Abstract
Abstract: :
Purpose: To investigate the correlation between optic disc structure and its function by psychophysical testing. Methods: 23 eyes (18 patients) with normal optic discs and Humphrey visual fields underwent optic disc scanning using the Zeiss Stratus OCT 3 and the Heidelberg retinal tomograph 2 (HRT). Retinal nerve fibre layer thickness and optic disc rim volume were measured on the two machines. For the OCT, three scans were performed on each eye which were then checked for quality and accuracy by 2 experienced observers. Some adjustments were made if the software failed to detect the disc margins adequately and the data was averaged for each eye. For the HRT, the disc contour line was drawn and agreed between the two observers. Psychophysical testing was performed on a computer–based program with desktop monitor using software previously designed for this purpose. Threshold values were measured using an adaptive staircase method for spatial frequency gratings of 0.32, 0.72 and 8.24 cycles per degree, and temporal frequencies of 5, 7.5 and 10 Hertz. These 6 values were utilised since they have previously been shown to be the most discriminating between normal, OHT and glaucomatous optic nerves and are therefore the most clinically useful. Results: We found no significant correlation between structure and function of the optic disc with these tests. The highest correlations were: R=0.34 for HRT rim volume and spatial frequency 0.36 R=–0.28 for HRT RNFL thickness and spatial frequency 0.72 R=–0.28 for OCT RNFL thickness and spatial frequency 0.72 Conclusions: It has been shown that the psychophysical tests we used can discriminate between glaucoma and ocular hypertensive patients. However in patients with normal discs we were unable to show any correlation with nerve fibre layer thickness and psychophysical performance for the respective frequencies examined. This lack of correlation was probably due to the higher order processing of this psychophysical test or due to its ability to detect differences in function that was not portrayed in any structural deficit. Further work needs to be done to determine if a correlation exists between this psychophysical test, visual field score and nerve fibre layer thickness in glaucoma
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer • optic disc