Corneal Dystrophies and Degenerations
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Direct answer
Corneal dystrophies are bilateral, hereditary, non-inflammatory, progressive conditions that typically affect the central cornea without vascularisation, whereas degenerations are unilateral or asymmetric, age-related or secondary changes, often peripheral and linked to environmental or systemic causes. The examinable stromal trio — granular dystrophy (autosomal dominant, hyaline deposits staining with Masson trichrome), lattice dystrophy (autosomal dominant, amyloid staining with Congo red showing apple-green birefringence) and macular dystrophy (autosomal recessive, mucopolysaccharide staining with Alcian blue, the least common but most visually disabling) — sits beside anterior dystrophies such as map-dot-fingerprint disease and endothelial Fuchs dystrophy with its corneal guttata. Among degenerations, arcus senilis, band-shaped keratopathy, spheroidal degeneration and Terrien marginal degeneration carry the examinable systemic and treatment links.
What you must remember
- The dystrophy definition (five words examiners want): bilateral, hereditary, non-inflammatory, central, progressive — and avascular; fail any one of these and the lesion is usually a degeneration.
- Granular dystrophy (Groenouw type I): autosomal dominant, discrete white "breadcrumb" or crushed-glass opacities separated by clear stroma in the central cornea, sparing the periphery; deposits are hyaline (Masson trichrome positive); TGFBI gene related; relatively good vision until late.
- Lattice dystrophy: autosomal dominant, branching refractile lattice lines plus subtle stromal haze, amyloid on Congo red with apple-green birefringence under polarised light; recurrent corneal erosion is the presenting problem; systemic amyloidosis accompanies the rarer gelsolin-related (Meretoja) variant.
- Macular dystrophy (Groenouw type II): autosomal recessive — the exception among the trio — diffuse stromal haze with localised grey opacities reaching the periphery and the limbus, caused by mucopolysaccharide (glycosaminoglycan) deposition (Alcian blue positive); earliest and most severe visual loss, frequently needing keratoplasty by young adulthood.
- Epithelial basement membrane dystrophy (map-dot-fingerprint, Cogan microcystic): the commonest anterior dystrophy and the leading cause of recurrent corneal erosion; treated with lubricants, hypertonic saline and bandage contact lens.
- Fuchs endothelial dystrophy: corneal guttata (excrescences of Descemet membrane) with a beaten-metal appearance, later stromal and epithelial oedema with morning blur, accelerated by cataract surgery; treated by endothelial keratoplasty (DSAEK or DMEK).
- Degenerations with exam hooks: arcus senilis is a peripheral lipid ring in the elderly, and its appearance under 40 (arcus juvenilis) warrants a lipid profile; band-shaped keratopathy is calcific interpalpebral opacity linked to chronic uveitis or hypercalcaemia, treated by EDTA chelation; spheroidal degeneration is UV-linked; Terrien marginal degeneration is painless peripheral thinning.
- Two ulcerative degenerations to separate: Mooren ulcer is a painful, progressive peripheral ulcerative keratitis with an overhanging central edge, treated with steroids and immunosuppression; rheumatoid and infective peripheral keratitis must be excluded first.
How to work through three white corneas in one clinic
Three patients, three mechanisms, three management lines. A 35-year-old with breadcrumbs of white in the central cornea of both eyes, clear periphery, vision 6/9: granular dystrophy — confirm the pedigree, reassure about slow progression; if the visual axis opacifies, lamellar keratoplasty restores it, though dystrophies can recur in the graft. The second, a 28-year-old with recurrent painful morning watering and sticky lids, shows branching refractile lines: lattice — manage the erosions (lubricants, hypertonic saline, bandage lens) and explain that amyloid, not infection, causes the picture. The third, a 20-year-old with dense central haze reducing vision to 6/36 and opacities that reach the limbus: macular — the recessive one, the severe one, and the one already needing keratoplasty; counsel the family on recessive inheritance and screen siblings. What changes across the three is only the deposit chemistry and tempo: the examinable stains — trichrome, Congo red, Alcian blue — map to the three in that order, a mapping Indian university papers ask every few years.
Where students slip
The first slip is calling a peripheral, unilateral, vascularised opacity in an elderly farmer a "dystrophy" — degenerations own those adjectives, dystrophies surrender them. The second is the inheritance mix-up: macular dystrophy is the autosomal recessive outlier, granular and lattice are dominant, and reversing this in a viva costs the whole question. Third, band-shaped keratopathy is not a stromal dystrophy but a calcific degeneration in the exposed interpalpebral strip — its associations (chronic uveitis, hypercalcaemia, renal failure) and its treatment by EDTA chelation are the marks. Finally, remember that Fuchs dystrophy decompensates after routine cataract surgery — the "healthy" cornea with guttata and thickened pachymetry needs protective, sometimes combined endothelial surgery, a decision made before the phaco, not after.
Frequently asked questions
How do corneal dystrophies differ from degenerations?
Dystrophies are bilateral, hereditary, non-inflammatory, centrally located, progressive and avascular; degenerations are age-related or secondary, often unilateral or asymmetric, frequently peripheral, and may show vascularisation.
Which stains identify the three classic stromal dystrophies?
Granular — hyaline, Masson trichrome; lattice — amyloid, Congo red with apple-green birefringence; macular — mucopolysaccharide, Alcian blue.
Which stromal dystrophy is autosomal recessive and most visually severe?
Macular dystrophy (Groenouw type II), with diffuse glycosaminoglycan deposition extending to the periphery and keratoplasty often needed by early adulthood.
What is the significance of arcus senilis appearing under age 40?
Termed arcus juvenilis, it warrants a fasting lipid profile — it may signal hyperlipidaemia and premature atherosclerotic risk.
How is band-shaped keratopathy treated?
By chelation with disodium EDTA after epithelial debridement, plus management of the underlying cause — chronic uveitis, hypercalcaemia or renal failure.