Corneal Oedema

Corneal oedema is excess water in the corneal stroma and epithelium, with loss of transparency and thickening. It results from failure of the endothelial pump and barrier, or epithelial barrier damage, or high intraocular pressure.

• Endothelial causes: Fuchs endothelial dystrophy, pseudophakic and aphakic bullous keratopathy after cataract surgery, trauma and birth trauma, iridocorneal endothelial syndrome, posterior polymorphous dystrophy, herpetic endotheliitis, toxic anterior segment syndrome, endothelial rejection, and congenital hereditary endothelial dystrophy.
• Pressure: acute angle closure and secondary glaucomas.
• Epithelial and stromal: contact lens overwear, hydrops in keratoconus, chemical injury, and inflammatory keratitis.
• Stromal thickness above 640 micrometres is abnormal (normal about 520 to 550 micrometres).

• Blurred, hazy vision, halos around lights, worse on waking and improving through the day (overnight lid closure reduces evaporation).
• Epithelial bullae that rupture, causing pain, tearing, photophobia and foreign body sensation.
• Stromal thickening, Descemet folds, haze, and in chronic cases subepithelial fibrosis, vascularisation, scarring.
• Associated features: guttae (Fuchs), anterior chamber intraocular lens, shallow chamber, high pressure, keratic precipitates.

• Slit lamp examination: microcystic epithelial oedema, stromal haze, folds in Descemet membrane.
• Pachymetry (central thickness above 600 to 640 micrometres), anterior segment OCT, specular microscopy for endothelial cell density (below 1000 cells/mm2 predicts decompensation; below 500 cells/mm2 is advanced failure).
• Intraocular pressure; gonioscopy; assess for uveitis and herpetic disease; review previous surgery.
• Check morning versus evening vision and pachymetry.

• Treat the cause: lower raised intraocular pressure (acetazolamide 500 mg intravenously or orally, topical timolol 0.5 percent, brimonidine 0.2 percent, dorzolamide 2 percent), treat inflammation and herpetic endotheliitis (topical prednisolone acetate 1 percent four to six times daily, oral valaciclovir 500 mg to 1 g daily to three times daily), reverse the cause (stop overwear of contact lenses).
• Hypertonic saline 5 percent drops four times daily and ointment at night, and blow drying the face at arm's length twice daily to evaporate surface fluid.
• Epithelial bullae pain: bandage soft contact lens with prophylactic antibiotic, cycloplegic (cyclopentolate 1 percent), lubricants.
• Rho kinase inhibitors: ripasudil 0.4 percent twice daily or netarsudil 0.02 percent once daily after descemetorhexis for early Fuchs.
• Surgery for visual or symptomatic failure: endothelial keratoplasty (Descemet membrane endothelial keratoplasty, DMEK; Descemet stripping automated endothelial keratoplasty, DSAEK), with rebound visual recovery in 3 to 6 months; penetrating keratoplasty for scarred corneas; Descemet stripping only (selected Fuchs with central guttae and healthy peripheral endothelium).
• For poor surgical candidates: anterior stromal puncture, conjunctival flap, amniotic membrane.
• Postoperative: topical steroids (prednisolone acetate 1 percent four times daily tapered over 6 to 12 months) and monitor for rejection (redness, photophobia, reduced vision, keratic precipitates).