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I now have enough textbook content from Kanski's Clinical Ophthalmology to compile comprehensive notes. Let me write them out.
Lens & Cataract - Complete Notes
Ophthalmology | NEET PG / INI-CET / FMGE
(Based on Dr. Sudha Seetharam's lecture + Kanski's Clinical Ophthalmology, 10th Ed.)
1. ANATOMY OF THE LENS
Macro-anatomy
- Biconvex, transparent, avascular, and has no nerve supply
- Located behind the iris, in front of the vitreous
- Suspended by zonules of Zinn (arising from ciliary body)
- Nutrition derived entirely from aqueous humor
- Refractive power: ~+20D (total eye ~+60D); second major refractive medium after cornea
Micro-anatomy (Histological Layers)
| Layer | Features |
|---|---|
| Lens capsule | Outermost; acellular elastic membrane; thicker anteriorly |
| Anterior epithelium | Single layer of cuboid cells; absent posteriorly |
| Germinative zone | At equator; cells divide continuously → differentiate into lens fibers |
| Lens fibers | Make up the cortex (new) and nucleus (old, compacted) |
| Nucleus | Central compact region; oldest cells |
Biochemical Composition
- Water: ~65%, proteins: ~35% (crystallins - alpha, beta, gamma)
- Crystallins maintain transparency
- Metabolism: primarily anaerobic glycolysis (Embden-Meyerhof pathway)
- Sorbitol pathway (polyol pathway): glucose → sorbitol via aldose reductase - significant in diabetes
- No blood vessels or lymphatics = dependent on aqueous humor for nutrients
2. CONGENITAL CATARACT
Causes (Aetiology)
| Category | Examples |
|---|---|
| Genetic | Autosomal dominant (most common hereditary type) |
| Intrauterine infections (TORCH) | Rubella (pearly white nuclear cataract), CMV, Toxoplasma |
| Metabolic | Galactosemia (oil-droplet cataract), Lowe syndrome, Hypoglycaemia |
| Idiopathic | Most common overall cause |
Exam point: Rubella = nuclear cataract; Galactosemia = oil-droplet (zonular) cataract
Morphological Types
| Type | Features |
|---|---|
| Zonular (Lamellar) | Most common type; affects a specific layer of lens; shell-like opacity; "riders" at periphery |
| Nuclear | Rubella; small, dense; common |
| Sutural | Along Y-sutures; vision usually not affected |
| Polar | Anterior or posterior; small opacity at pole |
| Blue-dot (cerulean) | Scattered small bluish opacities; usually benign |
| Total (complete) | Entire lens opaque; worst visual prognosis |
Most common congenital cataract = Zonular/Lamellar
Clinical Presentation
- Leukocoria - white pupillary reflex (key sign; DDx: retinoblastoma, ROP, PHPV)
- Nystagmus - indicates poor visual development (poor prognostic sign)
- Strabismus (squint) - due to unilateral poor vision
- Amblyopia ("lazy eye") - if untreated, especially unilateral cases
Management
- Surgery is urgent to prevent amblyopia - ideally within 6-10 weeks of birth for dense cataracts
- Posterior capsulotomy + anterior vitrectomy mandatory in children (posterior capsule fibroses rapidly)
- Post-op: patching of good eye + optical correction to encourage visual development
3. ACQUIRED (SENILE) CATARACT
Pathogenesis of Age-related Cataract
- Oxidative stress → protein aggregation (high molecular weight aggregates)
- Loss of glutathione (antioxidant) → disulfide cross-linking of crystallins
- Hydration of cortex, compaction of nucleus
- UV radiation plays a role
Types of Senile Cataract
A. Posterior Subcapsular Cataract (PSC)
- Opacity just in front of the posterior capsule
- Granular/plaque-like on oblique slit-lamp; black and vacuolated on retroillumination
- Vacuoles = swollen migratory lens epithelial cells (Wedl/bladder cells)
- Most symptomatic - at nodal point of eye → profound visual effect
- Worse in bright light (miosis moves pupil over opacity) and near vision
- Severe glare (e.g., headlights at night)
- Associated with: steroids (systemic or topical), trauma, uveitis, radiation
B. Nuclear Sclerotic Cataract
- Exaggeration of normal aging change
- Progressive yellowing → brown → black (due to urochrome pigment)
- Associated with myopia (increased refractive index of nucleus)
- Classic: "Second sight of the aged" = elderly person can suddenly read without glasses again (induced myopia)
- Best assessed with oblique slit-lamp beam
C. Cortical Cataract
- Starts as clefts and vacuoles in cortex due to cortical hydration
- Typical cuneiform (wedge-shaped) or spoke-like opacities
- Often begins in inferonasal quadrant
- Glare is a common symptom
D. Christmas Tree Cataract
- Polychromatic needle-like formations in deep cortex and nucleus
- Associated with myotonic dystrophy
- Uncommon
Maturity of Cataract
| Stage | Description | Clinical Features |
|---|---|---|
| Immature | Partially opaque lens | Iris shadow present (on oblique illumination) |
| Mature | Completely opaque; no fundal glow | Iris shadow absent; white pupil |
| Hypermature | Shrunken, wrinkled anterior capsule | Leakage of water out |
| Morgagnian | Liquefied cortex; nucleus sinks inferiorly | Floating nucleus |
Iris shadow test: In immature cataract, light from a torch casts a crescent shadow of the iris on the lens (iris shadow present). In mature cataract, no shadow (lens is fully opaque).
Complications of Advanced Cataract
Phacomorphic Glaucoma
- Intumescent (swollen) lens → pupillary block → Angle-closure glaucoma
- Occurs in mature/hypermature stage
- Mechanism: swollen lens pushes iris forward → obstructs angle
- Treatment: urgent lens extraction after controlling IOP
Phacolytic Glaucoma
- Hypermature cataract → leakage of lens proteins through the intact (but permeable) capsule
- Lens proteins → phagocytosed by macrophages → macrophages + proteins block trabecular meshwork
- Mechanism: Open-angle glaucoma
- Treatment: lens extraction (definitive)
Memory tip:
- Phacomorphic = Morphology (shape) problem → angle closure
- Phacolytic = Lysis (protein leak) → open angle
4. OTHER ACQUIRED CATARACTS
Metabolic Causes
| Disease | Cataract Type | Notes |
|---|---|---|
| Diabetes mellitus | "Snowflake" cortical opacities | Young patients; may resolve or mature rapidly; also causes nuclear sclerosis in older patients |
| Galactosemia | Oil-droplet / zonular | Reversible if galactose restricted early |
| Hypocalcaemia | Subcapsular, punctate | Associated with hypoparathyroidism |
| Wilson's disease | "Sunflower" cataract | Anterior capsular copper deposits; spoke-wheel pattern |
Toxic / Drug-induced Cataracts
| Agent | Type |
|---|---|
| Corticosteroids (systemic or topical) | Posterior subcapsular (PSC) |
| Phenothiazines | Anterior subcapsular |
| Busulphan | Posterior subcapsular |
| Amiodarone | Stellate anterior subcapsular |
Traumatic Cataract
- Blunt trauma → Rosette-shaped (stellate) cataract - classic exam answer
- Penetrating injury → rapid opacification
- Vossius ring = ring of iris pigment on anterior lens capsule after blunt trauma (not a cataract itself)
- Electric/lightning injury → subcapsular opacities
- Radiation → posterior subcapsular
5. PRE-OPERATIVE EVALUATION
History
- Visual demands of the patient (occupation, lifestyle)
- Systemic: Diabetes, hypertension, bleeding disorders, cardiac/respiratory status
- Tamsulosin (alpha-blocker for BPH) → Intraoperative Floppy Iris Syndrome (IFIS) - surgeon must be warned
- Any previous eye surgery, trauma, uveitis
Clinical Examination
Visual Acuity Testing
- Snellen chart - distance vision
- Check each eye separately
- Also assess vision in light/dark (functional assessment)
Pupillary Reflexes
- Afferent Pupillary Defect (APD/RAPD) - if present, suggests retinal or optic nerve disease → poor visual prognosis even after cataract surgery
Iris Shadow Test
- Immature cataract: iris shadow present
- Mature cataract: no iris shadow
- Helps differentiate without slit lamp
Projection of Rays (POR)
- In mature cataract (no fundal view), project light in 4 quadrants
- Good POR in all quadrants → retina likely intact
- Poor POR → suspect retinal detachment
Slit Lamp Examination
- Grade nuclear opalescence, cortical changes, PSC
- LOCS III grading system (Lens Opacities Classification System)
- Assess: corneal health (Fuchs' endothelial dystrophy), depth of anterior chamber (risk of angle-closure)
Posterior Segment Evaluation
- If cataract too dense for direct view → B-scan ultrasound to exclude retinal detachment, vitreous hemorrhage, posterior segment tumour
Lacrimal Sac Syringing
- Mandatory before cataract surgery
- Rules out chronic dacryocystitis (infection of lacrimal sac)
- Dacryocystitis → source of organisms → risk of post-operative endophthalmitis
Investigations
| Investigation | Purpose |
|---|---|
| A-scan ultrasound | Measures axial length of eye |
| Keratometry (K-readings) | Measures corneal curvature |
| IOL power calculation | Using SRK formula (Sanders-Retzlaff-Kraff): P = A - 2.5L - 0.9K (A = A-constant, L = axial length, K = keratometry) |
| B-scan USG | Posterior segment if dense cataract |
| Specular microscopy | Corneal endothelial cell count (if <1500 cells/mm², high risk of corneal decompensation) |
| Blood glucose & BP | Systemic control before surgery |
Pre-operative Preparation
- Topical antibiotics (e.g., ciprofloxacin) x 3 days before
- Pupil dilation - topical mydriatics (tropicamide + phenylephrine)
- Local anaesthesia options: peribulbar, sub-Tenon's, or topical (modern)
6. HIGH-YIELD EXAM SUMMARY
| Fact | Answer |
|---|---|
| Most common cause of reversible blindness worldwide | Cataract |
| Most common type of congenital cataract | Zonular (lamellar) |
| Rubella cataract type | Nuclear; pearly white |
| "Second sight of the aged" | Nuclear sclerotic cataract → induced myopia |
| Steroid-induced cataract | Posterior subcapsular (PSC) |
| Diabetic cataract (young) | Snowflake cortical |
| Traumatic cataract shape | Rosette / stellate |
| Wilson's disease cataract | Sunflower cataract |
| Phacomorphic glaucoma mechanism | Swollen lens → angle closure |
| Phacolytic glaucoma mechanism | Leaked proteins → open-angle |
| Most symptomatic cataract | PSC (nodal point, glare in bright light) |
| Worst glare in | PSC |
| Pre-op mandatory test (dacryocystitis) | Lacrimal sac syringing |
| Pre-op test for retina if dense cataract | B-scan USG |
| Drug causing IFIS in cataract surgery | Tamsulosin |
| IOL power formula (common) | SRK formula |
| Iris shadow: present vs absent | Immature vs Mature cataract |
| Morgagnian cataract | Hypermature; nucleus sinks in liquefied cortex |
Source: Dr. Sudha Seetharam - PW MedEd NEET PG Lecture | Kanski's Clinical Ophthalmology, 10th Ed.
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