We describe a compact and convenient clinical apparatus for the measurement of suppression based on a previously reported laboratory-based approach. In addition, we report and validate a novel, rapid psychophysical method for measuring suppression using this apparatus, which makes the technique more applicable to clinical practice.
By using a Z800 dual pro head-mounted display driven by a MAC laptop, we provide dichoptic stimulation. Global motion stimuli composed of arrays of moving dots are presented to each eye. One set of dots move in a coherent direction (termed signal) whereas another set of dots move in a random direction (termed noise). To quantify performance, we measure the signal/noise ratio corresponding to a direction-discrimination threshold. Suppression is quantified by assessing the extent to which it matters which eye sees the signal and which eye sees the noise.
A space-saving, head-mounted display using current video technology offers an ideal solution for clinical practice. In addition, our optimized psychophysical method provided results that were in agreement with those produced using the original technique. We made measures of suppression on a group of nine adult amblyopic participants using this apparatus with both the original and new psychophysical paradigms. All participants had measurable suppression ranging from mild to severe. The two different psychophysical methods gave a strong correlation for the strength of suppression (rho = −0.83, p = 0.006).
Combining the new apparatus and new psychophysical method creates a convenient and rapid technique for parametric measurement of interocular suppression. In addition, this apparatus constitutes the ideal platform for suppressors to combine information between their eyes in a similar way to binocularly normal people. This provides a convenient way for clinicians to implement the newly proposed binocular treatment of amblyopia that is based on antisuppression training.
Department of Optometry and Vision Science, University of Auckland, Auckland, New Zealand (JMB, BT), The Department of Ophthalmology, McGill University, Montreal, Canada (GM, RFH), Faculty of Human Sciences, Sophia University, Tokyo, Japan (GM), and Japan Society for the Promotion of Science, Tokyo, Japan (GM)
Received February 26, 2010; accepted October 25, 2010.
Robert F. Hess; Department of Ophthalmology McGill University, 687 Pine Avenue West, Room H4-14 Montreal, Quebec, Canada H3A 1A1 e-mail: firstname.lastname@example.org