[paper]Computer vision syndrome
Gaze Angle
At the eye examination, difficulty to replicate the specific gaze used when viewing the digital devices is an issue. Because users view different displays in different angles, ie laptop display - downward angle, desktop monitors - primary gaze, mobile phone - almost any direction.
Text Size
acuity reserve is required to to allow comfortable reading. ie for sustained comfortable reading text size should be at least twice the individuals visual acuity.
Glare
Reflection on display is bad. Place the screens perpendicular to fluorescent tubes. Don't place display directly in-front of or behind unshaded windows.
Correcting Refractive Errors
This is challenging because the required working distance vary from 70 - 17.5cm(form desktop to smartphone). It's also important to correct even the small amount of astigmatism(eye does not focus light evenly on the retina. This results in distorted or blurred vision at any distance) when using digital displays.
Accommodation and Convergence
since the near vision demands when using viewing digital screens are significant, a comprehensive assessment of accommodation and vergence system should be included for all digital screen users. Hart chart test is a good way to test the flexibility of accommodation and vergence.
Dry Eye
Environmental factors - low ambient humidity, high forced-air heating, high air-conditioning settings, use of ventilation fans, excess static electricity or airborne contaminants. Increased corneal exposure - displays used with eyes in primary position. Prevalence of dry eye increases with age and is higher in women. Systemic diseases and medications - arthritis, allergy , thyroid disease, taking antihistamines, antianxiety medications, antidepressants, oral steroids or vitamins.
Blink Rate
Blink rate get reduced using computer operation. 22/min - relaxed, 10/min , 7/min when viewing book or screen. Blink rate also get reduced when viewing decreased fond size and when contrast is reduced or the cognitive demand of task is increased. Beading identical text on hardcopy vs digital display didn't result in different blink rates. But digital displays resulted a higher level of incomplete blinks(may be due to eye in primary position)
Asthenopia(weakness or easy fatigue of the eye)
Symptoms commonly associated with this diagnostic term included eye strain, eye fatigue, discomfort, burning, irritation, pain, ache, sore eyes, diplopia, photophobia, blur, itching, tearing, dryness and foreign-body sensation.
The Blue Light Hypothesis
There is no published evidence that blue light emitted from digital displays cause DES, but it's being suggested. Blue light is generally considered to comprise wavelengths between 380 and approximately 500nm. Human retina is protected from short-wavelength radiation. Exposure to blue light has been widely reported to be involved in the regulation of circadian rhythm and the sleep cycle.