БИОМЕХАНИКА АККОМОДАЦИОННОГО ОТВЕТА В НОРМЕ И ПРИ ПРЕСБИОПИИ

Abstract

Purpose. To reveal of regularities of accommodation response formation in the norm and i n the development of presbyopia. Material and methods. Two groups of patients with emmetropic refraction (objective refraction in terms of medical cycloplegia not more than Ѓ}0.25D) were examined. The first group consisted of 30 healthy subjects (60 eyes) aged 18-30 years, the second group – 30 patients (60 eyes) aged 45 to 60 years with symptoms of presbyopia, without concomitant ophthalmic pathology. In all patients in addition to the standard ophthalmologic examination an examination of the anterior segment was made, using a rotating Scheimpflug camera and the ultrasound biomicroscopy at rest and at moment of presentation of the visual stimulus, which corresponds to a tension of accommodation in 3D. Results and discussion. In norm the biomechanics of the accommodative response is characterized by a change in the lens form and an increase of its density, a shortening of anterior portions of the ciliary zonules, an increase of the distance between the trabecula and the ciliary crown, a decrease of the posterior chamber volume, an increase of the irido-corneal angle, pupil narrowing, a change in the iris profile, a decrease in the anterior chamber volume and an enhancement of corneal asphericity. Modified accommodative response in the formation of presbyopia includes: an increased aspherical central and peripheral part of the cornea by 27%, an increased quadrofoil by 93%, a reliable narrowing of the pupil and a decrease in the ciliary body thickness. Conclusion. Accommodative response is normally a multicomponent process, which involved all the structures of the anterior segment of the eye. Involutional physiological changes of the eye with the presbyopia formation lead to a distortion of the accommodative response; however, in case of presbyopia the activity of ciliary muscle is retained, an active contraction of the pupil and a transformation of corneal optics occur that should be taken into account in the planning of surgical treatment in patients with presbyopia.