Scanning laser ophthalmoscopy of the optic disc at the level of the lamina cribrosa

Purpose. To determine the suitability and reproducibility of optic disc morphometry performed on images focused at the level of the lamina cribrosa, obtained by means of the scanning laser ophthalmoscope (SLO). Methods. Twenty-one eyes were imaged with argon blue and green, helium neon red and diode infrared laser sources of a scanning laser ophthalmoscope. Five images of the optic disc at the level of the lamina cribrosa were taken for each patient, digitized and traced by three trained observers, in order to identify the external contour of the optic disc and the inner edge of the neuroretinal rim. Dedicated software allowed the contours to be traced on the video and an estimate of the real sizes of optic disc parameters to be obtained according to Littman's equation. Standard deviation (SD) and coefficient of variation (CV) were used to determine the intra-and interobserver reproducibility in measuring 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 reflective area was achieved at all laser wavelengths. The ranges of CVs for all of the observers, using all the laser wavelengths, were as follows: disc: 0.018-0.036; dark annulus: 0.015-0.039; reflective center: 0.014-0.031; DA/D: 0.005-0.01; RC/D: 0.007-0.018. No significant difference was observed between the measurements performed on the images acquired, using the different laser wavelengths. Conclusions. SLO imaging of the optic disc at the level of the lamina cribrosa proved to be suitable and highly reproducible at all laser wavelengths. The coefficients of variation of the measurements of optic disc parameters obtained using this technique are smaller than those obtained by means of conventional photographic methods.