Development of a novel head-mounted perimeter - Measuring the visual field of both eyes by showing the target alternately and randomly to each eye -

Abstract

Purpose: We developed a head-mounted perimeter with a transmissive liquid crystal display for each eye that presents targets separately and randomly to the right and left eyes. One of its features is that it can measure the visual field concurrently with both eyes open. This study was designed to compare the visual field sensitivity of monocular and binocular perimetry using the head-mounted perimeter.

Methods: We can measure the visual field wherever we like as the perimeter is a head-mounted type. Its dimensions are W190 × D380 × H220 mm and weight is 1.6 kg. The target is presented on a transmissive liquid crystal display with high intensity LED backlight. Maximum brightness of the target is 10000 asb and backlight brightness is 31.4 asb. The target can be shown in an arbitrary size and form within 35° from the central visual field. We used Bayesian estimate and adaptive measurement of maximum-likelihood estimate as a threshold measurement algorithm. During the measurement, we can continuously monitor both eyes and each visual fixation. The location of the target is adjusted each time fixation disparity occurs. We can measure the visual field in both eyes at one concurrent examination by showing the target alternately and randomly to each eye without the subject being aware of which eye is tested. This study enrolled 11 normal subjects (age, 35.9 ± 7.18). All the subjects underwent both monocular and binocular perimetry using the head-mounted perimeter. The subjects were also checked if they noticed which eye was tested. We weighed the sensitivity in all the individual measurement points in monocular and binocular perimetry.

Results: The mean sensitivity with monocular perimetry for the right and left eyes were 30.3 ± 4.02 dB and 30.4 ± 3.69 dB, respectively and that with binocular perimetry for right and left were 30.6 ± 3.14 dB and 30.3 ± 3.32 dB, respectively. There was no statistically significant difference in all the individual measurement points (P < 0.05). In addition, all the subjects could not recognize which eye was tested.

Conclusions: The head-mounted perimeter enables us to measure the visual field in both eyes concurrently with the same precision as monocular perimetry while the subject is unaware of which eye is tested. This could contribute to the diagnosis of feigned blindness.