How can severe vitamin A deficiency lead to xerophthalmia and blindness?

Severe vitamin A deficiency leads to xerophthalmia and potential blindness through a progressive breakdown of ocular health.

Initially, a lack of vitamin A impairs the production of rhodopsin, a light-sensitive pigment in the retina essential for vision in low light, resulting in night blindness. As the deficiency persists, it affects the epithelial tissues of the eye, causing the conjunctiva and cornea to become abnormally dry (xerosis).213

This dryness stops the secretion of lubricating tears and causes the eyelids to become swollen and sticky. The mucous surfaces of the eye may erode, leaving the cornea vulnerable to bacterial infection, ulceration, and necrosis (keratomalacia). If these destructive changes to the cornea and deeper eye structures become too extensive, the condition results in permanent blindness. While early stages are treatable with vitamin A supplementation, advanced cellular damage is often irreversible.21