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Describe corneal oedema and bullous keratopathy.

Ophthalmology · 3rd Professional

Corneal transparency depends on relative dehydration (deturgescence), maintained by two barriers and one pump: the epithelium and endothelium as barriers to fluid entry, and the endothelial Na-K ATPase pump, which actively removes water from the stroma into the anterior chamber
The stroma also has a natural tendency to swell, because of the negatively charged glycosaminoglycans between the lamellae, which imbibe water. The endothelial pump works constantly against this
Corneal oedema therefore results from endothelial failure or from raised intraocular pressure overwhelming the pump — and endothelial failure is irreversible.

Cause	Examples
Endothelial cell loss	FUCHS endothelial dystrophy; pseudophakic or aphakic bullous keratopathy after cataract surgery.
Raised intraocular pressure	Acute angle-closure glaucoma, in which the epithelial oedema causes the characteristic coloured haloes and the hazy cornea; and congenital glaucoma
Inflammation	Keratitis, disciform keratitis, uveitis, endotheliitis and graft rejection
Trauma and chemical injury	Birth trauma with forceps causing descemet tears; blunt and surgical trauma; alkali burns
Ectasia	Acute hydrops in keratoconus, from a break in Descemet
Contact lens	Hypoxic oedema from overwear or a low-permeability lens
Congenital	Congenital hereditary endothelial dystrophy

Bullous keratopathy is the end stage: with sustained stromal oedema, fluid tracks forward into the epithelium and collects in subepithelial bullae (blisters)
Symptoms — blurred vision, worse ON waking and improving through the day (because the closed lids prevent evaporation overnight, and the open eye dehydrates the cornea by day) — a highly characteristic history; haloes around lights; and severe pain when a bulla ruptures, exposing the nerve endings.
Signs — a hazy, thickened cornea with epithelial bullae, folds in descemet membrane (striate keratopathy), guttata where the cause is Fuchs, and later subepithelial fibrosis and vascularisation

Ask when the vision is worst; morning blurring clearing through the day is close to diagnostic of endothelial decompensation
Count the endothelium before cataract surgery in an eye with guttata; operating on a marginal endothelium precipitates bullous keratopathy and is the commonest avoidable cause of it
Suspect raised pressure in a hazy cornea; acute angle closure presents with corneal oedema and haloes, and treating it as keratitis loses time
Use hypertonic saline and a hair dryer as first measures; they are cheap, effective for mild oedema, and rarely offered
Offer DMEK where there is visual potential; replacing the endothelium alone gives excellent results and has replaced penetrating keratoplasty for this indication

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