[Calculation of intraocular lens power in non-standard clinical situations].

Methods of intraocular lens (IOL) calculation in non-standard clinical situations have been developed and introduced. These include a formula that improves the calculation accuracy in patients with relatively short anterior-posterior axis and another method for eyes after previous radial keratotomy. A comparative clinical evaluation of the proposed methods has been performed. The results indicate good perspectives for their use in ocular surgery.

[Comparative estimation of a new empirical formula for the calculation of the focal power of intraocular lenses in the short anteroposterior axis of the eye].

This comparative clinical study has indicated the importance of correctly choosing a formula to calculate the focal power of an intraocular lens (IOL) in the short ocular anteroposterior axis (APA). The most accurate and comparable formulas SRK II and SRK/T at the mean ocular APA values have significant errors at an APA of less than 21 mm. The new empirical formula allows the accuracy of calculation of the focal power of IOL to be increased in the short ocular APA as compared with other currently used formulas.

[Calculation of the focal power of an intraocular lens in the anterior segment sizes disproportional to the length of the anteroposterior axis of the eye].

Ultrasound and optical coherent biometries were used to study the influence of the biometric parameters of the anterior segment of the eyeball on the precision of calculation of the focal power of an intraocular lens (IOL). A clinical study has demonstrated that among the biometric parameters of the anterior segment of the eyeball, there is a close correlation of miscalculation of IOL focal power with the diameter of the cornea "from white to white" and accordingly with the diameter of the floor of the corneal segment. Based on the findings, the authors have developed a procedure for calculating the focal power of an IOL for cases of the disproportion of the corneal segment to the IOL length of the eyeball.

[Formula for calculating the IOL focal power]. / Formula rascheta opticheskoi sily intraokuliarnykh linz.

A formula for calculating the focal IOL power based on SRK-II is suggested and clinically tested. Quadratic non-linear allowances in small (below 23 mm) and big values of the anterior-posterior eye axis are introduced into it, instead of linear allowances, to enhance the calculation accuracy.

[Formula for estimating the optic force of elastic intraocular lenses]. / Formula rascheta opticheskoi sily élasticheskikh intraokuliarnykh linz.

Formula for estimating the optic force of intraocular lenses made from elastic materials has been tried in 106 patients. The formula takes account of forward deflection of the elastic intraocular lens in the posterior chamber of the eye. The proposed method for estimation more than threefold decreases the mean error in estimation of optic force of elastic intraocular lenses in comparison with calculations with the use of known formulas. The mean error is 0.78 +/- 0.13 diopters, which corresponds to modern requirements to the accuracy of formulas for calculating the optic force of intraocular lenses.