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 is estimated at about 25 percent.7 Light of shorter wave lengths causes increased veiling glare due to increased light scatter.8 Readapta- tion time after white light glare is quickest, as compared to yellow colored glare.9 The opacities of the lens occurring with age and the scatter of light caused by these opacities contributes materially, approxi- mately 75 percent, to the effects of glare. Age as related to glare is shown by Figure 3.10
Readaptation time after glare is positively correlated with age as shown in Figure 4.9
The physiological aging process accounts for these phenomena. The vitreous has an increased number of floaters due to systemic chemical changes, fibrillar; condensations, and degenerative deposits such as colloid bodies or drusen which are hyaline degenera- tion.11
The cornea decreases in translucency and develops a smoky appearance or gerontoxan. It becomes hyper- trophic, the diameter and permeability decrease, and the endothelial ceils flatten. Astigmatism is produced. The posterior surface collects pigment granules that have separated from the iris. These processes decrease light transmissibility and increase refractive surfaces.12 The sclera has decreased opacity thus permitting stray light to enter the eye.
Because the lens continues to grow throughout life, it exhibits compensatory shrinkage and drying to prevent it from filling the globe. With this water loss the lens fibers are compressed; they are also arranged in an irregular fashion. The lens becomes thicker, less permeable, increasingly rigid, and loses its power of accommodation. The protein molecules significantly change as soluble alpha crystallin is converted to insoluble albuminoid. The crysteine oxidizes to cystine with precipitation to albuminoid. As this brown protein accumulates there is increased absorption of light, particularly blue. The amount of calcium and sodium deposits also increases with age. All these processes increase light scatter in the lens.13
Physiologically, the effects of glare reduce visual efficiency and can cause eye strain, eye fatigue, tenseness, general fatigue, and pain. Psychologically, annoyance and distraction may result. Measures should be taken to minimize or prevent glare whenever possible. Since the aged are more susceptible to glare it is extremely important to reduce glare for that age group, whatever their environment might be.
The amount of light plus light relationships must be considered. The brightness contrast level in the central visual field is an important factor in visibility. Increasing the critical details in the figure ground relationship can be accomplished by general illumina- tion plus direct supplementary lighting. Fine detail work is best done under localized light to the task and its immediate surroundings at a ratio of three to one. This localized supplementary light can be supplied by desk lamps, table lamps, and properly placed overhead fixtures. The brightness of the task-surrounding field is also important. Vision is best when the surrounding brightness level is the same as that of the task. This is shown in Figure 5.1 If the equal brightness ratio cannot be maintained, it is better to have the area around a task darker, not brighter. The task to immediate surround ratio should be no more than ten to one.5
The amount of background light in the peripheral field (that area outside the task-surround field) is also important as a brighter peripheral field tends to attract the eye away from the task. The same principles apply to this area of lighting as to the task and its surround. Bright background is needed, but not brighter than the central field. Ratios no greater than ten to one are desirable anywhere in the visual field and ratios of 30 to 40 are the maximum.5 All white ceilings with indirect lighting, for instance, can be very glaring. The same is true for a bright expanse of cloudless sky seen through a window while in a darkened room. Again, peripheral field light should not be in too much contrast to the light source. The ratios previously mentioned are in luminance (candella per square inch) and may vary with the general illumination level. Higher footcandle values lower the maximum permissible ratio.
Specular reflection factors can be eliminated or lessened. Printed matter should be on paper that is not glossy and printed with ink with low reflection factors. Glossy and polished surfaces of all varieties should be excluded, e.g., shiny desk and table tops, waxed and polished floors, glass covered items, and chrome. Because specular reflection is directional, it is possible to prevent this type of glare by positioning the light source, work surface, or the worker so the reflected light is directed away from the individual's eye. The use of light colors, dull nonglossy reflecting finishes on working surfaces, and large-area, low-brightness light sources will also help control specularly reflected glare.5
Persons over 60 years of age require twice the illumination as a 17- to 20-year-old needs for a given task. This is illustrated by Figure 6. Because the aged pupil is miotic, less light is allowed to enter the eye; therefore the aged person does need higher levels of illumination. But quantity of light may not ensure good illumination-quality of light will. Quality of lighting is an abstract that cannot be measured directly.5 To be considered in this abstract are luminance ratios in the total environment, control of room reflectances, and luminaire (classifications such as indirect, direct-indirect, and direct) selection. Lumi- nance ratios have been stated. Room reflectances includes walls, ceilings, and everything in a room. High reflectance (but not glary) surfaces help reduce brightness differences between the task and its surround and between the lightsource and its surround. Specular reflection control has been discussed. Luminaire selection is based on the objectives of efficiency, comfort, architectural suitability, and cost. Excessive glare in artificial illumination can be prevented by shielding all lamps from direct view, using light colors on walls and ceilings, installing light sources above the normal vision line, and using reasonable illuminance levels. Diffuse lighting (light coming from many directions as opposed to one direction) is usually best for most lighting environments. It prevents high brightness-contrast ratios and helps to prevent specular reflection. No single luminance pattern is best for all situations-the immediate seeing task must also be considered.
FIXED GLARE LEVELS ARE PLOTTED AGAINST AGE
Figure 3 GLARE LUMINANCES AND RECOGNITION OF TARGET IN RELATION TO AGE GROUP PERFORMANCES
DARK ADAPTATION THRESHOLDS AS RELATED TO AGE AFTER EXPOSURE TO GLARE
Implications for Health Workers
The effects of glare should be minimized or eliminated for the comfort, safety, and efficiency of the older person. Quantity of illumination, quality of illumination, specific lighting situation, education about glare, and individual need must be considered.
The quantity of light should be sufficient to the task. It is important to remember that the aged person requires twice the level of illumination as a younger person for a given task. Specific quantities cannot be stated, but evaluation can be done by noting the ease of seeing and ability to accomplish the task.
Care must be taken that there are no great lighting difference levels in the visual field. On bright sunshiny days, indoor areas with large expanses of windows should remain well lit, particularly in inner areas that would tend to be dark. For example, the dayroom should be equal, or almost equal, in amount of light when compared to the sunlit hallways that connect to it. Another solution would be to have room-darkening shades that would reduce the amount of light coming in through the windows. Then appropriate lighting could be at a lower illumination level. The advisability of erecting buildings for the aged population with many glass walls or windows must be evaluated in reference to the possible glare problem.
THE SENSITIVITY IS GREATEST WHEN THE SURROUNDINGS ARE AS BRIGHT AS THE VISUAL TASK
Light colored walls, ceilings, and furnishings of matte finish help maintain good lighting levels by diffusing light without glare production. Desk lamps, table lamps, or appropriately placed pull-down fixtures should be available for close task work. If high levels of illumination are required, surround levels may need to be increased to decrease the contrast of room versus task levels. It should be remembered that as the brightness of light increases, the permissible ratio of light to dark decreases; therefore, very high levels of illumination should be used only when necessary.
Stairways of even one step can be dangerous if they are between or at the edge of differing levels of illumination. Color coding the edge of all steps, providing adequate lighting, and decreasing the light-contrast levels will help remove the danger of steps. Adequate lighting for rooms at night by using night lights is essential. Night lights are intended as an orientation guide with the understanding that any movements out of bed should only occur after adjustment to better illumination. Light switches should be at the bedside within easy reach, so there is no excuse for not utilizing adequate illumination to move about at night. It is helpful to turn one's head aside when switching on a brighter light. The effect of looking at a bright light after having been in darker surroundings is similar to looking at flash bulbs as they are exploded.
When the older person is outside in bright sunlight in the summertime or in the winter when snow is on the ground and very reflective, measures should be taken to reduce the glare effects. Sunglasses usually transmit only 80 percent of the available light and would be helpful.15 Wearing hats with brims and bills can reduce the glare source and reflected light. The older person using an umbrella on cloudless bright days is protecting his field of vision. After being out in the glary sunlight, caution is necessary when going back into the home where lower levels of illumination exist. Dark adaptation requires time and it requires a longer period of time in the aged person.16
Specular reflection can be reduced. Matte finish should be on all surfaces, wherever possible. Laminated plastic covered items (such as table and desk tops, and kitchen or work areas) should be in matte, not shiny finish. Manufacturers of furniture and specialized equipment (such as wheel chairs, walkers, canes) should be made aware of the specular reflection problem. These items should have an anodized matte type finish instead of polished chrome. The use of highly polished table settings should be avoided. The possibility of a "glare-mare" truly exists in a community type dining area, for example, a nursing home dining room.
At noon the beautiful and bright sun shines into the nursing home dining room through three walls of windows. (Didn't the architect create a room with a gorgeous view?) The floor shows the effect of an efficient cleaning staff as it gleams with nonskid wax. (Even our housekeeping staff does their utmost to keep our home comfortable and safe for all the residents.) All the wheel chairs and geriatric chairs lined up around the tables glisten in their cleanliness and chrome polish. (Our staff takes very good care of any equipment that you might buy for your mother.) The dishes and silverware sparkle as evidence of the efficiency of the kitchen staff. (We use good china and silver to maintain a homey atmosphere.) But it is not surprising that the aged resident complains about the food looking and tasting all alike, because he really can't see it. He then spills his glass of water, as he could not see it, and complains of a headache.
When the aged person is admitted to a health care institution, the health workers concerned with his care must evaluate all aspects of their patient. Susceptibility to glare should be included in this evaluation as it can affect mobility, communication, and ability to function mentally, physically, and socially. Since glare sensitivity can not yet be specifically measured, the health care worker can evaluate with questions. "Does bright light affect your ability to see?" "When does it seem to affect your vision most?" and "Does bright light ever cause you to feel uncomfortable or become upset?" might be appropriate evaluative questions.
VISIBILITY LEVELS FOR DIFFERENT AGED POPULATIONS14
Specific to nursing, the nursing care plan must include factors as previously discussed here to reduce the possibility of glare problems. Each specific type of nursing unit should be evaluated for the possibility of glare effects. Patient placement in relation to light sources, with efforts to shield the eyes from bright glaring light (for example in the constant care units), should always be done.
Driving at night by the elderly may be dangerous due to increased susceptibility to successive glare. Driving on dark roads with the sudden appearance of oncoming car headlights can produce a period of almost total blindness. The elderly driver should be made aware of the possibility of scotomatic glare. Measures to counteract this type glare can be adopted.
1. Never look directly at the oncoming headlight.
2. Travel on divided highways to increase the distance of the approaching glare source.
3. Travel on routes that are lighted to decrease the brightness-contrast levels.
It has been suggested that yellow lenses would decrease glare effects at night. Since they also decrease the total illumination, they would also decrease the road visibility. They should not be used15; as stated previously, the aged require increased illumination for a given task. Possibly glare tolerance tests should be given to the aged driver at the time of his driver's license examination to sort out those drivers who would constitute a hazard to themselves and the population at large.
Education of the older individual in relation to his probable or potential glare problem is essential. The older person should be instructed to enter or leave darkened areas slowly and to wait for adaptation to occur. Excessively bright lights should not be switched on in a low level illumination area-increase in illumination levels should be done gradually. If the peripheral area seems to be distracting to a work task, it may be too bright and the level of illumination should be adjusted. The importance of level of illumination in task, surround, and peripheral needs to be understood by the elderly person. The wearing of brimmed hats or use of any similar item to shield the eyes from glare sources should be encouraged. Lamps or switchplates should be at convenient places so the level of illumination can easily and safely be controlled. The aged person should be encouraged to always use appropriate levels of illumination.
If an individual has tired eyes or feels tense in certain lighting situations, the lighting should be evaluated. Experimental changing of kinds of light sources, levels of illumination, quantity of light, and the angle of light should be encouraged when visual acuity goals are not being met. General lighting rules to remember are that light sources should be above the normal vision line and bright light sources should be shielded from view.
In addition to appropriate lighting intervention in each environmental situation, the health professional should be able to provide input into building or remodeling programs, decorating projects, and purchase of equipment and furnishings to effectively eliminate potential glare problems. Various health agencies should institute programs about glare to inform all concerned. For example, programs about the glare problem should be given to groups of elderly, to all nursing home personnel, to community health workers, etc. The aged person, plus all those workers involved in his care must understand and be able to effectively deal with the glare problem.
- 1. Luckiesh M: Light, Vision and Seeing. New York, DV Nostrand Co, 1944.
- 2. Rushton WAH: Visual pigments in man. In Held R, Richards W (eds): Perception: Mechanisms and Models. San Francisco, WH Freeman and Co, 1972, pp 104-114.
- 3. Hurviel LM, Jameson, D: The Perception of Brightness and Darkness. Boston, Allyn and Bacon, 1966.
- 4. LeGrand Y: Light, Colour and Vision, 2nd ed. London, Chapman and Hall Ltd, 1968.
- 5. Westinghouse Electric Corporation. Lighting Handbook. Bloomfield, NJ, Westinghouse Electric Corporation, 1974.
- 6. Wolf E, Gardiner J: Studies on the scatter of light in the dioptric media of the eye as a basis of visual glare. Arch Ophthalmol 74:338-346, 1965.
- 7. Boynton RM, Clarke F: Sources of entoptic scatter in the human eye. J Opt Soc Am 54:110-120, 1964.
- 8. Said FS, Weale RA: The variation with age of the spectral transmissivity of the living human crystalline lens. Gerontología 3(4) :213-231, 1959.
- 9. Reading V: Disability glare and age. Vision Res 8:207-214, 1968.
- 10. Wolf E: Glare and age. Arch Ophthalmol 64:502-514, 1960.
- 11. Brocklehurst JC: Textbook of Geriatric Medicine and Gerontology. London, Churchill Livingstone, 1973.
- 12. Freeman JT: Clinical Features of the Older Adult. Springfield, Illinois, CC Thomas, 1965.
- 13. Moses R: Adler's Physiology of the Eye. St Louis, CV Mosby, 1970.
- 14. Guth SK, Eastman AA, McNelis JF: Lighting Requirements of Older Workers. In Engineering 1951, cited by Borish in Clinical Refraction. Chicago, Professional Press Inc, 1970.
- 15. Borish I: Clinical Refraction. Chicago, Professional Press Inc., 1970.
- 16. Birren J, Casperson R, Botwinik J: Age changes in pupil size. J Gerontol 5:216-221, 1950.