Presbyopia | Definition | Description | Causes and symptoms | Treatment
Definition
The term presbyopia means "older eye," and is a vision condition involving the loss of the eye's ability to focus on close objects.
Description
Presbyopia is a condition that occurs as a part of normal aging. The condition develops gradually over a number of years. Symptoms are usually noticeable by age 40 to 45, and continue to develop until the process stabilizes some 10 or 20 years later. Presbyopia occurs without regard to other eye conditions.
Causes and symptoms
In the eye, the crystalline lens is located just behind the iris and the pupil. Tiny ciliary muscles pull and push the lens, adjusting its curvature, and thereby adjusting the eye's ability to bring objects into focus. As individuals age, the lens becomes less flexible and elastic, and the muscles become less powerful. Because these changes result in inadequate adjustment of the lens of the eye for various distances, objects that are close will appear blurry. The major cause of presbyopia is loss of elasticity of the lens of the eye. Loss of ciliary muscle power and loss of elasticity of the zonules that connect the ciliary muscle to the lens, however, are also believed to contribute to the problem.
Symptoms of presbyopia result in the inability to focus on objects close at hand. As the lens hardens, it is unable to focus the rays of light that come from near objects. Individuals typically have difficulty reading small print, such as that in telephone directories and newspaper advertisements, and may need to hold reading materials at arm's length. Symptoms include headache and eyestrain when doing close work, blurry vision, and eye fatigue. Symptoms may be worse early in the morning or when individuals are fatigued. Dim lighting may also aggravate the problem.
Diagnosis
Presbyopia is officially diagnosed during an eye examination conducted by optometrists (O.D.s) or ophthalmologists (M.D.s).
O.D.s or M.D.s, with the help of ophthalmic assistants, should perform a comprehensive eye exam to diagnose the condition. The assistant should take a detailed patient history prior to the exam. This is especially important when diagnosing premature presbyopia.
The optometrist or ophthalmologist, or in some cases a highly trained assistant, will begin the ocular examination by testing visual acuity and refraction. During the exam the clinician also will determine ocular motility and alignment, nearpoint of convergence, near fusional vergence amplitudes, relative accommodation measurements, accommodative amplitude and facility of accommodation.
To further determine presbyopia, the clinician should perform near retinoscopy and intermediate distance testing, which can be performed with a phoropter or trial lens.
There are five different types of presbyopia:
· Incipient presbyopia is the earliest stage in which symptoms are documented. Usually the patient has trouble reading small print, but may perform well on testing and may actually reject a near vision prescription.
· Functional presbyopia is the point at which patients usually notice the difficulties with near vision. The age when this occurs varies and depends on environment, task requirements, nutrition, and general health.
· Absolute presbyopia is the result of continuous gradual decline in accommodation, and is the next phase after function alpresbyopia. At this stage, little accommodative ability remains.
· Premature presbyopia is the appearance of the disease at an earlier age than expected because of nutritional, environmental, or disease-related causes. Pharmaceuticals may also be a cause of premature presbyopia.
· Nocturnal presbyopia occurs when accommodation decreases in low-light conditions.
Treatment
Presbyopia cannot be cured, but physicians can help patients compensate for it by prescribing reading, bifocal, or trifocal eyeglasses. A convex lens is used to make up for the lost automatic focusing power of the eye. Half-glasses can be worn, which leave the top open and uncorrected for distance vision. Bifocals achieve the same goal by allowing correction of other refractive errors (improper focusing of images on the retina of the eye).
In addition to glasses, contact lenses can be useful in the treatment of presbyopia. Contact lens technicians need to take the patient's medical history to ensure the patient is a good candidate for contact lenses. Some lenses require a greater care commitment, so each patient's expectations need to be discussed before any lens is prescribed.
The two common types of contact lenses prescribed for presbyopia are bifocal and monovision contact lenses.
Bifocal lenses come in two designs, simultaneous vision and alternating vision. Soft and rigid lenses are available in the simultaneous vision design, but only RGP lenses are available in the alternating vision design. Alternating vision lenses behave more like bifocal eyeglasses than the simultaneous design. This alternating lens allows patients to look through two distinct visual zones and adjust their gaze for distance vision or for reading. To prevent rotation while in the eye, bifocal contact lenses use a specially manufactured type of lens. Good candidates for bifocal lenses are those patients who have a good tear film (moist eyes), good binocular vision (ability to focus both eyes together) and visual acuity in each eye, and no disease or abnormalities of the eyelids. The bifocal contact lens wearer must be motivated to invest the time it requires to maintain contact lenses and be involved in occupations that do not impose high visual demands. Further, bifocal contact lenses may limit binocular vision. Bifocal contact lenses are relatively expensive, in part due to the time it takes the patient to be accurately fitted.
An alternative to wearing eyeglasses or bifocal contact lenses is monovision contact lenses. Monovision fitting provides one contact lens that corrects for near vision and a second contact lens for the alternate eye that corrects for distance vision. If distance vision is normal, the individual wears only a single contact lens for near vision. Monovision works by having one eye focus for distant objects while the other eye becomes the reading eye. The brain learns to adapt to this and will automatically use the correct eye depending on the location of material in view. Advantages of monovision lenses are patient acceptability, convenience, and lower cost.
Several problems exist with the use of contact lenses in the treatment of presbyopia. Health care professionals need to ask patients to report any headache, fatigue, or decrease in visual acuity during the adjustment period. Monovision contact lenses usually result in a small reduction in high-contrast visual acuity and reduced depth perception as compared with bifocal contact lenses. In addition, since monovision corrects one eye for distance and one for eye for near vision, intermediate distances are often out of focus, especially in absolute presbyopia.
Some ophthalmologists are performing laser thermal keratoplasty (LTK) on presbyopic patients. The LTK procedure was approved to treat hyperopia in mid-2000, but some surgeons are treating presbyopia as an "off-label" procedure. The LTK procedure takes three seconds per eye and involves no cutting or removal of corneal eye tissue. Instead, the surgeon uses a holium:YAG laser to direct eight simultaneous spots of laser energy to the periphery of the cornea to shrink the corneal collagen. The laser heats the corneal collagen and steepens its shape, improving its refractive (focusing) power. Presbyopes receiving this treatment should be advised of regression after possibly just a few years.
Laser-assisted in-situ keratomileusis (LASIK) is another option for presbyopes. Surgeons correct one of the patient's eyes to achieve a monovision effect. This technique allows for good intermediate vision that facilitates reading menus or putting on makeup, but it can cause reduction in binocular distance vision and depth perception.
In preparatory interviews with patients, physicians and ophthalmic assistants should stress that with whatever surgical treatment the patient chooses, there will be regression. The aging process continues and therefore advancing presbyopia is unavoidable.
Prognosis
The changes in vision due to aging usually start in a person's early 40s and continue for several decades. At some point, there is no further development of presbyopia, as the ability to accommodate is virtually gone.
Health care team roles
Nurses, ophthalmic assistants, and well-trained technicians can perform a number of tasks previously required of an ophthalmologist or optometrist. Technicians can assist in diagnosing presbyopia by performing the first-level testing of refraction, as well as taking medical and lifestyle history, retinal photography, automated refractometry, automated keratometry, and corneal topography.
Allied health professionals also play an important role in performing the contact lens examination. Before prescribing contact lenses, technicians take a written and oral interview of the patient to determine if the patient is a suitable contact lens candidate. The technician must assess the technical aspects of the patient's ocular status. Next, the technician must discuss the patient's needs and expectations and evaluate all the information to make the correct lens choice. This is especially important for presbyopic patients choosing monovision, as this modality requires a larger commitment from patients.
The physician, or sometimes a contact lens technician, selects the lens material and design, then determines which trial lens is needed. A technician determines the lens parameters by using the results from the trial lens insertion. The patient's palpebral aperture and visual iris diameter are measured to determine the appropriate diameter for the contact lens. The technician will review the findings and make the recommendation to the prescribing physician for the proper contact lenses.
Before the patient is sent home with the lenses, the technician will give a detailed demonstration of inserting, removing, and cleaning the lenses.
Nurses and assistants also prepare patients for surgery by taking history, blood pressure and inserting eyedrops. They also may be involved in preparing the surgical areas, especially if surgery is performed in an ambulatory surgery center. Ophthalmic nurses are specially trained to assist in ocular surgeries.
Patient education
Doctors should emphasize with patients the challenges of choosing monovision and bifocal contact lenses to treat presbyopia. Doctors also should stress that surgical procedures are not permanent, and that patients may have to be retreated if regression occurs.
Prevention
There is no known way to prevent presbyopia.
KEY TERMS
Accommodation— The ability of the eye to change its focus from near to distant objects.
Binocular vision— Using both eyes at the same time to see an image.
Ciliary muscles— The small muscles that permit the lens to change its shape in order to focus on near or distant objects.
Lens (or crystalline lens)— The eye structure behind the iris and pupil that helps focus light on the retina.
Visual acuity— Sharpness or clearness of vision.
Resources
BOOKS
Ernest, J. Terry. "Changes and Diseases of the Aging Eye." In Geriatric Medicine, edited by Christine K. Cassel, et al. New York: Springer, 1997.
Newell, Frank W. "Optical Defects of the Eye." In Ophthalmology: Principles and Concepts. St. Louis, MO: Mosby, 1996.
PERIODICALS
Gromacki, Susan J., and Eric Nilsen. "Comparison of Multifocal Contact Lens Performance to Monovision." Contact Lens Spectrum 16, no. 5 (May 2001): 34-38.
ORGANIZATIONS
American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. 〈http://www.eyenet.org〉.
American Optometric Association. 243 N. Lindbergh Boulevard, St. Louis, MO 63141. (314) 991-4100. 〈AmOptNEWS@aol.com〉.
Contact Lens Association of Ophthalmologists, 721 Papworth Avenue, Suite 206, Metairie, LA 70005, (504) 835-3937, 〈http://www.clao.org〉.
Lighthouse National Center for Vision and Aging. 111 E. 59th Street, New York, NY 10022. (800) 334-5497. 〈http://www.lighthouse.org〉.
National Eye Institute. 2020 Vision Place, Bethesda, MD 20892-3655. (301) 496-5248; Publications: (800) 869-5248. 〈http://www.nei.nih.gov〉.
OTHER
Glazier, Alan, O.D., F.A.A.O. "Presbyopia Update: Helping Emerging Presbyopes." Optometric Management Online. 〈http://www.optometric.com/archive_results.asp?loc=articles/03062000115646am.html/〉.
Kattouf, Richard S., O.D. "Achieving Maximum Efficiency (Without Sacrificing Quality of Care)."Optometric Management Online. 〈http://www.optometric.com/archive_results.asp?loc=articles/03062000121028pm.html〉.
"New Technologies Continue to Expand Options for Treating Keratoconus, Myopia, Hyperopia."Primary Care Optometry News. 〈http://www.slackinc.com/eye/pcon/200101/newtec.asp〉.
"Optometric Clinical Practice Guideline Care of the Patient with Presbyopia." American Optometric Association Online. 〈http://www.aoanet.org〉.
