Article courtesy Points de Vue
Dr. Sheedy received his optometry degree and his doctorate in physiological optics from the Ohio State University. He was a clinical professor at the University of California at Berkeley School of Optometry where he founded the first VDT Eye Clinic in 1985. He also established the Center for Ophthalmic Optics Research at Ohio State University and is recognized as an expert in the design and prescribing of progressive addition lenses. He has twice received the Garland Clay Award for the best clinical research published in the journal of the American Academy of Optometry and also received the William Feinbloom award for his work in vision ergonomics. He also received the Distinguished Service Award from Prevent Blindness America for his work with ultraviolet. He has over 140 published articles and has participated in the development of numerous ANSI and ISO standards and regulations. Currently Dr. Sheedy is the head of the Vision Ergonomics Research Laboratory and professor of optometry at Pacific University.
Symptoms of discomfort are common among patients who spend considerable time performing tasks at near viewing distances – such as is common among computer users.
Although the symptoms can be vague and seem elusive, they can usually be eliminated or reduced by diagnosis and treatment of the work arrangement and the visual system, including proper spectacle correction of presbyopia.
This article summarizes clinical management of vision-related discomfort.
Many of our patients have symptoms of discomfort associated with performing near tasks. Of course, the most common tasks performed at near involve reading, especially at computer displays1. Therefore, it becomes the task of the practitioner to diagnose the conditions causing the symptoms and to devise a treatment plan to eliminate or at least mitigate the symptoms.
The reading task itself, whether on hard copy or electronic display, is perhaps the most visually-demanding near task. Typical reading involves a series of 200 ms fixations sandwiched between 35 ms saccades. Each saccade moves the eyes 7-9 characters further in the text. Although this is very demanding, we have discovered that it is the cognitive uptake system that limits reading speed in subjects with vision systems that are performing well, not the visual system. By manipulating the text size and legibility we have noted that fixation durations and frequency are altered, but the reading speed is maintained2,3,4,5. Actually, it is remarkable that many people can read for hours with no symptoms.
Given that reading (near work) can be performed without symptoms under good conditions, it becomes our task to identify the reason(s) why our particular patient has symptoms of discomfort. I have observed clinically5,6and in laboratory research7,8,9,that symptoms may occur when either the environmental conditions or the visual system capabilities are compromised. Resolving the patient symptoms often requires analyzing both the visual system and the environmental conditions under which they have the symptoms of discomfort10.
Analysis begins with scrutiny of the patient symptoms. This can often directly lead the clinician to the correct diagnosis. The symptoms can be categorized into visual, musculoskeletal, and asthenopia as shown in Table 1.
|Visual symptoms||Post work blur at distance|
|Slowness in focusing|
|Musculoskeletal symptoms||Neck and shoulder ache|
Tab. 1: Three primary symptom categories.
Visual symptoms are the easiest to diagnose. They can easily result from an uncorrected refractive error. Errors as low as 0.50 DC can result in symptoms.
Presbyopic patients should be properly corrected for the unique viewing distance of their computer, and will report blur or musculoskeletal ache if not. Typically, presbyopic patients require an intermediate prescription in order to see their computer correctly. It is important to determine the distance at which they view their work (office computer displays are typically at a viewing distance of 50-60 cm). Demonstration and refinement of the near addition in free space can reassure both clinician and patient.
Slowness in focusing, or distance blur after near work, is typically due to accommodative infacility. If so, tests of accommodative function can assess if this is a problem. It is best to test accommodative infacility directly using +/- lens flippers.
Double vision (diplopia) is infrequently reported, but indicates a binocular vision difficulty when present. An intermittent diplopia usually indicates an intermittent strabismus. Analyze the binocular vision system to determine if there is an eso or exo strain on the visual system. The most common problem is a convergence insufficiency that causes intermittent exotropia at near distances.
Neck ache and back ache are quite common in computer-using patients. This can often be due to inappropriate location of the display or inappropriate spectacle correction of presbyopia.
The top of the display should be near eye level. If not, then adjustments need to be made to accomplish this. Our visual system has a strong preference for looking down about 10 degrees, i.e. depressing the eyes about 10 degrees11. If the display center is not about 10 degrees below the eyes, then neck and back adjustments are made12 resulting in strain.
Neck and backache can also be caused by presbyopia-correcting spectacles that cause an awkward viewing distance or posture to see the computer display or other uniquely-located near work. It is very common for general-issue bifocals or progressive addition lenses to be guilty of this, even though they might work for most other everyday tasks.
Wrist, back, and shoulder pain or ache can also be caused by other work-related factors and referral to a workplace specialist is indicated.
Asthenopia is a catch-all word for the less-specific symptoms such as eyestrain.
Our research has repeatedly shown13,14 that these symptoms fall into 2 constellations, both subjectively (i.e. patient sensations) and objectively (i.e. the inducing condition). We call these 2 constellations “external symptoms” and “internal symptoms”. They are summarized in Table 2.
|Symptom sensations||Perceived location||Including conditions|
|External symptoms||Dryness||Bottom of Eyes||Blur at near|
|Burning||Front of Eyes||Overhead light glare|
|Internal symptoms||Strain||Behind the eyes||Accommodative stress|
|Ache||Inside the eyes||Convergence stress|
|Headache||Astigmatic refractive error|
Tab. 2: External and internal symptoms
In general, the differentiation can be summarized as follows:External and internal symptoms
- External symptoms – dry eye and caused by environment
- Internal symptoms – felt inside the eye and caused by visual conditions
The clinician can use this symptom differentiation to help guide the diagnosis and management of the patient. External symptoms indicate a dry eye condition and possible environmental culprits such as lighting, display location, or text quality. Internal symptoms indicate an ophthalmic or visual problem related to accommodation, convergence, or refractive error. Clinicians may want to use the clinical tests shown in Table 3 to diagnose accommodative and binocular vision disorders.
|Visual symptoms||Positive and negative lens to blur (NRA and PRA)||NRA and PRA should each be 1.5D or greater|
|Accommodative flippers (+/-1.5D)||Expect 13 cycles/min monocularly, 10 cycles/min binocularly|
|Binocular alignment||Phoria||Any esophoria may be a problem. Exophoria less than 6PD is seldom a problem. Otherwise, see Sheard’s criterion.|
|Sheard’s Criterion – base-out prism to first blur divided by the phoria. Only effective for analysis of exophoria (15-16)||Prism-to-blur should be twice the amount of the phoria.|
|Near Point of Convergence||Should be easily repeatable and closer than 8cm. Note if patient as subjective difficulty in performing test.|
Tab. 3: Tests for accomodation and binocular alignment
Patient Treatment and Management
After diagnosing the reasons, either environmental or visual, that cause or contribute to the symptoms of discomfort, then the appropriate treatment measures from those below can be used to treat the patient.
Fitting the presbyope
To begin, the location of the primary work (e.g. computer display) must be determined. If a computer display location can be altered, then it should be located so that the top of the display is level with the eyes. If the display cannot be located differently, then its location should be noted and spectacles designed accordingly.
Most younger presbyopes (near add of 1.25 D or less) can often use their regular bifocals or PAL for their intermediate work (e.g. computer display). This is because such patients have enough remaining accommodation that they are able to comfortably view and focus upon the intermediate task through the distant portion of their spectacle lenses.
Presbyopic patients with a near add of 1.50 D or greater often require separate spectacles for performing near work comfortably, if that near work is at a unique viewing angle, or distance, such as commonly occurs at computers or on assembly lines. If the patient wears bifocals for everyday needs, then it is best to provide the patient with work-related bifocals in which, the top contains the intermediate prescription and the bottom contains the near prescription. Trifocals may be considered. If the patient wears PALs for everyday viewing, then it is best to provide Occupational Progressive Lenses (OPL) for the patient. OPLs are designed to provide extensive intermediate and near viewing areas. Usually the top of the lens also contains a small add of +0.50-0.75D. OPLs are very useful for most office and other indoor activities.
In prescribing adds and designing spectacles, it can be very useful to demonstrate the add and clear viewing distances in free space. If prescribing an OPL, it is also very useful to demonstrate the small distance blur through the top of the OPL, so that there are no surprises at time of dispensing.
Dry eye is a common complaint among office and computer workers. Very often the following conditions contribute to dry eyes and fixing them can improve the symptoms:
- Lower the computer display – especially if the top of the display is above the eyes.
- Reduce or eliminate glare from the patient’s field of view (see Lighting below)
- Correct refractive errors including presbyopia.
- Make sure the text is not too small or viewed from a larger-than-normal distance. Most text should be 10 to 12 point in size, viewed with 100% screen magnification, and viewed from no more than 60 cm.
- Eliminate any air drafts in the workers space.
- In addition to the above measures, it is advisable to provide artificial tears to be used only as needed. Counseling about work breaks and light rubbing of the lids may also be helpful. More severe cases of dry eye require additional measures such as punctual plugs.
Accommodation and Binocular Vision
Reduced amplitude of accommodation (for the patient’s age) and accommodative infacility can both be managed with either orthoptic training or prescription of plus lenses (usually +0.50 to 1.00D) for near work. Working patients often are unwilling to spend the time with an orthoptic program, and the plus lenses can cure the problem.
Likewise, patients with esophoria at near are best treated with a near add, which reduces the eso stress on their binocular system.
Patients with exo deviation, as often accompanied by convergence insufficiency, must be treated with orthoptics – lenses are not an effective treatment. Fortunately, convergence is the most easily trained visual function and can often be managed with push-up training alone.
Lighting is likely the most common environmental culprit insofar as causing and contributing to visual discomfort. All patients with near viewing symptoms should be counseled about eliminating glare from lights.
The most common lighting problem is shown in this picture: light from luminaires (or windows) directly impinging the eyes of the patient – i.e. the light source is very bright in the peripheral field of the patient. This can be demonstrated to the patient by taking the patient to an office location with a bright overhead light, and requesting the patient to shield their eyes from the offending light with their hand. Patients should be encouraged to note the improved comfort by doing so. The patient can then be instructed to repeat the test at their work place to test if lighting is a problem.
If lighting is determined to be a problem, then possible interventions include: turning off the offending light, use blinds or drapes on windows, remove white surfaces, use partitions, rotate the work station, use indirect lighting, or wear a visor.
For visual and musculoskeletal comfort, the work to be viewed most often must be directly in front of the person and located so that the person views it with eyes depressed at least 10 degrees and no more than 30 degrees. For computer displays, intended to be used with an upright posture, the top of the display should be at eye level, resulting in eye depression to view all elements of the display.
Upright posture while maintaining the normal convex curvature of the lower spine can be important to long term comfort. Arms should be supported by chair arm rests to avoid tension across the shoulders. Variable positioning, such as adjustable height desks and chair also can improve patient comfort.
- Sheedy, JE. Vision problems at video display terminals: a survey of optometrists. J Am OptomAssoc 63, 687-692, 1992.
- Tai, Y.-C., Yang, S.-N., Hayes, J. R., Sheedy, J. E. (2010). Effect of character spacing on text legibility. Presented in the Annual meeting of American Association of Optometry. November, 2010: San Francisco, CA.
- Yang, S.-N., Tai, Y.-C., Hayes, J. R., Doherty, R. A., Corriveau, P. J., & Sheedy, J. E. (2010). Effects of font size and display quality on reading performance and visual discomfort of developmental readers. Presented in the Annual meeting of American Association of Optometry. November, 2010: San Francisco, CA.
- Tai Y, Sheedy J. Blink is not just a random event in reading. Optom Vis Sci 2006;83:E-abstract 060065.
- Tai YC, Sheedy J, Hayes J. Effect of letter spacing on legibility, eye movements, and reading speed. Vision Sciences Society abstract 2006;248.
- Sheedy JE. Video display terminal users: clinical findings. Amer J OptomPhysiol Opt 65, 38p, 1988.
- Sheedy JE, Gowrisankaran S. Viewing compromised visual stimuli causes dry eye symptoms: role of the orbicularis muscle. Vision Sciences Society abstract 2006;26.
- Nahar N, Gowrisankaran S, Sheedy J, Hayes J. Eyelid squint response to visual and cognitive stress. Optom Vis Sci 2007;84:E-abstract 075096.
- Gowrisankaran S, Nahar N, Sheedy J, Hayes J. Visual and cognitive load determines severity of near work induced asthenopia. Optom Vis Sci 2007; 84:E-abstract 075095.
- Sheedy JE. How to eliminate visual symptoms – treat the eyes and fix the environment: A report from the VDT Eye Clinic. Work With Display Units ‘92, TechnischeUniversitat Berlin, Institut fur Arbeitswissenschaft, Berlin, D-23, 1992.
- Menozzi M., Buol A. v., Kruege H. and Miege Ch. Direction of gaze and comfort: discovering the relation for the ergonomic optimization of visual tasks. Ophthal. Physiol. Opt., 1994, Vol. 14, 393-399, October.
- Sheedy JE, Parsons SP. Vertical yoked prism – patient acceptance and postural adjustment. Ophthalmic and Physiological Optics 7: 255-257, 1987.
- Sheedy JE, Hayes JR, Engle J. Is All Asthenopia the Same? Optom Vis Sci. 2003;80:732-739.
- Gowrisankaran S, Sheedy JE, Hayes JR. Eyelid squint response to asthenopia-inducing conditions. Optom Vis Sci,2007;84(7):611-619.