Which of the following is listed as a cause of brown corneas?

• A. Desmetocoele
• B. Corneal edema
• C. Iris atrophy
• D. Retinal detachment

Answer: (A)

The main idea here is that a brown appearance of the cornea in horses is most consistent with a very deep corneal ulcer that has reached Descemet's membrane, forming a descemetocoele. This is a thin, vulnerable corneal state where the ulcer has penetrated to the deepest corneal layer, and the exposed tissue can give the cornea a brown, compromised look. It signals that the ulcer is at high risk of perforation and needs urgent surgical management to save the eye. The other options involve structures not producing a brown corneal surface: corneal edema typically causes haziness or a blue-white clouding, iris atrophy changes the iris rather than the cornea, and retinal detachment affects the back of the eye with no direct corneal color change.