Computer vision syndrome (CVS), also referred to as digital eye strain, describes eye and vision-related problems that result from prolonged computer, tablet, e-reader and cell phone use. Many individuals experience eye discomfort and vision problems when viewing digital screens. The level of discomfort appears to increase with the amount of digital screen use.
The main visual symptoms reported by visual display terminal (VDT) users include eyestrain, tired eyes, irritation, burning sensation, redness, blurred vision, and double vision, thus termed the phrase ‘computer vision syndrome’ (CVS). Vision problems and symptoms associated with the use of the eyes are the most frequently occurring health problems among VDT users. CVS not only causes pain and discomfort to the individual, but also reduces overall efficiency by reducing the time that a person can effectively work.
Majority of VDT patients had symptoms that were different than other near-point workers, especially as related to glare, lighting, and spectacle requirements. Greater frequency and severity of symptoms were also noted. One study shows higher degree of meibomian gland dysfunction (MGD) in symptomatic computer users than in computer users who have lesser degrees of ocular surface complaints.
Occupational Safety and Health Administration of the US Government (OSHA) has defined CVS as a ‘complex of eye and vision problems that are experienced during and related to computer use; it is repetitive strain disorder that appears to be growing rapidly, with some studies estimating that 90% US workers using computers from more than three hours per day experience CVS in some form’ (Nilsen, 2005). Anshel (2006) have defined CVS as the ‘complex of eye and vision problems related to near work, which are experienced during or related to computer use’. Chakrabarti (2007) defined CVS as the ‘excessive viewing of visual display terminal (VDT) screens without proper attention to practical visual hygiene’. The American Optometric Association (AOA) has defined CVS as ‘a complex of eye and vision problems related to activities, which stress the near vision and which are experienced in relation or during the use of computers’. It has now been concluded that CVS is characterised by visual symptoms which result from interaction with a computer display or its environment. In most cases the symptoms occur because the visual demands of the task exceed the visual abilities of the individual for comfortable performance of task.
Office work involves a range of activities including typing, reading, and writing. Each activity was adequately varied in the requirements of posture and vision. Computers have combined these tasks to where most can be performed without moving from the desktop, thereby improving quality, production, and efficiency. The popularity and affordability of personal computers with the internet capabilities at home introduced more computer users.
Studies have not clearly indicated a negative effect on computer user due to radiation levels from VDTs. VDTs are known to emit many types of radiation, including soft X-radiation, optical radiation, radiofrequency radiation, very low frequency radiation, and extremely low frequency radiation. Most women in offices, who work with VDTs, do not increase their risk of miscarriage.
It may well be that high computer usage raises the number of dry eye sufferers and/or increases the severity of symptoms, but studies have not produced any direct comparison of groups that would allow us to conclude that computer use bears a long- term causal relation to ocular surface disease. There needs to be more prospective studies to elucidate direct relationship between ocular surface disease (e.g. MGD) and CVS.
Symptoms of CVS may include:
The symptoms may be aggravated by poor lighting, improper work station design, uncorrected refractive errors, glare, bad posture and long periods of sitting. Playing electronic games for long periods, especially in children has also been linked to obesity.
Risk factors for CVS include:
There are several factors that contribute to CVS and dry eye syndrome (DES). They include the following:
The images produced on a VDT consists of thousands of tiny, bright spots (pixels) or horizontal lines (rasters), which collectively form unresolved images that blur together and lack sharp edges. The more the dots or lines displayed on a monitor to produce a picture, the sharper and clearer the image will appear. With time, the resolution of monitors has improved drastically, producing displays approaching that of typeset documents.
Many factors affect readability and legibility of characters on the screen. Words containing upper case in combination with lower case are more easily interpreted than all upper case documents. The spacing between characters and lines also affects picture quality. High levels of contrast and brightness are known to represent the most common causes of character blur. Screens should contain dark characters against a light background display screen, rather than the opposite. Switches from a light background hard copy to dark background display causes fatigue of the iris muscle.
In cases where it is not practical to reduce surrounding light, reduction of reflections and increase in contrast may be obtained from antiglare filters.
Recent studies demonstrate differing results in the efficacy of symptoms relief with screen filters. One recent study revealed that people who used a screen filter reported less occurrence, shorter duration, and less intensive eye and musculoskeletal complaints after one month of use. It was concluded that screen filters could improve the conditions for visual perception and thus relieve eyestrain. Another study showed that filters by themselves do not reduce the occurrence of asthenopia (rapid fatigue of the eyes). More research is needed to determine whether screen filters are effective in the relief of ocular symptoms.
Studies have shown that much higher refresh rates may decrease ocular symptoms and increase user functionality.
Numerous studies have shown that there is no evidence to support that VDT operators face health hazards or have exposure to electric, magnetic, or ionizing radiation fields significantly above ambient levels.
Eye focusing mechanism in human beings responds well to images with well defined edges with good background and contrast between the background and letters. Visual work on computer involves continuous muscular activity and it includes frequent saccadic eye movements (ocular motility), accommodation (focusing) and vergence (alignment demands).
Characters on computer screen are made up of tiny dots called pixels. Each pixel is bright at its center and decreases in brightness towards the outer edges. This causes electronic characters to have blurred edges as compared to letters on a paper with sharply defined edges. This makes very difficult for eye to maintain focus on pixels, and the eye relaxes to focus behind the screen. This is called the resting point of accommodation (RPA) or dark focus. Thus, eye constantly relaxes to RPA and strains to refocus on to the screen thereby leading to eyestrain.
Diagnosis depends upon the symptoms being faced by the patients and the clinical features.
A complete ocular surface examination is imperative to rule out local and systemic features associated with DES, blepharitis, inflammation, and lid margin disease. Patients with significant aqueous deficiency with basal or Schirmer test 1 value less than 5 mm should be evaluated.
CVS and meibomian gland disease (MGD):
The rate at which people blink decreases by more than 60% when they stare at a computer screen, suggesting that the acute decrease in blinks can acutely increase symptoms of Dry eye syndrome (DES) or keratoconjunctivitis sicca (KCS) . Computer users often complain that their eyes feel dry, burning, gritty, or heavy after an extended period at VDT. Their eyes may even reflexively tear in an attempt to properly lubricate and rewet the front surface of the eye. DES may be a primary cause of ocular fatigue, such as experienced when using a VDT, where the blink rate is decreased and the exposed ocular surface area is increased. Blink rate is decreased further in dark where it is difficult to read.
The tear film, which overlies and protects the cornea, consists of, from anterior surface inward, a lipid layer, an aqueous gel layer, and a mucin layer. DES results from evaporation of the aqueous component. The lipid surface layer protects the aqueous layer from evaporation. It is secreted as meibum by the meibomian glands embedded in the eyelids. The normal physiological mechanism of meibum secretion is associated with blink reflex. The normal blink expresses meibum from the glands and spreads it evenly on top of the aqueous layer. Several studies have shown that computer use produces considerable reduction of the spontaneous blink rate. Hence, computer use reduces meibum secretion and exposes tear film to increased aqueous evaporation. Because the tear film is maintained by a balance of secretion of the lipid meibum layer and the aqueous layer, reduction of secretion of either results in a tear film imbalance that can lead to symptoms and signs of DES.
An immediate reduction in blink rate acutely alters the ocular surface because it causes poor tear spreading and dessication. Longer term reduction of blinking may alter meibomian gland. Eventually, MGD may worsen, causing further reduction of the outflow of meibum, alteration in the normal bacterial flora, increase in inflammation, and obstruction of the glands. Thus, reduced blink rate at the computer contributes to poor tear film quality and increased evaporation, which reduces the overall efficiency and comfort of work. Furthermore, the positive correlation between lifetime computer usage and ocular surface disease index (OSDI) score shows that people who use the computer tend to have more significant ocular surface symptoms.
CVS and asthenopia:
Many individuals have marginal vision disorders, such as difficulties with accommodation, or binocular vision problems that do not cause symptoms when performing less demanding visual tasks.
Use of VDT creates asthenopia or a feeling of ocular discomfort or tiredness. In fact, symptomatic visual complaints were reported by 75% of VDT operators working 6-9 hours in front of their screens compared to 50% of the other workers (Mutti et al. 1996).
After working with the monitor, the most important changes are:
These results suggest that the weakness of important visual functions could be the cause of eyestrain in computer operators. Prolonged work at a VDT has been reported to result in changes in both relative accommodation and vergence.
One study noted a high prevalence of exophoria, convergence insufficiency, and low fusional convergence among VDT workers. They also found that the accommodative amplitude decreased significantly more for VDT users than for non-users.
VDTs are a major source of near work for many adults, but do not appear to result in losses of accommodative and vergence functions beyond the ordinary effects of age.
CVS and transient myopia:
Accommodative effort during near work is thought to be a causative factor in the development of myopia. It is clear that near work with VDTs result in a small, temporary myopic shift. In a cross-sectional comparison of VDT users and typists, VDT users experienced a myopic shift of about -0.12 Diopters after the work period, while the refractive error of typists was unchanged.
Management should be carried out under medical supervision.
The treatment of CVS requires a multidirectional approach due to the variety of complaints by the users. When treating a patient, it is important to consider ocular therapy as well as adjustment of workstation and habits of users.
Local ocular surface disorders should be treated aggressively and on a long term basis. Eye care providers and patients need to understand the chronicity of this disorder in order to maintain compliance to treatment.
Restoring aqueous deficiencies with
– Partial or complete punctal occlusion.
Short- and long- term inflammation control with
– Topical steroids.
– Omega 3.
– Topical cyclosporine A.
Isolation technique, that is, microenvironment glasses (MEGS) or specialised contact lenses, are helpful if the patients are moderately to severely symptomatic or have significant findings of dry eye or lid margin disease on clinical examination.
Previously, it was recommended that the eye should be 16- 30 inches from the screen. Recent data suggest that further distances may be more favourable to ocular symptoms. These studies suggest that distances of 35- 40 inches may produce fewer complaints of visual strain.
It is recommended that the screen should be placed 10-20? below (or the middle of the screen 5- 6 inches below) the eye level. When the screen is higher than this level, VDT users often tilt back their heads, causing muscle strain in the neck. Lowering the monitor allows the VDT user to gaze downward, thus exposing less ocular surface to ambient air and reducing tear film loss.
The actual type of lighting also appears to be important. One study focused on the visual work capacity with different sources of illumination. It was found that sodium lamps were the most adequate for high functional capacity of the visual analyser.
It is important to position the light carefully so that it does not throw bright light into the eyes.
Antiglare filters may not reduce symptoms of asthenopia, but have been shown to reduce glare and improve contrast from the screen. This provides an effective means to eliminate reflections and therefore improve visual comfort.
Long periods of work without breaks are thought to be detrimental to ocular symptoms. Frequent breaks are recommended to restore and relax the accommodative system, thereby preventing eyestrain. It is believed that looking away at a distant object at least twice in an hour during computer usage is sufficient for prevention of visual fatigue.
Omega 3 and topical steroids have also been used for control of inflammation.
Occasional computer viewers may be able to get away with using their general eyewear, but those who spend several hours a day, may benefit from the use of micro-environment glasses (MEGS). MEGS, unlike swim goggles, can be optically modified and still create an increase in humidified microenvironment that successfully reduces dry eye symptoms and signs as well as symptoms in symptomatic computer users.
Presbyopes need the right format of eyewear. Conventional bifocals are designed for viewing at 16 inches at an angle of 20? below primary gaze. Computer screens are usually 24 inches away and only slightly below primary gaze. Occupational progressive lenses are now available, which incorporate a large area in the top half of the lens for mid-distance viewing (i.e. VDT) and a bottom half of the lens for near distance (i.e. keyboard and desktop). Some lenses even contain a small area for distance viewing, usually at the top of the lens.