The impact of the lens component on the formation of regular total astigmatism

Component analysis of regular astigmatism (AS) involves determining the contribution of the cornea and the lens to the development of this type of ametropia. Most research in this area focuses on assessing corneal asphericity, while issues related to the lenticular AS remain less studied. Objective. This study evaluated the influence of the lenticular component on the formation of regular total AS in older patients. Material and methods. The potential impact of lenticular AS on total AS was assessed by analyzing the changes in parameters (magnitude and orientation of one of the principal meridians) after phacoemulsification with implantation of a monofocal intraocular lens (IOL). The study included 35 patients (41 eyes) aged 60—72 years. Preoperative AS ranged from 0.75 to 2.75 D. Results. No significant changes in magnitude or orientation of one of the principal meridians of total AS were found postoperatively (p=0.737 and p=0.965, respectively). Analysis of potential differences between total and corneal AS after surgery showed the following: in 13 cases (31.7%) values were identical, in 14 (34.2%) they differed by 0.25 D, in 5 (12.1%) — by 0.5 D, in 4 (9.8%) — by 0.75 D, and only in 5 cases (12.1%) the difference exceeded 1 D. Greater variability was noted in the orientation of one of the principal meridians: no cases had results coincide, and differences of 0—10°, 11—20°, 21—30°, and >30° occurred in 19 (46.4%), 13 (31.7%), 6 (14.6%), and 3 (7.3%) cases, respectively. Conclusion. The clinical model of pseudophakia after implantation of a monofocal IOL can be considered as a method for eliminating the impact of the lenticular component on total (clinical) AS. The need to refine keratometry data using subjective tests when determining the axis for toric IOL implantation remains due to the identified significant postoperative discrepancies in the orientation of one of the principal meridians of corneal and total AS.