A 35-year-old wears conventional low-Dk hydrogel lenses on an overnight extended-wear schedule. He presents with bilateral diffuse corneal oedema, epithelial microcysts, and superficial peripheral neovascularisation. The underlying pathogenesis is:

• A Aqueous tear deficiency causing epithelial desiccation
• B Type IV hypersensitivity to thimerosal preservative
• C Direct mechanical trauma from a tight-fitting lens
• D Hypoxia-induced anaerobic metabolism with lactic acid accumulation and stromal oedema ✓

Explanation

Closed-eye wear drastically reduces oxygen delivery. Hypoxia forces the epithelium into anaerobic glycolysis, lactate accumulates, draws water osmotically into the stroma, and produces oedema, microcysts, and limbal vascular ingrowth. Silicone hydrogel lenses were developed specifically to raise oxygen transmissibility above the Holden-Mertz criterion for overnight wear. Preservative allergy causes conjunctival hyperaemia and punctate staining rather than stromal oedema with neovessels.

Reference: Yanoff and Duker Ophthalmology, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.