computer vision syndrome: a widely spreading but largely unknown epidemic among computer users

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Computers in

Computers in Human Behavior 24 (2008) 2026–2042

Human Behavior

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Computer Vision Syndrome: A widely spreadingbut largely unknown epidemic among

computer users

Zheng Yan a,b, Liang Hu b, Hao Chen b, Fan Lu b,*

a University at Albany, Department of Educational and Counselling Psychology,

School of Education, Edu 227, Albany, NY 12222, United Statesb School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical College,

270 Xueyuan Road, Wenzhou, Zhejiang 325003, China

Available online 19 November 2007

Abstract

The present paper is intended to introduce behavioral researchers to Computer Vision Syndrome(CVS), a widely spreading but largely unknown epidemic among professional and ordinary com-puter users, and to call for behavioral research programs to help computer users address this visualepidemic. Beginning with three clinical cases, the paper analyzes the classic definition of CVS, dis-cusses the prevalence of CVS, reviews five major symptoms of CVS (i.e. eyestrain, headache, blurredvision, dry eyes, and neck/back pain), summarizes five types of contributing factors of CVS (i.e. com-puter screens, computer environments, human eyes, computer users, and computer tasks), and pre-sents basic preventive and treatment strategies. Finally, three future research directions forbehavioral science research are briefly discussed.� 2007 Elsevier Ltd. All rights reserved.

Computers have significantly impacted cognitive, social, physical, and various otheraspects of the modern daily lives of computer users. Extensive literature in ergonomicsand optometry has indicated that computer use is closely associated with various visualproblems, which are referred to as Computer Vision Syndrome (CVS) in medical science.The following three clinical cases demonstrate CVS.

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doi:10.1016/j.chb.2007.09.004

* Corresponding author.E-mail address: [email protected] (F. Lu).

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Z. Yan et al. / Computers in Human Behavior 24 (2008) 2026–2042 2027

Case 1. A 34-year-old female project manager visited an optometric clinic for both eyefatigue during near work and frequent frontal headaches in the early evening. She hadtreated her symptoms with Tylenol in the past but found no relief. Based on her eye exam-ination, she was diagnosed with Computer Vision Syndrome. Her eye fatigue and head-aches were due to (a) five hours of work per day at the computer over the last 12months, (b) a viewing distance of only 12 in. from the computer monitor, and (c) her com-puter monitor being positioned on top of the CPU creating a viewing angle that was aboveeye level. The treatment was to wear a pair of glasses for near work, increase viewing dis-tance from the computer, and lower the computer monitor (Glasser & Anshel, 2003).

Case 2. A 28-year-old female information technology manager came to an optometricclinic and reported increased eye fatigue and dry eyes. She had previously consulted herphysician but was found to be in good health. The eye examination suggested that shehad normal eye and vision conditions, but she was diagnosed with Computer Vision Syn-drome with transient nearsightedness. Her eye fatigue and dry eyes were associated withtwo factors: (a) working for 8 h or more a day at the computer during the past 12 months,though at a normal viewing distance of 22 in. and (b) the existence of various visual ergo-nomic problems – namely, her computer screen was higher than eye level and producedglare and reflection. The treatment was to adjust her computer workstation. She receivedsignificant improvement of her symptoms (Glasser & Anshel, 2003).

Case 3. A 32-year-old male attorney visited an eye clinic with complaints of distanceblur following long hours of computer use, and headaches about three times a week.He had taken Tylenol in the past with no relief of his symptoms. The eye examination indi-cated that he had normal eye conditions, but suffered from Computer Vision Syndrome.His symptoms were mainly due to 5 h of intense work at the computer daily. The treat-ment was to wear computer glasses for near work (Glasser, 2000).

The three clinical cases presented above are based on the actual records of two nation-ally-known optometrists who specialize in computer-related vision problems. From thesethree cases, one can observe several basic aspects of CVS. First, the three adult profession-als (project manager, IT supervisor, and attorney) all used computers at work for 5–8 hevery day for a period of months. Based on standards set by the National Institute ofOccupational Safety and Health, they would all be classified as occupational computerusers rather than occasional computer users. Second, they were all diagnosed as typicalCVS patients who suffered from a variety of typical symptoms of CVS on a daily basis,ranging from eye fatigue, frequent headaches, dry eyes, to blurred vision. Although thesesymptoms are not life-threatening as diseases such as cancer or AIDS, they can be as trou-bling as a nagging tooth problem or chronic back pain. Third, although these three indi-viduals had used computers extensively, none of them had basic knowledge of CVS. Whilesuffering from CVS, they show very limited knowledge of CVS, either wrongly takingTylenol or being puzzled when seeing a physician. Fourth, all three CVS patients eventu-ally received proper diagnoses and effective treatment, and all experienced substantialimprovement in their visual symptoms, showing that CVS is diagnosable and treatable.

These three cases represent only the tip of the iceberg of the widely spreading epidemicof CVS among computer-users worldwide and demonstrate the extent to which CVS is lar-gely unknown by computer users (Blehm, Vishnu, Khattak, Mitra, & Yee, 2005; Mutti &Zadnik, 1996; Sheedy, 2000; Sheedy & Parsons, 1990). CVS has been extensively studied –first in the field of visual and computer ergonomics in the 1980s, and more recently in thefield of environmental and occupational optometry in the 1990s. However, few behavioral

2028 Z. Yan et al. / Computers in Human Behavior 24 (2008) 2026–2042

studies (e.g. Dillon & Emurian, 1995) have been conducted to describe, analyze, and posesolutions for CVS. For researchers in the behavioral science of computer use, it is useful tolearn from the current CVS research in ergonomics and optometry in order to help com-puter users deal with CVS. With this consideration, this paper will review existing litera-ture, focusing on five basic questions about CVS: What is CVS? How many computerusers suffer from CVS? What are the major symptoms of CVS? Why do computer usersdevelop CVS? What should computer users do to fight against CVS? The paper concludeswith suggestions for future directions for researchers in behavioral sciences with regard toCVS. Instead of providing a comprehensive review of the existing literature in both ergo-nomics (e.g. Dillon, 1992; Smith, 1987; Tattersall, 1992) and optometry (e.g. Blehm et al.,2005; Cole, 2003; Mutti & Zadnik, 1996), the purposes of this paper are mainly to increasepublic awareness about CVS among computer users, and to call for effective research pro-grams among behavioral scientists. In addition, while there is a relatively large body ofhuman factors literature devoted to the study of visual fatigue (e.g. Fostervold, Aaras,& Lie, 2006; Megaw, 1995; Miyao, Hacisalihzade, Allen, & Stark, 1989; Rechichi, Car-melo, & Scullica, 1996), the present paper will focus more on the optometric literaturedirectly examining CVS in order to further familiarize readers with optometry as a disci-pline of medical science.

1. What is CVS?

According to the American Optometry Association (American Optometric Association(AOA)., 1995), CVS is defined as ‘‘the complex of eye and vision problems related to nearwork which are experienced during or related to computer use.’’

This classic definition provides three key pieces of information about CVS: (a) CVS is aformally accepted medical and clinical term, such as William syndrome, Down syndrome,and Stockholm syndrome, rather than a folk science notion. (b) It has a wide variety ofassociated symptoms related to both eyes and vision rather than just one or two symp-toms. (c) The major cause of CVS is the near work of using computers rather than othervisual processes. As the most widely used definition of CVS, it has had deep and broadimpacts on CVS research.

This definition, however, was developed by the American Optometric Association morethan 10 years ago. We would like to challenge three aspects of this definition. First, thephrase ‘‘eye and vision problems’’ might be too vague. Some commonly observed CVSsymptoms are vision-related (e.g. headache and neck pain) rather than vision-specific(e.g. eyestrain and accommodation disorder). Second, the phrase ‘‘near work’’ at the com-puter might be too simple. Near work at the computer is not the sole cause of CVS, andtwo major interconnected factors should instead be considered together: near work at thecomputer (a viewing distance of less than 20 in.) and long-hour work at the computer(intense computing work for more than 3 h per day). These two factors combined causeeye fatigue as well as other computer vision symptoms. In addition, the definition lacksan explicit description of near work (e.g. viewing distance vs. viewing angle). Third, theterm ‘‘computer use’’ might be too general. There are various types of professional or dailycomputer users (e.g. office workers, website designers, college students, telephone opera-tors), various computer screen devices (e.g. desktops, laptops, palm handhelds,cell phones), and various computer use tasks (e.g. emailing, browsing, gaming, chatting,


shopping). Consequently, the effects of differences in computer use on eyes and visionmight vary.

2. How many computer users suffer from CVS?

According to US Census Bureau’s latest data on computer use (Day et al., 2005, TableC and Table D), the computer user population (3 years and older) in the United States in2003 was estimated to be approximately 188 million, while the total national population (3years and older) in 2003 was approximately 275 million. That is, approximately 68% ofAmericans used computers in their daily lives. Among American computer users, howmany of them suffer from CVS? While no national census data is available, two methodshave been used in the CVS research literature to estimate the prevalence of CVS.

The first method is to estimate how many computer users have reported suffering fromCVS on the basis of various empirical studies. For instance, Mutti and Zadnik (1996)reported that 75% of computer users who worked long hours at the computer had com-plaints of visual symptoms. Various empirical studies reported diverse estimations, rang-ing between 23% and 90% (e.g. Blehm et al., 2005; Mutti & Zadnik, 1996; Sheedy, 2000;Yeow & Taylor, 1991), with a general estimation of about 70% of the computer user pop-ulation (Sheedy & Parsons, 1990). Since (a) different research studies had different targetpopulations and sampling approaches, (b) most of them were based on self-report datathat normally would underestimate the prevalence of CVS, and (c) these studies were con-ducted in different years between the 1980s and 1990s, it is understandable that these esti-mations have been very diverse. Given that the current national population in 2007 is 302million as reported at www.census.gov, if we choose 68% as the percentage of Americanswho use computers and 23% as the most conservative estimate of the percentage of Amer-ican computer users who suffer from CVS, the total CVS population in the United Statesin 2007 can be estimated to be at least 47 million (i.e. 309 · 68% · 23% = 47).

The second method is to calculate the percentage of eye patients visiting visual clinicsfor CVS rather than for other visual diseases. According to Sheedy’s (2000) estimation,14–17% of optometric patients had a chief complaint related to working at a computer,and approximately 15 million eye examinations were given annually due to CVS. Since thisestimation was based on optometrists’ clinic reports rather than research subjects’ self-reports, it can be considered more objective. However, on the other hand, the estimationwas limited only to those CVS patients who had substantial eye discomfort and actuallyvisited the clinic. Thus, this method of estimation might provide more accurate approxi-mations of the CVS clinic population with rather severe CVS symptoms. As a result,the true CVS population in the United States is likely much larger than 15 million.

Based on these two methods, it might be safe to estimate that the CVS population in theUnited States is at least 15–47 million and at least 14–23% of computer users might havedifferent degrees and types of CVS symptoms.

In contrast to the pervasiveness of computer use and the prevalence of CVS among com-puter users, CVS is largely unknown to professional computer users, ordinary computerusers, and even many optometrists (e.g. Anshel, 2005; Sheedy, 1992; Sheedy & Parsons,1990). As shown in the three clinical cases presented, after suffering from CVS symptoms,the three CVS patients either wrongly self-medicated with Tylenol, or initially consideredtheir symptoms to be unrelated to vision. Lack of knowledge and understanding, and evenmisconceptions about CVS, can often be observed among computer users. Interestingly

http://www.census.gov


enough, all of the authors of this paper (some of whom are optometrists and/or ophthalmol-ogists by training) have been suffering from CVS for years due to their long hours of com-puter use. Nevertheless, ten years ago none of us were aware of CVS as an actual medicalcondition. One of the initial motivations to study CVS was to address our own symptoms.

Why do many computer users who have long suffered from CVS nevertheless have lim-ited knowledge of CVS? There are several potential explanations for this phenomenon.First, CVS is essentially a visual problem. The adverse effects of CVS on computer usersare not serious or deadly. Thus, many computer users might not pay much attention totheir symptoms. Second, CVS requires interdisciplinary studies. There may be poor com-munication across different fields and the scientific research community as a whole. Third,CVS is a new and unique concept, and there may not be many educational programs toeffectively educate computer users about how to protect their eyes, despite the fact thatthe American Optometric Association conducted a public awareness campaign in 1995.Fourth, although many computer users may have had much experience with CVS, theymight not have the appropriate vocabulary to label and describe their symptoms. Finally,public and professional attention is primarily drawn to the well-known musculoskeletaldisorders associated with computer use (e.g. Carpal Tunnel Syndrome) rather than to acondition characterized primarily by visual problems.

3. What are the major symptoms of CVS?

CVS does not have only one or two symptoms, but rather, a wide variety of symptoms(e.g. AOA, 1995; Sheedy, 2000). Different terms have been used to describe symptoms ofCVS, such as visual discomfort, ocular disorder, visual difficulty, visual impairment, visualpain, visual problems, eye fatigue, eyestrain, visual stress, visual complaints, and visualdiseases. In general, CVS symptoms can be divided into three major categories (e.g. Blehmet al., 2005; Sheedy, 1996; Sheedy, 2000): (a) eye-related symptoms (e.g. dry eyes, wateryeyes, irritated eyes, burning eyes), (b) vision-related symptoms (e.g. eyestrain, eye fatigue,headache, blurred vision, double vision), and (c) posture-related symptoms (e.g. sore neck,shoulder pain, sore back). These symptoms can also be considered as either subjectivesymptoms (e.g. visual complaints reported by patients) or objective symptoms (visualproblems diagnosed by eye doctors).

The most comprehensive and widely cited research related to CVS symptoms was con-ducted by Sheedy in the early 1990s (Sheedy, 1992; Sheedy & Parsons, 1990). One study wasbased on a survey of over 1000 national optometrists, and another based on multiple yearsof clinical work from one of the earliest computer vision syndrome clinics. Various symp-toms were reported in these studies, including eyestrain, headaches, irritated eyes, sore eyes,slowness of focus change, dry eyes, lighting and glare discomfort, blurred vision, doublevision, neck pain, shoulder pain, back pain, after-image distortion, and color distortion.Among the various symptoms listed in these two reports, the top five CVS symptoms, eye-strain, headache, blurred vision, dry eyes, and neck/back pain, are reviewed in this section.

3.1. Eyestrain

Eyestrain normally refers to computer users’ subjective complaints about uncomfort-able, painful, and/or irritable visual experiences (Sheedy, 1992). It is the most widelyreported symptom of CVS among the top symptoms based on both clinic experiences of


optometrists nationwide and their own clinic records from the 1980s and 1990s (Sheedy,1992; Sheedy & Parsons, 1990).

Eyestrain results from visual disorders when visual demands exceed visual capacity(Anshel, 1997; Sheedy, 1996; Yeow & Taylor, 1989; Yeow & Taylor, 1991). Trusiewicz,Niesluchowska, and Makszewska-Chetnik (1995) found long-hour work at the computerreduced important visual functions such as accommodation and convergence and could bethe cause of eyestrain among computer users.

3.2. Headache

Headaches often accompany other CVS symptoms, though many patients might notconsider them to be a vision-related problem (Sheedy, 2000; Travers & Stanton, 2002).They are also difficult to diagnose correctly and treat effectively. Based on the clinicalexperience of CVS experts (e.g. Anshel, 2005), vision-related headaches most often occurtoward the front of the head with a few exceptions, on one side of the head more than theother, and typically occur toward the middle or end of the day.

3.3. Blurred vision

Eyestrain as an initial symptom can further develop into blurred vision or other tempo-rary visual difficulties (Anshel, 2005; Sheedy, 1992; Sheedy & Parsons, 1990). Blurredvision occurs when the eyes do not focus on an image accurately due to a lack of visualacuity (the ability to distinguish between two distinctive points at near, intermediate, orfar distance) or visual accommodation (the ability to change the focal power of the eye).

Blurred vision can result from several vision processing problems, including refractiveerror (e.g. hyperopia, myopia, astigmatism), an improper glasses prescription, or accom-modative disorders. A poor computer working environment such as a dirty computerscreen, a higher viewing angle, reflected glare, or a poor quality or defective computerscreen, can lead to blurred images (Anshel, 1997).

3.4. Dry eyes

Dry eyes are among the most common eye problems that cause CVS patients to consulttheir eye doctors (e.g. Hikichi et al., 1995; Miljanovic, Dana, Sullivan, & Schaumberg,2007; Nakaishi & Yamada, 1999; Tsubota & Nakamori, 1993). They represent one of the typ-ical symptoms of CVS. Dry eye syndrome refers to a breakdown in the quantity or quality oftears that are used to moisten, cleanse and protect the eyes. With each blink, tears moisten thesurface of the eyes and wash away dust and microorganisms. When tears dry up, the eyes mayfeel ‘‘gritty’’ as if there were sand in them. This can further cause burning or itchy eyes, dis-comfort wearing contact lenses, increased sensitivity to light or excessive tearing, and inextreme cases, blurred vision (Acosta, Gallar, & Belmonte, 1999; Tsubota, 1998; Tsubota& Nakamori, 1993).

3.5. Neck and backaches

Many common symptoms of CVS are vision-related, such as eyestrain, blurred vision,and dry eyes, but CVS also appears to be non-vision-related, causing symptoms such as


headaches and neck and back aches (Anshel, 2005; Sheedy, 1992; Sheedy & Parsons,1990). The major cause of neck and back pain related to CVS is an improper viewing posi-tion when using the computer. For instance, if the computer screen is higher or lower thaneye level, it causes an awkward posture that contributes to sore neck, back, or shoulders(Sheedy, 1995). In many office situations, workers’ vision is compromised, and they mustadapt their postures to ease the visual strain. For example, if an older worker uses single-vision glasses which are designed for a 15 in. viewing distance, he or she must lean intoward a computer screen, which may be 25 in. away, in order to see the image clearly(Anshel, 1997).

It has been nearly 20 years since Sheedy’s seminal work was published. Today, thelandscape of computer use has been changed dramatically, and computer user popula-tions have diversified significantly. There might be more newly emerging symptoms ofCVS due to online games, e-learning, e-business, and e-government and other newtypes of computer use with diverse computer users. New symptomatology studies areneeded in the field of optometry with visual clinic populations, and in ergonomics withindustrial clients, but more importantly in other fields, such as psychology, education,entertainment, and business, and with diverse populations such as addictive computerusers, college students, hard-core gamers, or online shoppers.

4. Why do computer users develop CVS?

It was generally believed that near work at the computer and long-hour work at thecomputer are two general factors contributing to CVS. In addition to these two generalfactors, the CVS research literature has suggested that a wide variety of specific factorsare associated with CVS. Fig. 1 provides a simple model of eye–computer interaction thatillustrates five major types of contributing factors of CVS.

As shown in Fig. 1, five types of vision-related components are involved when a com-puter user uses his or her eyes to interact with a computer: (a) a computer screen as thevisual object, compared with paper for reading, (b) a computer room as the visual environ-ment, compared with a kitchen for cooking, (c) human eyes as the visual organ, comparedwith teeth for eating, (d) a computer user as the visual subject, compared with a driver in acar, and (e) a computer task as the visual task, compared with other tasks such as readinga newspaper or enjoying a painting. We use this classification to discuss major factors thatcontribute to CVS.

4.1. Computer screen

The computer screen is a unique visual object. Since the 1970s, researchers in visualergonomics and other fields have conducted hundreds of studies to examine the effectsof computer screens on visual functioning (e.g. Anshel, 2005; Fostervold et al., 2006;Megaw, 1995; Miyao et al., 1989; Rechichi et al., 1996).

As a visual object, a computer screen is substantially different from paper inmany ways. These differences, as described briefly below, show that viewing a com-puter screen is much more visually demanding than viewing paper, thus contributingto CVS.

3. Human Eye

1. Computer Screen

4. Computer User

5. Computer Task

2. Computer Room

Fig. 1. A model of computer use illustrating five major factors that are associated with CVS.


� The computer screen is self-illuminated, whereas reading paper relies on the reflectionof light from other lighting sources. Its brightness is one of the key features of a com-puter screen, which is associated with visual fatigue (Anshel, 2005).� The computer screen constantly refreshes at a certain rate, whereas paper is steady. A

minimal screen refresh rate of 75 Hz is needed, and much higher refresh rates (300 Hzor higher) may decrease ocular symptoms and increase user functionality (Blehm et al.,2005; Jaschinski, Bonacker, & Alshuth, 1996; Kennedy & Murray, 1991).� Objects displayed on the screen consist of a series of pixel-based dots with decreasing

brightness on their outer edges, thus making it hard for eyes to focus, whereas objectson the paper are printed with solid ink images (Anshel, 2005).� The computer screen has different resolutions that affect visual fatigue and readability

(Miyao et al., 1989), whereas paper does not have this resolution issue.� The computer screen consists of different combinations of background and foreground

and thus results in varied contrasting colors, whereas paper typically has a white back-ground with black or color objects. A high degree of screen contrast makes the screenmuch brighter and thus is associated with visual strain (Anshel, 2005).� An ideal computer screen should be free of reflections and glare. Computer screens,

even anti-glare screens, are subject to interfering reflections from other lighting sources,thus making eyes fatigue more easily. In contrast, paper does not have a serious glareissue (Anshel, 2005).� Viewing the computer screen requires a much higher viewing angle, thus making one

susceptible to dry eyes and neck pain, as compared with reading the paper at a muchlower viewing angle. It is recommended that the screen should be placed 10–20 degreesbelow the eye level (Anshel, 2005).� Besides the viewing angle, the viewing distance between the eyes and the computer

screen is important and often not easily adjusted, as compared with simply movingbooks by hand to adjust the viewing distance. Recent empirical studies suggest thatviewing distances of 35–40 in. may actually reduce the incidence of visual strain (Jas-chinski, 2002; Jaschinski, Heuer, & Kylian, 1999).


4.2. Computer room

A typical computer room is an indoor office that provides a special visual environmentfor eye–computer interactions. There is extensive literature suggesting that various compo-nents of computer rooms are closely associated with computer users’ visual comfort andvisual functioning.

Lighting conditions are the most important component of computer rooms that affectvisual functioning. Proper lighting in the computer room will make viewing computerscreens easy and clear, and thus enable computer users to reduce visual fatigue andimprove work performance. Research has suggested that an ideal computer environmentshould have the following visual features: (a) The level of the primary source of light ina computer room should be half as bright as that normally found in a work place. Spe-cifically, recommended lighting levels are 40–50 Fc for ambient light, compared to100 Fc or more in previously non-computerized offices (Anshel, 2000b). A computer useris at a greater risk of experiencing visual discomfort when the source of light is brighterand closer to where the eyes are focusing. (b) The computer room should have equalizedbrightness. (Abelson & Ouster, 1999). Constant and bright illumination from surround-ing sources of light (overhead fluorescent lights, large open windows, desk lamps) canpotentially reduce the visibility of the screen, creating reflection and glare, leading tosensations of discomfort, and resulting in transient adaptation effects from fixating backand forth between the two luminance levels. In addition, other sources of extremebrightness differences in the computer room include bright-white clothing, light-coloreddesk surfaces, highly polished furniture and decorative accessories, large mirrors, desklamps directed toward the eyes, or desk lamps which illuminate the desk too brightly(Anshel, 1997). (c) The room should have the proper type of lighting. Among naturallight, filament lamps, luminescent lamps, sodium lamps, and mercury-arc lamps, itwas found that sodium lamps were the most conducive to high visual capacity (Blehmet al., 2005).

Besides room lighting, other factors affecting visual capacity include air flow, tempera-ture, and humidity. Research has suggested that strong air flow, high temperature, and lowhumidity increase dry eyes and other types of eye fatigue (Anshel, 2005; Sheedy, 1997).

With the increased use of laptop computers in diverse indoor and outdoor visual envi-ronments, such as the airport, restaurant, playground, track field, bookstore, and cafe-teria, more computer users work in challenging and unchangeable visual environments,as compared with the environment of a typical computer room. Empirical research isneeded to assess these variations of computer environments on computer users’ eyesand vision.

4.3. Human eyes

Human eyes are an extremely exquisite and complicated visual system. Beginning in the1980s, researchers in optometry, vision science, and other fields have studied how eyes andvision are related to CVS. Three major characteristics of human eyes associated with CVSare discussed below.

First, evolutionally and anatomically, human eyes are relaxed and comfortable viewingobjects at a long distance (e.g. over 20 ft) in the daylight, but need to use significantly more


eye muscles to focus on objects at a near distance (e.g. nearly 10 in.). This is one majorreason why human eyes tire easily when using computers, especially after a few hoursof continual near work.

Second, the front surface of the human eye is covered with tears. Tears are used to pre-serve moisture for normal eye functions, maintain the proper oxygen balance of the exter-nal eye structure, and maintain the proper optical properties of the visual system. Likelubrication for car wheels, tears make eye movement easy, smooth, effective, and comfort-able. Staring at a computer screen leads to two major changes in the tear dynamics. First,the spontaneous eye blink rate (SEBR) during computer use reduces significantly. Com-pared with SEBR during conversation (mean = 15–16 blinks per minute), the SEBR sig-nificantly decreases during initial computer use (mean = 5–6 blinks per minute) due tothe high visual demand and mental concentration while viewing computers (Freudenthal-er, Neuf, Kadner, & Schlote, 2003; Schlote, Kadner, & Freudenthaler, 2004). Fewer blinksmeans fewer tears to be cleaned off and refreshed. Second, the size of the eye openingincreases when staring at the computer screen, resulting in greater tear evaporation. Aswe gaze higher, the eyes open wider, and the tears are lost faster, like a pond with a largesurface area as compared with a pond with a small one. This is one of the reasons why longhours of computer use will lead to dry eyes.

Third, human eyes need to adjust themselves in order to see objects from different dis-tances, such as by enlarging or minimizing the pupil to control the amount of light goinginto the eyes, lengthening or shortening the lens to change eye focus, and making musclesoutside the eyes longer or shorter to coordinate the two eyes. If one needs to view a com-puter screen while looking at paper on the table from time to time, the eyes have to adjustconstantly. In addition, the words and images on a computer screen are difficult for theeyes to focus on due to their poor edge resolution. The eyes tend to change the focus toa resting point and then refocus on the screen. For these two major reasons, constantfocusing and refocusing is required. These constant changes take place thousands of timesa day when a computer user stares at a computer screen for hours, which then stresses theeye muscles leading to eye fatigue and discomfort (Hoenig, 2002). This is one of the majorreasons why computer users experience headaches (an indication of adjusting eyes toomuch) or blurred vision (lack of accommodation and convergence).

4.4. Computer users

Computer users consist of very diverse groups of visual subjects. Compared with com-puter screens, computer rooms, and human vision, the existing literature on the relation-ship between computer users and CVS is limited. Thus, little is known about what types ofcomputer users (e.g. being different in age, gender, occupation, personality, habits of life,social and economic status) will be more vulnerable to CVS. This is a field in which psy-chology and behavioral science can and should make significant contributions. Below is adiscussion of two important groups of computer users – users with existing visual prob-lems, and younger computer users.

One of the most important factors to consider in studying computer users and CVS iswhether computer users are visually normal or have existing visual disorders. For com-puter users wearing corrective lenses (regular glasses or contact lenses), they may havethree types of existing vision problems, including accommodative disorders (eye focusing),binocular vision disorders (eye coordination), or refractive error (hyperopia, presbyopia,


and myopia). With these visual problems, these computer users suffer from more severesymptoms of CVS or develop CVS more quickly. For instance, office workers wearingcontact lenses were found to be more likely to suffer a higher severity of ocular discomfort(e.g. Anshel, 2005).

Older and younger computer users are also at high risk for suffering from CVS. Forexample, millions of school children use computers for long hours at school and at home,though their vision is still not fully developed. It has been estimated that the averageAmerican child is now spending about 1–3 h per day on the computer, and that up to30% of the approximately 37 million American children who use computers at home orschool may need special computer eyewear to reduce their risk of premature vision prob-lems (Hoenig, 2002). Hoenig (2002) found a strong correlation between children who workmany hours at a computer and premature myopia (nearsightedness) among 253 childrenaged 6–10 years.

Unique aspects of how children use computers may also make them more susceptiblethan adults to the development of these problems (Anshel, 2000b; AOA, 2006). (a) Youngcomputer users often cannot control themselves when it comes to playing or studying onthe computer. Many children will continue performing an enjoyable task, such as playinga video game, for hours without a break. (b) Young computer users often misinterpret var-ious visual problems with their computer screens, computer rooms, or eyes as normal. Achild who is viewing a computer screen with a large amount of glare often will not considerchanging the computer surroundings. Due to a lack of knowledge and experience, childrenoften accept blurred vision caused by nearsightedness, farsightedness, or astigmatismbecause they assume everyone sees the way they do. (d) Most computer workstationsare arranged for adults’ use and many school computers are often set up incorrectly forchildren (Hedge, 2005). Children may have difficulties seeing the monitor, reaching thekeyboard, or placing their feet on the floor, causing them arm, neck or back discomfort.(e) Viewing computers requires various visual skills, such as visual acuity, visual fixation,accommodation, and binocular fusion; children have not fully developed these skills(Anshel, 2000b).

4.5. Computer tasks

Computer tasks refer to the varied activities for which computers are used. A computeris an artificial intelligence tool that can be used for performing various kinds of tasks (e.g.studying, browsing, shopping). Different computer tasks have different visual demands fordifferent computer users, and thus should be an important consideration in studying CVS.For example, data entry workers need to look at a hard copy document and occasionallyglance at the screen, while a graphic artist looks primarily at the screen (Anshel, 2000a).This is probably the most uncharted area of research in the CVS literature.

First, computer use has shifted from primarily office-based work to different majortypes of tasks, including study, communication, entertainment, business, and variousother computer tasks. Thus, research is needed to examine the differences and similaritiesamong different tasks.

Second, there are different media and materials used in different computer tasks, fromnumbers, to text, graphics, audio, and video. These media and materials have different fea-tures (e.g. static vs. dynamic, single vs. multiple, simple vs. complex) and will have differentimpacts on human vision.


Third, different activity tasks will impact human eyes differently, such as reading (Chi &Lin, 1998; Cushman, 1986; Garcia & Wierwille, 1985), gaming (Tsubota, Miyake, Mat-sumoto, & Shintani, 2002; Yamada, 1998), and editing (Sheedy, Bailey, & Fong, 1987).Research into new activity tasks such as browsing, emailing, chatting, instant-messaging,blogging, and shopping are needed.

5. What should computer users do to fight against CVS?

5.1. Prevention

Although currently there are more computer users who work with computers for longerhours than ever before, CVS is preventable, and developing good habits for using comput-ers is important. Researchers have suggested several preventative strategies.

First, computer users should place the computer screen a distance of at least 20 in.away, as suggested by clinical optometrists. Several studies have suggested that distancesof 35–40 in. may actually produce fewer complaints of visual strain (Jaschinski, 2002; Jas-chinski, Heuer, & Kylian, 1998; Jaschinski et al., 1999). Such a relatively long viewing dis-tance will allow the computer users’ eyes to relax.

Second, computer users should adjust their computer monitors to a viewing angle ofaround 15� lower than the horizontal level (Burgess-Limerick, Plooy, & Ankrum, 1998;Jaschinski et al., 1998; Mon-Williams, Plooy, Burgess-Limerick, & Wann, 1998; Psiho-gios, Sommerich, Mirka, & Moon, 2001). This viewing angle will likely reduce bothvisual discomfort (e.g. dry eyes) and musculoskeletal discomfort (e.g. neck pain andback pain).

Third, computer users should follow the 20/20/20 rule as suggested by clinical optom-etrists (e.g. Anshel, 2005). That is, after 20 min of computer use, one should look at some-thing 20 ft away for at least 20 s. Several computer programs have been developed to helpcomputer users follow the 20/20/20 rule (e.g. displaying a small pop-up for 20 s every20 min). Research has shown (Fenety & Walker, 2002; McLean, Tingley, Scott, & Ric-kards, 2001) that regular small breaks improved work efficiency and compensated for timelost on breaks. Frequent breaks are recommended to restore and relax the accommodativesystem, thereby preventing eyestrain.

Fourth, computer users should carefully check the screen lighting and room lighting,including glare, contrast, brightness, reflection, and dust (Novik, Soldatova, Martirosova,& Semenets, 1991; Sheedy, Smith, & Hayes, 2005). For instance, research suggests that anyluminous source within the computer user’s field of view should not exceed three times themean screen luminance (Sheedy et al., 2005).

Fifth, computer users should have a good sitting position to avoid neck ache, backache, and headache (Ketola et al., 2002; Liao & Drury, 2000; Lie & Watten, 1994). Com-puter users should pay attention to room conditions (e.g. humidity and dust) that can con-tribute to the occurrence of CVS. Simple changes at the home or office, such as using ahumidifier, turning down the thermostat, and avoiding smoke, may reduce or eliminatedry eyes.

Sixth, for those who need corrective lenses, it is important to have regular eye examsand have good eyeglasses or contact lenses to correct visual problems (Anshel, 2005; She-edy, 2000). Research indicates that sometimes even very small uncorrected eye problemswill cause substantial eyestrain due to the nature of long and intensive computer work.


Those who wear contact lenses should follow all care instructions closely, as contact lensesmay contribute to dry eyes.

Seventh, for occupational computer users who need to use computers for more than 3hours per day, warm eyelid massage every day is important (Schirra & Ruprecht, 2004;Takahashi et al., 2005). Computer users might place a warm towel over closed eyes,and at first gently massage the upper eyelid against the brow bone for 10 s and then gentlymassage the lower eyelid against the lower bone for 10 s. Such a simple eyelid massage willstimulate the tear glands, increase the blood circulation within the eyes, and reduce thechance of developing dry eyes.

5.2. Treatment

Most CVS symptoms are treatable after the correct eye/vision examination and diagno-sis (Sheedy, 2000). Since CVS has a wide variety of symptoms due to various contributingfactors, researchers in optometry and ergonomics have developed various diagnostic pro-cedures and treatment programs for those who have CVS.

First, in addressing any CVS symptoms, it is important to learn about CVS and haveregular eye/vision examinations. This is the starting point of any timely diagnosis andeffective treatment. The American Optometric Association recommends that professionalcomputer users should obtain a comprehensive eye/vision examination when beginningcomputer work and periodically thereafter. Computer users can also use web-based diag-nosis tools (e.g. www.cvsdoctors.com and www.Doctorergo.com) for an initial self-examination.

Second, eyestrain, one of the most observed CVS symptoms, usually results from acombination of poor ergonomics, improper work habits, or an undetected visual condition(e.g. Anshel, 2005; Gomzi, 1994). Thus, a complete eye exam, an on-site ergonomic eval-uation, and instruction on correct working habits should be considered in order to ensurea correct diagnosis. Possible treatment includes having proper computer glasses, perform-ing an ergonomic adjustment, and undergoing behavioral therapy. For those who spendmore than 3 h a day using computers, and especially for occupational computer users,it is useful to wear computer glasses.

Third, headaches are one of the major symptoms of CVS, but can be caused by a vari-ety of sources (Gomzi, 1994). Thus, a complete eye exam should be conducted first. If theheadaches do not seem to be eye-related, computer users should consider an internal med-ical exam. If it is determined that the inappropriate use of computers is causing the head-aches, then reducing the duration of daily computer use, ensuring a correct viewing angle,and maintaining a proper viewing distance will reduce or eliminate the headaches.

Fourth, general and computer glasses are the most likely solution to a blurred visionproblem (Butzon & Eagels, 1997; Butzon, Sheedy, & Nilsen, 2002). Computer glasses,according to the American Optometric Association, are specifically designed for the com-puter workplace and have a different lens design or prescription than general-wear glasses.Research has indicated that computer glasses have been shown to be effective in the reduc-tion of vision-related symptoms of computer users (Butzon et al., 2002). Vision therapycould also be considered based on the nature of the problem and the patient’s age, time,and preference (Lazarus, 1996; Ohlson, 2004).

Fifth, since multiple factors cause dry eyes, it is important first to have a properdiagnosis and ergonomic evaluation to consider various potential reasons for the

http://www.cvsdoctors.com

http://www.Doctorergo.com


problem. Treatment suggestions include: Blink frequently when using the computer(Tsubota, 1998); Replace natural tears with artificial tears. Artificial tears usually solvethe problem of mild to moderate dry eyes (Acosta et al., 1999; Biswas et al., 2003);Plug the eye’s drain on the lower eyelids to block drainage, which is recommendedfor moderate to severe dry eyes; and seal the eye’s drain to blocking tear drainagepermanently.

Sixth, for neck and back ache, it is important for computer users to maintain the correctposture, especially those who wear glasses (e.g. Bernard, 1997; Straker, Pollock, Burgess-Limerick, Skoss, & Coleman, 2007). It is important to get regular eye exams and to have aproper chair, table, and environment.

6. Where should behavioral scientists begin in studying CVS?

As previously discussed, eye–computer interactions concern five major components: thecomputer screen, computer environment, eyes, computer users, and computer tasks. Thereis extensive literature in behavioral ergonomics devoted to the study of both computerscreens and computer environments. There is also extensive literature in visual and occu-pational optometry related to the examination of eye problems. While research is neededto continue the advancement of current knowledge regarding computer screens (e.g. lap-top screens), computer environments (e.g. atypical environments such as airports or res-taurants), and human eyes (e.g. new environmental impacts), research is urgentlyneeded to study the following three specific areas.

First, efforts should be made to expand research in diverse computer user populations,especially younger computer users. Middle-age adult occupational computer users repre-sent the typical population that has been extensively studied over the past 20 years. Behav-ioral researchers should examine different CVS populations of computer users to examinefactors such as current prevalence, specific visual symptoms, unique causes, underlyingmechanisms, and risk and protective factors.

Second, efforts should be made to examine diverse computer tasks, especially in theareas of learning and entertainment. Computer tasks conducted in the workplace havebeen studied extensively. However, computer use has expanded greatly from the initialarea of professional work to other areas such as learning and entertainment. Behavioralresearchers should examine the effects of different computer tasks on CVS, including theeffects of: (a) text-based materials, graphics-based materials, multimedia-based materials;(b) reading, writing, games, online classes, chat rooms, instant messaging, email, WWW;and (c) comparative studies of paper-based reading and screen-based reading. Differentactivities might entail different intensity and duration of visual demands, subsequentlyimpacting CVS.

Finally, behavioral researchers should examine an urgent and important issue: Why isCVS, a widely spreading epidemic, largely unknown to professional and ordinary com-puter users? This topic is particularly interesting considering that extensive research hasbeen done in ergonomics since the 1980s and in optometry since the 1990s, and that pro-fessional organizations such as the American Optometric Association have been conduct-ing public awareness campaigns about CVS as early as 1995. Answering this question willhelp millions of computer users gain knowledge about CVS and develop healthy behaviorsfor using computers.


Acknowledgements

This work was supported by the Wenzhou Medical College Major Research ProjectGrant and the University at Albany Faculty Research Award awarded to Zheng Yan.The authors wish to thank Dr. Jia Qu for his support of the project and Carla Corinafor her assistance in preparing the manuscript.

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