Sensitivity to light may be due to local eye disease or systemic disease, but in both cases it is usually due to inflammation, with three exceptions: albinism because there is poor pigmentation of the iris and choroid, allowing more light to get in; migraine, where the explanation is still not available; and eye strain from astigmatism and, in particular, hyperopia.
Local eye disease
Following the path of light from the conjunctiva to the retina, one may easily recall the causes of photophobia. Conjunctivitis (chemical, allergic, and infectious), keratitis, foreign bodies of the cornea, iritis, retinitis, chorioretinitis, and optic neuritis may all be associated with photophobia.
Systemic disease
All the febrile states, especially those associated with conjunctival infection, cause photophobia. Measles, meningitis, encephalitis, hay fever, influenza, the common cold, and trichinosis are just a few. Certain toxins can cause photophobia, notably iodine, bromide, and atropine derivatives. Simply staying in the dark will cause photophobia. Hysteria and simple fear or annoyance with crowds will also cause this condition.
Approach to the Diagnosis
The approach to the diagnosis of photophobia is the same as that of blurred vision (see page 67).