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4.1.1 What Is Computer Vision Syndrome or Digital Asthenopia?

Computer Vision Syndrome (CVS) or Digital Asthenopia (DA) is a transient, non-specific, multifactorial disorder that is responsible for a range of ocular and visual symptoms associated with the use of computers as well as other electronic devices such as video game stations, tablets, smartphones, e-book readers, either for recreational purposes, or in work context, when used for 2 hours or longer.

They can affect children, young people and adults, anywhere (public or private) and at any time point1-3.

A North American study covering 70 million workers estimated that 90% of them use the computer for more than two hours a day, and 60% for more than 5 hours.

It is estimated in that same study that approximately 65% of Americans suffer from this syndrome to some degree1,4.

The increasingly widespread use of these devices to perform an increasing number of everyday activities makes this syndrome clinically and statistically very relevant.

Clinical Manifestations - The increasing use of electronic devices is associated with a greater effort of near vision, resulting in an increased near focus requirement (ciliary muscle effort - accommodation), a perpetuated convergence of the eyes and an increased visual attention (with consequent decreased blinking and dry eye complaints).

When this effort is great and/or maintained, adaptation mechanisms fail, causing exhaustion of the ocular muscles (intrinsic and extrinsic), and subsequently eye strain, with consequent inability to perform the intended tasks.

Dry eye is the main contributing factor for CVS/DA3.

The reduction of blinking associated with the use of electronic devices is documented and favors dry eye complaints by increasing the evaporation of the lacrimal film2,3.

In addition, reading in computers is performed according to a horizontal plane, which favors the increase of the palpebral opening (with consequent increased evaporation of the tear film), which is also an aggravating factor for this syndrome2.

Other causes of exacerbation include the presence of a large eyelid opening (especially when the screen is placed too high), the presence of dry environments and strong airflows, the use of contact lenses and the use of systemic drugs that decrease the tear film production, including beta-blockers, antihistamines, tricyclic antidepressants and some serotonin reuptake inhibitors, isotretinoin and some diuretics2,5.

The short working distance associated with the use of electronic devices as well as the need to maintain the focus continuously, lead to a permanent stimulation of the convergence-accommodation reflex, through which pupillary contraction, convergence, and contraction of the circular fibers of the ciliary muscle occur, with consequent relaxation of the zonular fibers and modification of the curvature of the crystalline lens in order to increase its refractive power and favor near vision5.

Thus, continuous contraction of the ciliary muscle, in order to maintain accommodation for prolonged periods of time, is responsible for asthenopia complaints manifested in this syndrome, namely the difficulty in reading clearly at the end of the day, as well as moving focus from near to distance vision1-3,5.

The presence of visual disturbances such as convergence insufficiency, accommodation difficulties and changes in binocular function are also a contributing factor for the visual complaints in this syndrome. Many of these individuals have insignificant complaints which may become manifest in the presence of situations with greater visual demand2,5,8.

It has been demonstrated that following the use of electronic devices there is an increased prevalence of decreased accommodation amplitude, increase of the near point of accommodation, convergence insufficiency and exophoria.

These changes appear to be transient, but they are objective indicators of the subjective visual fatigue experienced by these patients1-3,8.

From an ergonomic point of view, there are also several factors that relate to discomfort and visual fatigue1-3.

Lighting can significantly affect complaints.

A lighting deficit is deleterious because it tends to increase the visual requirement, favoring the approach of objects with poor posture, increased convergence and accommodation, as well as favoring the reduction of blinking rate, which contributes to the evaporation of the lacrimal film6.

On the other hand, excessive luminance (large windows, poorly placed desk lamps or light sources above the individual) and their erroneous distribution in the field of vision can increase the brightness on the screen, with consequent dazzling of the user, thus increasing eye fatigue complaints2,3,6

Overexposure to blue light emitted by LED displays can interrupt the secretion of melatonin, and change the quality of sleep; on the other hand, video games are associated with immersion of the player and with an intense flicker on the screen, which can stimulate changes in systemic and endocrine functions (high levels of cortisol) with consequent changes in behavior, mood, motivation, and learning7

Clinically this syndrome is manifested by 5 groups of symptoms1-3,5,8,9 that sometimes are vague or difficult to describe, and those who suffer from this disorder are often not aware of them:

- Symptoms related to ocular muscle effort: sensation of weight/eye fatigue, headache. The accommodative effort during close work may be responsible for the development of pseudomyopia. This disturbance is temporary (due to excessive accommodation), and the incidence of myopia in these users does not appear to be higher.9

- Symptoms related to dry eye: foreign body sensation, eye irritation/burning, red eye, tearing, contact lens intolerance.5

- Symptoms related to visual fatigue: blurred vision towards the end of the day, blurred vision after a prolonged time of near vision, slow focus and diplopia (less frequent and usually associated with a phoria).1-3,8

- Muscular symptoms: pain localized to the cervical region, shoulders, and spine in relation with posture.2

- Psychological symptoms: fatigue, irritability, decreased concentration, memory and sleep disturbances, among others.2,7

Despite the vague nature of its symptoms, CVS/DA can be attenuated or even eliminated if diagnosed and treated accordingly.

The treatment should approach associated ocular pathologies, as well as education of the patient regarding strategies of adaptation to their environment.


Eye ergonomics strategies:

- Refractive problems: Detection and correction of any refractive errors is imperative at an Ophthalmology appointment. Regarding patients with presbyopia, it is particularly important to choose progressive lenses with a widened channel in order to facilitate the transition between far, intermediate and near vision, or occupational lenses, in order to correct near and intermediate vision (in the absence of a refractive error for distance vision)2.

- Regarding users of electronic devices with complaints of eye fatigue, the use of low-magnification lenses for near vision with filter for the blue light emitted by these devices and antireflective filter may be associated with a reduction in their complaints6. Whereas users of occupational lenses should have their screens at horizontal plane with the eyes, users of progressive lenses should prefer their computer monitors a little lower, facilitating the proper use of these lenses and avoiding a backward moving of the head and neck10.

- Regular breaks during activities with electronic devices: It is believed that looking away at a distant object at least twice an hour while using the computer is sufficient for the prevention of visual fatigue.1-3
Alternatively, the 20-20-20 rule postulates that every 20 minutes the individual should pause for 20 seconds looking at a distance of 20 feet (equivalent to 6 meters). The implementation of these pauses will allow relaxation of the circular fibers of the ciliary muscle and will increase blinking rate, thus promoting lubrication of the eye.4

- Disturbances in binocular vision and accommodation: Anomalies of binocular vision (e.g. lack of convergence, etc.) and accommodation, with consequent orthoptic correction, should be addressed during the Ophthalmology appointment.

- Management of dry eye: Most of these patients are given eye lubricants, experiencing a significant reduction in complaints. It is given preference tears with higher viscosity polymers such as hyaluronic acid or carbomers5.


Environmental strategies:

- Humidity of the environment: Avoiding dry environments, strong airflows, dust or fumes. Other important strategies include careful regulation of temperature and airflow in central air conditioning and heating systems, maintaining a humidity level of about 45%, and also the use of plants in the workspace. The use of a glass of water near the work environment may contribute to the reduction of complaints associated with dry eye.1-3,5

- Lighting: The aim is to create an environment with a constant luminous intensity throughout the visual field by avoiding high-intensity light sources near the screens or the user, using curtains to filter out excessive light through windows and preferring light sources with a yellow tone (which seems to cause less glare).1-3,12

- Positioning of the screen: Maintaining a distance of 35-40 cm between the user's eyes and the screen promotes greater visual comfort and avoids the adoption of uncomfortable postures that are associated with neck and shoulder pain. The top level of the screen should be at eye level, creating an angle of about 10 to 20 degrees with the visual axis, because our visual system is adapted, and prefers, to look downwards.2

- Screen features: Screens with anti-glare filters appear to increase visual comfort, but with controversial effect on asthenopia. When reading documents, the patient should avoid texts only in upper case and should use larger spacing in the text to improve readability.2



Fortunately, this syndrome does not leave irreversible sequels.

It is important to diagnose it in a routine Ophthalmology appointment, because with those protective measures referred above, it is possible to attenuate or even eliminate their complaints, which, in addition to improving the quality of vision and life, improves professional performance and mental processing (by reducing fatigue, irritability, decreased concentration, and memory), thus avoiding 'human error'.



Ophthalmology Department, Prof. Doutor Fernando Fonseca E.P.E Hospital, Amadora, Portugal

(Head of Department: Isabel Prieto)

Ophthalmology Department, Prof. Doutor Fernando Fonseca E.P.E Hospital, Amadora, Portugal

(Head of Department: Isabel Prieto)

Portuguese Ergophthalmology Group (PEG) Coordinator 2017-2018