The results of use of alternating presentation of different stereoimages to study the ability to stereovision in children with postoperative residual microdeviation

Purpose. To study abilities to stereo-perception in children with postoperative residual micro-deviation via alternating presentation of different stereo stimuli.Material and methods. The study included 30 children aged 8 to 16 years (average 12.5 years) with operated strabismus who have postoperative residual micro-deviation (mean 6.8±0.4 pr.D) at the time of the observation. Residual esotropia was observed in 21 children (5 of them had also a vertical micro-deviation), exotropia – 9 children. Along with the usual ophthalmic examination and evaluation of stereovision by means of classical Lang-test and Fly-test we used our own stereo-tests developed on the basis of stereo images created by J. Ninio. Our stereo-tests included stimuli: 1) with a central location of vertical or horizontal stripes with a successful fusion and an ability to stereo perception of tilt relative to the horizontal axis (vertical strip) or turn around the vertical axis (horizontal strip); 2) with a peripheral location of vertical or horizontal stripes creating respectively the effect of tilt or reversal turn; 3) randomly-point stereo-grams, creating the impression of a successful fusion of vertical or horizont al cylinder. The subject observed the images shown on the monitor screen from a distance of 50 cm from the eyes through the red-blue light filters in conditions of full prismatic compensation of the angle of strabismus and optimal spectacle or contact correction of ametropia. The stimuli were presented both in the static version and in the modes of alternation via a computer pr ogram developed by M. V. Zhmurov. Three modes of alternative presentation of stimuli were used: 1) the mode with a consecutive monocular presentation of visual stimuli corresponding to the right and left eyes 2) the mode with the presence of an empty interval between monocular phases; 3) the mode with the presence of a binocular phase between monocular phases.Results. In all patients, the results of the study of stereovision with Lang-test, Fly-test and static version of our stereo-tests used in this work were negative. In eight children of the general group, the stereo effect appears only with stereo-images with a peripheral arrangement of vertical or horizontal stripes in all three modes of the alternating presentation. In 22 children, the stereo effect appears with stimuli both with peripheral and with the central location of the stripes in all three modes of their alternating presentation. The volume effect with random-dot stereo-stimuli occurred in only nine children, with a stable bifoveal fusion, and only in the mode of alternating presentation with an empty interval between monocular phases. Thus, in this mode of alternating presentation it was possible to perceive not only linear, but also random-dot stereo-images. Comparing the maximum durations of monocular phases for different images in this mode, a significant difference was found between the mean values for stimuli with peripheral vertical stripes (57±2.3 ms) and with central vertical stripes (43.2±2.6 ms; p<0.001), as well as between the mean values for stimuli with peripheral horizontal stripes (56±2.1 ms) and central horizontal stripes (43.6±3.4 ms; p<0.002). The maximum duration of monocular phases for random-dot stereo-images producing the effect of a vertical cylinder (32.2±5.8 ms) and a horizontal cylinder (31.1±6.7 ms) was significantly lower than the maximum duration for stimuli with peripheral vertical and horizontal stripes (p<0.001). The same regularities were observed for the maximum dur ation of the empty i nterval.Conclusion. The stereo-perception is possible in children with residual postoperative micro-deviation. At the same time, the most effective of the images we used are stimuli with a peripheral arrangement of elements that create a stereo effect in condition of a successful fusion. The mode of alternating presentation of stimuli with the presence of an empty interval between monocular phases creates more favorable conditions for the appearance of a stereo effect in comparison with the mode of alternating presentation of stimuli with the presence of a binocular phase between monocular phases and in comparison with the mode of alternating monocular phases. Stereovision with random-dot stereograms causes serious difficulties in most children with postoperative microdeviation, however, it is possible in some cases in the mode of alternating presentation of stimuli with the presence of an empty i nterval between monocular phases