Prevalence and types of corneal astigmatism in patients undergoing cataract surgery

Abstract

Introduction: Cataract surgery is one of the most commonly performed ophthalmic surgical procedures worldwide, with a high rate of successful and rapid anatomical and functional visual recovery. Goal of cataract surgery is to achieve a desirable induction of refractive outcome with minimal astigmatism after surgery. This brings to interest the question of influence of preoperative and surgically induced corneal astigmatism on the final postoperative unaided visual acuity. Pre-existing corneal astigmatism is an important limiting factor for optimal results of cataract surgery in a significant number of patients. It has been estimated that 15% to 29% of patients with cataract have more than 1.50 dioptres (D) of pre-existing astigmatism.

Methods: Prospective study was carried out to investigate the prevalence and pattern of pre-existing corneal astigmatism in patients undergoing cataract surgery at B.P. Koirala Lions Center for Ophthalmic Studies, T.U. Teaching Hospital for a period of 2 years. All patients underwent complete ophthalmic examination including visual acuity, refraction, slit lamp examination, applanation tonometry and dilated fundus evaluation, biometry and ultrasound B-scan examination. Corneal astigmatism was measured by Keratometer at least two times for each patient. Astigmatism was calculated from dioptric difference between vertical reading and horizontal reading. With the rule (WTR) astigmatism was considered when steep meridian was at 900 ± 300. Against the rule (ATR) astigmatism was considered when steep meridian was at 1800 ± 300.

Results: Study included 225 eyes of 185 subjects, out of which 38.7% were male eyes and 61.3% were female eyes. The mean age of the subjects was 64.45±12.89 years. Mean amount of corneal astigmatism in our study was 0.84±0.80 D. 16.9% had no significant corneal astigmatism while 65.3% had corneal astigmatism between 0.25 and 1.50 diopter and 17.8% had corneal astigmatism of 1.50D or higher. With-the-rule astigmatism (axis of correcting cylinder 180±30 degrees) was present in 44.4% eyes, 40.04% of the eyes had against-the-rule (ATR) astigmatism (correcting minus cylinder 90±30 degrees), and 12.9% of the eyes had oblique astigmatism.

Conclusion: Approximately two thirds of pre-operative cataract patients had 1D or less astigmatism. Corneal astigmatism increases with age. Hence, it is important to analyze the magnitude and pattern of pre-existing corneal astigmatism in aging population due to higher demand for improved vision and use of suitable methods for best visual results.