Mechanisms of divergent torsional accommodation in myopia

    Abstract

    Original article

    Mechanisms of divergent torsional accommodation in myopia

    D.I. Terekhina, A.N. Zakieva

    Izhevsk State Medical Academy, Izhevsk, Russian Federation

    Purpose. To study the mechanism of extralenticular accommodation under conditions of divergent torsional strain (DTS).

    Material and methods. This study involved 14 students (28 eyes) with mild and moderate myopia, whose average age was 21.7 years. Among them were 4 boys and 10 girls. The average value of refraction, determined by the subjective method, was (–)2.5 D. To conduct this study, optical systems were used to simulate DTS in the downward and outward direction and to simulate DTS in the upward and outward direction. The features of extralenticular accommodation under conditions of DTS were comparatively assessed using the method of determining the binocular stability of visual perception (SVP) to hyperopic retinal defocus.

    Results. Studies of SVP in the far-vision mode under no vergent strain showed that the average total value of visual resolution (VR) was equal to 70.2%. Under DTS in the downward and outward direction, the average total value of VR was 67.1%. At the same time, along the curve there was a fall of VR that on average equaled to 9.5%. Under DTS in the upward and outward direction, the average total value of VR was 76.4%. Moreover, along the curve there was a fall of VR, that on average equaled to 7.1%. The presence of the fall zones indirectly indicates a temporary increase in the transverse diameter of the eyeball under the influence of DTS.

    Conclusion. DTS can stimulate combined lenticular and extralenticular accommodation caused by a change in the tone of the ciliary muscle and the pressure of strained oculomotor muscles on the sclera. Thus, DTS can change the geometry of the eyeball.

    Key words: divergent torsional strain, transverse deformation of the eyeball

    For citation: Terekhina D.I., Zakieva A.N. Mechanisms of divergent torsional strain in myopia. Fyodorov Journal of Ophthalmic Surgery. 2025;1(143): 87–91.

    doi: 10.25276/0235-4160-2025-1-87-91

    Corresponding author: Dar’ya I. Terekhina, dashia333@gmail.com