Objective measurement of contrast sensitivity function using contrast sweep visual evoked responses
- aSchepens Eye Research Institute and Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, USA, bDepartment of Ophthalmology, Faculty of Medical Sciences, UNICAMP, Campinas, SP, Brazil
- Tatsuo Hirose, MD, c/o Library, Schepens Eye Research Institute, 20 Staniford Street, Boston, MA, 02114, USA.
- Accepted 29 September 1997
Abstract
AIM/BACKGROUND The contrast sensitivity function (CSF) measurement provides information that is not accessible by standard visual acuity determinations. The contrast sweep pattern reversal visual evoked responses (CSVER) technique was used to objectively measure the CSF in clinical practice.
METHODS The contrast thresholds were measured at five spatial frequencies in 10 normal subjects. The CSVER were recorded with sinusoidally modulated vertical gratings at 10 contrast levels (96, 64, 48, 32, 16, 8, 4, 2, 1, and 0.5%) presented in five spatial frequencies (0.5, 1.0, 2.0, 4.0, and 8.0 cycles per degree). Each of 10 contrast levels was displayed for 2 seconds at the desired spatial frequency. The CSVER amplitudes at the second harmonic were calculated by discrete Fourier transform. The results were compared with those obtained using a psychophysical method.
RESULTS An inverted U-shaped CSF which peaked at 2.0 cycles per degree with a contrast sensitivity of 34.5 (contrast, 2.9%) was observed. The CSF assessed electrophysiologically was 0.62 to 0.79 log units lower than the sensitivity measured using the psychophysical method. However, the overall shapes were highly correlated.
CONCLUSION One can objectively measure CSF with CSVER and this may be useful in patients in whom the psychophysical method is limited.
