Eye Exams - Cataract Examination

Cataracts occur when the lens of the eye becomes cloudy or opaque, resulting in blurred vision. Most people over the age of 60 have evidence of cataracts, and many eventually decide to have cataract surgery, which involves removal of the eye's natural lens and replacement with an artificial lens. Modern cataract surgery is among the most successful of all surgical procedures performed in the United States.

The first evidence of cataracts is usually discovered during a routine eye examination, and the problem is normally not treated until the symptoms begin to affect daily activities such as reading and driving. Although the term "ripe" is often used when referring to cataracts, the condition normally presents no danger to health, so the patient's decision on when to have surgery is strictly a personal one.

The elements of a cataract examination are much the same as a general eye exam with a few additional tests to determine whether or not surgery is a viable option.

Patient History

At the first visit, the cataract patient will need to record his or her address and telephone numbers, insurance information, names of other doctors, list of medications being taken, and past medical records if available. Because the exam includes dilating the eyes, it's a good idea to bring sunglasses to wear during the trip home. In addition, the cataract patient is asked about any vision problems under special conditions, such as low levels of light or situations where glare is a problem (headlights at night for instance). The patient will also be asked about any difficulties in performing normal tasks, such as driving, reading, performing occupational and recreational activities, and even moving around in unfamiliar surroundings.

A general health history will include any health or related problems that may have a bearing on the diagnosis and prognosis of the patient's cataract and suitability for surgery. A thorough review of any medications being taken by the patient is also necessary to determine whether such medications could affect surgical decisions or procedures. Any allergies to antibiotics and anesthetics should also be reported to the doctor during this phase of the exam.

The next step in the cataract exam process will be an examination of the eyes to determine the nature and severity of the cataract. At the same time, the eye care practitioner will assess the overall health of the eye to discover any problems that may limit the potential for good vision following surgery or any other treatment procedure.

An "objective" measurement of refraction is obtained with a procedure called a retinoscopy that allows the doctor to measure refractive error without input from the patient. It is often done before the phoropter exam to give the doctor a baseline or reference point from which to begin the refractive portion of the exam, and is especially useful for infants, nonverbal patients and difficult refractive cases.

Evaluation of Ocular Health

The eye doctor will perform the following tests to evaluate ocular health:

Visual Field Test
One of the tests conducted during the ocular health portion of the exam is a visual field test, which measures the ability of the eye to see straight ahead and to the side (peripheral vision). During a visual field test, one eye is temporarily covered and the patient is asked to look straight ahead at a fixed space.

There are two kinds of tests. In a moving target test, the targets are moved from the side, where they are not visible, towards the center of vision until the patient sees them. This test can be done with either a black screen on the wall or with a large bowl-shaped instrument.

The other is a fixed target test called computerized static perimetry. It uses small points of light that appear bright or dim but do not move. During this test, a patient sits in a chair facing either a bowl-shaped instrument or a computer screen.

The visual field examination is important in detecting many disorders of the eye, optic nerve and brain. One of the early symptoms of glaucoma, for instance, is the appearance of blind spots that can be detected by a visual field test.

Tonometry Test
Another important test that is part of every adult eye examination is tonometry which measures intraocular pressure (IOP), the internal pressure of the eye. The instrument used to measure eye pressure is called a tonometer and comes in two versions. One uses a pressure-sensitive tip that is placed gently against the surface of the eye, and is called applanation tonometry. The other directs a brief puff of air onto the eye and is known as air puff tonometry. Both versions of the test provide reliable IOP readings, although applanation tonometry is considered more accurate.

Opthalmoscopy
A part of every comprehensive exam is the examination of the inside and back of the eye with a hand-held instrument called an ophthalmoscope. The pupil is usually dilated (enlarged) with eye drops for this part of the exam so the doctor has a larger "window" to look through when examining the retina, which covers the back inside part of the eye. The ophthalmoscope also allows the doctor to examine other internal structures of the eye such as the vitreous, the jelly-like substance that fills the inside of the eye between the natural lens and the retina. The retina is particularly important because it is responsible for transmitting light signals from the lens to the brain. Any serious disorder of the retina can result in partial or total blindness.

Slit Lamp Test
The slit lamp is another important instrument used in a comprehensive eye exam. This specialized microscope projects a thin, intense beam of light into the eye giving the doctor a magnified, three-dimensional view of the interior of the eye from the cornea to the posterior capsule. The slit lamp aids in the diagnosis of diseases or trauma that affect the structural properties of the anterior eye segment, including the conjunctiva, cornea, anterior chamber, iris and lens.

Visual Acuity
Visual acuity is a measurement of how well a patient sees. This test uses the Snellen Eye Chart, a chart with rows of letters, numbers and symbols in standardized graded sizes, with a designated distance at which each row should be legible to a normal eye. A person with a normal optical system (20/20 vision) can see standardized symbols on the chart at a distance of 20 feet. A person with 20/30 vision can see symbols on the chart from 20 feet that a person with normal vision could see from 30 feet. This enables the eye doctor to quantify and classify the cataract.

Another chart is used to measure "near vision" or reading vision. This chart is held about 16 inches from the eyes, while the distance vision chart is placed at a distance (often by using mirrors) of 20 feet. For the cataract examination, measurements of visual acuity will be done under both high and low illumination.

Evaluation of Visual Abilities and Supplemental Testing

The doctor will initially perform several tests to define the patient's visual abilities. This will include an overall look at the appearance of the eye and surrounding area, checking for signs such as squinting, drooping of eyelids, facial muscles that do not appear to be working properly, and signs of irritation such as redness or swelling. A check of pupil function will also be done at this point using a pen light to see if the pupil responds normally. In addition, the eye care professional will perform the following checks:

• Eye alignment
• Near convergence - point at which both eyes together can see a single image
• Near point of accommodation - closest point at which an image is seen clearly
• Stereopsis - ability to see three dimensionally
• Color vision
• Confrontation fields - a test of peripheral (side) vision

If any of these initial tests indicate a potential problem, more extensive testing may be done later in the exam.

For cataract patients, a series of tests will assess functional disabilities and determine whether other disorders or diseases may prevent a good surgical outcome. For instance, patients with disease of the cornea, optic nerve or retina may not be good candidates for cataract surgery. Tests that may be done include the following:

Contrast Sensitivity
Contrast sensitivity is a measure of the eye's ability to distinguish images under varying degrees of lighting. A person with low contrast sensitivity may do well on the standard vision test and have difficulty seeing traffic lights or cars at night, spots on clothes, and facial gestures. In addition, the person may need a great deal of light to read or experience tired eyes while watching television.

The contrast sensitivity test is usually repeated after cataract surgery to document the degree of improvement that has been achieved.

Glare Test
Because cataract patients often complain that their vision is sharply reduced in brilliant sunlight and in nighttime driving, a glare test may be administered with a device that measures the effect of simulated glare on visual function. This allows the eye doctor to "quantify" the effect of glare on the person's vision, and it provides a benchmark for testing after cataract surgery to see if the situation has improved.

Specular Photographic Microscopy
During this procedure a specialized microscope is used to take a photograph of, or project a video image of, the endothelial layer of the cornea, which is a single layer of cells that regulates the water content of the cornea. This procedure is helpful in evaluating the health of the endothelium in preparation for cataract surgery, especially if the doctor suspects there may be an abnormality that could affect the surgical outcome.

Potential Vision (Acuity) Test
This test is sometimes used to predict potential vision improvement for patients as the result of cataract surgery. In simple terms, the patient looks through a pinhole at letters similar to those on a vision chart, but under very bright illumination. This procedure essentially eliminates or greatly reduces the effect of the cataract-clouded lens. It also allows the doctor to determine the visual capability of the macula, which is the small central portion of the retina that is responsible for straight-ahead vision.

Other tests that may be conducted as part of a cataract examination might include Amsler grid testing, fluorescein angiography, A-scan and B-scan ultrasonography, and tonography.

When the cataract exam is complete, the doctor will provide the patient with the findings of the examination, explain the options available for treatment, and advise of possible benefits and complications. The patient makes the final decision regarding surgery or other treatment. If surgery is selected as the preferred treatment, another appointment will probably be scheduled to conduct preoperative tests, including some of those mentioned in the previous paragraph. If the patient decides to delay surgery, the doctor will explain the importance of follow-up examinations and management of the cataract until a decision is made to proceed with the procedure.

See Cataracts in Eye Care Encyclopedia.