Can lighting help people with aging eyes?
The aging process produces some predictable and very common changes in the visual system. These changes happen slowly, so seniors may not even be aware that their eyes are seeing the world in a different way than when they were 20 or even 40. In order to understand these changes, we need to understand how the human eye works, and then understand what physical changes that result in reduced vision.
Horizontal cross section of the right eye.
Here is a cross-section of the human eye. Light enters the eye through the cornea, the glassy bulge on the outside of the eye that does most of the eye's refractive work. The light passes through the pupil, the dark-colored aperture surrounded by the colored iris. In younger people the pupil changes size to admit more or less light. Beyond the pupil is the M&M-shaped crystalline lens, which is controlled by muscles to focus the incoming light on to the retina at the rear of the eye.
The lens grows like an onion, with very pale yellow-tinted tissue layers that grow from the inside out. The lens, when young, is clear, and when you shift your focus from a near object to a distant object, it is the lens which changes shape to keep the new object clearly focused. Behind the lens is the vitreous humor, which is a clear jelly bag designed to keep the eye round. Then, at the rear of the eye is the retina, a densely-packed set of photoreceptors, which convert the light image into chemical signals and electrical signals which are then sent to the brain for interpretation.
The following are the principal changes typical in the aging process, although individuals vary in the degree of deterioration that occurs. The first sign of aging is that the crystalline lens begins to have so many layers of accumulated tissue built up that it becomes stiff and the iris muscles must work harder to bring near objects into focus.
Called "presbyopia", this problem usually noticed by individuals in their forties, and is fortunately easily overcome through the use of reading glasses. In the decades that follow, the individual may notice that their vision isn't as clear as it used to be, and more light is needed for reading. This is a result of the lens developing opaque or translucent spots. Imagine looking at the world through a sheer curtain, and you can get a feeling for how it feels to have a smeared vision of the world. The tissue layers that used to be pale, pale yellow now are distinctly yellow. Colors become muted, edges and details of the visual world become smeared and less distinct, and sources of glare appear larger and block more of the field of view. When these opacities become bad enough, they are called "cataracts", and in North America, cataract surgery is common and very successful.
In the senior years, pupils become very small and take longer to respond to changes in light level, if they change in size at all. This is called "senile miosis", and it means that older individuals have more difficulty moving from bright to dark spaces, or seeing details in shadowy areas. It takes them longer to adapt from darker indoor to bright outdoor spaces.
The vitreous humor may have small chunks of the jelly break off and move within the jelly bag, superimposing gray moving patches on the visual image. These are called "floaters", and they become progressively worse with time.
The retinal changes are least predictable. Some individuals experience "macular degeneration", where the photoreceptors in the central part of their vision die off.
This results in an inability to see details, because it is the central vision that does the majority of the detail work. These people need very high light levels on task areas to compensate for this. Another form of retinal degeneration may be due to glaucoma or diabetic retinopathy, where the perimeter of the visual field disappears. These persons now have tunnel vision. Try navigating the world looking through a paper towel tube. Without peripheral vision, you collide with furniture and run into walls, and it would be terrifying to drive!
Dining Room, the Stratford Senior Residence, San Mateo, CA. This space is uniformly lighted without appearing dull or institutional.
These changes can be divided into three areas of concern: focusing effects, reduced light transmission, filter effects, and slow adaptation to changes of light level. Here's a summary of what the designer can do to help seniors see to the best of their abilities, and make the built environment visually comfortable:
- Raise overall light levels slightly. A 25 to 50% increase in ambient light levels will help overcome some of the loss of transmission in the eye, but will not introduce significantly more uncomfortable glare.
- Increase task lighting levels significantly. The average 65-year-old needs 2.5 times the amount of light as the average 20-year-old. But older seniors or seniors with special visual problems may need up to 10 times that amount of light. Dimmable task lights, or flexible task lights that can be moved closer to the book (or needlework or game table or desktop) allow the user to create the right task lighting for his or her needs.
- Reduce glare by blocking the direct view of bright lamps, fixture lenses, or windows. This means choosing luminaires that put light on ceilings, walls, tables, artwork, etc, but NOT into the eyes of the senior uses. Valances, baffles, louvers,lenses, reflectors, etc. are all luminaire components that help distribute light only where it is wanted. This also means calculating when a window or skylight could be a source of glare, and providing blinds, light shelves, overhangs, awnings, curtains, etc. to control its brightness at the time of day when its brightness could be offensive.
- Provide relatively uniform light levels within spaces, and easy brightness transitions from space to space. Seniors have difficulty seeing in bright and dark conditions at the same time, and also need more time to adapt to new brightness conditions. Use larger amounts of bounced light from indirect lighting or wallwashing to make light levels even. Consider dimming lobby light levels at night to make lightlevels closer to that of the darkened parking lot. Conversely, keep lobby levels high in the daytime when seniors are coming in from the bright outdoors.
- Increase contrast. Since seniors have a hazy view of their world, help them see edges by using contrasting colors on baseboards, stair edges, ramp edges, door moldings, showers and bathtubs, etc. Use more saturated colors in markings and in accent colors. And use light sources with a greater blue content (i.e. warm-color fluorescent or compact fluorescent) to help seniors see blue, green, and purple tones more distinctly.
- Use larger, high-contrast characters in signage and printed materials for seniors.