Abstract
Purpose: :
The Heidelberg Retina Tomograph II (HRT II) is a confocal scanning laser ophthalmoscope designed for quantitative assessment of the optic disc. Previous studies have shown that optic disc characteristics vary between ethnic populations. The aim of this study was to characterise the disc morphology of the non-glaucomatous Pakistani population and compare HRT indices with clinical biomicroscopic readings.
Methods: :
Adults were examined in the Pakistan National Blindness and Visual Impairment Survey, a nationally representative population-based survey. One out of every 5 subjects over the age of 40 years consecutively attending for examination underwent optic disc analysis with the HRT II. 255 eyes of 130 patients were analyzed. Images from both eyes of each subject were acquired and then stored electronically. Images were exported onto the HRT-II software, the disc margin contour line drawn and analysis performed in the accredited reading centre at Moorfields Eye Hospital, London, UK. Biomicroscopy was performed through a dilated pupil at the slit lamp. The vertical dimensions of the disc and cup were measured using an eye piece graticule etched in 0.1mm units. The vertical cup diameter and disc diameters were measured using the graticule and the vertical cup to disc ration then calculated (vcdr). Biomicroscopic vcdr was compared to HRT II vcdr using a Bland Altman analysis.
Results: :
Mean age of subjects was 52.8 ± 9.9 (standard deviation) years. There was no significant difference in the mean vcdr comparing both methods: HRT II was 0.42± 0.28 (sd) and 0.41± 0. 25 (sd) as measured by biomicroscopy.Bland Altman plot was used to demonstrate the difference between biomicroscopic vcdr and HRT II measurements.
Conclusions: :
Many studies have indicated that there are differences in optic disc parameters between ethnic populations, using differing methods of optic disc assessment. By comparing the different methods of disc assessment in the non-glaucomatous/ "normative" group of subjects in the Pakistan population study, we hope to improve our understanding of the optic disc variations in different racial groups.
Keywords: optic nerve • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • anatomy