Corneal Dystrophy

Corneal dystrophies are a group of inherited, usually bilateral, symmetrical, slowly progressive, non-inflammatory and non-vascularised corneal opacifications that start in one layer. They are not secondary to systemic disease or injury.

• Classification by layer:
  • Epithelial and subepithelial: epithelial basement membrane (map-dot-fingerprint) dystrophy (commonest, often not inherited), Meesmann (KRT3 and KRT12), Reis-Bucklers and Thiel-Behnke (TGFBI).
  • Stromal: granular (types 1 and 2, TGFBI), lattice (TGFBI; gelsolin form in familial amyloidosis of Finnish type), macular (CHST6, autosomal recessive), Schnyder, and others.
  • Endothelial and Descemet: Fuchs endothelial, posterior polymorphous, congenital hereditary endothelial dystrophy (SLC4A11).
• Most are autosomal dominant; macular dystrophy and congenital endothelial dystrophy are recessive.
• Phenotype is variable even within families, and many patients are discovered incidentally.

• Recurrent corneal erosions in epithelial and Bowman layer disease, with sudden pain and tearing on waking.
• Gradual loss of vision, glare, photophobia, and haze as deposits enlarge and coalesce.
• Appearance: maps, dots, fingerprints (basement membrane); crumb like or snowflake white deposits with clear intervening cornea (granular); branching refractile lines (lattice); grey white haze extending to the limbus without clear zones (macular); beaten bronze guttae and oedema (Fuchs).
• Corneal sensation is reduced in some stromal dystrophies and in lattice type.
• Systemic: gelsolin related lattice dystrophy causes cranial neuropathy, cutis laxa like facies, and amyloidosis.

• Slit lamp with retroillumination, anterior segment OCT, confocal microscopy, specular microscopy, and topography.
• Genetic testing (TGFBI, CHST6, KRT3, KRT12, SLC4A11, TCF4, ZEB1) for atypical cases and counselling.
• Histology of keratoplasty specimens: Masson trichrome staining for hyaline in granular dystrophy, Congo red birefringence for amyloid in lattice, and Alcian blue for glycosaminoglycans in macular.
• Differential diagnosis: degenerations (Salzmann nodular, band keratopathy), metabolic deposits (cystinosis, mucopolysaccharidoses), infectious crystalline keratopathy, and dysproteinaemic keratopathy.
• Family examination.

• Asymptomatic patients: observation with periodic review (every 1 to 2 years).
• Recurrent erosions: lubricants, ointment at night, hypertonic saline 5 percent, bandage lens, doxycycline 50 mg to 100 mg twice daily for 6 to 12 weeks, epithelial debridement, anterior stromal puncture, and phototherapeutic keratectomy (also used for superficial stromal opacities).
• Visual impairment from stromal deposits: phototherapeutic keratectomy for superficial disease (with recurrence in a few years), deep anterior lamellar keratoplasty (preferred when endothelium is healthy), and penetrating keratoplasty. Deposits recur in the graft in granular and lattice types, sometimes needing repeat PTK or regrafting after 10 to 15 years.
• Avoid laser refractive surgery in granular dystrophy type 2 (Avellino), because deposits accelerate after the procedure; confirm genotype before refractive surgery in any family with unexplained corneal opacity.
• Endothelial disease (Fuchs, posterior polymorphous, congenital hereditary endothelial dystrophy): hypertonic saline 5 percent drops three to four times daily with ointment at night, bandage lens for bullae, and endothelial keratoplasty (Descemet membrane endothelial keratoplasty preferred, or Descemet stripping automated endothelial keratoplasty) when oedema impairs vision, with postoperative prednisolone acetate 1 percent four times daily tapered over 6 to 12 months.
• Contact lens (rigid gas permeable or scleral) for irregular astigmatism.
• Genetic counselling for inheritance (50 percent risk of transmission in dominant disorders).
• Complications: erosions, scarring, loss of vision, and recurrence in the graft.