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

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 Corporation, Tokio, Japan) 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 Corporation, Tokio, Japan) 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 the right eye and 7.7° and 12.1° in the left eye. On head-tilt of 20° and 40° to the left, OCR was 4.4° and 8° in the right eye and 4.2° and 8.7° in the 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 DFA than right eye. OCR occurs only in the roll plane. This information is of value when analyzing paired fundus photographs.

Keywords: Eye movements/physiology; Fondo de ojo; Fotografía; Fovea centralis; Fundus oculi; Fóvea central; Head movements/physiology; Movimientos cefálicos/fisiología; Movimientos oculares/fisiología; Photography; Rotación; Rotation.