Computer Vision Syndrome (Digital Eye Strain)

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Definition

American Optometric Association (AOA) defines CVS or digital eye strain as a group of eye and vision-related problems that results from prolonged usage of computers, tablets, e-readers, and cell phones which causes increased stress to near vision in particlular.[1]It is also describes the inclusion of ocular, visual and musculoskeletal symptoms due to prolonged use of computer.[1]

Magnitude of the problem

The digital era has already revolutionised the usage of these electronic gadgets. In the current scenario, the novel corona virus has really changed it all. With the social distancing in practice, the new norm is to work from home and attend classes, webinars and consultations online. This indeed has increased the time spent on these electronic and digital gadgets and is the sole contributor of CVS.[2][3][4] It is estimated that the average American worker spends seven hours a day on the computer either at the office or working from home.[1]

Prevalence

According to the Vision Council, at least 60% of American men and 65 % of American women reported symptoms of CVS, 80% of adults use digital devices for at least 2 hours daily and more than 65% of adults use at least 2 devices simultaneously. Around 80% of adults use digital devices just before sleep and atleast 70% of adults report that their children have a screen exposure time of at least 2 hours. Simultaneous use of 2 or more devices increased the risk of CVS compared to the use of 1 device at a time and the reported prevalence was 75 % and 53 % respectively.[5]

A cross sectional study conducted to analyse the relationship between CVS in computer users and contact lens users showed that the prevalence of CVS in contact lens users was 65 % in contrast to 50 % in non-contact lens users. Also, workers who worked for more than 6 hours a day with contact lens usage were likely to show symptoms of CVS than their counterparts without contact lens usage. The study concluded that regular contact lens usage increased the risk of CVS after 6 hours of computer use.[6]A prevalence of 75 % vs 50 % was reported in another study comparing computer users and non-computer users.[7]

CVS was reported to be 54.6 % in call centre operators in Sao Paulo, Brazil.[8]Another study reported that the symptoms were dose dependent and increased significantly with more than 4 hours of computer usage.[9]Studies have shown positive correlation between symptom score reported and the number of hours infront of the computer.[6][10]

Symptoms[2][4]

  • Extraocular symptoms - Shoulder pain, neck pain, neck stiffness, headache and backache.
  • Visual symptoms - Blurred vision, double vision, presbyopia and slowness of focus change.
  • Ocular - Internal symptoms (Asthenopic) - Eye strain, ache in the eye, ache around the eyes, tired eyes and sore eyes.
  • Ocular - External symptoms - Burning, dryness, redness, gritty sensation, tearing and irritation.

The symptoms reported in children with a prolonged history of screen exposure include reduced attention span, poor behaviour, irritability, dry eyes, ocular irritation, eye strain, headache, neck pain and shoulder pain.[5]

Factors contributing to CVS

Refractive errors

Even small refractive errors (especially astigmatism)[11] can aggravate the symptoms of CVS.[3]

Abnormal binocular interaction

Abnormalities of vergence may cause asthenopia with prolonged use of eyes and may aggravate the symptoms of CVS.[3][12][13] These disorders include:

  • Convergence insufficiency
  • Poor vergence facility, and
  • Decompensated heterophoria

Accomodation abnormality

The triad[14] of near reflex or near response or near synkinesis happens when an individual focuses on near objects. This triad consists of accommodation, miosis, and convergence. Problem with any of the components of this reflex may cause difficulty or strain in near work and may aggravate CVS.

  • Uncorrected presbyopia[15]- The symptoms include difficulty in near vision at the usual reading distance, headache, asthenopic symptoms, tiredness, and need for bright light during reading fine prints. This is the most common abnormality of accommodation usually seen at around 40 years of age.[16] In females, the onset may be earlier.[16]
  • Poor accommodative facility
  • High accommodative lag

Dry eye or abnormal ocular surface

Dry eye and ocular surface disorders are important source of discomfort in VDT (video display terminal[4] or visual display terminal[17]) users. Multiple factors increase the risk of dry eye disease in users of digital devices, especially computers. These include

  • Reduced blinking: Though the normal blinking rate is around 15-20 /min, the blinking rate is significantly reduced while working on VDT. This causes the eye to be opened for a longer duration and thereby increases the chances of dryness.
  • Incomplete eye closure
  • Larger palpebral fissure while viewing a screen in horizontal gaze compared to while reading in downgaze (increased exposed area of the eye)
  • Higher age
  • Female sex- especially postmenopausal women
  • Environment- air conditioner, dry air [low humidity], air-borne particles including dust, the toner of digital printer, building contaminants, ventilation fans, etc.
  • Contact lens use

Cosmetics over the eyelid

  • Lid condition- anterior blepharitis, meibomian gland dysfunction
  • Medications: preservatives of topical medication, systemic
  • Medications including anticholinergic drugs and diuretics

Suboptimal properties of the digital device

  • Blue light: Most digital screens (especially LED - light-emitting diodes) are known to emit blue light (400-500nm). The blue light
    • May cause damage to the retina especially at acute suprathreshold dose.[18][19] Maximum damage is thought to occur with 440nm.[20]Circadian rhythm depends on exposure to light, especially blue light. Melatonin is secreted at night and plays a crucial part in the sleep cycle in humans. Intrinsically photosensitive retinal ganglion cells (ipRGCs), or photosensitive RGC (pRGC), or melanopsin-containing RGC (mRGCs) play a critical role in the circadian rhythm by sending messages to the pineal gland. These cells have the highest sensitivity at 482nm. [21] Thus presentation of blue light not in sync with the sun may alter the coupling of the biological clock with the geographical clock of that area resulting in abnormal circadian rhythm and sleep pattern. May have an association with age-related macular degeneration,[22] but further work in this field is warranted to confirm or refute this claim.
  • Quality of display: Various attributes of the display may predispose to CVS. These include
    • Lower Resolution of the screen-
      • Fewer dots per inch (dpi) and fewer pixels
      • For significantly larger characters readability was noted to be similar in low-resolution screen (720 x 350 pixels) and higher resolution screen (1664 x 1200 pixels).[23] However, readability was better with a higher resolution screen while reading very small characters. [23]
    • Poor Image stability
    • Poor readability and Legibility:[4]
      • High brightness and high contrast may cause blurring of characters
      • Words with all capital letters are difficult to interpret compared to sentence case
      • Less than one character space between lines
      • Less than ½ character space between words
      • Light characters against a dark background (negative display polarity) should be avoided. Dark character against a light background (positive display polarity) is recommended.[24][25]
  • Refresh rates of the screen: In the digital screens, the screen is repainted at a frequency measured in Hz. Critical flicker fusion frequency (CFF) is the refresh rate at which the human visual System fails to recognize the flickering nature of the screen and the screen appears to be constantly illuminated. The normal value of CFF is 30-50Hz. Low refresh rates can cause fatigue, headache, annoyance reduced accommodation, increased blink interval, reduced blink time and reduced reading speed.[4] Standard desktop and laptop monitor refresh rate is 60Hz or 64Hz, but newer monitors have higher refresh rates 120Hz, 144Hz or 240Hz.
  • Improper lighting condition aggravates CVS that include:
    • Surrounding light (like window behind the monitor)
    • Reflection

Other risk factors

  • Use of electronic materials outside work[26]
  • Frequent switching between digital display and hard copy which have different brackground.[4][17][25]

Other considerations regarding VDT use

Radiation

VDTs are known to emit infrared radiation and the visible spectrum of light.[27] Internal X-rays (X-radiation) originates within cathode ray tube (CRT) displays but does not leave the monitor due to the filter at tube face.[27] Different studies by various governments, regulatory authorities, and independent researchers have indicated that the level of emitted radiation from VDT is highly unlikely to cause health hazards in humans.[27] The assessed electromagnetic radiations includes ionizing (X radiation) and non-ionizing radiation (ultraviolet ray, visible light, infrared and radiofrequency radiation including microwave).[27]

Cataracts

Available data on VDT use does not support the claim that cataracts may be caused by VDT.[27] Most of the reported cases had other obvious causes of cataracts.[27]

Pregnancy

A study by the National Institute for Occupational Safety and Health (NIOSH), USA noted that the use of VDT during pregnancy did not increase the risk of preterm or low (or reduced) birth weight babies.[28] Another study on telephone operators using VDT found no excess risk of spontaneous abortion among women who used VDT in the first trimester of pregnancy.[29] A meta-analysis excluded significant excess risk of for spontaneous abortion, low birth weight and congenital malformations due to the use of VDT.[30]

Sleep and circadian rhythm

Blue light plays a crucial role in the circadian rhythm. It has been shown that performing an exciting VDT task with a BD (bright display) suppresses the nocturnal changes in melatonin concentration and other physiological indicators (nocturnal reduction in rectal temperature and heart rate, and nocturnal increase in sleepiness) of human biological clocks.'[31] Overuse of VDT for at least 6 hours was suggested to be related to insomnia in a study on 2417 clerks in Japan.[32] Specifically, the use of digital devices just before sleep may alter sleep patterns.[33] Exposure to computer screens [LED with low wavelength light in blue range] at evening was noted to suppress evening rise of melatonin and sleepiness. Such exposure was also noted to enhance sustained attention and declarative memory performance in the evening.[34]

Neuro-Psychiatric issues

National research council noted that screens with very low refresh rates (8-14Hz) can be epileptogenic.[4] Exposure to LED light at night may cause misalignment of social and biological rhythms and sleep loss.[35] This, in turn, may be linked to daytime sleepiness, fatigue, poor academic achievement and behavioral problems in adolescents.[35] Increased risk of job burnout and occupational stress was noted in internet staff working on VDT for more than 11 hours daily.[36] However, neuropsychiatric implications of digital screen use need further research.

[Video credit Eyesmart- American Academy of Ophthalmology}

Development in child

Screen time has been suggested to be associated with childhood obesity probably due to less physical activity, more calorie intake, and reduced metabolic rate.[37] Other possible associations include altered sleep time, hypertension, dyslipidemia and cardiovascular disease.[38] Though home computer use may slightly improve academic performance, high screen time has been linked to loneliness and depression.[39] Some studies, however, suggest that increased screen time can affect socio-emotional and cognitive development, promote depression, anxiety and irritability ultimately leading to poor academic performance.[40] Violent video games may increase aggression and may affect the child's ability to distinguish reality from simulation.[39] Other suspected complications of excessive screen use include effects on refractive error (especially myopia), [41] reduced bone density, attention deficit hyperactivity disorder (ADHD), difficulty to focus and the tendency for depression and suicidal thoughts.[39][42] Larger future studies are needed to explore this area. The World Health Organization guidelines on Children under 5 years of age are given below in images:[43]

The World Health Organization guidelines on Children under 5 years of age To grow up healthy, children need to sit less and play more [Internet]. [cited 2021 Jun 2];Available from: https://www.who.int/news/item/24-04-2019-to-grow-up-healthy-children-need-to-sit-less-and-play-more
The World Health Organization guidelines on Children under 5 years of age To grow up healthy, children need to sit less and play more [Internet]. [cited 2021 Jun 2];Available from: https://www.who.int/news/item/24-04-2019-to-grow-up-healthy-children-need-to-sit-less-and-play-more

History and Physical

All patients presenting with symptoms of CVS must be asked about the predisposing factors, particularly, prolonged use of digital devices. Comprehensive Ophthalmic examination should follow which includes visual acuity, refraction, intraocular pressure, pupillary examination, examination of ocular adnexa and ocular motility, slit-lamp examination of the anterior segment, and examination of the posterior segment. Specifically, the lids and ocular surface should be examined thoroughly.

Evaluation

Evaluation of a patient with CVS can be performed using objective or subjective methods. Associated Dry eye disease should be evaluated as denoted in the eyewiki articles available at https://eyewiki.aao.org/Dry_Eye_Syndrome and https://eyewiki.aao.org/Dry_eye_diagnosis_and_management.

Objective methods include:

Accommodation and vergence parameters

Accommodation parameters should be checked in patients presenting with asthenopia. The evaluation includes near point of accommodation, lag of accommodation, microfluctuations in accommodative response and accommodative facility. Accommodation lag may be higher in individuals using VDT compared to individuals using printed material. However, the results from different studies regarding this are mixed.[3]

  • Squint evaluation and examination or vergence abnormalities should also be performed.

Critical flicker fusion frequency (CFF)

CFF is the frequency at which the human visual system perceives a flickering light as continuous non-flickering light. Negative changes in CFF after prolonged computer use may be correlated with subjective symptoms of CVS,[44] though other studies did not find a correlation.[45]

Blinking

Computer work and work that needs concentration are known to reduce the blinking rate and thereby increase the exposure time of ocular surface and dry eye.[46] Blinking plays a crucial role in the maintenance of ocular surface and good tear film. Blinking helps in maintaining the equilibrium of tear by playing a vital role in redistribution, drainage of tear and renewal of tear film over the ocular surface.[47] Computer use has also been associated with incomplete blinks (upper eyelid does not cover the entire cornea). which worsens the symptoms of dry eye.[46]

Pupil size

A large pupil may cause visual fatigue due to reduced depth of focus.[48] Visually demanding tasks including computer work may cause an increase in pupil size.[49] Around 1/3rd of individuals can have pupillary constriction after completion of such demanding task or intense near work which might be due to spasm of the pupillary sphincter and ciliary muscle.[50][51]

Subjective

Multiple questionnaires are available to determine the severity of CVS. Some of the questionnaires include:

  • Dry Eye Questionnaire (DEQ-5)
  • Questionaire by Hayes and colleagues (has 10 items)[52]
  • Visual fatigue scale
  • Computer vision symptom scale (CVSS17)
  • CVS questionnaire (CVS-Q)[53]

       

Computer Vision Syndrome Questionnaire (CVS-Q)[53]
Parameter Frequency Intensity Frequency x Intensity
Never [0] Occasionally [1]

(sporadic episodes or once a week)

Often or always [2]

(2 or 3 times a week or almost every day)

Moderate [1] Intense [2]
Burning
Itching
Feeling of a foreign body
Tearing
Excessive blinking
Eye redness
Eye pain
Heavy eyelids
Dryness
Blurred vision
Double vision
Difficulty focusing for near vision
Increased sensitivity to light
Colored halos around objects
Feeling that eyesight is worsening
Headache
Total
Calculate Frequency multiplied by intensity for each item. Record Frequency x intensity as 0 = 0; 1 or 2 = 1; 4 = 2. Then add these value to get the total value. A total value of at least 6 suggests computer vision syndrome.
[Seguí Mdel M, Cabrero-García J, Crespo A, Verdú J, Ronda E. A reliable and valid questionnaire was developed to measure computer vision syndrome at the workplace. J Clin Epidemiol. 2015 Jun;68(6):662-73. doi: 10.1016/j.jclinepi.2015.01.015. Epub 2015 Jan 28. PMID: 25744132.]

Management

Ergonomics

The workplace should be ergonomically designed. A detailed checklist is available from the Occupational Safety & Health Administration (OSHA), USA at https://www.osha.gov/etools/computer-workstations/checklists/evaluation

Improved ergonomics reduces discomfort and increases productivity.[54][55]

Basic principles of optimal ergonomic design and placement of the computer screen include:[56]

  • Top of the monitor should be at or just below eye level. Higher screen causes strain in the neck and upper trapezius muscles.[57][4]
  • Head and neck should be balanced and in line with the torso.
  • Shoulders should be relaxed.
  • Elbows should be close to the torso and supported.
  • Lower back should be supported.
  • Wrists and hands should be in line with the forearms.
  • There should be adequate room for the keyboard and the mouse.
  • The feet should be lying flat on the floor.
  • Sit at arm's length from the computer screen. A shorter distance may cause eye strain.
  • Position the monitor so that the looks slightly down and not straight ahead or up.[58]Studies have shown that a viewing distance of 90 cms and a slightly downward gaze of 10 degrees reduced ocular discomfort.[59]
  • A humidifier may be considered for the working room to improve the moisture of the air.
  • To reduce eye strain, the room lighting may be adjusted and the contrast of the computer screen may be increased. Matte screen filter can be considered.

An interactive etool is available for demonstration at https://www.osha.gov/etools/computer-workstations

Workplace Wellness EyeStrain Infographic_2020 taken from: Looks Like the Home Office is Here to Stay. Here’s How to Protect Your Eyes [Internet]. Am. Acad. Ophthalmol.2021 [cited 2021 May 31];Available from: https://www.aao.org/newsroom/news-releases/detail/protect-your-eyes-in-home-office ©American Academy of Ophthalmology

Lighting at workspace

Lights causing glare should be limited. Excessive light from the window near the computer monitor should be reduced by closing or shielding windows. Lights (especially fluorescent ones) causing glare should be switched off. If the source of light cannot be modified, the workplace or monitor should be shifted to a favorable position. Antiglare filter reduces contrast, reflection, and glare but may not reduce asthenopia.[4]

Breaks in between work[26]

Duration of exposure to digital screen should be limited and dependence on smartphones should be reduced, if possible.

Individuals who work for a prolonged period at computer screens, should take breaks and remember to blink frequently during work to reduce the CVS symptoms. This relaxes and restores the accommodative system reducing digital eye strain. According to the famous 20-20-20 rule, every 20 minutes, an individual should take the eye off from the screen for about 20 seconds and look at a distant object (situated at 20 feet away).[60] Regular breaks can actually improve work efficiency by compensating for time lost due to the break.[61][4] A quick walk or stretching or workstation exercise in between work can give relief to the strained and fatigued body muscles, reduce the monotony of the work, and provide possible relaxation and reduce discomfort.[62] The National Institute for Occupational Safety and Health (NIOSH) noted that frequent short breaks in work reduces discomfort and improves productivity compared to typical morning and afternoon breaks for 15 minutes.[4]

Multiple softwares (user discretion is advised) are available for reminding the user to take a break during continuous work of computers:

Glasses

Even small uncorrected astigmatism (0.50- 1.00) causes visual discomfort in CVS and needs correction.[11][63] Small amount of residual astigmatism in contact lens users may increase the visual discomfort while working in VDT.[64] Higher uncorrected astigmatism (1.00- 2.00) may increase task errors drastically 3 to more than 3.5 times.[3][63] Uncorrected cylinder is particularly a problem in individuals using over the counter reading glasses. The difficulty of a glass prescription includes multiple working distances in some individuals who might need multiple glasses that are tailormade for a specific working distance. For presbyopes who use VDT for a long duration, progressive addition lenses with wide corridors are usually preferred. The advantages of such glasses include the absence of a defined marking at the upper margin of near add (which is progressively increasing downwards) that can cause image jump and make working in the intermediate distance (computers difficult). However, the peripheral part of such lenses causes distortion and the user has to learn to use the central part of the glass during near and intermediate works. Also, the glasses should be prepared after carefully measuring the interpupillary distance. Contact lenses might worsen CVS and thus glasses may be preferred for computer work.

Blinking

Softwares are available to remind the user to blink or take microbreaks during work. The American Optometry Association recommends taking rest as per the 20-20-20 rule and at least 15 minutes after each continuous 2 hours of computer work. Blink training may be helpful to reduce the symptoms of CVS.[1]

Management of vergence or accommodation problems

Associated problems with binocular interaction and accommodation should be managed.

Management of dry eye disease

  • Blepharitis and meibomian gland dysfunction (MGD) should be managed properly and lid hygiene should be maintained. Warm compress and lid massage should be explained to the patients of MGD. Anti-inflammatories, antibiotics with intense pulse light therapy can be given in appropriate cases.[59]
  • Environmental factors that can aggaravate dry eye symptoms include low ambient humidity, air conditioners, and ventillation fans. Modifications to improve humidity and ergonomic design of the workplace should be planned to reduce dry eye as mentioned under ergonomics.[2][59]
  • Lubricating drops may reduce dry eye symptoms including dryness, irritation, ocular discomfort, tiredness and difficulty in focusing though complete resolution may not occur.[3][65][66] Higher viscosity eye drops were noted to normalize interblink interval and reduced ocular discomfort compared to the balanced salt solution.[67] However, higher viscosity eye drops may reduce visual acuity.
  • Blinking exercises every 20 minutes by closing the eyes for 2 seconds, opening and again closing for 2 seconds followed by squeezing for 2 seconds showed positive effect on alleviating dry eye symptoms and signs.[68]
  • Polyvinyl alcohol, dextran and polyvinyl pyrrolidine have been found to be effective for evaporative dry eyes but with less evidence. Lubricants ranging from carboxymethyl cellulose to highly viscous topical drops and ointments reduce the symptoms of dry eye but do not increase the blink rate.[69]
  • Omega 3 fatty acids were shown to improve dry eye symptoms and Nelson grade in CVS-related dry eye. Freedom from symptoms was reported in 70% cases in a study by Bhargava and colleagues.[70] However, most of the CVS-related dry eye cases respond favourably to treatment and irreversible damage to the ocular surface is unlikely.

Special glasses

Blue cut lenses/Blue blocking lenses:

These lenses block the short-wavelength visible light (blue light). Blue blocking lenses may lower the reduction of CFF and may reduce eye fatigue.[45] However, a recent randomized control trial noted no improvement of CVS with blue-blocking lenses.[71]

According to the American Academy of Ophthalmology 'There is no scientific evidence that the light coming from computer screens is damaging to the eyes. Because of this, the Academy does not recommend any special eye wear for computer use.'

Microenvironment glasses

Such glasses may increase the humidity and reduce evaporation of tear film thus reducing the dry eye symptoms. It may also protect from particulate matters/irritants in the air.

Promote circadian rhythm

The use of VDT (blue light) especially before sleep time should be reduced to avoid alteration of the sleep cycle and circadian rhythm. Software (F.lux, Twilight 🌅 Blue light filter for better sleep) are available to change the color of the desktop screen according to the time of the day and thus to possibly promote circadian rhythm. Future research is needed to find out the exact utility of such software.

Suggested reading

Occupational Safety & Health Administration (OSHA), USA workstation checklist: https://www.osha.gov/etools/computer-workstations/checklists/evaluation

https://www.aao.org/newsroom/news-releases/detail/protect-your-eyes-in-home-office

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