No, the pigmentation that gives color to the iris of the eyes has nothing to do with sensitivity to light. Those who answer for this are the so-called photosensitive cells – the cones (in brighter places) and the rods (in places with little clarity) – which are found in the retina, inside the eye. Photophobia, discomfort caused by light, only occurs in specific cases. “One of them would be cone dystrophy, a hereditary disease. As these cells that capture more luminosity do not work, the light becomes aggressive. Another case is that of people who have astigmatism but do not correct it, that is: they do not wear glasses. In the effort of trying to see, the images become blurred and the light also becomes disturbing”, says ophthalmologist Márcio Nehemy, from the Federal University of Minas Gerais (UFMG). Photophobia is also manifested as a symptom of keratoconjunctivitis, a word that gives its name to inflammation of the cornea and conjunctiva (membrane that surrounds the white part of the eyes).
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Normally, light passes through the cornea as if it were glass. With inflammation, however, the rays are diverted, causing reflections that bother the person. “Furthermore, there is a pigmentation in the retina that is added to the light receptors, to transform the light stimulus into nerve impulses (which will be sent to the brain to process the image). We all have this pigmentation, with the exception of albinos, who have neither the iris pigment (which only gives the eye color, without influencing vision), nor this specific retinal pigment, so important in the cerebral processing of light. It is for this reason that the eyes of albinos are extremely sensitive to it”, says Márcio.