Ocular straylight is a phenomenon where parts of the eye scatter light, creating glare. It is analogous to stray light in other optical systems; scattered

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

reaches the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

, but does not contribute to forming a correct

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...

. 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.Vos JJ. "Disability glare - a state of the art report". ''Commission International de l'Eclairage Journal''. 1984;3/2:39-53 As a consequence, disability glare was subsequently defined by this true light, called "straylight".

Individual differences

Straylight can differ considerably between individuals. Aging of the

crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it ca ...

of the human eye causes straylight to become worse.Van den Berg TJTP et al. "Straylight effects with aging and lens extraction". ''Am J Ophthalmol.'' 2007;144:358-363 Lens extraction and artificial lens implantation is an effective treatment. Less common causes for straylight include: *Diseases of the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...

, e.g.

Fuchs' dystrophy Fuchs dystrophy, also referred to as Fuchs endothelial corneal dystrophy (FECD) and Fuchs endothelial dystrophy (FED), is a slowly progressing corneal dystrophy that usually affects both eyes and is slightly more common in women than in men. Althou ...

. *Lack of

pigmentation A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

, e.g.

albinism Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino. Varied use and interpretation of the term ...

. * Laser refractive surgery, with occasional

haze Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates suspended in air obscure visibility and the clarity of the sky. The World Meteorological Organization manual of codes includes a classification ...

formation. *Excessive

floater Floaters or eye floaters are sometimes visible deposits (e.g., the shadows of tiny structures of protein or other cell debris projected onto the retina) within the eye's vitreous humour ("the vitreous"), which is normally transparent, or betwee ...

s in the

vitreous humour The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous humor ...

. *

Contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

es.Van der Meulen IJ et al. "Straylight measurement in contact lens wear". ''Cornea'' 2010;29:516-522

References

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