The cornea and lens focus light onto the retina, where photoreceptors turn it into nerve signals the brain reads as sight.
How it works, step by step
Light passes through the cornea and pupil.
The lens fine-tunes focus onto the retina.
Rods and cones convert light into electrical signals using vitamin A–derived retinal.
The optic nerve carries signals to the visual cortex at the back of the brain.
Nutrition links
Vitamin A is part of the light-sensing pigment rhodopsin. Lutein and zeaxanthin concentrate in the macula.
When to get help
Sudden vision loss, flashes, a curtain over vision or eye pain need urgent care.
Evidence & sources
Vitamin A deficiency is a leading cause of preventable blindness in children worldwide. Evidence: established. Known: Well documented in low-income settings. Unknown: — Source: World Health Organization, Micronutrient deficiencies: Vitamin A deficiency (Current revision).
In the AREDS2 trial, a supplement with lutein and zeaxanthin slowed progression to advanced age-related macular degeneration in people who already had intermediate disease. Evidence: moderate. Known: Large randomized trial. Unknown: Doesn't show prevention in people without AMD. Source: US National Eye Institute, AREDS/AREDS2 Clinical Trials (2013 (updates since)).