**Core Concept**
Snow blindness, also known as photokeratitis or ultraviolet keratitis, is a condition that occurs when the cornea is exposed to intense ultraviolet (UV) radiation from the sun, typically in snowy or icy environments. This exposure can cause damage to the corneal epithelium and underlying tissues, leading to pain, photophobia, and vision impairment.

**Why the Correct Answer is Right**
Ultraviolet rays, particularly UVA and UVB, are the primary cause of snow blindness. When UV radiation enters the eye, it can cause the corneal epithelium to become damaged, leading to inflammation and pain. This condition is often seen in individuals who spend extended periods outdoors in snowy or icy environments without proper eye protection. The cornea's natural protection against UV radiation is compromised in these situations, allowing the damaging effects of UV rays to occur.

**Why Each Wrong Option is Incorrect**
**Option B:** Infrared (IR) radiation is not typically associated with snow blindness. While IR radiation can cause heat-related damage to the eye, it is not the primary cause of snow blindness.

**Option C:** Microwave radiation is not relevant to snow blindness, as it operates at a much higher frequency than UV radiation and is not commonly associated with eye damage in this context.

**Option D:** A defect in a mirror is not related to snow blindness. This option seems to be a distractor and is not relevant to the condition.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that snow blindness can be prevented by wearing proper eye protection, including sunglasses with UV-blocking lenses, when spending extended periods outdoors in snowy or icy environments.

**✓ Correct Answer: A. Ultravoilet rays**