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.
· Dry eyes.
· Even watering of eyes by some computer users.
· Burning sensation.
· Blurred vision.
· Double vision.
· Foreign body or gritty sensation.
· Blurred distant vision even after work.
· Musculo-skeletal problems such as pain in neck, back pain, and shoulder problems.
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.
I. Factors influencing surface disease:
There are several factors that contribute to CVS and dry eye syndrome (DES). They include the following:
· Environmental factors: The cornea is very sensitive to drying and chemical imbalances from environmental factors such as dry air, ventilation fans, electrostatic build up, airborne paper dust, laser and photocopy toner, and building contaminants.
· Reduced blink rate: Most individuals blink normally 10- 15 times/ minute. Studies have shown that the blink rate at the computer is significantly less. A reduced blink rate at the VDT contributes to a poor-quality tear film and temporary as well as long-term stress upon the cornea and ocular surface. This results in symptoms of DES.
· Duration of computer use: Longer duration of the computer work tends to result in long-lasting complaints that persist, even when the work is completed.
· Height and inclination of monitor: Increased odds ratio (eye strain) for certain eye symptoms is observed when the computer monitor is kept at about the eye level instead of below the eye level. The VDT should be at least 5 to 6 inches below the straight line of the viewer’s vision. Such measures reduce not only dry eye, but also the severity of the spasm of neck muscles. OSHA has recommended that the center of computer monitor should normally be located 15 to 20 cm below the horizontal eye level and that the entire visual area of the display screen should be located such that the downward viewing angle is greater than 60 degrees.
· Taking frequent breaks: Taking frequent breaks from computer use is shown to increase the efficiency because the breaks relax eye accommodative system, thus decreasing eye fatigue and headache.
· Distance of VDT from the eyes: Distance of VDT from the eyes is an important risk factor for CVS. Closer the VDT to the eyes, it is more difficult for the eyes to accommodate. Excess accommodation results in overwork on ciliary muscles which manifest as eye fatigue and headache.
· Increased exposure due to position of monitor: Normally reading of text on paper is done while looking downwards and it results in the eyelid covering a good deal of the front surface of the eye. This covering minimises the evaporation of tears. On the other hand, computer users look at their reading material in straight ahead gaze. This result in a wider opening between the eyelids, and an increased surface area exposed to the effects of evaporation.
· Gender: The prevalence of DES is twice as frequent in females as compared to males.
· Age: Tear production normally decreases with age. Although DES can occur at any age in both men and women.
· Menopause: Hormonal changes have been identified as contributing to DES. Postmenopausal women represent the group of individuals affected most by DES. Sometimes it is difficult to assess the relative contributions of menopause and ageing.
· Systemic diseases and disease syndromes: DES is associated with various systemic diseases. In the case of Sj?gren’s syndrome, dry mouth and rheumatoid arthritis can assist in making the diagnosis. Several autoimmune diseases also have association with DES.
· Systemic medications: There are several systemic medications which contribute to ocular drying. Most prominent among them are diuretics, antihistamines, and anti-hypertensives.
· Spectacle wear: CVS with eye redness has significant association with the use of spectacles.
· Contact lens wear: Contact lens comfort is highly dependent on the fit of the lens and lubrication of the eye. If the eye is dry, the lenses dry easily and adhere to the upper eyelid during the blink. This ‘friction effect’ from DES produces discomfort.
· Cosmetics: Cosmetics may block the openings of the oil-secreting meibomian glands and create debris and inflammation. This leads to rapid evaporation of the water component of the tear film and deposition of foreign bodies from cosmetics in the tear film or on the ocular surface with resultant discomfort.
· Cholesterol: There may be statistically significant decreased prevalence of low high-density lipoprotein (HDL) in patients with moderate to severe MGD. The cause of this is unknown, but the findings suggest that elevated HDL may be a risk factor for the development of MGD, despite being known as ‘good cholesterol’ with its cardio-protective effects.
II. Visual effects of display features:
· Display quality: Visual performance is affected by a number of display parameters, such as character size, structure, and style; and by image contrast and stability.
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.
· Lighting and glare: Improper lighting conditions of a workstation can also adversely affect ocular comfort. Constant and bright illumination from surrounding sources of light creates reflection and glare. These problems do not produce chronic visual disorders but are sources of annoyance and possibly visual fatigue.
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.
· Refresh rates: The refresh rate of a VDT represents the number of times per minute (measured in Hertz) the screen is repainted to produce an image. If the refresh rate is too slow, the characters on the screen may appear to flicker. Perceived flicker has resulted in subjective complaints of annoyance, fatigue, and headache. The critical fusion frequency is the refresh rate at which humans can no longer distinguish the pulsating beams of light as separate entities. In most viewing situations, this rate is 30- 50 Hertz.
Studies have shown that much higher refresh rates may decrease ocular symptoms and increase user functionality.
· Radiation: The potential of health risk concerns that radiation emissions from VDTs could be responsible for hazardous effects to the computer user. However, VDTs neither produce nor emit alpha, beta, gamma, or hard X-radiation. Small amount of soft X-rays is produced, but almost all of the radiation is contained by the glass screen of the monitor.
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.