A new method for analyzing smooth-pursuit eye movements. Description of a microcomputer program and evaluation in healthy volunteers

Abstract

The study of ocular movements has been increasingly used to detect subtle pathological modifications, caused by a wide variety of neurological diseases. We have developed a new microcomputer-based method for the analysis of smooth-pursuit ocular movements induced by constant velocity targets moving unpredictably at different velocities (including velocity values as high as 100 deg/s). The ocular movements are recorded by an electro-oculographic technique using silver-silver chloride electrodes fixed near the inner and outer canthi of both eyes. The signals are amplified by two DC amplifiers after a low-pass filtering (50 Hz), sampled at 250 Hz and digitized in a 12-bit form by an analog/digital converter. For each patient's evaluation, a series of 20 sweeps of the target is generated. The data analysis, which is performed automatically by the microcomputer, is based on the calculation of four parameters: average peak eye velocity (APEV); typical target velocity (TTV); percent target matching index after saccade removal (PTMI); typical matching target velocity (TMTV) after saccade removal. APEV is calculated as the average of the peak velocities estimated from the 20 sweeps. The purpose of TTV, which is defined as the value of target velocity at which the percent gain has decreased to slightly more than one third of the maximum percent gain, is to provide an overall index of the rate at which the percent gain decreases as the target velocity increases. PTMI describes the eye performance for each value of target velocity.(ABSTRACT TRUNCATED AT 250 WORDS)