Presbyopia

Presbyopia is an inability to focus on near objects. It differs from hyperopia in that it’s primarily age-related.

The focussing ability of an eye is determined by the curvature of the cornea (front surface), the power of the crystalline lens, and the overall length of the eye.

Presbyopia occurs due to changes in the structure of the crystalline lens in the eye. In early years, the crystalline lens is extremely soft and flexible, and can be easily squeezed by the muscles that surround it to make it more curved. This “accommodation” mechanism allows us to focus on near objects, and relaxes when we look into the distance, to permit clear distance vision. As we age the crystalline lens becomes less flexible, a process that begins almost as soon as we’re born, although we only really notice the effect in our early forties. The effort required to squeeze the lens into the required shape makes focussing on very close objects (such as reading matter) increasingly difficult, until we’re forced to hold print further away simply to focus on it clearly. This is when we begin to need reading glasses.

Contact lenses have been designed to allow existing wearers to continue wearing lenses, yet incorporate extra power to assist with near tasks.

This process applies to people requiring corrections for myopia, hyperopia and astigmatism in their younger years. Where previously contact lens wearers were tempted to give up their lens wear as presbyopia became a problem, they can now have lenses designed to cope with the problem. Equally, some patients who, up until now, have never had to wear glasses and are reluctant to be seen in spectacles, can use this type of lens to assist near work even though they don’t need a distance correction.

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