Disc-foveal angle and ocular counterrolling as a key in its interpretation

Abstract

Abstract Purpose Describe a time-sparing technique to measure disc-foveal angle (DFA), determine normal values and its role when analyzing paired fundus photographs. Methods DFA was analysed using the software program Keynote V 6.2.2 on 440 fundus photographs (3D OCT 2000, Topcon) of 20 individuals. The 11 different head positions were determined with the cervical range of motion device (CROM, Performance Attainment Associates). A reproducibility and correlation study between two fundus cameras (OCT 3D-2000 and TRC-50EX, Topcon) was performed. Results Mean DFA of the right and left eye was 5.5 ± 3.4° and 8.6 ± 2.9°, with a difference of 3.1° (p = 0.001 Wilcoxon signed-rank test) in the upright head position. Mean absolute difference in DFA between eyes was 3.5 ± 2.6°; an increase was seen with increasing head tilt (p = 0.000 Wilcoxon signed-rank test). Mean sum of DFA in both eyes was 14.1 ± 5.4°. On head-tilt of 20° and 40° to the right, mean ocular counterrolling (OCR) was 7.1° and 12.2° in right eye and 7.7° and 12.1° in left eye. On head-tilt of 20° and 40° to the left, OCR was 4.4° and 8° in right eye and 4.2° and 8.7° in left eye (p = 0.000 Wilcoxon signed-rank test). The two cameras showed strong correlation and high reproducibility. Conclusions Our DFA measurement technique is time-sparing and reproducible. Left eye shows higher disc-foveal angle than right eye. OCR occurs only in the roll plane. Absolute difference in disc-foveal angle between eyes changes according to head tilt, this information is of value when analyzing paired fundus photographs.