SCANNING LASER OPHTHALMOSCOPY OF THE OPTIC DISC AT THE LEVEL OF THE LAMINA-CRIBROSA

Purpose. To determine the suitability and reproducibility of optic dis c morphometry performed on images focused at the level of the lamina c ribrosa, obtained by means of the scanning laser ophthalmoscope (SLO). Methods. Twenty-one eyes were imaged with argon blue and green, heliu m neon red and diode infrared laser sources of a scanning laser ophtha lmoscope. Five images of the optic disc at the level of the lamina cri brosa were taken for each patient, digitized and traced by three train ed observers, in order to identify the external contour of the optic d isc and the inner edge of the neuroretinal rim. Dedicated software all owed the contours to be traced on the video and an estimate of the rea l sizes of optic disc parameters to be obtained according to Littman's equation. Standard deviation (SD) and coefficient of variation (CV) w ere used to determine the intra-and interobserver reproducibility in m easuring disc, dark annulus (DA), and reflective center (RC) areas, DA area/disc area (DA/D) and RC area/disc area (RC/D) ratios of each set of images taken with all laser wavelengths. Results. A high contrast between the dark annulus of the lamina and the central highly reflecti ve area was achieved at all laser wavelengths. The ranges of CVs for a ll of the observers, using all the laser wavelengths, were as follows: disc: 0.018-0.036; dark annulus: 0.015-0.039; reflective center: 0.01 4-0.031; DA/D: 0.005-0.01; RC/D: 0.007-0.018. No significant differenc e was observed between the measurements performed on the images acquir ed, using the different laser wavelengths. Conclusions. SLO imaging of the optic disc at the level of the lamina cribrosa proved to be suita ble and highly reproducible at all laser wavelengths. The coefficients of variation of the measurements of optic disc parameters obtained us ing this technique are smaller than those obtained by means of convent ional photographic methods.