The need for reading glasses is a common problem for most people as they enter their middle years. As people age, the natural lens in their eyes hardens and loses its flexibility, impairing its ability to vary its shape for different ranges of focus. This condition is known as presbyopia and develops in most people in between 45 and 50 years of age.
There are a number of ways to deal with the focusing problems caused by presbyopia. People with a small amount of nearsightedness can simply remove their glasses to read. However, people with previously normal vision, or those who wear contact lenses for nearsightedness may need to use reading glasses for close work such as reading, using a computer, or sewing. Bifocals or varifocals can also be used to provide both near and far vision without having to constantly put on and take off a pair of glasses or repeatedly switch back and forth between two pairs of glasses. However, some people find it difficult to adjust to these glasses and others consider reading glasses to be an inconvenience. Another option, known as monovision, is available for some people with presbyopia.
Monovision can be achieved through corrective lenses or through refractive surgery. If a person has less than 1.5D of nearsightedness ,one eye can be surgically corrected to provide good distance vision, and the other eye can be left uncorrected for near vision. People with greater amounts of nearsightedness may have one eye corrected for distance vision, and the other eye undercorrected to provide better close vision. If this option seems desirable, people may wish to consider trying to achieve the similar effect with contact lenses prior to surgery to determine its suitability for their individual needs and their ability to adapt to this situation. People who are zero or "plano" can also have one eye made a little short-sighted to achieve the same result.
The chief advantage of monovision is the freedom it provides from reading glasses. Monovision makes it possible to repeatedly change the range, of focus, without having to constantly remove or add corrective lenses. This can be particularly useful for people who change their focus frequently - particularly teachers, public speakers, salespersons, and people involved in the performing arts.
As with any good thing, monovision comes with some drawbacks. People with monovision may have decreased depth perception without corrective lenses. They may also notice blurred vision in the "near" eye when glancing in the side mirror of their cars or when the, vision in the "distance" eye is blocked by an object. Some people with monovision elect to wear corrective lenses for activities such as driving or prolonged reading so that both eyes are then in focus. If the eyes have less than 1.5 Dioptres between them, then there is not usually a problem in the older patient.
Monovision is most appropriate, for people who answer "yes" to two or more of the following questions:
- Would it bother me to wear reading glasses and carry them wherever 1 go?
- Does my lifestyle permit a slight impairment of depth perception for many activities?
- When I require reading glasses, would 1 need to wear them most of the time?
- Could I adapt to one eye being out of focus for distances unless glasses are worn?
People who are entering mid-life, and are interested in monovision should discuss the matter with their doctor prior to undergoing refractive surgery. Should they choose monovision and subsequently become unhappy with it, enhancement surgery is an option.