Biomedical subjects
Publications and source records attributed to S E Avetisov.
The authors discuss changes of various anatomic and functional eye parameters after keratorefraction operations. Necessity of ophthalmic ergonomic studies in refraction surgery is stressed, occupational indications are justified.
The paper analyses results after examination of 276 patients (495 eyes) with different types of rigid and soft contact lenses. A study of some ways for improvement of contact lens tolerance has shown that improvement of rigid contact lenses can be achieved both by perfection of their construction (in particular by using spherotoric rigid lenses) and with the help of gas-permeable materials (in particular, cellulase acetobutyrate). The improvement of soft lens tolerance can be achieved by reducing the thickness of the lens as well us by using highly hydrophilic gels. If the known methods for improvement of contact lens tolerance fail to be effective, medicamentous preparations (such as solcoseryl, taufon, emoxipin) can be used as a method of choice; their usage is justified in keratoconus of stages II-IV, when rigid lenses are a single kind of optic correction and their tolerance is lowered.
Investigations were carried out in 4 rabbits. The right eyes of the animals were experimental, the left eyes--tentative (radial keratotomy with 8 incisions, maximum depth of the central zone--3.0 mm in diameter). Mechanical trial of isolated corneas with a scleral rim were made 6 months after surgery by means of a trial machine "Instron-1122" and a special clamping device. After trial, the specimens were investigated by a method of scanning electron microscopy. As a result of mechanical action, the rupture of the cornea in the zone of contact with the punch was recorded in all cases. In the control eyes, the area of the cornea was practically the same as the zone of the punch pressure on the cornea. In tentative eyes, the rupture was connected with keratotomy scars in all cases. The values of destructive load, transference of the punch at the moment pattern destruction and destructive tension along the punch contour were determined. The results obtained have shown that anterior radial and not crossing the limbus incisions in the cornea produce changes in mechanical characteristics of the cornea: in the sites of keratotomy scars, "conditionally" weak places of the corneoscleral coat are formed, the probability of breaks and tears of which in contusions of the increases.
The accuracy of fixation topogometry that allows to assess the form of the cornea along its whole surface has been studied experimentally. For this purpose, a special metallic standard with a mirror surface has been manufactured, representing a paraboloid of rotation (by the formula Y2 = 2RX, where R = 7.7 mm). The standard was fixated on a face support of ophthalmometers (of the firms "Rodenstock" and "Karl Zeiss") by means of a support providing transference of the standard in two reciprocally perpendicular meridians on the given (5-35) number of grades. The measurements were made in 15 points. At first sagittal radii of the cornea were determined, then the distance height of the points from the central axis (h) and the sag (P) were calculated. The position of points built with the help of P and h in coordinate axes was compared with the standard curve. The range of divergences was minimum (0.01-0.04 mm), this speaking about sufficient accuracy of the method of fixation topogometry.
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The paper analyses literature data and personal observations concerning the usage of radial keratotomy as a method of choice for correction of myopia and myopic astigmatism. It is pointed out that till now some rather important aspects of the usage of this operation are not yet comprehensively elucidated. To these aspects belong contraindications to the operation, its late sequelae, peculiar manifestations of age pathology in the eyes after keratotomy and a number of other questions. The author considers that such patients should receive a rather detailed information on the possible complications and outcomes of the operation, in particular on those negative points which are already known. The traditional and surgical methods available in ophthalmology should be regarded not as alternative ones, but as supplementing each other, i.e. as methods of choice.
In the period after surgical correction of myopia and astigmatism in 30 patients (44 eyes) by radial keratotomy, contrast sensitivity deteriorated slightly. The disturbances, however, were transitory, and the general trend was toward restoration of function. Strict adherence to an adequate operative technique prevented a marked decline in contrast sensitivity. The decrease must be considered before surgery, particularly in patients who need a high degree of fine motor control.
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Functional results of aphakia correction by different methods (eyeglasses, contact and intraocular lenses) are compared. The difference of this study from previous is that it was carried out in a group of patients to whom these methods were prescribed in succession. The rightfulness of such an approach to evaluation of functional results of various methods for aphakia correction is dictated by the fact that the norm is a relative parameter for many ophthalmic ergonometric studies, and thus the investigations need to be standardized (e.g., investigations in the same patients). Comparison of the efficiencies of different methods demonstrated that the best results are attained with intraocular lenses.
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A unique clinical case is presented: LASIK in a 12-year-old child for correction of posttraumatic corneal astigmatism after penetrating wound of the eye and extraction of traumatic cataract with IOL implantation. The patient was observed for 3 months postoperation.