; presbyopia is therefore due to loss of lens elasticity with age

Disorders

Congenital Anomalies

(See Ch. 5, Pediatrics/Strabismus)

Cataracts

Congenital Cataracts

(See Ch. 5, Pediatrics/Strabismus)

Acquired Cataracts

Classified by location or etiology

Cortical

lens fiber fragments, degenerated protein, liquefaction

Spokes and vacuoles: radial lines and dots (Figure 10-5)

Mature: completely white

Hypermature: leakage of degenerated cortical material, wrinkled capsule; may have calcium deposits

Morgagnian: total liquefaction of lens cortex; nucleus floats freely within capsule; lens material can leak through intact capsule (Figure 10-6)

Pathology: hydropic swelling of lens fibers; morgagnian globules (eosinophilic, globular material between lens fibers)

Figure 10-5 Cortical cataract.

(From Collin J: The morphology and visual effects of lens opacities. In Yanoff M, Duker JS [eds]: Ophthalmology, London, Mosby, 1999.)

Figure 10-6 Morgagnian cataract.

(From Collin J: The morphology and visual effects of lens opacities. In Yanoff M, Duker JS [eds]: Ophthalmology, London, Mosby, 1999.)

Nuclear sclerosis

increased nuclear density, then opacification occurs with aging; lenticular myopia results from increased index of refraction; ‘second sight’ (presbyopes can often read again without spectacles)

Cataract brunescens (poor blue discrimination), cataract nigrans, calcium oxalate crystals in nucleus

Pathology: inwardly sequestered lens fibers degenerate (analogous to desquamating skin); homogenous loss of cellular laminations

Posterior subcapsular (PSC)

posterior migration of lens epithelium, and bladder (Wedl) cell formation (eosinophilic globular cells with nuclei; swell to 5–6× normal size)

Etiology: age, trauma, steroids, inflammation, ionizing radiation, retinitis pigmentosa, atopic dermatitis, Werner’s syndrome, Rothmund’s syndrome, diabetes

Symptoms: glare and poor vision from bright lights; affects near vision more than distance vision

Pathology: posterior migration of lens epithelial cells, which swell along posterior capsule (swollen cells are called Wedl cells)

Anterior subcapsular (ASC)

fibrous plaque beneath folded anterior capsule, secreted by irritated metaplastic anterior epithelial cells (due to trauma or uveitis), can also occur in atopic dermatitis

Pathology: cells surrounded by basement membrane

Glaukomflecken

necrosis of lens epithelial cells due to ischemia from elevated IOP (angle closure); appears as central subcapsular small white dots and flecks

Traumatic and toxic cataracts

Contusion: petalliform or rosette pattern due to separation of lens fibers around lens sutures

Vossius’ ring: with blunt injury, pigment from pupillary ruff is imprinted onto anterior lens capsule

Soemmering’s ring: doughnut of residual equatorial cortex; after cataract surgery or trauma; can be associated with an adherent leukoma

Siderosis lentis: iron deposits in lens epithelium; anterior subcapsular orange deposits; photoreceptor and RPE degeneration resulting in pigmentary retinopathy with peripheral visual field loss; iris heterochromia (involved iris darker)

Chalcosis lentis: copper deposits in lens capsule; green discoloration of anterior lens capsule and cortex in petaloid configuration occurs in Wilson’s disease, forming a sunflower cataract; also Kayser-Fleischer ring (copper deposition in peripheral Descemet’s membrane); can also occur in multiple myeloma and lung carcinoma

Other intraocular foreign bodies: gold, silver, platinum, aluminum are inert; lead and zinc may cause mild nongranulomatous reaction

COPPER: if concentration ≥85%, an acute inflammatory reaction occurs; if concentration between 70 and 85%, chalcosis develops; lesser concentrations are relatively inert

Mercurial lentis: mercury deposits in lens capsule (occupational)

Electrical: lens vacuoles in anterior midperiphery; linear opacities (stellate pattern) in anterior subcapsular cortex; burns >200 volts cause conjunctival hyperemia, iritis, hyphema, iris atrophy, sphincter changes

Argon laser: blue light absorbed by yellow sclerotic nucleus

Nonionizing radiation: infrared causes true exfoliation (glassblower’s cataract) with splitting and scrolling of anterior lens capsule; ultraviolet (UV-B) causes cortical cataracts

Ionizing radiation: a threshold level of radiation is required to induce cataract development (PSC)

Medications:

CORTICOSTEROIDS: PSC from long-term use of any form of steroids, most commonly topical; develop in 33% of patients on long-term daily dose of 10 mg; also associated with inhaled steroids

MIOTICS: echothiophate iodide and demecarium bromide cause anterior subcapsular vacuoles in adults (not children)

PHENOTHIAZINES AND AMIODARONE: pigmented deposits in anterior lens capsule; axial, spoke-like configuration; dose and duration dependent

BUSULFAN: PSC

Cataracts associated with systemic disease

Atopic dermititis: PSC and ASC shield-like plaque

Also associated with chronic keratoconjunctivitis, keratoconus, vernal keratoconjunctivitis

Diabetes: osmotic cataract due to high glucose levels and aldose reductase, which results in high sorbitol levels

Snowflake cataract (punctate white subcapsular opacities) can occur rapidly with high blood sugar

Myotonic dystrophy (AD): mapped to chromosome 19

FINDINGS: characteristic presenile ‘Christmas tree’ cataract consisting of polychromatic cortical crystals; ptosis, lid lag, light-near dissociation, mild pigmentary retinopathy; ERG – low voltage

OTHER FINDINGS: myotonia (bilateral facial weakness, difficulty relaxing grip, muscle wasting), testicular atrophy, frontal baldness, cardiac abnormalities, mental retardation; excessive contractility of muscles

Neurofibromatosis type 2: presenile PSC opacities

Werner’s syndrome: syndrome of premature aging, scleroderma-like matting of skin, and bilateral PSC cataracts in 3rd to 4th decade of life

Wilson’s disease (hepatolenticular degeneration): deficiency of ceruloplasmin (alpha-2 globulin)

FINDINGS: green sunflower cataract due to deposition of copper in anterior lens capsule and cortex in petaloid configuration; Kayser-Fleischer ring (copper in peripheral Descemet’s membrane)

OTHER FINDINGS: cirrhosis, renal impairment, degeneration of basal ganglia

TREATMENT: penicillamine to lower serum copper

Lens Capsule Abnormalities

True Exfoliation

Delamination/schisis of anterior lens capsule, forming scrolls; often due to infrared radiation (glassblowers), can be an aging change; not associated with glaucoma

Pseudoexfoliation Syndrome (PXS)

Material produced by lens epithelial cells and extruded through lens capsule

Appears to be an ocular sign of systemic elastosis; also found in conjunctiva, skin, lung, and liver

Usually elderly, Caucasian females; increased incidence in Scandinavians and with increasing age

Findings

white fibrillar material on anterior lens capsule, iris, ciliary body, zonules, anterior vitreous with characteristic pattern of deposition on lens surface (central disc, clear zone, then peripheral annulus, often with bridging strands to central disc); may see flakes on pupillary margin; Sampaolesi’s line (pigment band anterior to Schwalbe’s line) on gonioscopy; up to 50% develop glaucoma (PXG); poor dilation due to iris muscle degeneration or lack of iris stromal elasticity; peripupillary transillumination defects; weak zonules (phacodonesis, increased incidence of angle closure, lens subluxation, and complications during and after cataract surgery [vitreous loss, IOL and capsular dislocation])

Posterior Capsular Opacification (PCO; Secondary Cataract)

Proliferation of residual lens epithelial cells (Elschnig’s pearls) and fibrosis

Incidence

up to 50% of patients within 2 years of extracapsular cataract surgery; influenced by optic material (acrylic < silicone < PMMA) and edge design (square edge < round edge); with newer IOLs, the incidence has decreased to ∼10%. Incidence approaches 100% in children and patients with uveitis

Treatment

Nd : YAG laser posterior capsulotomy when visually significant

In young children, primary posterior capsulotomy and anterior vitrectomy are performed at the time of cataract surgery

Ectopia Lentis

Displacement of lens

Subluxation

partial displacement, remains in pupillary axis

Dislocation (luxation)

complete displacement from pupil

Findings

decreased vision, astigmatism, monocular diplopia, iridodonesis, phacodenesis, malpositioned lens

DDx

trauma (most common acquired cause), Marfan’s syndrome, homocystinuria, aniridia, congenital glaucoma, megalocornea, Ehlers-Danlos syndrome, hyperlysinemia, sulfite oxidase deficiency, hereditary ectopia lentis (AD >> AR; bilateral; may not present until 3rd–5th decade), ectopia lentis et pupillae (AR; lens and pupil are displaced in opposite directions; bilateral, asymmetric), tertiary syphilis, Weill-Marchesani syndrome, medulloepithelioma, Stickler’s syndrome, pseudoexfoliation (rare)

Marfan’s Syndrome (AD)

Mapped to chromosome 15q; defect in fibrillin (elastic microfibrillar glycoprotein, major constituent of zonules); 15% have no family history

Findings

ectopia lentis (65%; usually superotemporal); glaucoma, keratoconus, cornea plana, axial myopia, retinal degeneration (salt and pepper fundus), high risk of retinal detachment

Other findings

tall stature, spidery digits, arm span is larger than height, cardiac disease, dissecting aneurysm of the aorta

Homocystinuria (AR)

Deficiency of cystathionine β-synthase, which converts homocysteine to cystathionine; methionine and homocysteine accumulate; zonules are deficient in cysteine and weakened because of reduced sulfhydryl cross-linkage; degeneration of entire zonule occurs

Findings

bilateral ectopia lentis (90%; usually inferonasal; 30% in infancy, 80% by age 15), enlarged globe, myopia, peripheral RPE degeneration, increased risk of retinal detachment after cataract surgery, early loss of accommodation due to disintegration of zonules

Other findings

blonde, tall (marfinoid habitus with arachnodactyly), osteoporosis, fractures, seizures, mental retardation (50%), cardiomegaly, platelet abnormality with hypercoagulability (risk of thromboembolic problems, especially with general anesthesia); infants appear normal at birth; 75% mortality by age 30 years

Hyperhomocystinemia occurs in patients heterozygous for homocystinemia

high serum homocysteine increases risk of arterial and venous thrombosis (CRAO and CVO) and cardiovascular disease, especially in type 2 diabetic patients. In nondiabetic patients younger than 55 years of age who have had a stroke or MI, 25% have elevated homocysteine levels (5% in normal population)

Diagnosis

increased urinary excretion of homocysteine (nitroprusside urine test), amino acid assays; check renal function (homocysteine levels rise with elevated creatinine levels); subnormal or low levels of folate are associated with elevated levels of homocysteine

Treatment

vitamin B₆ (folate), methionine-restricted diet, supplementary cysteine (this diet can reduce lens dislocation); certain medications (methotrexate, phenytoin, carbamazepine) can elevate homocysteine levels by interfering with folate metabolism

Weill-Marchesani Syndrome (AR)

Findings: ectopia lentis (usually inferiorly or anteriorly), microspherophakia, high lenticular myopia, cataract, microcornea, glaucoma (pupillary block)

Other findings

short stature; short, stubby fingers with broad hands; hearing defects; inflexible joints; mental retardation

Ehlers-Danlos Syndrome (AD, AR, or X-Linked)

Defect in type III collagen; at least 9 types

Findings

ectopia lentis, easy lid eversion (Metenier’s sign), epicanthal folds, myopia, microcornea, blue sclera, keratoconus, angioid streaks, retinal detachment

Other findings

hyperextensible joints and skin, poor wound healing, easy bruising

Sulfite Oxidase Deficiency (AR)

Enzymatic defect causing molybdenum deficiency and increased urinary sulfite

Findings

ectopia lentis (50%), enophthalmos, Brushfield’s spots

Other findings

seizures, mental retardation, frontal bossing

Hyperlysinemia (AR)

Deficiency of lysine dehydrogenase

Findings

ectopia lentis, microspherophakia

Other findings

growth, motor and mental retardation

Surgery

Nd : YAG Laser

Posterior Capsulotomy

Open visually significant posterior capsule opacity

Power: 1.0–2.0 mJ; make an opening equal to the size of the pupil in ambient light

Treatment: pretreat with Iopidine (apraclonidine), then topical steroid qid × 1 week

Complications

increased IOP (glaucoma patients – 17% have rise after 2 hours; 14% with high IOP at 1 week; nonglaucoma patients – 6% have rise after 2 hours, 3% with high IOP at 1 week), retinal detachment (RD), cystoid macular edema (CME), rupture of the anterior hyaloid face, IOL dislocation, iritis, pitting of IOL, corneal or retinal burn

Vitreolysis

Disrupt anterior vitreous face in aphakic and pseudophakic eyes with malignant glaucoma

Power: 3–11 mJ, focused on anterior hyaloid; deepening of anterior chamber signifies success

Treatment: topical steroid qid × 1 week and cycloplegic; vitrectomy if regimen described here fails and in phakic eyes

Relieve CME due to vitreous wick

Power: 5-10 mJ bursts, often best to aim near wound or pigmented area of incarcerated vitreous; success occurs with a change in the pupil shape back to round

Treatment: pretreat with pilocarpine to induce miosis and stretch the strand, then topical steroid × 1 week

Cataract Surgery

Indications

altered vision (based on patient’s functional impairment; when patient is having visual difficulty performing tasks and does not achieve adequate improvement from corrective lenses), also medical indications (phacolytic glaucoma, phacomorphic glaucoma, phacoantigenic uveitis, dense cataract that obscures view of fundus in patients who require regular retinal evaluation [i.e. diabetes, glaucoma])

IOL Calculations (see Ch. 1, Optics)

Formulas: rough estimation, use IOL power (D) = A constant of IOL − 2.5 (axial length) − 0.9 (average keratometry)

ACD (anterior chamber depth) approximately 3.5 mm

First generation: ACD is constant

Second generation: ACD is based on axial length (AL)

Third generation (Holladay 1, Hoffer Q, SRK/T): ACD is based on AL and keratometry (K)

Fourth generation (Holladay 2): variables include AL, K, corneal diameter, ACD, lens thickness, refraction, and patient age. (Haigis): ELP (effective lens position) derived from a function rather than a single number; used in the IOLMaster instrument

Most accurate formulas according to axial length

Long eyes (AL > 26.0 mm): SRK/T, Holladay 2, Haigis (customized)

Medium-long eyes (AL 24.6–26.0 mm): Holladay 1 or 2

Medium eyes (AL 22.0–24.5 mm): Hoffer Q, Holladay 1 or 2, SRK/T, Haigis

Short eyes (AL < 22.0 mm): Hoffer Q, Holladay 2

A scan

error of 0.1 mm = 0.3 D error in lens power; however, the shorter the axial length, the greater the effect of a measurement error

Myopia: 1.75 D error per mm of AL error

Emmetropia: 2.35 D error per mm of AL error

Hyperopia: 3.75 D error per mm of AL error

Ultrasound waves travel faster through lens (1640 m/s) than either aqueous or vitreous (1532 m/s)

To correct any AL, use the formula: AL_corrected = AL_measured × (V_correct/V_measured)

Average measurements

Axial length: 23.5 mm (22.0–24.5 mm)

Keratometry: 43.0–44.0 D

Anterior chamber depth (ACD): 3.25 mm

Lens thickness: 4.6 mm

Ultrasound speeds:

PHAKIC EYE = 1550 m/s (avg)

APHAKIC EYE = 1532 m/s

PSEUDOPHAKIC EYE (depends on IOL material and thickness) = 1556 m/s for PMMA lens, 1487 m/s for silicone lens, and 1549 m/s for acrylic lens

More accurate method for calculating pseudophakic AL is to measure at 1532 m/s and to use correction factors:

PMMA: AL_corrected = AL₁₅₃₂ + 44% IOL thickness + 0.04

SILICONE: AL_corrected = AL₁₅₃₂ − 56% IOL thickness + 0.04

ACRYLIC: AL_corrected = AL₁₅₃₂ + 75% IOL thickness + 0.04

SILICONE OIL = 980–1040 m/s (this is only for the portion of the eye containing silicone); thus to find the correct AL, the previous formula can be used, or the eye can be measured using an average velocity: phakic eye with silicone oil = 1140 m/s. Alternatively, use optical biometry (IOLMaster or Lenstar)

If silicone oil is to be left in the eye, the index of refraction of the oil will cause a hyperopic refraction; therefore, adjust the IOL power by adding 3.0–3.5 D

Immersion technique is more accurate than contact because of corneal compression (0.1–0.2 mm) for the later method. Optical biometry is most accurate.

Contact A scan

5 spikes corresponding to beam reflection from interfaces: cornea, anterior lens surface, posterior lens surface, retina, sclera (Figure 10-7)

Causes of falsely long axial length:

Posterior staphyloma in high myopia; fovea may be located more anteriorly than the staphyloma

Measurement of the sclera rather than the retina

Wrong ultrasonic velocity (too fast)

Fluid meniscus between probe and cornea

Wrong gate position

Causes of falsely short axial length:

Excessive indentation of cornea with contact probe

Nonperpendicular measurement

Choroidal thickening or effusion

Vitreous opacity

Wrong ultrasonic velocity (too slow)

Wrong gate position

Figure 10-7 A-scan pattern of a phakic eye with the initial spike removed from the screen display. Identified are the 2 corneal peaks (CI and C2), the anterior lens spike (L1), the posterior lens spike (L2), and the retinal spike (R).

(From Shammas HJ: Intraocular lens power calculations. In Azar DT [ed]: Intraocular Lenses in Cataract and Refractive Surgery, Philadelphia, WB Saunders, 2001.)

Keratometry in patient following refractive surgery

need to determine accurate central corneal curvature; keratometer measures at 3 mm from center of cornea

CLINICAL HISTORY: K = preopK + (refraction preop − refraction postop)

Convert for vertex distance: refraction (corneal surface) = refraction (spectacle plane)/(1–0.012 refraction [spectacle plane])

CONTACT LENS: use plano rigid gas-permeable contact lens with known base curve

K = base curve of CL + power + refraction (with CL) − refraction (without CL)

Convert for vertex distance

CORNEAL TOPOGRAPHY: use central 1 mm effective power reading from the Holladay diagnostic summary map (not sim K readings)

FORMULAS: numerous methods; online calculators available

Presence of cataract may induce myopia, causing error in first method, and may cause poor vision with inability to perform adequate CL overrefraction; therefore, a variety of methods should be used, then take flattest K to use in IOL calculation and consider using a final IOL 1–2 D stronger to avoid a hyperopic result

Piggyback IOL

Hyperopia (1.5 D per 1.0 D of hyperopia)

if patient is +6.00, place a +9.00 D piggyback IOL.

Myopia (1.0 D per 1.0 D of myopia)

if patient is −6.00, place a −6.00 D piggyback IOL

Interface membranes have been reported between piggyback lenses

Viscoelastic Device (Ophthalmic Viscosurgical Device [OVD])

Variety of clear gel-like materials composed of sodium hyaluronate and chondroitin sulfate

Used intraocularly to maintain and preserve space, displace and stabilize tissue, and coat and protect corneal endothelium

Vary in molecular weight, viscosity, clarity, ease of removal, and potential for IOP spike if retained in eye (peak usually 4–6 hours postoperatively)

Classification

Cohesive agent (ability to adhere to itself): long-chain, high-molecular-weight, high surface tension (low coating capability), high degree of pseudoplasticity (ability to transform from high viscosity at rest [zero shear rate] to lower viscosity at high shear rate)

ADVANTAGES: capsulorhexis, insert IOL, ease of viscoelastic removal

Examples: Healon, Healon GV, Amvisc, Amvisc Plus, Provisc

Dispersive agent: short-chain, low-molecular-weight, low surface tension (high coating ability), low to moderate pseudoplasticity

ADVANTAGES: corneal coating, less IOP rise if retained, maintain space, move tissue

Examples: Viscoat, Vitrax, Ocucoat

Viscoadaptive agent: ultrahigh-molecular-weight, superviscous and cohesive at low shear rates, more dispersive at increasing shear rates; thus combines the advantages of cohesive and dispersive agents

Example: Healon 5

Phacodynamics

Irrigation

rate of fluid delivery; determined by bottle height above eye (34–110 cm); not adjusted by machine; depends on aspiration rate and wound leakage; maintains anterior chamber depth

Flow (aspiration rate [AFR])

rate of fluid removal (0–60 mL/min); determines how quickly vacuum is created; attracts material to tip

Vacuum (aspiration level)

negative pressure created at tip by pump (0–500 mmHg); holds material onto occluded tip

Pump systems

Flow-based: independent, direct control of AFR and vacuum; vacuum rise requires tip occlusion; physically contacts and regulates aspiration line fluid

PERISTALTIC: rollers compress tubing; AFR not smooth because of peristaltic wave; less accurate, especially at higher vacuum levels

SCROLL: scroll element orbits against housing; more accurate; can act clinically like Venturi pump

Vacuum-based: direct control of vacuum only; AFR indirectly controlled by vacuum level; vacuum not affected by changes in tip occlusion; indirectly contacts aspiration line fluid by the induced vacuum in rigid drainage cassette between line and pump

VENTURI: compressed air flows through tube; rapid, precise aspiration and vacuum response; requires external air supply

DIAPHRAGM: flexible membrane moves like a piston; outmoded, large noisy system

ROTARY VANE: wheel with vanes rotates; does not require external air supply

Hybrid: programmable like peristaltic or Venturi

Vacuum rise time

time for vacuum to reach preset limit; affected by aspiration rate; requires tip occlusion with peristaltic pump

Postocclusion surge (vacuum rush)

collapse of AC due to increase in aspiration rate to level of pump speed; during occlusion, vacuum builds to preset level, no flow occurs, and tubing collapses; when occlusion breaks, pump pulls fluid at preset rate and rebound of tubing pulls additional fluid through tip. Prevented by venting, rigid tubing, microprocessor in pump

Followability

ability to bring material to tip; function of flow and vacuum

Holdability

ability to keep material at tip; function of vacuum and power

Phaco power (0–100%)

depends on frequency and stroke length; surgeon (linear) or panel control; pushes material away from tip; generates heat.

Power factors: amplitude (fixed vs linear) and duration (continuous vs intermittent)

Power modulation: pulse, burst, bimodal, dual linear

Ultrasound effect

Fragmentation: mechanical (jackhammer effect)

Cavitation: sound waves expand and compress liquid, creating shock wave and microbubbles, which implode, forming cavity and dissolving nucleus in front of needle tip

Ultrasound instrument

Handpiece: produces vibration of needle

MAGNETORESTRICTIVE: converts magnetic energy into motion

PIEZOELECTRIC CRYSTAL: converts electricity into motion

Needle: oscillation produces phaco power

FREQUENCY: rate of oscillation (25–62 kHz)

STROKE LENGTH: distance of travel (0.002–0.004 inch [0.05–0.1 mm])

BEVEL: occlusion vs cutting (0–45°)

TIP SIZE/BORE: 0.9, 1.1, flared

SHAPE: straight, angled

INNOVATIONS: microflow, microseal, aspiration bypass (ABS), torsional, elliptical

Footpedal: usual settings; can be programmed differently

KICK LEFT: reflux

POSITION 0: resting

POSITION 1: irrigation

POSITION 2: aspiration

POSITION 3: ultrasound

Audible clues:

METALLIC CLICK: irrigation (plunger opens)

HUMMING: aspiration

BUZZING: ultrasound (harmonic overtones)

BELLS: occlusion (no flow)

Customized tones

Alternative systems: Sonic, Fluid, Laser

Complications of Cataract Surgery

Preoperative (retrobulbar/peribulbar injection)

Globe perforation

Retrobulbar hemorrhage

Strabismus (inferior rectus fibrosis or myotoxicity)

Central anesthesia

Retrobulbar Hemorrhage

May occur following retrobulbar injection or trauma; risk of CRAO as orbital pressure rises

Findings

marked proptosis, rapid orbital swelling and congestion, limited extraocular motility, hemorrhagic chemosis, lid ecchymosis and edema

Treatment

consider emergent surgical decompression with lateral canthotomy and cantholysis, hyperosmotic agents to lower IOP

Strabismus

Due to inferior rectus damage

Paralysis or fibrosis result from anesthetic injection

Central Anesthesia Following Retrobulbar Block

Agent spreads along meningeal cuff of optic nerve to enter CSF

Increased risk with 4% lidocaine

Findings

mental confusion, dysphagia, dyspnea, apnea, amaurosis of fellow eye

Wound Burn

Thermal injury from phaco needle due to lack of irrigation

Etiology

excessively tight incision, low or empty infusion bottle, low-flow settings, occluded phaco tip (with dispersive viscoelastic agent or impaled nucleus), phaco needle without thermal protective design

Findings

wound whitening, distortion, and astigmatism

Treatment

scleral relaxing incision, horizontal suture, bandage contact lens; if severe, may require astigmatic surgery after stabilization or patch graft

Iris Prolapse During Phaco

Wound too large or too posterior, bottle too high, posterior pressure, suprachoroidal hemorrhage

Intraoperative Floppy Iris Syndrome (IFIS)

Altered iris dilator tone due to systemic α-1 blocker medications (most commonly tamsulosin [Flomax]) with varying degrees of poor iris dilation and atonic floppy iris tissue (billows and prolapses), which may increase the risk of intraoperative complications during cataract surgery

Treatment

one or a combination of approaches depending on the severity of IFIS including preoperative topical atropine, intraoperative use of preservative free epinephrine, Healon 5, pupil expansion devices (i.e. Malyugin ring, Graether expander, Morcher dilator), iris hooks. Stopping the medication does not prevent IFIS and may lead to urinary retention

Descemet’s Membrane Detachment

Due to inadvertent stripping of Descemet’s from instrument insertion during surgery or viscoelastic injection; causes corneal edema or decompensation

Treatment

air or gas bubble, may require suture repair

Expulsive Suprachoroidal Hemorrhage

May occur during intraocular surgery or days later; incidence of 0.5%

Risk factors

elderly patient, hypertension, atherosclerosis, diabetes, sudden drop in IOP during surgery, high myopia, vitreous loss or previous vitrectomy, previous expulsive hemorrhage in fellow eye, glaucoma, aphakia, postoperative Valsalva maneuver

Findings

forward movement of intraocular contents during surgery and loss of red reflex (ominous sign), subretinal hemorrhage, choroidal detachment, and extrusion of intraocular contents; delayed hemorrhage presents with severe eye pain, nausea, vomiting, and rapid loss of vision

Treatment

close wound rapidly; may require surgical drainage

Prevention

decompress eye preoperatively, small wound, control BP during surgery, prevent bucking in patients under general anesthesia

Phototoxicity

Occurs in up to 39% for surgical time >100 minutes

Prevention

dim light, oblique light, pupil shield

Corneal Edema

Etiology

trauma to endothelium, elevated IOP, endothelial chemical toxicity, Descemet’s detachment, decompensation in patient with Fuchs’ corneal endothelial dystrophy

Corneal Ulceration and Melting

Occurs most commonly after cataract surgery in patients with keratoconjunctivitis sicca and rheumatoid arthritis; melting several weeks after uncomplicated cataract surgery due to collagenase release from surrounding inflammatory cells

Uveitis-Glaucoma-Hyphema (UGH) Syndrome

Due to repeated trauma to angle structures and iris by IOL; scarring and degeneration occur

Treatment

atropine, topical steroids, ocular hypotensive medications; consider argon laser of bleeding site; usually requires IOL explantation

Hyphema

Result of fine neovascularization of scleral incision (Swan syndrome) or mechanical trauma from IOL haptics

Occurs with more posteriorly located incisions

IOP can become dangerously elevated

Pupillary Capture

Portion of IOL optic anterior to iris

Risk factors

large or incomplete capsulorhexis, sulcus haptic placement, nonangulated IOL, upside-down IOL placement, vitreous pressure

Treatment

observe if long-standing and stable without symptoms; dilate and place patient supine if occurs early postoperatively; may require lens repositioning with microhook

IOL Decentration

Causes diplopia or polyopia because of prismatic effect

Sunset syndrome

inferior displacement of IOL within capsular bag; occurs with unrecognized zonular dialysis, capsular tears, or asymmetric IOL haptic implantation (1 in bag and other in sulcus)

Sunrise syndrome

asymmetric IOL haptic placement

Treatment

consider pilocarpine; IOL repositioning or exchange may be required

Capsular Block Syndrome

Due to retained viscoelastic behind IOL

Causes myopic shift

Treatment

Nd : YAG laser anterior capsulotomy

Anterior Capsular Contraction Syndrome (Capsular Phimosis)

Due to small capsulorhexis with retention of lens epithelial cells

Treatment

Nd : YAG laser radial anterior capsulotomies

Endophthalmitis

(See Ch. 8, Uveitis)

Rhegmatogenous Retinal Detachment

Incidence

Risk factors

high myopia, lattice degeneration, history of RD in fellow eye, vitreous loss

Mydriasis

Due to sphincter damage (mechanical from iris stretching or ischemic from elevated IOP (Urrets-Zavalia syndrome))

Ptosis

Due to trauma from lid speculum

Review Questions (Answers start on page 369)

1 The most helpful test for evaluating macular function in a patient with advanced cataract is

a blue field entoptic phenomenon

b 2-light separation

c red-light discrimination

d directional light projection

2 Ectopia lentis is least likely to be associated with

b pectus excavatum

c short stature

d mental retardation

3 Anterior segment signs of ciliary body melanoma include all of the following except

a corneal edema

b increased IOP

4 Which of the following is least characteristic of ICE syndrome?

a corneal edema

b increased IOP

c ectropion uveae

5 The crystalline lens is formed from which embryologic tissue?

6 A stellate anterior subcapsular cataract is most likely to be found in a patient with

a Fabry’s disease

b atopic dermatitis

c myotonic dystrophy

d electrical injury

7 The most useful diagnostic test in an infant with an oil-droplet cataract is

a urine amino acids

d urine reducing substances

8 Which of the following does not occur in siderosis bulbi?

b retinal atrophy

c sunflower cataract

9 A patient has a history of increased IOP with exercise; which finding is associated with this condition?

a Krukenberg spindle

d pars plana snowbank

10 Separation between the longitudinal and circumferential fibers of the ciliary muscle is called

b angle recession

c iridodialysis

d cyclodialysis

11 Characteristics of pigment dispersion syndrome include all of the following except

a increased IOP with exercise

b Krukenberg’s spindle

d radial iris transillumination defects

12 Genetics of aniridia are best summarized as

13 A sickle cell patient with a hyphema develops increased IOP; which of the following treatment choices is best?

14 A pigmentary retinopathy occurs in which mesodermal dysgenesis syndrome?

a Axenfeld’s anomaly

b Alagille’s syndrome

c Rieger’s syndrome

d Peter’s anomaly

15 Of the following causes of iris heterochromia, the involved iris is hyperchromic in

b Horner’s syndrome

c Waardenburg’s syndrome

d Fuchs’ heterochromic iridocyclitis

16 Which of the following iris lesions is a true tumor?

a Kunkmann-Wolffian body

b Koeppe nodule

d juvenile xanthogranuloma

17 At which location is the lens capsule thinnest?

a anterior capsule

b posterior capsule

c equatorial capsule

d anterior paracentral capsule

18 The iris sphincter is derived from what embryologic tissue?

a neural crest cells

b surface ectoderm

c neural ectoderm

19 Which of the following is not associated with sunset syndrome?

a asymmetric IOL haptic placement

c pseudoexfoliation

20 Lens epithelial cells differentiate into lens fibers

a anterior to the equator

b at the equator

c posterior to the equator

d in the fetal nucleus

21 Light of which wavelength is absorbed greatest by a dense nuclear sclerotic cataract?

22 A patient with background diabetic retinopathy and clinically significant macular edema desires cataract surgery. The most appropriate management is

a cataract surgery

b focal laser treatment then cataract surgery

c cataract surgery then panretinal photocoagulation

d cataract surgery with intraoperative laser treatment

23 After finishing phacoemulsification on a dense cataract, the surgeon notes whitening of the clear corneal incision. The most likely cause is

a tight incision

b high aspiration flow rate

c high phaco power

d 45° bevel phaco needle

24 Nuclear brunescence increases with higher concentrations of which lens protein?

a alpha crystallin

b beta crystallin

c gamma crystallin

d main intrinsic polypeptide

25 Lens fibers contain nuclei in all of the following conditions except

d Lowe’s syndrome

26 The most likely cause of an intraoperative complication during cataract surgery in a patient with pseudoexfoliation syndrome is

b thin posterior capsule

d shallow anterior chamber

27 The majority of glucose metabolism in the lens is by

b pentose phosphate pathway

c reduction to sorbitol

d conversion to glucuronic acid

28 The most appropriate systemic treatment for a patient with a sunflower cataract is

b penicillamine

29 Which of the following is the least likely cause of decreased vision 2 years after cataract surgery?

b retinal detachment

c posterior capsular opacity

d cystoid macular edema

30 Which type of cataract is most closely associated with UV-B exposure?

a anterior subcapsular

c nuclear sclerotic

d posterior subcapsular

Suggested readings

Abelson MB. Allergic Diseases of the Eye. Philadelphia: WB Saunders; 2001.

American Academy of Ophthalmology. Lens and Cataract, vol 11. San Francisco: AAO; 2012.

Boruchoff SA. Anterior Segment Disorder: A Diagnostic Color Atlas. Boston: Butterworth-Heinemann; 2001.

Elander RE, Rich LF, Robin JB. Principles and Practice of Refractive Surgery. Philadelphia: WB Saunders; 1997.

Jaffe NS, Jaffe MS, Jaffe GF. Cataract Surgery and Its Complications, 6th edn. St Louis: Mosby; 1997.

Mackie IA. External Eye Disease. Boston: Butterworth-Heinemann; 2003.

Watson P, Hazleman B, Pavesio C. Sclera and Systemic Disorders. Philadelphia: Butterworth-Heinemann; 2003.

Related

Review of Ophthalmology Expert Consult - Online and Print