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 symptom of blur. This process is true for all distances with the viewing range of the human eye- which we routinely consider from within 20 feet to 16 inches.

Whenever we direct our gaze to some point within 20 feet, we must activate our focusing mechanism to increase the focal power of the eye and regain the clear image on the retina. The ability of the eye to change its focal power is called accommodation and our focusing ability is dependent upon age. Therefore, we must consider many factors when discussing the accommodative ability of the individual.

Blurred vision symptoms can result from refractive error (e.g., farsighted, nearsighted, astigmatism), improper prescription lenses, presbyopia (aging changes) or other focusing disorders. It has been found that small amounts of refractive error contribute to the visual discomfort of computer users. Considering the working environment, blurred images can also arise from a dirty screen, poor viewing angle, reflected glare or a poor quality or defective monitor. All of these factors should be considered when this symptom occurs.

A condition known as ‘transient’ myopia has been shown to be more prevalent in a population of computer users. Research has found that 20% of computer workers had a nearsighted tendency toward the end of their work shift. Studies showing permanent nearsighted changes have not shown this to be a concern at this time. However, many of those studies suffer from poor controls.

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 like your image is reflected in a mirror) and the screen image can appear blurred. This can become more noticeable as the usage time is increased.