With aging, the natural lens inside the human eye gradually starts losing its elasticity. As a result of this change, the lens is unable to change its shape while focusing at near objects and it becomes progressively difficult to read small prints, read sms messages on mobile phone etc. This phenomenon is referred to as presbyopia, and usually starts around the age of forty, and affects all individuals. (Myopic individuals ie people using minus power lenses, may not experience this change as their far point of focus is situated close to the eye. Hence the tendency to read fine prints at near, without distance glasses) Presbyopic individuals have to strain to focus at near objects, and this often results in eye symptoms such as blurred vision, & eye pain, often associated with headache.
So how is presbyopia corrected.
Most commonly, reading glasses are prescribed, which can be used alone or in addition to the distance correction. Bifocal glasses have the upper segment correcting sight for distance vision, and the lower segment correcting for near vision. Progressive addition lenses, have gradual increase in power from the upper to lower segment of the glasses. Hence there is a gradual increase in power, which allows an individual to focus at all distances from distance to near, unlike bifocals wherein there are only two focal points ? distance and near. Computer users may require a reduced addition for near, for intermediate vision.
Monovision is a situation, wherein one eye is corrected for distance vision, and the fellow eye for near vision. However in this situation the binocular vision ie depth perception is affected hence not every individual is comfortable with this option of treatment for presbyopia. An initial trial with contact lens is usually attempted for monovision, and if an individual is comfortable with this situation, permanent correction can be attained using laser refractive surgery or conductive keratoplasty. However, these procedures need to be repeated over a period of time.
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