Objective:

Understand the impact of head position on measurement of ocular torsion when taking fundus photos.

Background:

Ocular torsion can be evaluated by the disc foveal angle (DFA) on fundus photos. In routine fundus photography, the head position is not controlled for even though it can affect ocular torsion through the vestibulo-ocular response known as the ocular counter-roll. Here, we examined the position of head and how it may affect measurement of ocular torsion during fundus photography. 

Design/Methods:

Fundus photos were taken of 10 participants. The head position was measured using a gyroscope attached to the head. Three photos were taken of each eye in a standard condition with the head on chin rest without adjustment. For comparison, three photos were taken from each eye (i) with the head on the chin rest adjusted upright and (ii) with the head on the chin rest and tilted 10° to the left and right. The DFA was measured and compared between the three conditions. 

Results:

There was a significant difference in DFA when the head was tilted 10° compared to the upright position (p<0.0001). There was a larger head tilt angle in the standard condition compared to when the head position was adjusted upright (Standard 1.31°±0.09°; Upright 0.07°±0.01°; p<0.0001). However, there was no significant difference in DFA between the standard and upright conditions (Standard OD=4.41°±0.79°, OS=5.56°±0.68°; Upright OD=4.27°±0.94°, OS=5.24°±0.77°; p=0.62). 

Conclusions:

The positioning of the head during fundus photography can affect DFA measurement. While large head tilts can cause change in DFA measurement, the standard head position with the head upright on the chin rest does not have a significant effect.