Often referred to as “old man’s eyes” or the “aging eye condition,” presbyopia is the gradual loss of a person’s eyes’ ability to focus on nearby objects. It is a very natural result of aging and usually becomes noticeable in early to mid-40-year-olds and continues to worsen until about age 65. A basic eye exam can confirm presbyopia and it can be corrected with glasses, contact lenses, or surgery.
Anatomy and Physiology
The eyes are organs necessary for vision and use light to focus an image on the retinas, which are the photosensitive layers at the back of the eyes. At the front of the eye are the cornea, pupil, lens, and ciliary muscles. For vision to be clear, the eye must rely on the cornea and lens to focus light onto the retina. The lens can change shape with the help of contracting ciliary muscles that flank it. This process is called accommodation, which changes the optical power of the lens and maintains a clear image on the retina. Accommodation allows a person to see from a far distance and then up close (within centimeters from the face) without losing focus. Accommodation occurs very rapidly, particularly in young persons, within hundreds of milliseconds; however, the ability to accommodate decreases in older adults. This is because the lens in the eye is very prone to aging. Lenses do not have the ability to turn over proteins within their centers (nuclei). This results in a thickening or scar tissue (sclerosis) buildup within the nucleus of the lens. Thus, the elasticity of the lens reduces over time and its ability to change shape is decreased.
Research was performed to determine the stiffness of different regions of human lenses as a function of age and to correlate the biophysical measurements in the lens center with nuclear water content. A custom-made probe was designed to fit a dynamic mechanical analyzer that was used to measure stiffness values at 1-millimeter increments across humans’? lenses. The results showed there was a pronounced increase in the nucleus of the lens as well as stiffness over the age range from 14 to 78 years old. Thus, the thickness of the lens nucleus was shown to be a major contributing factor to presbyopia.
Signs and Symptoms
The primary sign and symptom of presbyopia is blurred vision at normal reading distances. This is most notable when a person is trying to read a menu and needs to hold the menu farther away to make the words clear. Additionally, persons with presbyopia may develop headaches after reading or doing close work. These symptoms can worsen when tired, drinking alcohol, or in dimly lit or dark rooms.
A person should visit an eye doctor (optometrist) if blurry close-up vision is keeping him or her from reading, doing close work, or doing other normal activities. Current treatments for presbyopia include prescription glasses, prescription contact lens, or surgery.
If the patient does not require corrective lenses for distance vision, then the best treatment is an optical aid for near vision. These can include prescription glasses or over-the-counter magnifying/reading glasses purchased at a pharmacy or grocery store.
For patients who are diagnosed with myopia (nearsightedness, which requires corrective lenses for their distance vision), it is best if they take off their glasses to read up close. Most people with myopia can read without their corrective lenses well past the age of 40. However, if an adult patient is considering refractive surgery like LASIK (laser in-situ keratomileusis or laser-assisted in-situ keratomileusis), the ophthalmologist will advise that correcting the nearsightedness will not slow down the natural aging process of presbyopia. Thus, the patient may need reading glasses when he or she is older.
Some myopic patients may also have astigmatism. As these persons age, they may have better up-close vision without their corrective lens. However, if their astigmatism is severe, their optometrist may prescribe two different contact lenses. One eye would be the “reading eye” and the other the “distance eye.” This is called monovision. If the patient likes monovision produced by contact lenses, then he or she has the option to make it permanent by a surgical technique that reshapes the corneas. Monovision is not suggested for glasses, as the wearer may not always look through the center of the lens, which would result in double images.
Persons with hyperopia (farsightedness) may need a prescription that corrects both distance and near vision with bifocal lenses.
Renee Johnson and Jennifer L. Hellier
See also: Accommodation; Amblyopia; Astigmatism; Diplopia; Myopia; Visual System
Ai Hong Chen, Daniel J. O’Leary, & Edwin R. Howell. (2000). Near visual function in young children. Ophthalmology, Physiology, and Optometry, 20, 185—198.
Heys, Karl R., Sandra L. Cram, & Roger J. W. Truscott. (2004). Massive increase in the stiffness of the human lens nucleus with age: The basis for presbyopia? Molecular Vision, 10, 956—963. Retrieved from http://www.molvis.org/molvis/v10/a114/
National Eye Institute (NEI). (2010). Facts about presbyopia. Retrieved from https://nei.nih.gov/health/errors/presbyopia