Corneal Dystrophies & Degenerations

Corneal dystrophies are bilateral, symmetric, inherited, progressive disorders with no relation to systemic disease or inflammation, whereas degenerations are usually unilateral or asymmetric, often age-related or secondary to other ocular/systemic conditions. This single distinction (inherited & symmetric vs. acquired & asymmetric) is the backbone of almost every NEET PG question on this chapter, and the staining/inheritance triad of the stromal dystrophies is a perennial favourite.

Quick conceptual framework

Think of the cornea as five layers from front to back — epithelium → Bowman membrane → stroma → Descemet membrane → endothelium. Dystrophies are classically grouped by the layer they primarily affect, and this anatomical localisation also predicts the symptoms:

• Epithelial/Bowman dystrophies → recurrent corneal erosions, pain, photophobia.
• Stromal dystrophies → progressive painless loss of vision (opacities in the stroma).
• Endothelial dystrophies → corneal oedema, morning blurring of vision (Fuchs).

High-yield: Dystrophies are bilateral, symmetric, hereditary, progressive, avascular and NOT associated with systemic disease or prior inflammation. Any unilateral, vascularised, or post-inflammatory corneal lesion is a degeneration, not a dystrophy.

Classification of corneal dystrophies (by layer)

Layer	Dystrophy	Inheritance	Key feature
Epithelial	Cogan / Map-dot-fingerprint (EBMD)	AD (often sporadic)	Commonest; recurrent erosions
Epithelial	Meesmann dystrophy	AD	Tiny intraepithelial cysts
Bowman	Reis–Bücklers (CDB1)	AD	Geographic Bowman opacities, erosions
Stroma	Granular (Groenouw type I)	AD	Discrete crumb/breadcrumb deposits
Stroma	Macular (Groenouw type II)	AR	Diffuse haze, earliest visual loss
Stroma	Lattice	AD	Refractile branching lines (amyloid)
Stroma	Schnyder crystalline	AD	Cholesterol crystals, ↑ lipids
Descemet/Endothelium	Fuchs endothelial	AD (late onset)	Corneal oedema, guttae
Endothelium	Posterior polymorphous (PPMD)	AD	Vesicular/band lesions
Endothelium	CHED	AR (CHED2) / AD (CHED1)	Congenital oedematous cloudy cornea

High-yield: Of all stromal dystrophies, macular dystrophy is the only autosomal recessive one and is also the earliest to cause visual impairment and most severe. Granular and lattice are autosomal dominant.

The stromal dystrophy triad — staining (most-tested)

This is the single most frequently asked image/match-the-following in ophthalmology. Memorise the deposit + stain pairing.

Dystrophy	Inheritance	Deposit	Special stain	Pattern
Granular (Groenouw I)	AD	Hyaline	Masson trichrome (red)	Discrete white "breadcrumbs", clear intervening stroma
Macular (Groenouw II)	AR	Mucopolysaccharide (GAG)	Alcian blue / colloidal iron / PAS	Diffuse cloudy opacities reaching limbus, hazy intervening stroma
Lattice	AD	Amyloid	Congo red (apple-green birefringence) / Crystal violet / Thioflavin-T	Refractile branching glass-like lines

High-yield: Granular = Hyaline = Masson trichrome (red). Macular = Mucopolysaccharide = Alcian blue/PAS (mucin). Lattice = Amyloid = Congo red (apple-green birefringence).

Mnemonics:

• "Marilyn Monroe Always Gets Her Men in LA County" — Macular → Mucopolysaccharide → Alcian blue; Granular → Hyaline → Masson; Lattice → Amyloid → Congo red.
• For inheritance: "GRanular & Lattice are Right (dominant), Macular is Mum's recessive."

Two extra exam pearls on stromal dystrophies:

• Lattice dystrophy is associated with recurrent corneal erosions (amyloid involves superficial stroma/Bowman) and the gene is TGFBI (BIGH3) on chromosome 5q31 — the same gene mutated in granular and Reis–Bücklers. Macular dystrophy is due to CHST6 gene mutation (carbohydrate sulfotransferase) → defective keratan sulphate.
• Lattice type II = Meretoja syndrome (systemic gelsolin amyloidosis): lattice lines + cranial/peripheral neuropathy + mask-like facies + cutis laxa. This systemic association is a classic distractor — it is the exception where a "dystrophy" has systemic links.

Fuchs endothelial dystrophy (most clinically important)

A bilateral, late-onset (>50 years), female-preponderant, autosomal dominant endothelial dystrophy caused by progressive loss/dysfunction of corneal endothelial pump cells.

Pathophysiology flow: Endothelial cell loss → reduced pump function → stromal & epithelial oedema → Descemet membrane thickening with guttae → bullous keratopathy → ruptured bullae → pain & scarring.

Clinical stages:

1. Cornea guttata — beaten-metal / "endothelial dewdrops" appearance on specular reflection; central Descemet excrescences. Asymptomatic.
2. Stromal & epithelial oedema — patient complains of blurred vision worse in the morning (lids closed overnight trap moisture; clears through the day as evaporation occurs).
3. Bullous keratopathy — epithelial bullae, pain on rupture, eventual subepithelial fibrosis.

High-yield: Morning blurring of vision that improves through the day is the hallmark symptom of Fuchs (overnight hypoxia/oedema clears with daytime evaporation). The earliest sign is corneal guttae seen on specular microscopy.

Investigations:

• Specular microscopy — ↓ endothelial cell density (normal ~2500–3000 cells/mm²), ↑ polymegathism (variation in size) and ↑ pleomorphism (variation in shape), guttae appear as dark bodies.
• Pachymetry — increased central corneal thickness (oedema; normal ~540 µm).
• Confocal microscopy / slit-lamp — beaten-bronze endothelium.

Management ("least → most"): Topical hypertonic saline (5% NaCl) drops/ointment + warm-air drying → lowering IOP → therapeutic soft bandage contact lens for painful bullae → definitive surgery: endothelial keratoplasty (DSEK / DMEK) is now preferred over penetrating keratoplasty (PK).

High-yield: DMEK/DSEK (endothelial keratoplasty) is the surgery of choice for Fuchs/bullous keratopathy because the pathology is confined to Descemet + endothelium; DMEK gives the best visual outcomes. Cataract surgery in a Fuchs patient (low cell count) risks pseudophakic bullous keratopathy — a common post-op cause of corneal oedema.

Corneal degenerations (acquired)

Degenerations are age-related or secondary, frequently unilateral/asymmetric, may be peripheral and vascularised. Key entities for NEET PG:

Arcus senilis (gerontoxon)

• Bilateral peripheral white/grey ring of lipid (cholesterol) deposition in peripheral stroma, separated from the limbus by a clear zone (lucid interval of Vogt).
• Common & benign >60 years. When seen <40 years (arcus juvenilis) → suspect hyperlipidaemia / familial dyslipidaemia — investigate lipid profile.
• Unilateral arcus suggests contralateral carotid disease (decreased lipid delivery to the normal side).

Band-shaped keratopathy (band keratopathy)

• Horizontal band of calcium (hydroxyapatite) deposition in the interpalpebral zone at the level of Bowman membrane, with characteristic "Swiss-cheese" lucent holes (where corneal nerves pierce Bowman) and a clear interval at the limbus.
• Causes: chronic uveitis (esp. juvenile idiopathic arthritis), hypercalcaemia (hyperparathyroidism, sarcoidosis, vitamin D excess, milk-alkali), chronic glaucoma, phthisis bulbi, silicone oil, hyperphosphataemia.
• Treatment: chelation with EDTA (disodium edetate) after epithelial removal; phototherapeutic keratectomy (PTK) for residual.

High-yield: Band keratopathy = calcium at Bowman's in the interpalpebral strip; treat with EDTA chelation. A child with band keratopathy → think JIA-associated uveitis.

Other degenerations (one-liners)

• Salzmann nodular degeneration — bluish-white superficial nodules, often post chronic keratitis/trachoma.
• Terrien marginal degeneration — peripheral thinning, superonasal, with lipid line, slowly progressive, painless.
• Spheroidal (Labrador / climatic droplet) degeneration — golden-yellow spheroidal deposits from UV/actinic exposure.
• Vogt limbal girdle, Hassall–Henle bodies (peripheral guttae, normal ageing — the benign peripheral counterpart of central Fuchs guttae), and crocodile shagreen are benign ageing changes.

Pterygium vs. pseudopterygium (classic differentiation)

A pterygium is a triangular, wing-shaped fibrovascular degeneration of the bulbar conjunctiva encroaching onto the cornea, typically nasal, related to chronic UV/dust exposure (elastotic degeneration of subepithelial tissue). A pseudopterygium is a fold of conjunctiva adherent to the cornea following a peripheral corneal ulcer/chemical burn/trauma — i.e., an inflammatory scar, not a true degeneration.

Feature	Pterygium (true)	Pseudopterygium
Nature	Degenerative (UV/actinic)	Inflammatory / post-ulcer scar
Site	Usually nasal interpalpebral	Any site (where the insult was)
Age/onset	Older, chronic	Any age, follows specific event
Stocker line	Iron line at advancing head	Absent
Probe test	Probe cannot pass beneath (adherent throughout)	Probe CAN pass beneath the neck (only head adherent)
Progression	Progressive	Stationary

High-yield: The probe (bridge) test is the single best bedside discriminator — a probe passes under the neck of a pseudopterygium but cannot pass under a true pterygium because the latter is adherent throughout. Pterygium has a Stocker line (iron) and a cap (Fuchs islets) at its advancing head.

Pterygium parts: Head (apex on cornea) → Neck (limbus) → Body (sclera/conjunctiva), with the cap (avascular halo, Fuchs islets) ahead of the head. Treatment: surgical excision with conjunctival autograft (lowest recurrence) — bare-sclera excision has the highest recurrence; adjuncts include mitomycin-C.

Keratoconus — a non-inflammatory ectatic "degeneration"

Although ectasias are sometimes classified separately, NEET frequently bundles keratoconus here. It is a bilateral, asymmetric, progressive central/paracentral corneal thinning and conical protrusion.

Signs:

• Munson sign — V-shaped lid bulge on downgaze.
• Fleischer ring — iron deposit at the base of the cone.
• Vogt striae — vertical deep stromal stress lines that disappear on pressure.
• Oil-droplet reflex on retroillumination; scissoring on retinoscopy; acute hydrops (Descemet rupture → sudden oedema).
• Associations: atopy/eye-rubbing, Down syndrome, Marfan, Leber congenital amaurosis, Ehlers–Danlos, retinitis pigmentosa.

Investigation of choice: corneal topography / tomography (Placido disc / Scheimpflug e.g. Pentacam) showing inferior steepening. Management ladder: spectacles → rigid gas-permeable (RGP) contact lens → corneal collagen cross-linking (C3R with riboflavin + UV-A) to halt progression → intrastromal corneal ring segments (INTACS) → keratoplasty (DALK/PK) for advanced disease or scarring.

High-yield: Collagen cross-linking (riboflavin + UV-A) halts progression of keratoconus; acute hydrops is due to a break in Descemet membrane, presents with sudden pain and corneal oedema, and is managed conservatively.

Diagnosis & investigation of choice — summary

• Slit-lamp biomicroscopy — first and most important examination for all corneal opacities.
• Specular / confocal microscopy — endothelial dystrophies (Fuchs cell count, guttae).
• Pachymetry — corneal thickness (oedema in Fuchs; thinning in ectasias).
• Corneal topography/tomography — keratoconus, Terrien.
• Histopathology with special stains — definitive for stromal dystrophies (Masson/Alcian/Congo red as above).
• Genetic testing — TGFBI for granular/lattice/Reis–Bücklers; CHST6 for macular.

Management/drug of choice — quick map

• Recurrent erosions (EBMD/lattice): lubricants, hypertonic saline, bandage contact lens; refractory → anterior stromal puncture / PTK / debridement.
• Fuchs/bullous keratopathy: hypertonic 5% NaCl → DMEK/DSEK.
• Band keratopathy: EDTA chelation ± PTK; treat the underlying hypercalcaemia.
• Pterygium: excision + conjunctival autograft.
• Stromal dystrophies with significant scarring: lamellar (ALK/DALK) if anterior, PK if full thickness — but note dystrophies recur in the graft, lattice recurring earliest.

Complications

• Recurrent corneal erosion syndrome (epithelial/Bowman dystrophies, lattice).
• Bullous keratopathy with painful ruptured bullae and secondary microbial keratitis (Fuchs).
• Graft recurrence of the original dystrophy after keratoplasty (lattice > granular > macular tends to be the order of recurrence frequency for the anterior triad).
• Pseudophakic/aphakic bullous keratopathy after cataract surgery in low-endothelial-count corneas.
• Corneal hydrops and scarring in keratoconus; visual axis opacification.
• Amblyopia in congenital dystrophies (CHED) if visual axis blocked early.

Key differentials

• Dystrophy vs. degeneration — symmetry, heredity, vascularity, systemic association (already detailed).
• Granular vs. macular vs. lattice — clear vs. hazy intervening stroma, deposit & stain, inheritance.
• Fuchs guttae (central, pathological) vs. Hassall–Henle bodies (peripheral, normal ageing).
• Arcus senilis (peripheral lipid ring, lucid interval) vs. band keratopathy (interpalpebral calcium at Bowman).
• Pterygium vs. pseudopterygium — probe test, site, Stocker line.
• Keratoconus vs. pellucid marginal degeneration (inferior thinning, "kissing doves"/crab-claw topography) vs. keratoglobus.

Recently asked / exam angle

• Match the dystrophy with stain — Granular–Masson trichrome, Macular–Alcian blue/PAS, Lattice–Congo red (apple-green birefringence). This is the most repeated single-best-answer/assertion-reason format.
• Which stromal dystrophy is autosomal recessive / earliest visual loss? → Macular (also CHST6 gene, keratan sulphate).
• Gene common to granular, lattice, Reis–Bücklers → TGFBI/BIGH3 (5q31).
• Lattice + systemic amyloidosis + facial neuropathy → Meretoja syndrome (lattice type II, gelsolin).
• Morning blurring improving by evening + beaten-metal endothelium → Fuchs; investigation = specular microscopy; surgery = DMEK/DSEK.
• Calcium band at Bowman in a child with arthritis → JIA uveitis-associated band keratopathy; treat with EDTA.
• Probe passes under the lesion → pseudopterygium.
• Riboflavin + UV-A → corneal collagen cross-linking for keratoconus.
• Arcus in a young patient → screen for hyperlipidaemia.

Rapid revision

1. Dystrophy = bilateral, symmetric, hereditary, progressive, avascular, no systemic link; degeneration = acquired/age-related, often unilateral, may be vascular.
2. Granular = AD, hyaline, Masson trichrome (red), discrete breadcrumbs with clear intervening stroma.
3. Macular = AR (only recessive stromal), mucopolysaccharide, Alcian blue/PAS, diffuse haze, earliest & most severe visual loss, CHST6 gene.
4. Lattice = AD, amyloid, Congo red (apple-green birefringence), refractile branching lines, recurrent erosions; TGFBI gene; type II = Meretoja.
5. TGFBI (BIGH3, 5q31) unites granular, lattice and Reis–Bücklers dystrophies.
6. Fuchs = AD, >50 yr, female; guttae (beaten metal), morning blurring, Descemet thickening; Dx specular microscopy, Rx 5% NaCl → DMEK/DSEK.
7. Hassall–Henle bodies = benign peripheral guttae of ageing; Fuchs guttae = central & pathological.
8. Band keratopathy = calcium at Bowman, interpalpebral, Swiss-cheese holes; causes = chronic uveitis/JIA, hypercalcaemia; Rx EDTA chelation.
9. Arcus senilis = peripheral lipid ring with lucid interval; if young (arcus juvenilis) → check lipid profile.
10. Pterygium (nasal, UV, Stocker line, probe does NOT pass) vs pseudopterygium (post-ulcer scar, probe passes under neck). Best surgery = excision + conjunctival autograft.
11. Keratoconus signs: Munson, Fleischer ring, Vogt striae, oil-droplet, hydrops; Dx topography; halt with collagen cross-linking (riboflavin + UV-A).
12. Dystrophies recur in corneal grafts; choose DALK/PK based on depth, endothelial keratoplasty for endothelial disease.