COMPUTER VISION SYNDROME (CVS): HOW TO TREAT THE PATIENTS YOU MAY NOT KNOW YOU HAVE

BACKGROUND

Over the last twenty years, the pace of advance in electronic technology has been breathtaking. From the first limited-use personal computers and their fuzzy-imaged information exchange monitors (also known as CRTs and VDTs), the industry has evolved to offer faster chips, more capable software, higher storage capacity, the promise of the Internet with on-line living and the tease of a paperless society.

The change in capability has been rapid and massive, but the information exchange medium for the computer user has evolved only a little. Now, we view slightly less fuzzy VDT monitors and liquid crystal display (LCD) screens, which are still not at all friendly to the human visual system. Twenty years ago, optometrists began to hear the first murmurings of vision-related complaints from their computer-using patients. Today, we hear the same array of symptoms from a great many more patients, but we seem to be no closer to a good set of reliable answers.

How do we put the puzzle pieces together? First, it is necessary to understand what the components of CVS are. The American Optometric Association defines Computer Vision Syndrome as a collection of symptoms experienced by computer users in the course of their work. They include: fatigue, headaches, dry eyes, inability to maintain near focus, progressive refractive changes, neck and shoulder discomfort, changes in color perception and pain in or around the eyes.

Figure 1: Do you know any patients who may look like this at work?

Note that some of the symptoms are clearly ocular, while others may seem primarily somatic. Some are age related and some are not. All of them, however, share the characteristic of being visually related.

Next, we must understand that CVS symptoms can stem not only from VDT/LCD screens but from office lighting, glare sources, equipment positioning and other aspects of workplace ergonomics as well. Optometrists have the most immediate control over eye/screen interaction. That is where this course will focus. By better grasping their role in the total picture, doctors of optometry can more meaningfully motivate both patients and their employers to the role of proper computer vision care.

 

THE VDT/LCD SCREEN AS A VISUAL STIMULUS

Human eyes are meant to be good contrast detectors. Seeing borders and distinguishing figure from ground are survival traits. Early hunters had to see prey before they were seen as prey by things with big teeth and claws. Our eyes like sharp, well-defined edges in the visual field. 

When writing became the next wave in human communication, after talking, looking at print was not much different from trying to spot dinner on the hunting field. Sure, there were those who could not handle the prolonged proximity of the reading task, but print on paper presented about the same sharp-edged figure ground visual demand as had been previously experienced in the real world.

Fast forward now to the mid-2Oth Century. Television has just hit the American economy. Moms and dads across the nation are warning children not to sit too close to the screen. Why? What did our parents know that we seem to have forgotten?

The answer is that any electronically-generated image has fuzzy edges.

 

Figure 2: Sharp-edged Print vs. Fuzzy-edged Pixels

 

Figure 3A: Graphical Plot of VDT  

Figure 3B: LCD Pixel Output 

Our vision system responds to those indistinct edges by reverting to the resting point of accommodation, i.e., the point in space where the individual tonic level of neurological activity allows the muscles in the ciliary body to drift. We are all hard-wired to unique and different resting points. The end result is that a lag of accommodation developes against which we fight trying to keep the image clear. So, by sitting too close to the TV screen, we children of that era were creating our own visual repetitive stress condition, as our eyes tried to keep a fuzzy image viewable. 

Now, at the beginning of the 21st Century, we are still sitting too close to the TV in the form of VDT monitors and LCD screens. We never did get the message from our parents. So, on a day-to-day basis, we and our patients pay the price of repetitively stressing our vision systems by experiencing the symptoms of CVS.

Figure 4: Lag of Accommodation is Shown in Schematic Form

MAGNITUDE OF THE PROBLEM

If you believe that CVS is real and that there are patients in your communities who need your help, you ought to be asking yourselves: how many patients might there be, what ages are they, how common are their computer experiences?

I did a study in 1997 which involved sending a questionnaire to over 7000 randomly-selected, AOA-member optometrists. More than 1300 responses (18.5% response rate) were analyzed. On average, 17.3% of all the reported monthly primary-care eye examinations were performed specifically to treat symptoms related to the use of VDT monitors/LCD screens, for a total of 14.9 million computer-related exams performed in 1996. That works out to about 60 exams per month (or 3 patients per day) per AOA member doctor just for CVS problems. 

In another study, published in the Journal of the American Optometric Association, I reported that the majority of computer workers were females whose average refractive errors ranged between +1.OOD and -3.OOD. That range is the bread and butter of optometry. 

NIOSH (National Institute for Occupational Safety and Health) had reported in 1991 that approximately 85% of 70 million computer users in the workforce of the United States experienced one or more of the symptoms of CVS. 

The numbers, then, appear to add up. If a practice should elect to establish a computer vision specialty, the patient flow can be created to make the decision a sound and profitable one. 

One must also consider the high school and college students who are heavy computer users and whose numbers are not reflected in the data presented above. They will experience CVS, too, and the care you provide might mean the difference between academic success or failure for some of them.

SETTING UP THE OFFICE

To be seen by your patients as a specialist in CVS, you must look like one. Your office surroundings should reflect your commitment to provide this type of care. Let patients know from the start that you understand and appreciate how visually demanding a task computer viewing can be.

First and foremost, the office should be computerized. VDT monitors must be in use and prominently visible. Have anti-glare screens on the monitors and make sure that those staff members at the front desk can answer some simple questions about glare and eyestrain.

Next, provide computer glasses for each of your staff who work at the computers. Make sure that they wear the glasses. Patients must notice your staff giving credibility to your belief that this type of eye protection is crucial for visual hygiene. Also, make it a policy for anyone scheduled for a computer exam to be sent a measuring strip to use for determining computer working distance. This can be a 30" length of string to mark the eye-to-screen distance, or you may send a printed tape measure for the patient to use.

Place a 5"x 7" or 8.5"x ll" announcement at the front desk that the practice specializes in computer vision problems. You might start the message by asking: Do you work at a computer screen? Do you have eyestrain? Or you may simply want to request: If you work for hours at a time on a computer screen and your eyes hurt, please let the receptionist know. Also, develop a short questionnaire for computer patients to fill out. This might include questions on other symptoms, screen placement, lighting, hours viewing the screen and workstation furniture. Check out www.doctorergo.com for help in this area.

Have information on display from the manufacturers of specialty computer lenses. Seeing what lens makers have to say about their products will reinforce the special nature of CVS care, the need for specific eyewear to solve problems and your own expertise as a doctor. We will talk more about lenses later.

If space is available, dedicate a small area to CVS testing. This could be as simple as a keyboard and monitor mounted on a desk-height table. The VDT should be able to display a basic word-processing document. Such a setup is used to refine the Rx for computer glasses after your exam. More complex, and more expensive, choices would have you set aside an entire room for CVS testing which could give you the ability to change lighting conditions, workstation angles and distances and window-placement considerations.

Other budget-sensitive items would include replacing the standard fluorescent light tubes with full-spectrum lighting and installing parabolic reflector inserts in the fluorescent light housings. These are fairly expensive modifications, but choosing to make them would again highlight your commitment to and expertise in CVS care.

THE COMPUTER EXAM

So, now that you have made the commitment to include CVS vision care in your practice and you have your office appropriately equipped and laid out to serve your patients, how should you proceed with your exam sequence?

In my opinion, the most important finding for writing a computer-specific prescription is the manifest refraction at distance. Doing a very careful analysis of binocular-balance distance lens power will build the soundest foundation for any special-purpose glasses.

Now go to the 40 cm nearpoint. Using a best-acuity stimulus, determine that the patient is comfortably and consistently binocular. If not, assess the need for prism to achieve binocularity. Also assess the accommodative system for stability and function.

The patient should have used the measuring string to report computer working distance.

Place a reduced-Snellen card on the reading rod at that distance. (We will discuss suggested distances and angles in the next section.) Add plus power until the best-acuity line becomes blurry. Now bring the ±.50D crossed-cylinder lenses into play; replace the reduced Snellen card with a 90/180 crossed-cylinder target; and reduce plus until the darker lines reverse. 

I have found that the crossed-cylinder result taken at the computer working distance will put you within .25D of the final accepted computer lens power. At this point, you have a choice to make.

You may prescribe the power you have just determined. You may modify that power based on your 40 cm evaluation of the patient. You may take the patient to your CVS testing area and use a trial frame with loose lenses or flippers to refine the power that final .25D at the actual working distance used by the patient at work. 

The last choice may even be something one of your technicians can be trained to do, depending on how your individual state laws are written. 

The important point to remember is that ±.25D differences in the Rx can be significant when prescribing for CVS, since the visual demand of the task is so high. 

Keep in mind that there are vision testers on the market which claim to provide more accurate visual prescription outcomes for computer glasses. Whether you choose to go that route or not might depend on your own confidence in your abilities and, perhaps, on your budget (at least one of the specialty testers is asking a purchase price of about $5000).

Good, consistent results can easily be obtained by following the guidelines discussed above without the need for "bells and whistles" equipment.

 

THE BASICS OF COMPUTER ERGONOMICS

In about 1995, the American Optometric Association published its own ergonomic guidelines for the visual comfort of VDT users. Ergonomics is, in one sense, the study and change of workplace conditions that are not compatible with safe, efficient human interaction.

Of course, there's more to it than that one simple statement, but AOA wanted to give optometrists basic guidelines to share with their patients.

What AOA suggests is as follows:

1) Working distance from eye to screen should be set between 20" and 26".

2) Viewing angle for the screen should be 10 degrees to 15 degrees below straight-ahead gaze position. That would be equivalent to about a 10" drop from the straight-ahead gaze line directly above the screen to the center of the screen. 

3) Room lighting should be free of glare sources as much as possible. Screen anti-glare cover filters should be used where necessary (glass filters only; do not use plastic mesh filters).

4) Cover or mask windows to prevent glare from sunlight, and place computer screens at 90 degrees angles to windows whenever possible.

5) Reduce room lighting so that screen brightness and contrast can also be reduced to more comfortable levels. Use task lighting at each desk to illuminate copy work.

Sharing these guidelines with your patients will again boost your credibility and strengthen your reputation as an expert in CVS vision care.

SELECTING THE PROPER COMPUTER LENS

Now you have the basic computer-distance-related sphero-cylinder prescription for your patient. What do you do with it? 

One choice might be to select a single-vision lens for the computer glasses. That would be fine if the patient works in a cubicle all day with a visual demand of no greater than 4 feet. If the person needs to see around or across the room, single vision lenses will not work efficiently. 

In that case, and especially if your patient has previously worn a flat-top (FT) segmented bifocal lens, you could prescribe an occupational trifocal lens design. The newest of these have a 14mm x 35mm ribbon intermediate segment with an add power set at 2/3 of the distance power, are available in lightweight polycarbonate materials and provide the width of field which is desirable in a computer environment. Keep in mind that poly material may have annoying chromatic aberration in higher powers.

For those patients comfortable with a lined bifocal but decidedly not comfortable with a trifocal, select a FT35 or FT4O lens with the computer power set on top and the full near power in the seg. Again, this design will not provide any real distance viewing.

In either case, make sure to set the seg line higher than you normally would for dress wear. For success in prescribing computer eyewear, you must place the lens power where the patient views the screen. Too low a seg will cause neck and shoulder problems for your patient.

Figure 5 shows three screen placements seen in workplaces. For the low sceen, set the seg at the lower edge of the pupil. For the middle screen, set the seg at mid-pupil to the upper edge of the pupil. For the high screen, first see if you can get the patient to lower the screen at least to the mid setting. If this is not possible, set the seg midway into the upper iris and warn the patient that the seg will be in the way for all other activities away from the screen.

 

Figure 5: Setting seg lines for flat-top computer glasses

The decade of the 1990s saw the introduction of several specialty progressive addition lenses aimed at the computer user. Of the eight or so designs first available, four have maintained the recognition and distribution to be worth examining in greater detail here:

American Optical (AO) -

AO developed a modified PAL design, called the Technica, which has been fairly successful over the years as a computer lens. The design addresses the need for a wide intermediate field to facilitate computer viewing. The near zone is 25mm wide and the add progression is such that 75% of the full add power is achieved at a distance of only 9mm below the major reference point (MRP). Remember to fit the MRP at mid-pupil.

This characteristic allows for computer viewing without the need to lift the chin to bring the add power into range.

Also, the lens has a small distance viewing area at the very top of the lens, so that the patient can see the office environment without blur. Peripheral distortion is minimized by placing most of the unwanted astigmatism in the nasal portion of the lens.

 

SOLA Optical USA -

SOLA's answer to a computer lens solution came in the form of the Access lens. The design is a double progressive (top and bottom) which offers clear viewing for both computer and distance with minimal peripheral distortion.

The lens is fit with the MRP at mid-pupil. The doctor determines the computer power as usual. Then the top progressive area reduces that power by either .75D or by 1.25D (in effect providing a negative add). The doctor specifies to the lab which of the two lens change options is desired.

Thus, the patient would have reasonable room-distance viewing only up to computer powers of 1.5OD over the manifest. Anything above that, even with the lens that changes l.25D, would leave the user in +.5OD blur or greater. That may not be comfortable for most patients even in the close confines of the office workspace.

Be sure to check with your lab for details on how you should order the Access lens. It has been my experience that not all labs follow SOLA's manufacturing guidelines the same way. Maintaining an open and clear communication channel with the rep should avoid any problems.

 

Shamir Optical -

Shamir took the negative-add progressive idea one step further. They offer a lens, called the Office lens under their trademark and the Desktop lens under a private label arrangement with a major regional laboratory, which provides the same .75D and 1.25D change options as above, but then expands the parameters to include a 1.75D change lens as well.

With this lens, you have the flexibility to prescribe a computer-specific application to those patients with computer powers as high as 2.OOD over manifest and still have usable distance vision in the office setting. 

Set the MRP at mid-pupil or higher as before to avoid chin raising by the patient when viewing the screen. Also, check with your lab rep both for availabiltiy of this lens design and for how you should specify the lens parameters in your order.

 

Essilor of America (Varilux) -

Varilux once offered a lens, called Readables, which was actually a very nice application for the more advanced presbyope. It offered ±.75D changes around a center area set for the computer distance. Poor sales and a perceived small market led to the lens being discontinued. I believe that the company was both premature in its decision and visionary in its design, given the projected demographics on the numbers of "baby-boomer" presbyopes entering the bifocal market in the next 15 years.

To replace Readables, Varilux introduced the Interview lens. This is similar in concept to the other double progressives, but it comes in only one change choice with the top of the lens being approximately 20% of the power of the computer area. So, for computer adds of from +1.OOD to +2.OOD over manifest, the top of the lens would provide relative blur of from approximately +.25D to ±.50D.

Please check with your lab for the availability of this lens as well. Actually, using your lab rep as a source of information for any new lens product is a very good practice-management strategy.

 

TO COAT OR NOT TO COAT

Do coatings on computer glasses really help? If they do, which ones are best to use for most of your patients?

To answer those questions, you must know something about the patient's working environment. If work is done at home, without fluorescent lighting and with windows that can be controlled for the amount of light they let in, the only coating you might consider is an anti-reflection (AR) treatment on the lenses.

AR coatings are fast gaining in popularity and with good reason. Ophthalmic lenses virtually disappear when treated with AR. The efficiency of the lenses as a refracting medium increases dramatically. In fact, many who have tried AR for the first time report that they would never wear uncoated lenses again.

On the minus side, the AR coating is still more difficult to keep clean even with the newest technology applications. Some patients may find this to be too much of a bother. 

However, if work is done in a typical office setting with too bright fluorescent lighting, you may want to consider two additional coatings with the AR mentioned above:

400nm Coating (also known as UV coating)

Most daylight or coolwhite fluorescent tubes have output that is rich in harsh, short-wavelength light. This blue light is difficult for the human eye to focus due to its scattering characteristics. 

Improper lighting can account for up to 30% of the visual symptoms your computer patients report. So, it makes sense to include a coating that would eliminate at least some of the blue-component light in the office. The UV coating does just that.

 

Figure 6: Fluorescent light output vs. UV coating absorption

Figure 6 shows how a 400nm or UV coating (dashed line) absorbs about half of the fluorescent tube output in the range of 4lSnm to 420nm. This action makes the room light appear less harsh and increases worker visual comfort.

A UV coating is definitely recommended on computer glasses.

Tint Coating

Most offices with fluorescent lighting also tend to be too bright. A 10% absorbing tint (#1 tint) can reduce the strain associated with such high light levels.

In addition to the degree of tint selected, the hue of the tint can also impove visual performance. We saw above that the blue wavelengths of flourescent lighting decrease our visual efficiency. Monitor output tends to be moderately strong in that area as well. 

 

Figure 7: Output curves for various computer monitors

Blue wavelengths act most directly on the rods and short-wavelength cones ("S" cones) of our visual systems. So, if a tint color were selected which would maximize the performance of the long ("L" cones) and mid-wavelength ("M" cones) cones, overall efficiency of vision at the workplace would, in theory, be at its peak.

Amber color tint filters for computer glasses exhibit the characteristics we seek. Figure 8 shows how amber filtering selectively reduces illuminance for rods and S-cones more than for L-cones and M cones. Pink color tint filters reduce illuminance much less and rather non-selectively. Given a choice, I would recommend amber filter tint coatings to round out the coating package for the computer lenses you will be prescribing.

  

Figure 8: Amber vs Pink tint absorption to receptor types

CONCLUSION

Computer Vision Syndrome affects millions of office workers, students and even retired people in the United States today. You may not realize that the majority of your patients are included in those groups.

With a little effort and planning, your practice can serve the vision needs of those patients. In doing so, you will realize practice growth and the satisfaction of helping people to be more efficient workers through ergonomically appropriate intervention.

BIBLIOGRAPHY: FURTHER READING

1. Salibello, C, Nilsen, E. Is There A Typical VDT Patient? A Demographic Analysis. J Am Optom Assoc 1995; 66:479-83.

2. Salibello, C, Nilsen, E. Survey of AOA Members Regarding Prevalence and Treatment of Visual Stress Symptoms Related to VDT Use (Extended

Abstract). Optometry and Vision Science 1997, 12s, 74:216.

3. Nilsen, E, Salibello, C. Evaluating the Effectiveness of VDT Eyeglasses in Reducing Visual Stress Symptoms (Extended Abstract). Optometry and Vision Science 1996, 12s, 73:212.

4. Salibello, C, Using a Computer? Watch Out for Eyestrain. The Secretary 1995;

55-7: 11-13.

5. Cole, BC, Maddocks, JD, Sharpe, K. Effects of VDUs on the eyes: report of a 6-year epidemiological study. Optom and Vis Sci 1996; 73(8):512-28.

6. Sheedy, JE. The bottom line on fixing computer-related vision and eye problems. J Am Optom Assoc 1996; 67(9):512-17.

7. Nilsen E, et al. Reducing visual stress symptoms of VDT users with prescription eyeglasses. CHI '95 Mosaic of Creativity 1995; Proceedings:Short paper.

8. Scheiman, M. Accommodative and binocular vision disorders associated with video display terminals: diagnosis and management issues. J Am Optom Assoc 1996; 67(9):531-9.

9. Sheedy, JE. Vision problems at video display terminals: a survey of optometrists. J Am Optom Assoc 1992; 63(1O):687-92.

10. Mutti, DO, Zadnik, K. Is computer use a risk factor for myopia? J Am Optom Assoc 1996; 67(9):521-30.

11. Bommarito, PF. Computer vision syndrome: the cure is in your hands. R of Optom 1996; 133(11):35-7.

BIOGRAPHY FOR COSMO SALIBELLO, OD, CIE, FAAO

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