Cataract: Differential Diagnosis, Investigation, and Management

Definition & Overview

Symptoms

• Reduced visual acuity - initially correctable with spectacles
• Loss of contrast sensitivity
• Change in colour perception - particularly impaired perception of blue colours
• Glare - from light scattering; worse with posterior subcapsular types; difficulty with night driving
• Monocular diplopia - especially with point sources of light
• "Second sight" - paradoxical improvement in near vision in nuclear sclerotic cataract due to increased refractive index causing acquired myopia

Classification & Differential Diagnosis

A. Age-Related (Acquired) Cataract

1. Posterior Subcapsular (PSC) Cataract

• Granular or plaque-like opacity just in front of the posterior capsule
• On retroillumination: appears black and vacuolated (Wedl/bladder cells)
• Located at the nodal point - disproportionately profound effect on vision
• Worse symptoms: glare, near vision difficulty (miosis makes it worse in bright light and near tasks)
• Strong association with: corticosteroids, diabetes, radiation, uveitis, retinitis pigmentosa

2. Nuclear Sclerotic Cataract

• Exaggeration of normal ageing
• Yellowish-brown hue from urochrome pigment deposition
• Best assessed with oblique slit-lamp beam
• Retroillumination: good red reflex but subtle nucleus-cortex distinction
• When advanced: brunescent (brown) or rarely black (nigra) cataract
• Associated with acquired myopia ("second sight of the aged")

3. Cortical Cataract

• Involves anterior, posterior, or equatorial cortex
• Begins as clefts and vacuoles due to cortical hydration
• Classic cuneiform (wedge-shaped) or radial spoke-like opacities
• Often starts in the inferonasal quadrant
• Glare is a prominent symptom

4. Christmas Tree Cataract (Uncommon)

• Polychromatic needle-like formations in deep cortex and nucleus
• Often associated with myotonic dystrophy

Advanced States of Maturity

Fig. 10.2 - Age-related cataract morphological types (Kanski's Clinical Ophthalmology)

B. Cataract in Systemic Disease

Fig. 10.4B - Stellate PSC spokes in myotonic dystrophy (retroillumination) (Kanski's)

C. Secondary (Complicated) Cataract

• Uveitis - anterior plaque opacities; extensive posterior synechiae
• Glaucoma - Glaukomflecken: anterior subcapsular grey-white opacities after acute angle-closure attack
• Retinitis pigmentosa / Leber congenital amaurosis / Gyrate atrophy / Stickler syndrome - PSC opacity
• Medications: systemic and topical corticosteroids (PSC); chlorpromazine (anterior star-shaped opacity)

D. Traumatic Cataract

• Most common cause of unilateral cataract in young people
• Penetrating trauma: direct lens capsule breach
• Blunt trauma: classic flower-shaped opacity (Vossius ring imprint)
• Electric shock/lightning: diffuse milky-white or multiple snowflake stellate subcapsular opacities
• Infrared radiation ("glassblower's cataract"): true exfoliation of anterior lens capsule
• Ionizing radiation: PSC opacity (delayed, months-years post-exposure)

E. Congenital Cataract

• Incidence: ~3 in 10,000 live births
• Aetiology: 1/3 systemic disease; 1/3 inherited (most commonly autosomal dominant); 1/3 unknown
• 2/3 bilateral (cause found in ~50%); unilateral cases usually sporadic

• Rubella: pearly nuclear or diffuse bilateral opacity (~15%)
• Toxoplasmosis: cataract + chorioretinitis
• CMV: cataract + chorioretinitis + microcephaly
• Varicella: cataract + microphthalmos

• Galactosaemia: oil-droplet opacity (reversible with dietary exclusion of galactose)
• Lowe syndrome: universal cataract + microphakia + congenital glaucoma in 50%
• Mannosidosis: posterior cortical spoke-like opacities

Differential Diagnosis of Leukocoria (White Pupil)

Investigation

Ophthalmic Assessment (Pre-operative)

Systemic Workup (Pre-operative)

• Routine tests (bloods, ECG) are not required for local anaesthesia
• If general anaesthesia planned: U&E, random blood glucose, FBC, ECG
• Relevant medication review: alpha-blockers (intraoperative floppy iris syndrome - IFIS), anticoagulants (INR check within 72 hours), metformin (if contrast planned)

Investigation for Congenital Cataract

• TORCH serology (rubella IgM, CMV, toxoplasma)
• Urine for reducing substances (galactosaemia)
• Urine amino acids (Lowe syndrome)
• Serum galactose-1-phosphate uridyltransferase
• Chromosomal karyotype if dysmorphic features
• Paediatric/genetics referral

Management

Conservative (Non-Surgical) Measures

• Refractive correction: spectacles or contact lenses may help in early cataract
• Pupil dilation (mydriatic drops) can transiently improve vision in PSC cataracts by allowing light around the opacity
• Lifestyle advice: increase lighting, magnification aids
• No proven pharmacological therapy to prevent or reverse cataract

Surgical Indications

1. Visual indications: opacity sufficient to interfere with daily activities (driving, reading, occupation)
2. Medical indications:
   • Phacolytic glaucoma (mature cataract leaking protein causing macrophage-mediated trabecular obstruction)
   • Phacomorphic glaucoma (intumescent lens causing angle-closure)
   • Improved fundus view for monitoring/treating posterior segment disease

Surgical Options

1. Phacoemulsification with IOL Implantation (Gold Standard)

1. Preparation: topical antiseptic (povidone-iodine 5%), draping, speculum
2. Incisions: corneal side port + main clear corneal incision (typically temporal)
3. Viscoelastic injection into anterior chamber
4. Continuous curvilinear capsulorhexis (CCC): circular opening in anterior capsule
5. Hydrodissection: fluid injection under capsule to separate nucleus from cortex
6. Nuclear division: "Divide and conquer" (two perpendicular grooves, cracking into quadrants) or "Phaco chop" (faster, lower energy)
7. Emulsification and aspiration of nuclear quadrants
8. Cortex aspiration: irrigation-aspiration (I/A) handpiece
9. IOL implantation into capsular bag
10. Wound closure: typically self-sealing

• Topical (drops/gel ± intracameral lidocaine) - most common; no akinesia
• Sub-Tenon block - good anaesthesia, variable akinesia
• Peribulbar block - effective anaesthesia and akinesia; avoid in long eyes (axial >25 mm)
• General anaesthesia - children, uncooperative patients, tremor, dementia

2. Femtosecond Laser-Assisted Cataract Surgery (FLACS)

• Laser performs incisions, CCC, and nuclear fragmentation
• Standard phacoemulsification provides equivalent results in most studies

3. Small Incision Cataract Surgery (SICS) / Manual ECCE

• Used in low-resource settings or very hard nuclei

Intraocular Lens (IOL) Types

Post-operative Care

• Topical antibiotic + steroid drops (e.g., 4-6 weeks)
• Review at Day 1, Week 1, 4-6 weeks
• Refraction at ~6 weeks for spectacle prescription

Complications of Cataract Surgery

Intraoperative

• Posterior capsular rupture with vitreous loss (<1% experienced surgeons)
• Zonular dehiscence
• Dropped nucleus (~0.2%)
• IFIS (with alpha-blockers)

Early Post-operative

• IOP spike
• Iridocyclitis
• Corneal oedema
• Wound leak

Late Post-operative

• Posterior capsular opacification (PCO): most common late complication; Elschnig pearl formation or fibrosis-type PCO; treated with Nd:YAG laser posterior capsulotomy
• Cystoid macular oedema (CMO)
• Retinal detachment (<1%)
• IOL dislocation/subluxation
• Endophthalmitis (0.1%) - most serious infectious complication

PCO Treatment (Nd:YAG Capsulotomy)

• Indication: reduced VA or glare from PCO
• Power: start at 1 mJ/pulse; cruciate or circumferential pattern; opening ~4-5 mm
• Complications: IOL pitting, IOP spike, retinal detachment risk (warn myopes), CMO

Congenital Cataract Management

• Timing is critical - amblyopia risk means surgery should not be delayed
• Bilateral visually-significant cataracts: surgery within first weeks of life
• Unilateral: surgery within 6-10 weeks, followed by aggressive patching of the fellow eye
• Optical correction post-surgery (contact lenses in infants, glasses when older)
• Amblyopia treatment (occlusion/patching) is essential