Presbyopia - what is, definition,

Presbyopia - what is, definition,

Presbyopia is a progressive change in the eyes that occurs with aging, in which it becomes increasingly difficult to focus on near objects. Presbyopia occurs because the LENS loses FLEXIBILITY, limiting its ability to adjust between near and far focus. The lens becomes unable to contract to thicken in the center as near focus requires, resulting in the inability to see objects that are close, such as when reading. Most people begin to notice presbyopia when they reach their mid-40s in age. People who have MYOPIA (nearsightedness) may also find that their distant vision improves as presbyopia advances. The EYE changes responsible for presbyopia reach their end point by about the mid-50s, after which the stiffening of the lens stabilizes. Eyeglasses, contact lenses, and surgery offer options for correcting presbyopia.

Eyeglasses

The conventional treatment for presbyopia is reading glasses, which are magnifying lenses that enlarge near objects to allow the eyes to focus on them. Many retail and optical stores sell standard reading glasses that come in common magnifications typically ranging from +1.00 to +3.00 in gradations of 0.25 power. This is often the least expensive and most convenient option. An optometrist also can prescribe custom-strength lenses.

People whose eyes otherwise do not require refractive correction wear reading glasses as needed for close vision. People who have other REFRACTIVE ERRORS, such as myopia or ASTIGMATISM, and wear eyeglasses require bifocal or trifocal CORRECTIVE LENSES that provide multiple levels of correction to accommodate both the refractive correction and the magnification for close vision. Eyeglass lenses may be progressive, in which there are no discernible lines on the lens to mark the transition from one level to another. People who wear contact lenses to correct refractive errors often choose to wear reading glasses as needed with the contacts for close vision, or may choose to switch to eyeglasses.

Contact Lenses

Contact lenses may also have multiple levels of refractive correction (multifocal contact lenses). Another approach using contact lenses is monovision, in which one eye, typically the dominant eye, wears a lens that fully corrects for refractive error and the other eye wears a lens that undercorrects. The BRAIN learns to distinguish which eye to use for close and for distant focusing, automatically shifting as necessary. It may take a week or two for the brain to make the adjustment and for monovision to feel comfortable. However, some people do not adjust to monovision at all. Monovision results in some loss of depth perception, which some people find barely noticeable and other people find intolerable.

Surgery

In the United States, the two most commonly used surgical methods to correct presbyopia are conductive keratoplasty and LASIK (an acronym for laser-assisted in situ keratomileusis), both done as ambulatory procedures that require no overnight hospital stay. In conductive keratoplasty, the ophthalmologist uses radiofrequency energy applied in a concentric pattern around the base of the CORNEA to shrink corneal collagen. This constricts the cornea’s base, causing the center of the cornea to thicken and rise, which improves close focus. It may take several weeks to experience the full effect. In LASIK, the ophthalmologist uses an excimer laser to reshape the cornea. There is little recovery time with LASIK, and effects are apparent almost immediately.

Each surgical method establishes a permanent degree of monovision. Depending on the age of the person and the anticipated progression of the presbyopia, the ophthalmologist may leave a margin of correction to allow for future changes. Many ophthalmologists recommend a trial of monovision with contact lenses before surgery to determine whether the approach produces acceptable results. The risks of surgical correction for presbyopia include INFECTION, vision that still requires corrective lenses even after surgery, and, rarely, worsened vision. Some people may have other eye conditions, vision problems, or general health conditions that exclude them from surgery as an option to correct presbyopia.

See also HYPEROPIA; REFRACTIVE SURGERY; SURGERY BENEFIT AND RISK ASSESSMENT.

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