Inter-ocular temporal asynchrony (IOTA): psychophysical measurement of inter-ocular asymmetry of visual latency

Ocular pathology can be associated with inter-ocular asymmetry of conduction latency. We describe a relatively low-cost psychophysical method of quantifying this asymmetry of delay, an 'inter-ocular temporal asynchrony' (IOTA) system. Testing of 28 visually normal young adults gave IOTA results with a mean of 0.11 ms (SD +/- 2.4 ms). These results correspond to 95% confidence limits of -4.6 ms and +4.8 ms. Inter-ocular differences in retinal illumination, induced by using monocular neutral density filters in visually normal subjects, significantly affected IOTA in accord with an imposed perceptual delay in the 'filtered eye'. This demonstration that the IOTA technique is capable of detecting induced asymmetry of perceptual delay in visually normal subjects, along with the small measured confidence limits reported above, suggests that the apparatus should be capable of detecting inter-ocular asymmetries in response latencies with ocular disease, which have been previously measured by other techniques.