Presbyopia

reading glasses Derived from the Greek 'presby' and 'ops' meaning old-age sight, presbyopia occurs because the eye’s lens gradually loses its ability to change shape when acted upon by the ciliary muscle - the smooth muscle within the ciliary body that surrounds the lens. Similar to grey hair and wrinkles, presbyopia is a symptom caused by the natural course of aging. Presbyopia is not a disease and it cannot be prevented.

The ability to focus on near objects declines throughout life. The first symptoms are usually first noticed between the ages of 40-50.

Symptoms of Presbyopia

You'll likely become aware of presbyopia when you start needing to hold print at arm's length in order to read it. If you're nearsighted, you might temporarily manage the problem by reading without your glasses.

Print appears unclear at a normal reading distance
Eyestrain or headaches from prolonged reading or close work

presbyopia scale

The near-point of accommodation gradually moves outward from about 10 inches (20 cm) at age 40, to 12 inches (30 cm) at age 45, and 16 inches (40 cm) at age 50 years.

A basic eye exam can confirm presbyopia. You can correct the condition with nonprescription reading glasses or prescription eyeglasses or contact lenses. Surgery also may be an option.

Presbyopia, like other focus defects, becomes much less noticeable in bright sunlight. This is not the result of any mysterious 'healing effect' but just the consequence of the iris closing to a pinhole, so that depth of focus, regardless of actual ability to focus, is greatly enhanced, as in a pinhole camera which produces images without any lens at all. Another way of putting this is to say that the circle of confusion, or blurredness of image, is reduced, without improving focusing.

A delayed onset of seeking correction for presbyopia has been found among those with certain professions and those with miotic pupils. In particular, farmers and housewives seek correction later, whereas service workers and construction workers seek eyesight correction earlier.

Causes of Presbyopia

cillary muscles The exact causes of presbyopia are not known with certainty. Current research most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens' curvature from continual growth and loss of power of the ciliary muscles have also been postulated as its cause.

In order to "create" an image, your eye relies on two structures to focus the light reflected from objects: the cornea — the clear front surface of your eye — and the crystalline lens inside the eye, held in place by ciliary muscles (the muscles that bend and straighten the lens). Both of these structures bend (refract) light entering your eye to focus the image on the retina, located on the inside back wall of your eye.

The crystalline lens, unlike the cornea, is somewhat flexible and can change shape with the help of a circular muscle that surrounds it. When you're looking at something far away, the circular muscle relaxes. When you're looking at something nearby, the muscle constricts, allowing the relatively elastic lens to curve more steeply and change its focusing power.

Presbyopia and the 'payoff' for the nearsighted

Many people with myopia are able to read comfortably without eyeglasses or contact lenses even after age 40. However, their myopia does not disappear and the long-distance visual challenges will remain. Myopes with astigmatism will find near vision better though not perfect without glasses or contact lenses once presbyopia sets in. But, the greater the amount of astigmatism the poorer their uncorrected near vision. Myopes considering refractive surgery are advised that surgically correcting their nearsightedness may actually be a disadvantage after the age of 40 when the eyes become presbyopic and lose their ability to accommodate or change focus, because they will then need to use glasses for reading.

Treatment of Presbyopia

Presbyopia is not routinely curable - though tentative steps toward a possible cure suggest that this may be possible. The loss of focusing ability can be compensated for by corrective lenses including eyeglasses or contact lenses. In subjects with other refractory problems, convex lenses are used. In some cases, the addition of bifocals to an existing lens prescription is sufficient. As the ability to change focus worsens, the prescription needs to be changed accordingly.

Around the age of 65, the eyes have usually lost most of the elasticity. However, it will still be possible to read with the help of the appropriate prescription. Some may find it necessary to hold reading materials farther away, or require larger print and more light to read by. People who do not need glasses for distance vision may only need half glasses or reading glasses.

While bifocals and multifocals offer a working solution to everyday problems, they are disliked by many, especially engineers, camera operators, and those used to having a good sharp distortion-free image in their work. Varifocals cause straight lines to look bent, and can leave some feeling dizzy after extended use. The power of simple, multiple prescriptions should not be underestimated. Reading glasses hastily prescribed may be fine for reading, but not good for shopping and generally walking around in. A slightly weaker prescription however, just powerful enough for reading using the full remaining accommodation of the eye, may feel much more comfortable for more general use too. Careful calculation of working ranges, together with a certain amount of trial and error, can restore undistorted vision for critical tasks for many people who do not find multifocals to their liking.

In order to reduce the need for bifocals or reading glasses, some people choose contact lenses to correct one eye for near and one eye for far with a method called "monovision". Monovision sometimes interferes with depth perception. There are also newer bifocal or multifocal contact lenses that attempt to correct both near and far vision with the same lens.

Presbyopia

Symptoms of Presbyopia

Causes of Presbyopia

Presbyopia and the 'payoff' for the nearsighted

Treatment of Presbyopia

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