How is the extent of the disease of retinopathy of prematurity described?

• A. Stages
• B. Zones
• C. Levels
• D. Clock hours

Answer: (D)

In retinopathy of prematurity, how far the disease spans around the retina is described using clock hours. This measures the circumferential extent of involvement, giving a sense of how much of the retina is affected around the midline. For example, disease that involves a 6-hour arc from 3 to 9 o’clock covers six clock hours. This is different from zones, which describe distance from the optic nerve (location), and from stages, which describe severity of the disease. So clock hours specifically quantify the extent around the retinal circumference.