Contrast Sensitivity Experts
CONTRAST SENSITIVITY AND LOW VISION
To evaluate low vision in a patient, place the CSV-1000LV test 1 meter from the patient and ask him or her to start reading across each row in the upper left hand corner. Record the lowest contrast level for which two out-of-three letters can be identified. The contrast levels for the CSV-1000LV are shown below.
| CONTRAST LEVEL: | |
| 1 | standard acuity |
| 2 | 35.5% |
| 3 | 17.8% |
| 4 | 8.9% |
| 5 | 6.3% |
| 6 | 4.5% |
| 7 | 2.2% |
| 8 | 1.1% |
Low Vision Aids:
Clinical use suggests that if a patient is unable to obtain contrast level 3 or higher, the patient will have difficulty using low vision aids.
When a patient is fit with a low vision aid, contrast sensitivity should be reassessed to determine the functional benefit for the patient provided by the lenses.
Tracking Disease:
In many patients with progressing disease, changes in contrast sensitivity are detected before changes in visual acuity. Contrast sensitivity should be evaluated on each visit so that the status of the patient's visual health can be properly monitored. Importantly, if a patient has a change in treatment regimen, contrast sensitivity should be closely monitored to determine if the change in therapy has an impact on visual function.
Comparison of CSV-1000LV with other tests of Low Vision:
Pelli-Robson versus CSV- 1000LV
Considerable data has not been collected using the CSV-1000LV to evaluate low vision patients. The scatter plot below shows the contrast sensitivity as measured on the CSV-1000LV versus that measured on the Pelli-Robson chart. A very high correlation is found between the two tests.
Contrast sensitivity as tested on the Pelli-Robson versus CSV-1000LV. (From Stelmack et al. Opt Vis Sci Abstract 1996).
Patients with Marginal Low Vision:
Patients who are on the borderline of low vision should be tested with both the CSV-1000E and the CSV-1000LV. The CSV-1000E should be tested at 4 feet while the CSV-1000LV should be used at 2 meters. This comprehensive examination will provide the necessary information to evaluate the patient's change in vision over time. If the patient improves, such as recovery from optic neuritis, then future evaluation should be accomplished with the CSV- 1000E at 4 feet and at the standard test distance of 8 feet. If the patient worsens, then the patient test distance can be changed to the standard 1 meter test distance for evaluation with the CSV-1000LV test face. It is important to record the test distance if it is different from the standard.
Contrast sensitivity determines the lowest contrast level which can be detected by a patient for a given size target. Normally a range of target sizes are used. In this way contrast sensitivity is unlike acuity.
Contrast sensitivity measures two variables, size and contrast, while acuity measures only size.
