- Asthenopia represents a subjective complaint of uncomfortable, painful, and irritable vision. There are 24 different  types  of  asthenopia  based  on  various causes. Because of its subjectivity, however, it can have a myriad of meanings to any number of people. Asthenopia can be caused from some underlying conditions  such  as  focusing  spasm,  different  vision  in  each  eye, astigmatism, hyperopia, myopia, excess light, voluntary focusing, eye coordination difficulties, and more.
- Because computer use is such a high visually demanding task, vision problems and symptoms are very common. Most studies indicate that computer operators report more eye-related problems than noncomputer office workers.  A  number  of  investigators have indicated that visual symptoms occur in  75  to  90%  of  computer  workers (Anshel, 2005).  In  contrast,  a  survey  released  by  the National Institute for Occupational Safety and Health (NIOSH) showed that only 22% of computer workers have musculoskeletal disorders.
- A survey of optometrists (Sheedy, 1992) indicated that 10 million primary care eye examinations are given annually in this country, primarily because of  visual  problems  at  computers.  This  study  eventually  culminated  in  the compilation of the series of symptoms that are now collectively known as computer  vision  syndrome  (CVS).  This  condition  most  often  occurs  when the viewing demand of the task exceeds the visual abilities of the computer user.  The American  Optometric Association  defines  CVS  as  that  “complex of eye and vision problems related to near work that are experienced during or  related  to  computer  use.”  The  symptoms  can  vary  but  mostly  include
eyestrain, headaches, blurred vision (distance or near), dry and irritated eyes, slow refocusing, neck and backache, light sensitivity, double vision, and color distortion.
It is imperative to elicit a thorough case history to distinguish the type of headache involved. The patient should  be  queried  about  the  time  of  onset,  location  of  the  pain, frequency, duration, severity, and precipitating factors such as stress, certain foods or medications. Associated signs and symptoms such as nausea, vomiting, light sensitivity, and noise sensitivity should also be noted.

Computer workers most likely get tension-type headaches. These can be precipitated  by  many  forms  of  stress,  including  anxiety  and  depression; numerous eye conditions, including astigmatism and hyperopia; improper workplace  conditions,  including  glare,  poor  lighting,  and  improper  work-station  setup.  These  types  of  headaches  are  mild  to  moderate  in  intensity, often occur on either or both sides of the head, are not aggravated by physical activity,  develop  during  the  early  to  middle  part  of  the  day,  last  from  30 minutes  to  the  rest  of  the  day,  and  are  relieved  by  rest  or  sleep.  Chronic tension headaches vary somewhat from this but have the same overall symptoms and occur much more frequently.

Visual  and  environmental  conditions  are  the  first  places  to  look  for  a solution to a headache problem. If all obvious factors have been considered, medical management is in order, often starting with a complete eye examination to rule out a visual cause.
Visual acuity is the ability to distinguish between two distinctive points at a particular distance. This requires the image formed on the retina to be well circumscribed  and  distinct.  If  the  image  focuses  in  front  of  or  behind  the retina, it will strike the retina in an unfocused state, creating the subjective
symptom of blur. This process is true for all distances with the viewing range of the human eye, which we routinely consider to be from within 20 feet to 16 inches.

A condition known as transient myopia has been shown to be more prevalent in a population of computer users. This is a condition in which a person exhibits myopia toward the end of the day but not at any other times. Many times, the myopia is not present early in the day or on weekends.

Glare  is  also  a  concern  because  of  the  eye  attending  to  the  glare  image rather  than  the  screen  image.  If  a  specular  reflection  is  noticeable  on  the screen, the eye will attempt to focus on it. The image of the glare source will appear to be somewhere behind the screen (much as your image is reflected in a mirror) and the screen image can appear blurred. This can become more noticeable as computer usage time is increased.
The lachrymal glands secrete the tears that cover the eye surface and keep the  eye  moist,  which  is  necessary  for  normal  eye  function.  The  tears  help maintaining  the  proper  oxygen  balance  of  the  external  eye  structures  and  to keep the optical properties of the eye sharp. The normal tear layer is cleaned off and refreshed by the blinking action of the eyelids.

The blink reflex is one of the fastest reflexes in the body and is present at birth. However, our blink rate varies with different activities — faster when we are very active, slower when we are sedate or concentrating. Yaginuma et al. (1990) measured the blink rate and tearing on four computer workers and noted that the blink rate dropped very significantly during work at a computer  compared  with  before  and  after  work.  There  was  no  significant change in tearing. Patel et al. (1991) measured blink rate by directly observing a  group  of  16  subjects.  The  mean  blink  rate  during  conversation  was  18.4 blinks per minute, and during computer use it dropped to 3.6 — more than a five-fold decrease.

Tsubota and Nakamori (1993) measured blink rates on 104 office workers. The mean blink rates were 22 blinks per minute under relaxed  conditions,  10  blinks  while  reading  a  book  on  a  table,  and  only  7 while viewing text on a computer. Their data support the fact that blink rate decreases during computer use, but also show that other tasks can decrease the blink rate.

EyeScience.org is a source of scientific information about visual ergonomics and human-machine interactions..
Computer Vision Syndrome (CVS)
Definition: CVS is a series of signs and symptoms that are common to those who experience computer-related eye discomfort.
Etiology: The main causes for the visual complaints are a combination of individual visual problems and poor visual ergonomics either at home or at work, or even in both environments.
Most frequent Signs and Symptoms
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