Why do I have photophobia?

Optom
Photophobia is an involuntary reaction of the eyes when it comes in contact with light, either the natural sunlight or the artificial light from either our bulb or car light; and it is often accompanied with discomforts such as deep piercing ocular pains in the eyeball, associated eyebrow headaches, hyperemia of the conjunctiva, mild to severe blespherospasm etc or sometimes it might present with much milder like slight sandy sensation, but nonetheless ones visual acuity (the extent one sees in open space) is often compromised as a result.
Photophobia could be as a result of active pathology of the eye, it could be as a result of Physiological state of the pupils and the iris pigment or it could affect the individual as a result of error of refraction.
In any active inflammation of the eyes, the iris, which is the most vascularised part of the anterior eye, often responds to postalglandins and other immuno-inflammatory substances present in these area of the eyes. The resultant effect is a breakdown of the blood barrier provided by the iris epithelium with a consequent movement of fluid into the iris spaces and the fluid-logged iris responds to light very sluggishly, rubbing each other in the process, and with am effort too. The pain receptor of the eyes are activated in this situation. Hence, the photophobia experienced in that condition.
When the pupil of the eyes is very large, the extent of contraction under a very bright illumination and/or in an unfavorable glare situation, the pupils often fail to contract enough to allow 'optimum' illumination get into the retina. The individual involuntarily keeps his/her face frowned to cut off the 'excess' light entering the eye and the result is ocular discomfort, pseudo-spasm of the eyebrow and consequently a physiological photophobia ensues. Again, iris with little or no pigment, as seen in light-skinned or Albinos, often exhibits photophobia secondary to light scatter into the eyes. The iris pigments absorbs light from outside the eyes and inside hence reducing total internal reflection of light in the eyes. In absence of these pigments or when these pigments are minimal, total internal reflections, light scatter, enhanced glare sensation results in photophobia.
Photophobia can manifest when an individual is either myopic, hyperopic, astigmatic or anisometropic.  Apart from Myopia, the other cases are a consequence of an impaired relationship between accommodation-convergence mechanism of the eyes. The Myopes often have larger than normal pupils and this is an important reason why individuals with myopia exhibit photophobia! It should be remembered that myopes don't accommodate and the induced Amplitude of accommodation they acquire, seldom induces photophobia....
Pupillary sizes change with different levels accommodative changes. Somehow the involuntary 'spasm' that accompanies illumination and the associated change in the accommodative amplitude triggers a form of 'pain' especially if the induced accommodation is beyond the accommodative reserve of the subject, which is always the case in hyperopia, Astigmatism and Anisometropia.
Photophobia as a result of pathology can be relieved when the source of such pathology, e.g. when a patient with anterior uveitis and an associated photophobia has his/her uveitis treated with medications. Physiological Photophobia can only be managed with wearing dark sunshades, especially when outdoors or when exposed to bright light. While the later can be managed by restoring emmetropia with optical lenses that could either be tinted or that could possess be photochromic properties.
Finally, I will advice you with a symptom of photophobia to go and receive an Optometric eye care. This essential step can help you cope and manage with photophobia and the general use of dark sunshades is highly recommended! Don't let any form of photophobia disturb your visual comfort...its your right to enjoy comfortable vision... The Optometrist is your friend. Take care.
Dr Victor Ezebuiroh Okwudiri.