Certified Ophthalmic Medical Technologist (COMT) Practice Exam

At what endothelial cell count is corneal edema likely to occur?

1. 1600 cells/sq. mm

2. 1000 cells/sq. mm

3. 800 cells/sq. mm

4. 400 cells/sq. mm

The correct answer is: 1000 cells/sq. mm

Corneal edema is a condition that can arise when there is a decrease in the endothelial cell density of the cornea. The endothelial cells play a critical role in maintaining corneal transparency by regulating fluid balance. When the cell count drops below a certain threshold, the ability of the endothelium to pump fluid out of the corneal stroma diminishes, leading to fluid accumulation and subsequent edema. A count of approximately 1000 cells per square millimeter is recognized as a significant threshold at which corneal edema is likely to develop. At this density, the endothelial cells’ ability to regulate hydration of the cornea declines, increasing the risk of swelling. The physiological function of the corneal endothelium becomes compromised, resulting in corneal cloudiness and visual impairment associated with edema. Higher cell densities, such as 1600 and above, generally maintain adequate pump function to prevent edema, while counts significantly lower than 1000, such as 800 or 400 cells per square millimeter, would suggest a severe risk of edema and corneal decompensation. Therefore, 1000 cells per square millimeter is the key point where the risk of edema starts to become significant.