Cataract disease is a clouding of the lens which causes light scatter on the retina. This light scatter reduces image contrast and causes dimness of vision. One of the more striking problems in evaluating cataract vision loss is that many cataract patients preserve good acuity, but complain about their visual capability. The true “real-world” functional vision of cataract patients can be established as a functional acuity score using contrast sensitivity and glare testing.
These tests are most useful for cataract patients who have good acuity, i.e. 20/40 or better. For these patients, test the patient on Row B, 6 cycles/degree, of the CSV- 1000 and determine the lowest contrast level grating that can be identified by the patient both with and without glare. Remember that contrast sensitivity is affected by refractive error and that patients should always be tested with best correction. Determine the functional acuity from the recording chart as shown below.
Recording Form for CSV-1000S
The functional acuity is determined by the lowest level of contrast sensitivity that can be detected by the patient. The functional acuity score is shown in a bracket next to the contrast sensitivity score. The example shows a patient who could see the grating in contrast level 2 without glare and only the first grating with glare This patient’s functional acuity scores are circled on the example on the left. This patient has 20/50 functional acuity for contrast sensitivity and 20/100 functional acuity for glare sensitivity. These results would suggest that the patient has a significant vision problem not detected by standard acuity.
After cataract surgery, it is always best to retest the patient for contrast and glare sensitivity to demonstrate and document the tremendous improvement in functional vision. This retest is most important in patients who have normal acuity before surgery, 20/25 or better, because these patients may experience minimal or no improvement in visual acuity after cataract surgery.
Educating the Relatives of Patients
In some cases, relatives of cataract patients are very concerned because the complaints of the patients do not match the vision measured at the driver’s bureau. For example, it is not unusual for the daughter of a patient with cataracts to visit the practice and indicate that she is very concerned because her father complains bitterly about his ability to drive at night. But when he is tested at the driver’s bureau, he easily passes the vision test.
To educate the relative to cataract vision loss, the relative should take the contrast test at the same time as the patient. This evaluation is easiest when a distance test for contrast sensitivity and glare is used and both the patient and relative can view the test simultaneously. The relatives are often astonished at the many levels of contrast that cannot be seen by the cataract patient. The need for surgery becomes immediately clear to the patient and relatives.