DECEMBER 1997 MEETING

TOPIC: "VISUAL STRESS AND HEADACHES"

Peter S. Visendi, O.D., was the guest speaker for the December 9th meeting of the East Bay Headache Support Group. The meeting was held in the Sterns Conference Room at John Muir Medical Center with 31 people in attendance.

Dr. Visendi received his Doctor of Optometry degree from the University of California, Berkeley where he is now an Assistant Clinical Professor of Optometry. He also is in private practice in Walnut Creek and Antioch.

Dr. Visendi began his presentation by stating that most cases of headache referred to him are not related to the eye; however, a small group of headaches do relate to the eye, which he called "ocular headaches."

Use of a VDT screen (video display terminal) is a popular source of visual stress. 75% of those using VDT’s have symptoms including headaches, blurred vision, double vision, eyestrain, glare, burning, and neck and back pain. Most are visually related, including headaches (50%).

Visual symptoms can occur when an individual has a particular visual disorder (far- or near-sightedness or astigmatism, etc.) or when there are visual compromises in the VDT work environment (reflections, glare, poor lighting, poor contrast or resolution, etc.). A compromised visual environment can cause symptoms in an individual with a marginal visual disorder.

Symptom remediation must necessarily involve individual visual assessment and correction as well as VDT workstation environment analysis. When a patient comes to Dr. Visendi complaining of headaches or eyestrain, he takes a case history and checks out the following:

What Are the Symptoms?

1) Are the headaches or eyestrain caused by accommodative (focusing), oculomotor

(eye muscles), refractive, spectacle design, environment, or health problems?

2) Is the pain a dull, diffuse ache that occurs after doing close (near) work?

3) Does it feel like a "tight band around the head" ache? This is related to stress and

can be induced by improper workstation posture or job design issues.

4) Late morning headaches that improve after lunch may be hypoglycemia related.

5) Throbbing headaches with a specific location are not visually related.

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Do You Have an Ocular Condition?

Dr. Visendi drew a picture of an eyeball and proceeded to explain various ocular conditions which can cause eyestrain. He said that 33% of the population in any environment will have problems with focus.

Hyperopia, or far-sightedness. When light comes in parallel, the focus is behind the retina and so is blurry. It takes lots of energy to clear the focus and eyestrain results. Also, some people have sluggish focus, which causes eyestrain.

Astigmatism. The cornea is out of round—shaped more like a football than a basketball—and so causes a distorted image. Then, eyestrain results because it takes energy to focus.

Presbyopia. This is a condition that occurs as people age, where the lens hardens and thus has difficulty focusing. As we get into our 40’s we find that we have to hold reading material further and further away from our eyes in order to focus.

Myopia. This condition, commonly known as "near-sightedness," doesn’t cause headaches, according to Dr. Visendi.

Exophore. This is a muscular imbalance, where the person’s eyes are turned out when they are closed. Exophoria can be corrected with glasses, or with training.

Esophore. An esophoric’s eyes are turned in, another muscular imbalance, which can be corrected with glasses. Dr. Visendi said esophores tend to have more problems than those whose eyes are turned out.

Diplopia. This is the term for double vision.

Burning Eyes. Are burning eyes caused by allergies, or dryness (lack of hormones), or horizontal viewing? Contact lens wearers can have problems with dryness, especially in a computer environment.

Glare Sensitivity. Does the patient have cataracts? Dr. Visendi stated that there is no relationship between cataract development and computer use.

What About Environment?

Lighting, media clarity, posture at workstation causing neck or back pain? Perhaps the patient has workstation design problems, or improper spectacle design (multifocals).

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Opthalmic Correction

Plus Power lenses relieve focus in presbyopia, hyperopia and esophoria patients. Single vision lenses, not bifocals, are the best to use when working with a VDT. 90% of Dr. Visendi’s patients who work with VDT’s have single vision lenses. Bifocals usually don’t work well, as the working distance is too close, and the viewing angle is too low, which may cause posture problems. Bifocals should not be used when working on computers, as they will cause a headache. The only bifocal Dr. Visendi will prescribe is one where intermediate power is above reading power. Trifocals can be used with a VDT, but they must have a wide intermediate zone. He mentioned progressive addition lenses, which have an intermediate zone and a near zone and a small central zone. These are very poor for use with a VDT, according to Dr. Visendi, as they cause distortion, a narrow field, and excessive head movement.

What about colored lenses? He said tinted lenses are mostly cosmetic--the color of the lens doesn’t make a difference when working with a VDT. A light pink tint, however, helps when working under fluorescent lights. Yellow lenses are promoted in industry, but are of little value. You can get your lenses coated for U/V protection. Also, anti-reflection coatings are available. This is very limited--most problems are at the screen, not on your glasses.

Correction of VDT-Environment Problems

Proper lighting is essential for visual comfort, and Dr. Visendi said that inadequate lighting in most work places is rare. However, ideally all objects in the field of view should have the same brightness, as areas considerably brighter than others lead to discomfort glare. The problem is that the VDT is much dimmer than a normally lit room. To eliminate eyestrain and headache you need to equalize the environment by darkening the room. The VDT is typically is measured at 5 to 20 foot candles of light, whereas we need 50 to 200 foot candles for reading.

Another source of visual stress is transient adaptation. An example of this is when you’re focusing on a VDT and then look over to a bright reference document. Most offices have situations with both discomfort glare and transient adaptation.

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Improving the Lighting in Your Work Place

1) Turn down the overhead lights. Try taking out one-half of the fluorescent light tubes.

If you have a halogen lamp, turn it around so it reflects off the wall.

2) Don’t use an auxiliary light (lamp) by your computer.

3) Retrofit fluorescent lights with louvers of parabolic design to direct light downward.

4) Paint ceiling with highly reflective paint (80-90% reflectance), and walls with 40-50%

reflectance paint. Have diffuse light throughout the room.

5) Avoid highly reflective horizontal surfaces such as white desk tops. Use matte medium

reflective surfaces.

6) Reorient your workstation so that you are looking along the rows of luminaries

(fluorescent lights), and not sitting perpendicular to them.

7) Use blinds or drapes on windows.

8) Erect partitions to eliminate glare.

9) Use a visor.

Reduce the Reflections on Your VDT

Reflections are the result of high luminance behind you, and cause stress. Most VDT’s have front surface reflection diffusers that reduce specular reflection, but are prone to windows or overhead luminaries.

1) Put a cardboard hood above the screen to eliminate reflection.

2) Add an anti-reflection coating to your VDT screen.

a) Nylon mesh: eliminates oblique light but not perpendicular sources.

b) Glass screen: filter or polarize.

Note: Applying an anti-reflective coating on spectacles does not address this problem.

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VDT Design Parameters.

1) The most important VDT characteristic for visual comfort is the resolution. Poor

resolution causes eyestrain.

2) Pixels are the matrix of dots that form the character, and the denser the pixels the better

the resolution. The minimum recommended pixel density is 5X7 (ANSI).

3) The font size should be 20/60 or better.

4) Lower case is easier to read than capital letters.

5) It is better to have black print on a white document than the other way around. Black

on white is less sensitive to reflections and a better match to background illumination.

6) White backgrounds are not usually used on VDT’s because the flicker is more noticeable.

7) A flicker frequency (or vertical scan rate) of 100 cycles per second is best. If flicker rate

is higher than CFF, the flicker will not be perceived. A white background increases CFF.

More flicker equals more stress. If bothered by flicker, turn down the brightness.

8) Screen color is not very important to visual comfort, but Dr. Visendi recommended that

we not use a white screen. Most screens are green, amber, or white.

What About the Amount of Time Spent Staring at a VDT?

Dr. Visendi said that the typical recommendation is for a worker to spend two hours at a VDT and then take a ten minute break. He said that two hours is too long, though, to go without a break for your eyes. When you look at a VDT screen, you’re looking at something that is not real, that is fluctuating all the time, so it causes more eyestrain. Therefore, resolution is very important.

Conclusion

In conclusion, Dr. Visendi mentioned that we can blame eye problems on our parents, as the ocular conditions listed above tend to be inherited. Being tested and fitted for the right spectacles or contact lenses will relieve stress. Also, follow his recommendations to reduce visual stress in your environment and keep eyestrain at a minimum.

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After his talk, Dr. Visendi welcomed questions from the audience.

Q. Can migraines be triggered by eyestrain?

A. Yes.

Q. What does Refresh Rate mean?

A. After some discussion, it was decided this has to do with the rate of flicker on the VDT.

Dr. Stein mentioned that a movie is shown at 24 frames per second, and the flicker is

not noticed.

Q. A question was asked about CFF.

A. CFF is not 40 to 50 cycles per second for everything. For a white screen it is lower, and

for a complex environment, it is lower yet. CFF is dependent on the object you’re viewing.

Q. How is an ocular headache described?

A. Diffuse, dull, frequent (all the time). Duration: Lasting a few minutes to a few hours, or

as long as working on the task. If one is in an acute environment and has acute ocular

problems, the headache could occur daily.

Q. How can we reduce formation of cataracts?

A. Take multi-vitamins with anti-oxidants, such as C, E, Betacarotene, Zinc.

Dr. Visendi stated that 50% to 60% of all people who work on computers will have ocular

problems, such as eyestrain, uncomfortable but not severe headache, dry eyes, etc. He prescribes a computer glass (single vision lens) for people working on VDT’s. Therefore, many people will need two pairs of glasses (a separate pair just for the computer). The range of clear vision is 19" to 26."

Q. Will insurance companies cover two kinds of glasses for an individual?

A. "Some do, some don’t," responsed Dr. Visendi.

Dr. Visendi also passed out a hand-out entitled Using Your Eyes and Your VDT, which is attached. If you have any questions for Dr. Visendi, don’t hesitate to contact him at:

Peter S. Visendi, O.D.

2801 Ygnacio Valley Road

Walnut Creek, CA 94598

(510) 933-2600

The intention of the East Bay Headache Support Group is to provide information and resources. It does not provide medical advice, which should be obtained directly from a physician.

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Using Your Eyes and Your VDT

It’s 11:30 in the morning. You’ve been working at your video display terminal (VDT) since 9:00 AM. Your eyes feel irritated and fatigues, your vision is blurry and you still have several hours of work ahead of you.

The symptoms that you are experiencing are common among people who work with VDT’s They may be a result of the way that you use the equipment and furnishings in your workstation. But they may also be, at least partly, the result of a vision problem. Anytime you experience symptoms like headaches, eye strain, blurred vision, eye irritation, double vision, excessive tears or dry eyes, pain in the eyes or excessive blinking or squinting, you should visit your doctor of optometry for a comprehensive eye examination. And, when you do, be sure to tell the doctor about the VDT work that you do.

After you have have a comprehensive eye examination, there are a number of things that you can do to arrange and use the elements of your workstation to eliminate or minimize discomfort.

Adjusting Your Chair

Many times, your chair can be adjusted to make your workstation much more efficient and comfortable. For instance:

• Your feet should be flat on the floor (or on a slightly angled foot rest) with your knees

bent near or greater than 90 degrees.

• Your seat should support your legs without excessive pressure on the back of your thighs.

• Your back should be snug against the seat to fit your spinal contour. Your thigh to trunk

angle should be 90 degrees or greater.

Following is

1)