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Keratoconus and corneal dystrophies
Keratoconus is progressive thinning and protrusion of the cornea into a cone, starting in adolescence and causing irregular astigmatism; cross-linking halts progression. Dystrophies are inherited bilateral diseases recognised by the layer in which material accumulates.
Why it matters in the exam
Keratoconus in the exam: an adolescent who changes glasses often and whose vision is poorly corrected, with eye rubbing and atopy. Signs: a "scissoring" reflex on retinoscopy, Vogt striae in the stroma, a Fleischer ring of iron at the base of the cone and the Munson sign — the lower lid bows on downgaze. Associations: atopy and rubbing, Down syndrome, Ehlers-Danlos syndrome, Leber congenital amaurosis. Acute hydrops — a break in Descemet membrane with sudden oedema — resolves on its own within weeks to months and leaves a scar. Corneal topography or tomography diagnoses early cases too.
Treatment is stepwise: glasses early, rigid or scleral lenses for irregular astigmatism, and corneal cross-linking (riboflavin and UVA) when progression is documented — it stiffens the collagen and halts progression but does not restore the shape. The standard method needs a thickness of at least 400 microns to protect the endothelium. With a scar or lens intolerance — corneal transplantation, usually deep anterior lamellar (DALK). LASIK is forbidden in keratoconus and a suspicious cornea, because it causes ectasia.
Dystrophies: Fuchs endothelial — the commonest, a woman over 50, "droplets" (guttae) on the endothelium, blurred vision in the morning that improves during the day; treatment is endothelial transplantation (DMEK). Epithelial basement membrane — a "map, dot and fingerprint" pattern and recurrent erosions. Lattice — amyloid, the TGFBI gene, recurrent erosions. Granular — hyaline material, TGFBI. Macular — recessive inheritance, the CHST6 gene, glycosaminoglycans, affecting vision early. A recurrent erosion appears in the morning on opening the eye with sharp pain.
Key points
- Keratoconus: progressive cone from adolescence, irregular astigmatism.
- Signs: Vogt, Fleischer, Munson.
- Progression → cross-linking; no LASIK.
- Fuchs: guttae and morning blur → DMEK.
- Lattice and granular: TGFBI; macular: recessive.
Summary table
| Disease | Layer | Sign | Treatment |
|---|---|---|---|
| Keratoconus | Stroma | Cone, Vogt, Fleischer, Munson | Rigid lenses, cross-linking, DALK |
| Fuchs endothelial | Endothelium | Guttae, morning blur | DMEK |
| Epithelial basement membrane | Epithelium | Map, dot, fingerprint | Lubrication, epithelial debridement, PTK |
| Lattice | Stroma | Amyloid lines, TGFBI | Lubrication; graft if it worsens |
| Macular | Stroma | Diffuse haze, recessive, CHST6 | Corneal graft |
A free exam question
מה מהבאים נכון לגבי דיספוטופסיות שליליות )dysphotopasias negative( לאחר ניתוח קטרקט? (the question as examined, in Hebrew)
- א. דיסטרופיית קרנית ע"ש פוקס dystrophy endothelial s’Fuch מגדילה את הסיכון לדיספוטופיה שלילית
- ב. מ"מ מגדיל את הסיכון לדיספוטופסיה שלילית 6.5 רקסיס של
- ג. גבוה מפחיתה את הסיכון לדיספוטופסיה שלילית Index of refraction עדשה עם
- ד. מגדיל את הסיכון לדיספוטופסיה שלילית Square edge IOL
In the full version for subscribers
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Sources
- AAO Preferred Practice Pattern: Corneal Ectasia, 2018 — Diagnosis and corneal cross-linking
- IC3D Classification of Corneal Dystrophies, 3rd edition (2024) — Epithelial, stromal and endothelial dystrophies
- AAO Basic and Clinical Science Course, Section 8: External Disease and Cornea, 2024-2025 — Ectatic disorders and corneal dystrophies
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.