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Ocular straylight is a phenomenon where parts of the eye are able to scatter light, creating glare. It is analogous to stray light in other optical systems; scattered light reaches the retina, but does not contribute to forming a correct image.

One can observe the effect of straylight by looking at a distant bright light source against a dark background. If the source is small, it would look like a small bright spot if the eye imaged it perfectly. Scattering in the eye makes the source appear spread out, surrounded by glare. The disability glare caused by such a situation has been found to correspond precisely to the effect of true light.^{[1][clarification needed]} As a consequence, disability glare was subsequently defined by this true light, called "straylight".^{[1][clarification needed]}

Individual differences

Straylight can differ considerably between individuals. Aging of the crystalline lens of the human eye causes straylight to become worse.^[2] Lens extraction and artificial lens implantation is an effective treatment.

Less common causes for straylight include:

• Diseases of the cornea, e.g. Fuchs' dystrophy.^[3]
• Lack of pigmentation, e.g. albinism.^[4]
• Laser refractive surgery, with occasional haze formation.^[5]
• Excessive floaters in the vitreous humour.^[6]
• Contact lenses.^[7]

References