Cornea and sclera: keratitis, dystrophies and scleritis

Lesion

The clear cornea can be infected, scarred, thinned or clouded with fluid; the white sclera can be inflamed in autoimmune disease.

Updated Nov 12, 2026

Key points

Bacterial keratitis: contact lens wear (Pseudomonas), trauma; stromal ulcer with neutrophils, can perforate.
Herpes simplex keratitis: dendritic epithelial ulcer, later stromal inflammation with granulomatous reaction to Descemet membrane and scarring.
Acanthamoeba: contact lens with tap water, painful ring infiltrate, cysts in stroma; fungal keratitis after plant trauma.
Band keratopathy: calcium in the Bowman layer, with chronic uveitis or hypercalcemia; actinic band keratopathy from ultraviolet.
Keratoconus: thinning with breaks in the Bowman layer, cone-shaped cornea, irregular astigmatism; acute hydrops when Descemet membrane ruptures.
Fuchs dystrophy: endothelial loss with guttae on a thick Descemet membrane, stromal edema and bullous keratopathy; a main reason for corneal transplant.

What it is

The cornea is clear because it is avascular, regularly organised and kept dry by its endothelium. Infection (bacteria, herpes, fungi, Acanthamoeba) causes keratitis and ulcers that scar or perforate. Degenerations deposit material such as calcium (band keratopathy), and dystrophies are inherited, usually bilateral disorders, of which Fuchs endothelial dystrophy is the most common. Keratoconus is a progressive thinning and bulging of the cornea. The sclera can be inflamed in rheumatoid arthritis and vasculitis, sometimes to the point of necrosis.

Step by step

The corneal endothelium pumps water out of the stroma to keep it clear.
In Fuchs dystrophy endothelial cells are lost and lay down excrescences (guttae).
Pump capacity falls and the stroma swells.
Fluid reaches the epithelium, which forms painful blisters (bullous keratopathy).
Vision blurs, worst in the morning; transplant of the endothelium restores clarity.

Corneal and scleral disorders

Disorder	Layer	Hallmark	Cause or association
Bacterial keratitis	Epithelium and stroma	Ulcer with neutrophils	Contact lenses, Pseudomonas, Staphylococcus
Herpetic keratitis	Epithelium, then stroma	Dendritic ulcer; stromal scarring	HSV-1, herpes zoster
Acanthamoeba keratitis	Stroma	Ring infiltrate, cysts	Contact lenses and tap water
Band keratopathy	Bowman layer	Calcium band across the fissure	Chronic uveitis, hypercalcemia
Keratoconus	Stroma and Bowman layer	Thinning, cone, Bowman breaks	Eye rubbing, atopy, Down syndrome
Fuchs endothelial dystrophy	Endothelium and Descemet	Guttae, stromal edema	Inherited (TCF4 repeat), older women
Necrotising scleritis	Sclera	Granulomatous inflammation with necrosis	Rheumatoid arthritis, granulomatosis with polyangiitis

Clinical notes

Painful red eye with an ulcer in a contact lens wearer is an emergency.
Necrotising scleritis signals active systemic vasculitis or rheumatoid disease and can thin the sclera (scleromalacia).

Test yourself

Think of the answer, then tap the question to see it.

In which corneal layer is calcium deposited in band keratopathy?

The Bowman layer, usually in the exposed band across the lid fissure.

What are guttae?

Drop-like excrescences of abnormal basement membrane on Descemet membrane, made by failing endothelial cells in Fuchs dystrophy.

What is acute hydrops in keratoconus?

Sudden corneal swelling when Descemet membrane ruptures and aqueous enters the thinned stroma.

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Corneal Disease | Cornea | MedlinePlus (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.