Sophisticated diagnostic tests now allow vision care specialists to determine the type, location, and stage of a cataract, helping you and your provider decide in advance whether surgery is prudent and likely to be successful (see Treatment and Care of People with Cataracts). In the following article, we’ll describe the tests that might be used to gather this information and prepare you for surgery.
An optometrist, ophthalmologist, or general practitioner can diagnose cataracts, but only an ophthalmologist - a physician who specializes in eye care - can perform cataract surgery. Your provider will want to determine whether you have a cataract or cataracts, confirm whether or how much the condition is impairing your vision, rule out other eye diseases that could account for your low vision, and check for any conditions that might make surgery risky.
Cataracts can be diagnosed from your description of signs and symptoms, a visual acuity test using an eye chart, and a physical examination of the eyes. Specialized tests can be used to evaluate particular problems. Below are descriptions of some of the diagnostic tests your provider is likely to perform.
Standard Eye Examination
Visual Acuity Testing
Most of us are familiar with the "big E" chart, so named for the large block letter at the top. This chart measures how well you see at various distances. From a specified distance, usually 20 feet, the provider will ask you to read aloud progressively smaller rows of high-contrast (black type on a white background) capital letters and numbers.
However, a person's score on the visual acuity test may not reflect functional impairments, such as glare sensitivity and reduced contrast sensitivity. Specialized tests can be performed to measure diminished function.
Ophthalmoscopy Followed by Slit-Lamp Examination
Cataracts can be seen with an ophthalmoscope, a hand-held, microscope-like viewing instrument. After using special drops to dilate your pupils, your vision care provider will examine the internal structures of the eye to assess the cataract, if one is found, and to check for other eye diseases. A slit lamp, which is a high-intensity light source combined with a low-power microscope, will then be used to examine the frontal structures of the eye.
A tonometer is a hand-held instrument that measures intraocular pressure (the pressure of fluids inside the eye) after anesthetic drops are instilled. This test is performed to rule out glaucoma.
Keratometry and A-Testing
To fit you with an IOL of the proper size and magnification, your vision care provider will use keratometer to measure the curvature of your cornea. Then the length (optical axis) of your eye will be measured using painless ultrasound waves to determine the ocular power of the IOL lens. This test is called an A-scan.
People who have good visual acuity but poor contrast sensitivity may fail to see low-contrast objects, such as curbs and steps, under conditions of reduced visibility, such as in the shade or twilight. They may also have trouble reading and walking at a normal speed, identifying faces from a distance, and doing tasks such as sewing and preparing food.
Contrast sensitivity testing assesses the eye’s ability to detect subtle shade variations by asking you to view letters and numbers or groups of figures, such as gray bars, that vary in contrast, luminescence, and spatial frequency.
Glare Sensitivity Testing
Glare is simply scattered light that reduces visibility. Reading lamps, illuminated computer monitors, street lights, and headlights are various sources of glare that can interfere with the ability to see targets in the visual field. These objects might range from text on a glossy magazine page or a laptop screen to a jogger on the shoulder of the road at dusk.
Cataracts disperse light that enters the lens, reducing the contrast of the retinal image. Glare sensitivity is markedly increased in those with advanced cataracts, so testing for it can help indicate the stage of the opacity. You may be asked to read a chart under simulated lighting conditions that include direct sunlight, a partly cloudy day, and fluorescent lighting. Your performance will then be compared to your score under ideal lighting conditions.
Corneal Endothelium Testing
The corneal endothelium, a layer of tissue that lines the posterior surface of the cornea, is particularly apt to be injured during surgery, so your provider must examine its condition microscopically before operating. A low cell density indicates that the cornea may not function well after cataract surgery, eventually necessitating a transplant.
Potential Acuity Testing
Potential acuity testing uses a meter to examine macular function. The purpose of the test is to estimate how well you can expect to see after surgical removal of a cataract. It is most accurate if your cataracts are not advanced.
Symptoms are sometimes disproportionate to the degree of cataract formation observed during the physical examination. New wavefront technology uses computer analysis of a laser beam to track the distortion of light as it passes through the eye. This technology can corroborate a person’s report of disabling symptoms, establishing that a medical need exists (for insurance reimbursement) and allowing surgery to take place earlier in the disease’s progression.
Living with Cataracts
Ultimately, only those who live with cataracts can say whether the condition is merely a nuisance or is significantly compromising their quality of life - or perhaps falls somewhere in between. Most people with cataracts, however, do not proceed immediately to the operating room. You and your provider may prefer to take a "wait and see" approach and monitor the progression of the condition.
Unless your work requires visual precision, making small adjustments may suffice early in the course of the disease. For example, you can reposition lights to reduce glare, rearrange furniture and rugs to remove hazards, update your eyeglasses prescription frequently, and read large-print publications when available. (For more suggestions, read: Living Better at Home)
When accommodating the condition becomes too burdensome, though, most people with cataracts can undergo safe, effective surgery to restore their sight.