Gaze-shift dynamics in subjects with and without symptoms of convergence insufficiency: influence of monocular preference and the effect of training

We studied gaze-shift dynamics during several gaze-shift tasks and during r eading, in five subjects with convergence insufficiency (C.I., a diminished ability to converge), and in ten subjects without C.I. Furthermore, we stu died the effect of vergence training in order to verify previous claims tha t orthoptic exercises can improve vergence performance. We recorded binocul ar eye movements with the scleral coil technique. Subjects switched fixatio n between nearby and distant light emitting diodes (LEDs) arranged in isove rgence arrays (distances 35 and 130 cm) in a dimly lit room. In both the C. I. and non-C.I. group, two classes of subjects occurred: vergence responder s and saccadic responders. During pure vergence tasks, saccadic responders made saccades with no or little vergence; vergence responders made vergence movements with no or small saccadic components. In saccadic responders, fi xation of nearby targets was monocular. Subjects with a preferred eye. acco rding to our determination, used the preferred eye. The five C.I. subjects showed idiosyncratic responses with insufficient vergence during most trial s. They all had a tendency to alternate fixation between the left and right eye. Vergence-version tasks always elicited larger vergence components tha n pure vergence tasks. During a reading task, vergence angles were more acc urate than during gaze-shifts between LEDs. After the pre-training sessions , nine subjects (one of which had C.I.) practised a pure vergence task thre e times a day for at least 2 weeks. Vergence amplitudes of four of these su bjects were larger after training. We conclude that vergence training can c hange oculomotor performance. Although C.I, is often associated with abnorm al vergence dynamics, there are no typical C.I. vergence dynamics. Unstable monocular preferences may play a role in the aetiology of C.I. (C) 1999 El sevier Science Ltd. All rights reserved.