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Cataract and the Aging Eye
The Normal Eye
What is a Cataract?
A cataract is a clouding of the lens of the eye. To understand what a cataract is, it's helpful to know that the lens is a clear, oval structure with three layers: nucleus, cortex and capsule. The analogy of a peach can be used to describe these layers. The nucleus or center of the lens is the pit of the peach, the cortex is the flesh surrounding the pit, and the capsule or elastic covering is the skin of the peach. The lens is supported inside the eye by tiny ligaments (zonules) that support the lens capsule.
In a young person, the lens is crystal clear and allows light to pass through and focus on the retina. As the lens ages, the nucleus turns yellow and loses its ability to accommodate (focus for close work) although the lens usually remains clear. As the lens continues aging, the nucleus turns from yellow to amber and ultimately to brown. Aging changes do not necessarily result in a cataract unless the nucleus becomes opaque, or opacities that block or scatter light develop in the cortex or under the capsule.
Are all cataracts the same?
There are three types of cataracts: nuclear, cortical and subcapsular. Each type affects a specific part of the lens, causing different symptoms and vision problems.
A nuclear cataract is the most common type of cataract and is age-related. In a nuclear cataract, the center of the lens gradually hardens and becomes opaque. As the nucleus changes color, from white to yellow to amber, it may also become so opaque that your eye doctor cannot clearly see the details of the retina. At that point, you might experience difficulty identifying colors and seeing at a distance. Some people become near-sighted (myopic) as a result of a nuclear cataract and notice an improved ability to read without glasses. Individuals with a nuclear cataract do not usually complain of increased light sensitivity. Surgical removal of a nuclear cataract may be safely postponed when symptoms do not interfere with daily activities. However, your eye doctor needs to monitor the condition of the lens, and will recommend surgery based on your symptoms and on the appearance of the cataract.
The second most common cataract is the cortical cataract. It starts as wedge-shaped opacities or "spokes" in the cortex (the layer between the nucleus and the capsule) that extend from the periphery towards the center of the lens. As the spokes reach the center, they interfere with the passage of light, causing glare and loss of contrast. Many people with diabetes develop this type of cataract. Although a cortical cataract usually develops slowly, it may impair both distance and near vision so significantly that surgery may be suggested at a relatively early stage.
A subcapsular cataract develops slowly and starts as a small opacity under the elastic covering (capsule), usually at the back of the lens (posterior). Significant visual symptoms may not appear until late in its development as the opacity increases, blocking light and causing glare sensitivity and blur. Typically, this type of cataract is found in people with diabetes or high myopia, adults with retinitis pigmentosa, and in people taking cortisone. If glare can be controlled with tinted lenses and anti-glare filters, the need for surgery is not as urgent.
Can I tell if I have a cataract?
In the early stages, only your doctor may detect a cataract because you may not have any visual complaints. Your first symptom may be hazy vision only in bright light. However, at some point, you may notice other changes in your vision that could mean you're developing a cataract. Since the signs and symptoms listed in the list below could also be symptoms of other eye conditions, it's important to have your eyes tested regularly -- every year -- or whenever you notice a change in vision. Don't overlook any symptoms or attribute them to age.
Common signs and symptoms
Distance vision is blurry, especially outdoors, but, in some cases, reading vision may be improved.
The edges of stairs and curbs are difficult to discern.
Streaks or rays of light seem to come from light sources, such as headlights and stop lights, at night.
You instinctively shade your eyes from the sun or feel more comfortable wearing a visor.
The reflection of light from metal on a car, road pavement, or a bright, cloudy sky may cause glare.
Fluorescent ceiling lights or bright reading lamps may cause glare.
Print appears faded and lacking in contrast.
Sunglasses appear to reduce your vision.
Highway signs, particularly on bright days, are difficult to read.
Print is difficult to read in dim light.
Colors appear faded or changed in hue. For example, blue may appear as a shade of green, white as gray or beige, and yellow as white.
While there are no known causes, studies have identified a number of risk factors:
Cataracts are a normal part of aging. Approximately 50% of Americans between 65 and 74, and 70% over age 75 have cataracts.
Excessive exposure to sunlight
Boaters, sunbathers, and people who do not habitually wear adequate protective eyewear are at risk.
High cholesterol / triglycerides
Probably related to faulty glucose metabolism.
Taken orally over a long period of time for medical conditions such as severe arthritis, lupus or related diseases.
Can cataracts be prevented?
Currently, there is no proven way to prevent the development of cataracts other than controlling medical conditions that may be the cause. Antioxidants like beta carotene and vitamins C and E have been identified as reducing the risk of developing cataracts and slowing their progression.
How is a cataract diagnosed?
An ophthalmologist, optometrist or family practitioner can diagnose the presence of a cataract through a routine eye examination. However, once a cataract is detected, your ophthalmologist or optometrist will monitor its progression. The eye examination evaluates:
the general health of your eye and the type of cataract;
how your activities are affected by the cataract;
whether your cataract should be surgically removed by your ophthalmologist.
What can I expect in an eye examination?
Your eye doctor will take a functional history and perform various tests.
Your eye doctor will ask if you've noticed vision changes while working, driving, performing household chores, reading, watching television, sewing, or playing bridge, golf or tennis. If you're experiencing difficulty, describe your symptoms to the doctor. This will help determine whether nonsurgical intervention such as using eyeglasses, sunglasses or magnifiers is appropriate or if surgery should be considered.
Visual acuity test
Your near and distance vision is tested by viewing an eye chart. A refraction (evaluation of the eyes for the correct strength of glasses) is perfomed to try to improve your vision with eyeglasses.
Glare/brightness acuity test
Glare sensitivity is evaluated by viewing an eye chart under different lighting conditions. Sunglasses (tints or filters) may be recommended based on your symptoms and the test results.
Dilation of pupils
Dilating your pupils is a procedure that allows your eye doctor (optometrist or ophthalmologist) to see the inner parts of your eye more clearly in order to evaluate the general health of your retina and optic nerve. Your doctor may use a special prism (gonioscope) to determine the safety of this procedure. Once established, eyedrops are used to dilate your pupils. An ophthalmoscope, which has a light source that can focus on the inside of the eye, enables the eye doctor to view your retina and optic nerve. A slit lamp -- a microscope with a light source that can focus on the lens of the eye -- may be used to determine the position and extent of the cataract. If your vision improves after the pupil has been dilated, your eye doctor may prescribe eyedrops for daily use.
Tonometry for intraocular pressure
This test utilizes a special attachment on the slit lamp to measure the eye pressure (glaucoma test).
As the cataract progresses, additional tests, such as contrast sensitivity and potential vision testing, may be done:
Contrast sensitivity is the ability to perceive differences between objects and their background and can be evaluated by a variety of methods. A contrast sensitivity test confirms vision difficulties you may experience reading print or seeing steps, stairs, curbs or color contrast.
Potential acuity meter (PAM)
The potential acuity meter projects a small eye chart through the cataract directly onto the macula (center of the retina that sees details best), bypassing the effect of the cataract on your vision. Although the acuity from this test is only a rough estimate of your "potential" vision after cataract surgery, the test results provide a fairly accurate prediction of postoperative vision.
The laser interferometer is another instrument that may be used to determine your "potential" visual acuity after cataract surgery. However, instead of projecting a visual acuity chart onto the macula as the PAM does, patterns of finer lines are projected onto the back of the eye. As with the PAM, this test can be done in the doctor's office.
The results of the contrast sensitivity, potential visual acuity or laser interferometry tests may influence the timing of surgery, particularly if you are experiencing visual difficulties.
Nonsurgical treatment options
If surgery is not advisable or should be delayed as long as possible -- as in the case of people with only one eye due to an accident or eye disease -- optical devices can alleviate some of the visual symptoms. Very strong reading glasses and hand-held magnifiers that enlarge print can be useful to continue routine activities such as reading a newspaper or a recipe in a cookbook. As a rule, an illuminated hand or stand magnifier with a built-in light source may be helpful unless the light causes glare, which is most common with cortical cataracts. Other optical devices, such as a hand-held monocular telescopic lens, can aid in seeing street signs as well as directories in buildings and airports. Sunglasses can decrease glare and increase contrast so that objects are more easily seen.
Numerous products such as large-print watches, books, playing cards, calculators and adjustable lamps for reading are available. Lighting is particularly critical for reading because too much light may create glare whereas too little light may cause the print to appear faded. Lamps, preferably with an indoor reflector bulb of 50 or 75 watts, placed one foot away from the page are generally adequate.
By Eleanor E. Faye, MD, FACS; Bruce P. Rosenthal, OD, FAAO; and Carol J. Sussman-Skalka, CSW, MBA