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      Preoperative corneal astigmatism among adult patients with cataract in Northern Nigeria


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          The prevalence and nature of corneal astigmatism among patients with cataract has not been well-documented in the resident African population. This retrospective study was undertaken to investigate preexisting corneal astigmatism in adult patients with cataract. We analyzed keratometric readings acquired by manual Javal-Schiotz keratometry before surgery between January 1, 2011 and December 31, 2011. There were 3,169 patients (3286 eyes) aged between 16 and 110 years involved with a Male to female ratio of 1.4:1. Mean keratometry in diopters was K1 = 43.99 and K2 = 43.80. Mean corneal astigmatism was 1.16 diopter and a majority (45.92%) of eyes had astigmatism between 1.00 and 1.99 diopters. Two-thirds of the eyes (66.9%) in this study had preoperative corneal astigmatism equal to or above 1.00 diopter. Findings will help local cataract surgeons to estimate the potential demand for toric intraocular lenses.

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          Contribution of posterior corneal astigmatism to total corneal astigmatism.

          To determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using a dual-Scheimpflug analyzer. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Case series. Total corneal astigmatism was calculated using ray tracing, corneal astigmatism from simulated keratometry, anterior corneal astigmatism, and posterior corneal astigmatism, and the changes with age were analyzed. Vector analysis was used to assess the error produced by estimating total corneal astigmatism from anterior corneal measurements only. The study analyzed 715 corneas of 435 consecutive patients. The mean magnitude of posterior corneal astigmatism was -0.30 diopter (D). The steep corneal meridian was aligned vertically (60 to 120 degrees) in 51.9% of eyes for the anterior surface and in 86.6% for the posterior surface. With increasing age, the steep anterior corneal meridian tended to change from vertical to horizontal, while the steep posterior corneal meridian did not change. The magnitudes of anterior and posterior corneal astigmatism were correlated when the steeper anterior meridian was aligned vertically but not when it was aligned horizontally. Anterior corneal measurements underestimated total corneal astigmatism by 0.22 @ 180 and exceeded 0.50 D in 5% of eyes. Ignoring posterior corneal astigmatism may yield incorrect estimation of total corneal astigmatism. Selecting toric intraocular lenses based on anterior corneal measurements could lead to overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism. The authors received research support from Ziemer Group. In addition, Dr. Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Calhoun Vision, Inc., NuLens, and Optimedica Corp. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.
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            Prevalence of corneal astigmatism before cataract surgery.

            To analyze the prevalence and presentation patterns of corneal astigmatism in cataract surgery candidates. University of Valencia, Valencia, Spain. Refractive and keratometric values were measured before surgery in patients having cataract extraction. Descriptive statistics of refractive and keratometric cylinder data were analyzed and correlated by age ranges. Refractive and keratometric data from 4,540 eyes of 2,415 patients (mean age 60.59 years +/- 9.87 [SD]; range 32 to 87 years) differed significantly when the patients were divided into 10-year subsets. There was a trend toward less negative corneal astigmatism values, except the steepest corneal radius and the J(45) vector component, in older groups (Kruskal-Wallis, P<.01). In 13.2% of eyes, no corneal astigmatism was present; in 64.4%, corneal astigmatism was between 0.25 and 1.25 diopters (D) and in 22.2%, it was 1.50 D or higher. Corneal astigmatism less than 1.25 D was present in most cataract surgery candidates; it was higher in about 22%, with slight differences between the various age ranges. This information is useful for intraocular lens (IOL) manufacturers to evaluate which age ranges concentrate the parameters most frequently needed in sphere and cylinder powers and for surgeons to evaluate which IOLs provide the most effective power range.
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              Topographic analysis of the changes in corneal shape due to aging.

              We studied the aging changes in corneal shape using corneal topography. Normal corneas (1,343) from 734 volunteers were examined by Topographic Modeling System-1 (TMS-1). All eyes were divided into eight groups according to age: (a) 80. The age-related changes in the averaged map of TMS-1 were evaluated. The findings noted in this map were confirmed by analyzing the data as well as by assessing the average-of-difference map. The averaged maps of subjects from 80 revealed a horizontal oval-shaped steep area, suggesting against-the-rule astigmatism. The average-of-difference map demonstrated a marked corneal steepening at the horizontal meridians. In the data analysis of the averaged map, the mean refractive powers of the cornea increased with age. Moreover, the refractive powers in the horizontal meridians exceeded those in the vertical meridians when they were in the 60s, which verified against-the-rule astigmatic shift. In conclusion, normal cornea becomes steeper and shifts from with-the-rule to against-the-rule astigmatism with age.

                Author and article information

                Indian J Ophthalmol
                Indian J Ophthalmol
                Indian Journal of Ophthalmology
                Medknow Publications & Media Pvt Ltd (India )
                November 2014
                : 62
                : 11
                : 1094-1095
                [1]Department of Ophthalmology, Aminu Kano Teaching Hospital, Kano, Nigeria
                [1 ]Department of Optometry, Makkah Specialist Eye Hospital, Albasar Foundation, Kano, Nigeria
                Author notes
                Correspondence to: Dr. Isyaku Mohammed, Department of ophthalmology, Aminu Kano Teaching Hospital, Kano, Nigeria. E-mail: drisyaku@ 123456yahoo.com
                Copyright: © Indian Journal of Ophthalmology

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Brief Communications

                Ophthalmology & Optometry
                cataract,corneal astigmatism,keratometer,nigeria,toric intraocular lens
                Ophthalmology & Optometry
                cataract, corneal astigmatism, keratometer, nigeria, toric intraocular lens


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