Aging and the Glare Problem

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Abstract
The articles prior to January 2008 are part of the back file collection and are not available with a current paid subscription. To access the article, you may purchase it or purchase the complete back file collection here Jean Hatton The normal aging process causes a multiplicity of problems for the aged person. Increased suscep- tibility to visual glare is one of these problems. Knowing the causes, plus ways to alleviate glare is essential for all health professionals. Glare is the dazzling effect associated with a source of light of apparent high brightness. Glare reduces the sensitivity of the visual system and is usually present to some degree in all seeing conditions.1 Visual efficiency is reduced causing a disability effect. A discomfort effect can also occur which can vary from a slight irritation to actual pain. Glare can be classified into two kinds, simultaneous and successive. Simultaneous glare occurs when the peripheral field is at a much lower luminance than the more powerful source. Successive glare is produced by passing from a field of lower level illumination, to which the eye is adapted, into a field of much higher illumination. Glare source light is scattered by the optic media of the eye and produces a "halo" or veiling luminance which is superimposed upon a retinal image. This veil masks fainter objects and reduces apparent brightness of any object. A glare source does lower the sensitivity of the retina. Bright light "bleaches" the rods and cones thus changing the local photochemical composition of the retina. Physiological regeneration has to occur in adaptation to various light sources.2 Blind spots and/or after images can develop in relation to this process, especially with prolonged viewing of glare sources. Intense dazzling light produces a blinding or scoto- matic glare. Fundamentals to appraise glare1 are as follows: 1. The visibility effect of glare depends directly on the candle power of the glare source toward the eyes and inversely on the square of its distance from the eyes. 2. The effects of any glare source are decreased as the overall brightness of the surround area increases. 3. As the angular distance from the line of vision increases, the effects of glare lessen. 4. A glare condition may not be uncomfortable for short periods of time but may become very uncomfortable and fatiguing over long periods of time. 5. The secondary sources of glare do add their equivalent luminances to the total effect.3 6. The apparent diameter of a single glare source or its spectral composition do not seem important.4 Glare can also result from specular reflection which is the reflection of more or less imperfect images of light sources. Specularly reflected images of bright sources of light are called highlights. These images can be helpful, but usually they decrease visibility by reducing brightness-contrasts of critical details in relation to their background.1 Figure 1 illustrates the direct and reflected glare zones.5 Glare originates in relation to light sources, is enhanced by an altered state of adaptation in the retina, but is caused by light scatter in the optic media. There are many causes of light scatter. Light is diffusely transmitted through the sclera and iris. Halation occurs as light comes from the wrong direction. Flares (reflected light) are caused by various refractive surfaces, specifically the cornea and lens. The non- homogenous media of the vitreous and aqueous humors also can produce light scatter. For many years the optic media was assumed to have a high degree of light transmissibility. More recent studies show in- creased absorption and scatter of light. The effects of glare are entoptic, measurable, and a function of age as illustrated in Figure 2.6 In the normally aging eye, changes in the trans- mission of light by the vitreous are almost negligible when compared with lenticular changes. The amount of light scattered by the cornea… 10.3928/0098-9134-19770901-09

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