In Part 1 of this series (see “Computing for the Visually Impaired, Part 1,” 9 January 2015), I described several people’s experiences with visual impairments, as well as my own experience with temporary eye disabilities. Enduring such an acute trauma gave me empathy for my fellow low vision users — as well as fierce determination to learn more about what can go wrong, both clinically and for those with “normal vision.”
When accounting for the various types of visual impairments, one must understand the physiology of the eye in order to predict what can go wrong with it. For example, my impairment stemmed from inflammation of the conjunctiva (the thin membrane that lines the inside of the eyelids and covers the sclera). Damage to the optic nerves caused my brother’s impairment, whereas my friend’s problems were caused by crystals forming on his retinas. Finally, my acquaintance Roy’s achromatopsia stems from malfunctioning cone
cells (the retinal cells that detect color).
In other cases, glaucoma can also damage the optic nerves, cataracts cloud the lens of the eye, and corneal abrasions can cause pain, blurred vision, and photophobia. If a user is limited to the use of one eye, asthenopia (eye strain) can result from taxing the muscles in and around the remaining good eye — and, although not typically relevant to computer use, three-dimensional perception is lost. (To prevent asthenopia, refer to Lighthouse International’s “Tips for Preventing Computer Eye Strain.”)
Some degenerative eye diseases, such as retinitis pigmentosa, can gradually degrade even perfect vision to near or total blindness. The tragic but ultimately inspiring story “What It’s Like to Slowly Lose Your Eyesight” describes one woman’s journey through this process.
Other common types of visual impairments include extreme nearsightedness or farsightedness that is difficult to correct with prescriptive lenses; hypersensitivity to even slightly imprecise prescriptions (this is a problem for me even when I’m not suffering from a serious visual impairment); artifacting such as floaters, flashes, or ghosting; colorblindness; contrast sensitivity loss; and continually dry or irritated eyes.
My highly competent and affable ophthalmologist Dr. Benjamin B. Bert explained, “because of all the subtle differences even within particular diseases, each person may need to use different coping mechanisms.” This is one of the sub-specialties in the field of vision care known as [Low Vision][rewrite17]. Low Vision practitioners work very similarly to occupational therapists, with a focus on the eyes.
[rewrite17]: http://www.iapb.org/vision-2020/what-is-avoidable-blindness/low vision
Risks for “Normal Vision” Users — Even without serious visual impairment, “normal vision” users are susceptible to some common risks associated with sustained computer screen use.
According to my optometrist, Dr. Stewart F. Gooderman (whose precision in lens prescription is unparalleled), the most common visual problems that interfere with computer use include “uncorrected binocular deficits and deficiencies in tear film construction and maintenance.”
Fortunately, simply requiring prescription lenses isn’t enough to cause problems. Dr. Gooderman says, “Corrected optical errors like nearsightedness, farsightedness, astigmatism, and presbyopia have relatively little effect if the optical device to correct for it is properly chosen and used.” In addition, “[Poor] binocular eye coordination — the inability to use both eyes efficiently as a team — causes far more problems because computer work is more meticulous and lasts longer than other tasks.
And the task itself is being shown to have a detrimental effect on the tear film. Without a good tear film, visual clarity is simply impossible.” (For those with binocular deficits, Dr. Gooderman recommends vision training and therapy with an optometrist who specializes in binocular vision.)
Dr. Bert emphasizes that the majority of eye problems encountered with computer use result from a breakdown in the tear film, which has three layers:
- A lipid (oil) layer on the exposed surface that helps prevent evaporation
- An aqueous (liquid) layer in the middle
A mucinous (mucous) layer closest to the eye (adjacent to the corneal surface)
Dr. Gooderman explained that under normal circumstances, lid blinking refreshes the tear film and reestablishes its proper configuration. During computer use, however, the blink rate reduces drastically from the average rate of twelve times per minute. This produces a double detrimental effect, with one exacerbating the other. First, without the proper refresh, the tear surface breaks down and impairs the pristine optical surface that the eye needs to bend light properly — because the cornea itself does not have a smooth surface. The cornea needs the tear film to fill in the irregularities.
The second effect is that the lack of blinking prevents the massaging of the oil glands in the eyelids, which is necessary to distribute oil onto the tear film’s surface. Without this massage, oil builds up in the glands, creating inflammation and swelling, which can seal off the exit ducts of the glands. This can eventually cause the glands to degenerate. Eye care specialists refer to this condition as chronic evaporative tear disease; without that oil, the tears evaporate much faster and the normal tear structure is no longer supported. This condition has recently been noticed because young people are
starting to exhibit the tear film and oil glands of post-menopausal women, who more commonly suffer from tear film damage.
Dr. Bert expounded on the breakdown of the tear film, which affects both comfort and vision. “The tear film is the first thing that light hits as it is entering the eye,” he said. So, with an irregular tear film, or with areas of dryness, the tear film diffracts, rather than refracts, the light. A healthy tear film is like a plate glass window, whereas irregular tear film is more comparable to a frosted glass window. Frosted glass produces much more disruption of a point source of light and, in the case of a damaged tear film, glare as well.
Aging can intensify the problem with the common onset of blepharitis, which affects the meibomian glands that produce most of the oil for tears. If the lipid layer is compromised, tears evaporate more quickly. In addition, when using a computer, driving, watching TV, reading, or performing any other intensive visual task, the blink rate decreases. Dr. Bert compares this to engaging in a staring contest with an inanimate object. “As we all know,” he quipped, “the inanimate object always wins.”
To protect the tear film, Dr. Gooderman recommends looking away from the monitor every 20 minutes and consciously blinking for one minute; regular breaks are crucial. You can experiment with break-reminder apps and combining eye-blinking breaks with walking around at least once an hour, which, tangentially, is vital for cardiovascular health.
In addition, Dr. Gooderman and Dr. Bert recommend liberal use of supplementary ocular lubricants (“artificial tears”).
Dr. Bert points out another risk: an accommodative spasm, which can occur with prolonged “near activity,” such as reading print material or viewing computer or smartphone screens. While uncommon, an accommodative spasm causes the eye muscles that focus on a “near object” to spasm and fail to relax. An accommodative spasm can blur distance vision and cause eye pain, nausea, and headaches. As with preventing tear film damage, Dr. Bert recommends frequent breaks and looking at a distant target at least once an hour.
Computer Vision Syndrome — If computer use is wreaking havoc on your eyes, you’re not alone. In fact, eye care specialists so routinely treat computer-related vision problems that they’ve dubbed the related issues “Computer Vision Syndrome” (CVS). Symptoms of CVS include general discomfort, such as headaches and neck and shoulder pain, as well as specific eye woes (burning, tired, and red eyes, as well as twitching eyelids) and visual impairments (loss of focus, double vision, and blurred vision).
Although nascent, CVS is a growing field of interest among eye care specialists. For example, the Pacific University College of Optometry hosts conferences with topics such as “Optimizing Text Legibility and Readability,” “Measuring Visual Performance and Comfort,” “Vision and Workstation Design,” and “Vision Corrections and Interventions for Computer Users.” My hope is that the conclusions from this research will soon make their way into public knowledge.
If dealing with my ocular crisis and its resultant vision loss made me feel helpless, then learning about how the eye works has been somewhat empowering, at least from an academic perspective. In the next installment of this series, I’ll detail the myriad common obstacles and frustrations that low vision users encounter during typical computer use.
Articles in this series: