The dose-response curve associated with cataract formation is best described as which type?

• A. Non-linear threshold
• B. Linear non-threshold
• C. Non-linear non-threshold
• D. Linear threshold

Answer: (A)

Cataract formation from radiation shows a threshold and a non-proportional increase in risk as dose rises. That means there is a dose level below which cataracts are unlikely, and once that threshold is exceeded, the probability and severity of cataracts increase with dose, but not in a straight-line fashion. This nondirectional rise reflects the underlying biological response in the lens, where damage accumulates and manifests as opacity only after a certain dose is reached.

If a model predicted risk at any dose with a straight-line increase, or a non-threshold relationship, it wouldn’t fit the observed behavior of needing a safe dose before effects appear or the nonlinear escalation after that point. Hence, the best description is a non-linear threshold dose-response.