Abstract
Abstract: :
Purpose: There is no previous research on the effect of early interruption on binocular vision development as in congenital squint syndrome and childhood strabismus on the tOKN response. We investigated the tOKN response in patients with CSS and CS. Methods: Torsional OKN was elicited using a rear projected sinusoidal stimulus of cycle size 90º subtending 50.8 º in diameter. Eye movements were recorded using a three dimensional pupil and iris tracking video oculography technique (Strabs system, Sensomotoric instruments GmbH, Teltow, Germany). Eye movements were recorded monocularly while subjects viewed the rotating stimulus at velocities of 40º/s, 200º/s and 400º/s in the clockwise and anticlockwise directions. Results: A total of 14 patients were tested (6CSS and 8CS). All patients in CSS group demonstrated dissociated vertical deviation (DVD). In the CSS group 5/6 demonstrated tOKN with 4/5 of these patients demonstrating a response in the intorsion direction alone when viewing rotating stimuli in both eyes. Mean slow phase velocities (MSPV) in this group varyied from 2.12º/s to 5.12º/s across all three stimulus velocities. Of the CS patients tested 4/8 demonstrated tOKN to a rotating stimulus, one of these patients demonstrated equal directional preponderance in response to clockwise and anticlockwise stimulation. One subject showed a bias in the extorsion direction and the remaining 2 subjects in the intorsion direction with MSPV varying from 1.16º/s to 8.08º/s. In total across both groups 8/14 showed an asymmetrical response with 5/14 demonstrating no response in any direction of rotation. A control group of 8 normal subjects showed equal tOKN response in response to clockwise and anticlockwise stimulation with the MSPV reaching its maximum of approximately 3º/s in response to a stimulus rotating at 200º/s. There was no obvious correspondence between asymmetry found in the tOKN response and that found in previously tested horizontal OKN across subjects. Conclusions: In patients with CSS there was prevalence for tOKN in the intorsion direction. The development of a symmetrical torsional OKN response may be influenced by factors affecting the normal development of binocular vision.
Keywords: eye movements • nystagmus • strabismus