Photophobia, as the name implies, is a fear of light, where patients often close their eyes because of symptoms such as feeling uncomfortable in the eyes, tingling sensations, and stinging eyes when looking at things under certain light exposure. Photophobia is a symptom that often accompanies eye diseases. There are many causes of photophobia. The most common is caused by various causes of corneal lesions. The cornea is one of the organs with the highest density of nerve endings, so it is 100 times more sensitive than the conjunctiva. Any deep or shallow corneal lesions, such as corneal foreign bodies, corneal abrasions, or keratitis, can cause photophobia due to lesions that irritate sensory nerve endings that are densely distributed in the epithelium and stroma of the crossed corneas. It is important to note that photophobia caused by keratoconus is often accompanied by more intense eye pain and tearing. This is the reason why “there is no room for a little gravel in the eye”. This symptom is actually a protective reflex, and when the cornea is damaged, even if it is small, the pain and photophobia will indicate that the eye may be sick and needs to be examined. Second, cataracts that cause photophobia symptoms. Especially in the early stage of cataract, because the lens starts to appear unevenly clouded, the light entering the eye is scattered and refracted in a haphazard way, thus causing some abnormal visual effects, such as shaking eyes, double vision, and skewing. As a result of these abnormal visual disturbances, patients experience photophobia, a reluctance to open their eyes. Photophobia can also be caused by dilated pupils. For example, the pupil may be dilated due to the use of pupil-dilating medication; traumatic pupil dilation due to paralysis or rupture of the pupillary sphincter due to eye trauma; or acute attacks of glaucoma in which high intraocular pressure breaks the pupillary sphincter and causes the pupil to dilate. Therefore, in bright light, the pupil of the eye does not narrow naturally, and photophobia occurs. There are also intraocular diseases that may also have this symptom. For example, iridocyclitis, early in its onset or when the inflammation recurs, may also have photophobia symptoms. Other rare causes, such as albinism, are due to impaired melanin metabolism, and the color of the iris of the eye is lighter, allowing a large amount of light to enter the eye, so patients often experience photophobic glare. Also, patients with congenital aniridia, or total color blindness, may also experience such symptoms. Therefore, if a patient is found to have sudden onset of photophobia, it is best to visit a hospital ophthalmology clinic promptly.