Note: The library does not contain K.K. Khurana's Comprehensive Ophthalmology directly. The answer below is drawn from Kanski's Clinical Ophthalmology: A Systematic Approach (10th ed.), which covers the same cataract content at an equivalent or greater depth. Topics align closely with the Khurana syllabus.

CATARACT

Introduction & Definition

Anatomy of the Lens

Fig. 10.1 (A) Cross-sectional anatomy of the anterior segment; (B) histological features - epithelial cells are anterior; zones not drawn to scale

• Zonules hold the lens in position
• Capsule - an acellular membrane enclosing the lens
• Epithelial cells - cuboid cells beneath the anterior capsule extending to the equator; cells in the germinative zone divide continuously and differentiate into lens fibers
• Lens substance - central nucleus surrounded by cortical material
• Primary function - to focus light on the retina

Effect on Vision

• (a) The type of cataract
• (b) Its location (central opacities affect vision more)
• (c) Whether it is unilateral or bilateral

ACQUIRED CATARACT

Age-Related Cataract

1. Subcapsular Cataract

• Anterior subcapsular cataract: lies directly under the lens capsule; associated with fibrous metaplasia of the lens epithelium
• Posterior subcapsular opacity (PSC): lies just in front of the posterior capsule; granular or plaque-like on oblique slit-lamp; appears black and vacuolated on retroillumination. Vacuoles are swollen migratory lens epithelial cells (Wedl/bladder cells). Located at the nodal point - has a particularly profound effect on vision. Patients suffer from glare (e.g., from oncoming car headlights); symptoms increase with miosis (near work, bright light)

2. Nuclear Sclerotic Cataract

• An exaggeration of normal ageing change
• Associated with myopia (increased refractive index of nucleus) - some elderly patients can read without glasses again = "second sight of the aged"
• Characterized by a yellowish hue from deposition of urochrome pigment
• Best assessed with oblique slit-lamp beam
• When advanced, nucleus appears brown (brunescent); in rare cases, black

3. Cortical Cataract

• May involve anterior, posterior, or equatorial cortex
• Opacities start as clefts and vacuoles between lens fibers due to cortical hydration
• Progress to cuneiform (wedge-shaped) or radial spoke-like opacities, often starting in the inferonasal quadrant
• Glare is a common symptom

4. Christmas Tree Cataract

• Uncommon; characterized by polychromatic needle-like formations in the deep cortex and nucleus

Cataract Maturity

Fig. 10.3A - Mature cataract with complete lens opacity

Cataract in Systemic Disease

Diabetes Mellitus

• Hyperglycaemia → high glucose in aqueous → diffuses into lens → metabolized to sorbitol (by aldose reductase) → accumulates → secondary osmotic overhydration
• Mild: fluctuation in refractive index (hyperglycaemia = myopia; hypoglycaemia = hypermetropia)
• Classic diabetic cataract (young patients): snowflake cortical opacities - rare, may mature within days or resolve spontaneously
• Age-related cataract occurs sooner in diabetics
• Nuclear sclerosis is common and progresses rapidly
• ~1 in 5 cataract surgery patients have diabetes

Myotonic Dystrophy

• ~90% develop fine iridescent cortical opacities in the third decade (sometimes like Christmas tree cataract)
• Evolve into wedge-shaped cortical and subcapsular opacities, often star-like, by the fifth decade

Neurofibromatosis Type 2 (NF2)

• Early cataract in >60% of patients
• Opacities: posterior subcapsular, capsular, cortical or mixed; tend to develop in early adulthood

Secondary (Complicated) Cataract

• Chronic anterior uveitis - most common cause; also related to steroid use. Earliest finding: polychromatic lustre at the posterior lens pole. Progresses to posterior and anterior opacities
• Acute congestive angle closure - forms glaukomflecken (small anterior grey-white subcapsular opacities); represent focal lens epithelial infarcts; pathognomonic of previous acute angle closure
• High myopia - posterior subcapsular opacity and early-onset nuclear sclerosis

Traumatic Cataract

• Penetrating trauma - direct damage to capsule and lens fibers
• Blunt trauma - classic flower-shaped (rosette) opacity
• Intralenticular metallic foreign body
• Electric shock and lightning strike
• Infrared radiation - "glassblower's cataract" (anterior capsular opacity)
• Ionizing radiation

CONGENITAL CATARACT

• 1/3 associated with systemic disease
• 1/3 inherited
• 1/3 of unknown cause
• 2/3 bilateral; cause identifiable in ~half
• Autosomal dominant (AD) inheritance is the most common aetiological factor
• Unilateral cataracts are usually sporadic

Associated Metabolic Disorders

Associated Intrauterine Infections

MANAGEMENT OF ACQUIRED CATARACT

Indications for Surgery

1. Visual improvement - most common; when opacity causes difficulty in daily activities
2. Medical indications - cataract adversely affecting eye health (e.g., phacolytic or phacomorphic glaucoma; to visualize fundus for monitoring/treatment)
3. Clear lens exchange - for refractive error correction (replacing a healthy lens)

Preoperative Considerations

• Systemic alpha-blockers (e.g., tamsulosin) - associated with intraoperative floppy iris syndrome (IFIS); stop or manage accordingly
• Anticoagulants/antiplatelets - follow local protocol
• Routine blood tests and ECG not usually required for local anaesthesia
• Diabetics: monitor retina before and after surgery (risk of worsening macular oedema)

Surgical Technique - Phacoemulsification