Experts at the Milan Eye Center liken the melanin in our irises to that of a pair of sunglasses — it serves as a protective barrier. For those with brown eyes, for example, when light makes contact with the iris, all that heavy pigmentation helps obstruct the light from entering the back of the eye. For people with gray eyes, however, less melanin means more light is allowed to enter the eye. Even more, some people additionally have less melanin in their retinas too, which can further compound the effects of photophobia.
While those with gray eyes may be more susceptible to photophobia, there are a number of other factors that can influence the development of the condition as well. This includes certain neurological conditions, eye infections, chronic dry eye, LASIK surgery, or the use of certain medications (via AARP). But it’s not just the sun that can evoke the discomfort of photophobia. Those with the condition may also be affected by automobile headlights, bright indoor lighting, or blue light from devices.