Cataract resultant of Nagasaki atomic bomb
One of the effects of radiation exposure over 1 Gy is an increased incidence of cataract formation in the years following exposure. When exposure reaches 5-6 Gy, there’s a spike in cataract cases within the following two years.
Ionizing radiation does the majority of its damage to dividing cells. Because the cells of the eye divide around the periphery (outer border) and move inwards toward the center of the lens as they replace old cells, the initial damage from radiation is not concentrated in one place, and lens opacity does not immediately occur.