First, what is photophobia?
Photophobia simply means that light feels uncomfortable, or even painful, in one or both eyes. When it affects one eye more than the other, it usually comes down to one of two things: either more light is entering that eye than the other, or the eye is irritated and has become intolerant of light. Knowing which of these fits your experience is the sensible place to begin, because the causes are quite different.
When more light is entering the eye
The pupil is the opening that controls how much light reaches the inside of the eye. If the pupil on one side is larger than the other, that eye admits more light and can feel dazzled or uncomfortable in bright conditions, particularly in sunshine. A difference in pupil size is worth understanding in its own right, and is covered on its own page.
A difference in pupil size that has been present for a long time, and that others in your family may share, is usually harmless. A new difference, especially one that appears with a drooping eyelid, double vision, or pain, is different and should be assessed promptly.
When the surface of the eye is irritated
The cornea is the clear front window of the eye, and it is richly supplied with nerves, which is why anything that disturbs its surface tends to cause light sensitivity along with discomfort. A scratch, a stray lash or speck of grit, dryness, or an infection of the cornea, known as keratitis, will all make that eye sensitive to light, and usually red, watery, and gritty as well.
This is the group to take most seriously in a contact lens wearer. A painful, light-sensitive eye in someone who wears lenses can indicate a corneal infection, which needs same-day assessment.
- One eye is red and painful as well as sensitive to light
- You wear contact lenses and one eye has become painful or light-sensitive
- Vision in that eye has blurred
Inflammation inside the eye (uveitis)
Uveitis is inflammation inside the eye, and light sensitivity is one of its hallmarks. It typically comes with a red, aching eye, sometimes with blurred vision, and occasionally the pupil on that side looks smaller or slightly irregular. Uveitis needs prompt ophthalmic assessment, because it is treated with specific drops and, left alone, can affect vision.
Two milder and temporary causes are worth mentioning as well. Migraine often brings light sensitivity, which can feel one-sided even though both eyes are usually involved, and if you have recently had dilating drops at an eye examination, that eye will be sensitive to light for a few hours until the drops wear off.
Gauging the urgency
Light sensitivity in an eye that is otherwise white, comfortable, and seeing normally is rarely an emergency, though it is still worth having examined if it persists. Light sensitivity with a red, painful eye, with blurred vision, or in a contact lens wearer should be treated as a same-day matter. If you are unsure, it is always reasonable to have the eye looked at.
Common questions
Is light sensitivity in one eye serious?
Often it is not, particularly if the eye is white and comfortable. Light sensitivity with a red, painful eye, or with blurred vision, should be assessed promptly.
I am sensitive to light and wear contact lenses. What should I do?
Take the lenses out and seek same-day assessment, keeping the lenses and case in case they need testing. Light sensitivity with pain or redness in a lens wearer can signal a corneal infection.
Can a larger pupil on one side cause light sensitivity?
Yes. A bigger pupil lets in more light, so that eye can feel dazzled in bright conditions. A longstanding difference is usually harmless; a new one, especially with a drooping lid, double vision, or pain, should be checked.
