Influence of Head Position on Blind Spot location in Visual Field Assessment

Abstract

Purpose :
To investigate variation head tilt angle during the visual field testing, and whether this affects structure-function correlation in the assessment of glaucoma.

Methods :
In Method 1, 44 subjects were enrolled, consisting of 30 normal eyes, 11 glaucomatous eyes and 3 eyes with ocular hypertension. (Average of SE; -3.2+- 2.9 D, best corrected acuity better than log MAR 0.1.) In Method 2, 6 eyes of 6 normal subjects were assessed. Head tilt angle was recorded every 100 ms by a gyro sensor (IMU-Z Tiny Cube (ZMP^®)). The positions of both pupils were measured by photography, first only with the subject positioned on the chinrest (at rest), and then during location of the blind spot (testing condition) using automated perimetry (Octopus 900). This testing protocol was repeated five times. Lastly, both pupils were aligned to horizontal using a built-in accelerometer (LUMIX DMC-TZ4, Panasonic) and head tilt angle was measured.

Results :
The Fovea-disc angle found by fundus photography ranged from 0 to 17 degrees. The Fixation-blind spot angle found by perimetry ranged from -4 to 17 degrees. There was correlation between fovea-disc angle and the BS -fixation angle (p<0.01, R²=0.65). The average head tilt angle was between -3.6 and 3.9 degrees. The maximum intra-individual difference in head tilt angle was 5.8 degrees at rest. The average head tilt angle was between 4.2 and -3.6 degrees during testing. The maximum intra-individual difference in head tilt angle was 5.1 degrees. The variation of head tilt angle during testing was not significantly different from the resting condition (P=0.11) The intra-subject variation of head tilt angle during testing ranged from 0.25 to 0.52 degrees. This was smaller than the intra-individual variation of head tilt angle at rest. There was correlation between BS -fixation angle and head tilt angle. (p<0.01, rS -0.57).

Conclusions :
The maximum intra-individual difference of head tilt angle was 6 degrees, and inter-individual difference of head tilt angle was 8 degrees. Head tilt could influence visual field testing as well as assessment of the temporal retinal nerve fiber raphe angle. Consideration should be given to these factors to better correlate structural and functional changes in glaucoma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.