Contrast Sensitivity Experts
NORMALIZED CONTRAST SENSITIVITY
Recently, Drs. Brian Boxer Wachler and Ron Kreuger created the concept of eliminating the contrast sensitivity log values and curves. They developed a scale for the contrast sensitivity score at each spatial frequency. This scale is determined by the ratio of a patient's result and the normal score for the patient's age group. This concept is similar to visual field testing. For perimetry, the results are recorded on scale from O to 30 dB representing the range of scores for the population. The log values for the actual luminance levels used in perimetric testing are now never used. Similarly for normalized contrast sensitivity, the log values are not used. The normalized scale extends from .10 to 1.35, with a score of 1.0 indicating that the patient has the same contrast sensitivity as the population. Higher than 1.0 indicates higher contrast sensitivity than the population and a score lower than 1.0 means the patient has lower sensitivity.
The following table shows the normalized contrast sensitivity scores for the CSV-1000. To determine the normalized score, test the patient as described in the CSV-1000 product manual for the CSV-1000E test face. For patient records, note the normalized score obtained by the patient on each row. This percent value represents the "normalized contrast sensitivity" for this patient compared to a young (refractive surgery age) population. This score provides an easy method to evaluate a patient's contrast sensitivity without the use of the contrast sensitivity curves.
| Right Eye | A | .90 | B | .95 | C | 1.0 | D | .95 |
| Left Eye | A | 1.0 | B | 1.0 | C | 1.1 | D | 1.10 |
Normalized Contrast Sensitivity Scores:
| A (.40) | 1 (.60) | 2 (.70) | 3 (.80) | 4 (.90) | 5 (1.0) | 6 (1.10) | 7 (1.15) | 8 (1.25) |
| B (.50) | 1 (.65) | 2 (.70) | 3 (.80) | 4 (.90) | 5 (.95) | 6 (1.05) | 7 (1.10) | 8 (1.20) |
| C (.40) | 1 (.60) | 2 (.70) | 3 (.80) | 4 (.90) | 5 (1.0) | 6 (1.10) | 7 (1.15) | 8 (1.25) |
| D (.15) | 1 (.40) | 2 (.55) | 3 (.70) | 4 (.85) | 5 (.95) | 6 (1.10) | 7 (1.20) | 8 (1.35) |
Immediately after LASIK refractive surgery, contrast sensitivity falls such that the patient's quality of vision is well below the normal range. After several weeks, or in some cases several months, the quality of vision and contrast sensitivity recover to normal levels.
For PRK refractive surgery, the amount of time required to recover completely to normal levels may be longer, up to six months.
