Description:
<jats:p>Purpose. To study the features of extralenticular accommodation in horizontal convergence and divergence stresses. Material and methods. The study involved 25 students including 18 girls and 7 boys (50 eyes) with mild myopia, whose average age was 21.7 years. The refraction value was determined by the subjective method and averaged (-) 1.5 dptr. Pairs of prismatic lenses with a power of 2.0 dptr were used as an effective optical accommodation model. The lenses were mounted in a spectacle frame with their bases either to the temple or to the nose. A comparative assessment of the features of the extralenticular capabilities of the visual system was carried out by determining the binocular stability of visual perception to hypermetropic retinal defocus. Results. The study of visual perception stability in far-vision mode in the absence of vergence stress revealed that the total value of the visual resolution was 564 %. Under convergence stress, the total value of the visual resolution was equal to 989 %, and under divergence stress, it was 988 %. In studies without any vergenсe stress, the avergence accommodation curve had a smooth downward trend. In studies of visual systems under vergence stresses, curves had a concave arc shape and turned downward abruptly in the middle. Conclusions. Convergence and divergence movements can stimulate combined lenticular and extralenticular accommodation caused by ciliary muscle contraction and oculomotor muscle pressure on the eye sclera. Extraocular muscle pressure causes temporary deformation of the eyeball, that leads to a temporary change in the eye refraction. Keywords: extralenticular accommodation, convergence and divergence stresses, temporary deformation of the eyeball.</jats:p>