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Kristian Naeser - One of the best experts on this subject based on the ideXlab platform.
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Influence of Posterior Corneal Astigmatism on Total Corneal Astigmatism in Eyes With Keratoconus
Cornea, 2016Co-Authors: Giacomo Savini, Kristian Naeser, Domenico Schiano-lomoriello, A. MularoniAbstract:To measure posterior corneal Astigmatism (PCA) and investigate its influence on total corneal Astigmatism (TCA) in eyes with keratoconus. Keratometric Astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Naeser polar value method. We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique Astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR Astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR Astigmatism by 0.16 D and underestimated TCA in eyes with ATR Astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged −0.83 ± 0.40, −0.40 ± 0.37, and −0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r2 = 0.16) between the meridional powers of TCA and PCA. In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning Astigmatism correction by toric intraocular lenses.
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an analysis of the factors influencing the residual refractive Astigmatism after cataract surgery with toric intraocular lenses
Investigative Ophthalmology & Visual Science, 2015Co-Authors: Giacomo Savini, Kristian NaeserAbstract:PURPOSE: To investigate the influence of posterior corneal Astigmatism, surgically-induced corneal Astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. METHODS: Five models were prospectively investigated. Keratometric Astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal Astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric Astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive Astigmatism (ERA) as the difference between the postoperative refractive Astigmatism and the target refractive Astigmatism. RESULTS: We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal Astigmatism was used instead of keratometric Astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement. CONCLUSIONS: Posterior corneal Astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal Astigmatism rather than keratometric Astigmatism improves the prediction of the residual refractive Astigmatism.
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an analysis of the factors influencing the residual refractive Astigmatism after cataract surgery with toric intraocular lenses
Investigative Ophthalmology & Visual Science, 2015Co-Authors: Giacomo Savini, Kristian NaeserAbstract:Abstract To investigate the influence of posterior corneal Astigmatism, surgically-induced corneal Astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. Five models were prospectively investigated. Keratometric Astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal Astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric Astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive Astigmatism (ERA) as the difference between the postoperative refractive Astigmatism and the target refractive Astigmatism. We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P
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influence of posterior corneal Astigmatism on total corneal Astigmatism in eyes with moderate to high Astigmatism
Journal of Cataract and Refractive Surgery, 2014Co-Authors: Giacomo Savini, Francesco Versaci, Gabriele Vestri, Pietro Ducoli, Kristian NaeserAbstract:Purpose To evaluate the influence of posterior corneal Astigmatism on total corneal Astigmatism in patients with 1.00 diopter (D) or more of corneal Astigmatism. Setting Private practice, Bologna, Italy. Design Prospective case series. Methods Corneal Astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric Astigmatism, anterior corneal Astigmatism, posterior corneal Astigmatism, and total corneal Astigmatism were evaluated. Vector analysis was performed according to the Naeser method. Results One hundred fifty-seven eyes were enrolled. Keratometric Astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal Astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal Astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal Astigmatism, keratometric Astigmatism overestimated WTR Astigmatism by a mean of 0.22 D ± 0.32 (SD), underestimated ATR Astigmatism by 0.21 ± 0.26 D, and overestimated oblique Astigmatism by 0.13 ± 0.37 D. In the whole sample, a difference in Astigmatism magnitude of 0.50 D or more was detected between keratometric Astigmatism and total corneal Astigmatism in 16.6% of cases and the difference in the location of the steep meridian was greater than 10 degrees in 3.8% of cases. Conclusion In patients who are candidates for surgical correction of Astigmatism, measuring only the anterior corneal curvature can lead to inaccurate evaluation of the total corneal Astigmatism. Financial Disclosure Mr. Versaci and Mr. Vestri are employees of Costruzione Strumenti Oftalmici Srl. No author has a financial or proprietary interest in any material or method mentioned.
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assessment and statistics of surgically induced Astigmatism
Acta Ophthalmologica, 2008Co-Authors: Kristian NaeserAbstract:Abstract The aim of the thesis was to develop methods for assessment of surgically induced Astigmatism (SIA) in individual eyes, and in groups of eyes. The thesis is based on 12 peer-reviewed publications, published over a period of 16 years. In these publications older and contemporary literature was reviewed(1). A new method (the polar system) for analysis of SIA was developed. Multivariate statistical analysis of refractive data was described(2-4). Clinical validation studies were performed. The description of a cylinder surface with polar values and differential geometry was compared. The main results were: refractive data in the form of sphere, cylinder and axis may define an individual patient or data set, but are unsuited for mathematical and statistical analyses(1). The polar value system converts net Astigmatisms to orthonormal components in dioptric space. A polar value is the difference in meridional power between two orthogonal meridians(5,6). Any pair of polar values, separated by an arch of 45 degrees, characterizes a net Astigmatism completely(7). The two polar values represent the net curvital and net torsional power over the chosen meridian(8). The spherical component is described by the spherical equivalent power. Several clinical studies demonstrated the efficiency of multivariate statistical analysis of refractive data(4,9-11). Polar values and formal differential geometry describe astigmatic surfaces with similar concepts and mathematical functions(8). Other contemporary methods, such as Long's power matrix, Holladay's and Alpins' methods, Zernike(12) and Fourier analyses(8), are correlated to the polar value system. In conclusion, analysis of SIA should be performed with polar values or other contemporary component systems. The study was supported by Statens Sundhedsvidenskabeligt Forskningsrad, Cykelhandler P. Th. Rasmussen og Hustrus Mindelegat, Hotelejer Carl Larsen og Hustru Nicoline Larsens Mindelegat, Landsforeningen til Vaern om Synet, Forskningsinitiativet for Arhus Amt, Alcon Denmark, and Desiree and Niels Ydes Fond.
Giacomo Savini - One of the best experts on this subject based on the ideXlab platform.
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Influence of Posterior Corneal Astigmatism on Total Corneal Astigmatism in Eyes With Keratoconus
Cornea, 2016Co-Authors: Giacomo Savini, Kristian Naeser, Domenico Schiano-lomoriello, A. MularoniAbstract:To measure posterior corneal Astigmatism (PCA) and investigate its influence on total corneal Astigmatism (TCA) in eyes with keratoconus. Keratometric Astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Naeser polar value method. We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique Astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR Astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR Astigmatism by 0.16 D and underestimated TCA in eyes with ATR Astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged −0.83 ± 0.40, −0.40 ± 0.37, and −0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r2 = 0.16) between the meridional powers of TCA and PCA. In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning Astigmatism correction by toric intraocular lenses.
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an analysis of the factors influencing the residual refractive Astigmatism after cataract surgery with toric intraocular lenses
Investigative Ophthalmology & Visual Science, 2015Co-Authors: Giacomo Savini, Kristian NaeserAbstract:Abstract To investigate the influence of posterior corneal Astigmatism, surgically-induced corneal Astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. Five models were prospectively investigated. Keratometric Astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal Astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric Astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive Astigmatism (ERA) as the difference between the postoperative refractive Astigmatism and the target refractive Astigmatism. We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P
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an analysis of the factors influencing the residual refractive Astigmatism after cataract surgery with toric intraocular lenses
Investigative Ophthalmology & Visual Science, 2015Co-Authors: Giacomo Savini, Kristian NaeserAbstract:PURPOSE: To investigate the influence of posterior corneal Astigmatism, surgically-induced corneal Astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. METHODS: Five models were prospectively investigated. Keratometric Astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal Astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric Astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive Astigmatism (ERA) as the difference between the postoperative refractive Astigmatism and the target refractive Astigmatism. RESULTS: We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal Astigmatism was used instead of keratometric Astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement. CONCLUSIONS: Posterior corneal Astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal Astigmatism rather than keratometric Astigmatism improves the prediction of the residual refractive Astigmatism.
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influence of posterior corneal Astigmatism on total corneal Astigmatism in eyes with moderate to high Astigmatism
Journal of Cataract and Refractive Surgery, 2014Co-Authors: Giacomo Savini, Francesco Versaci, Gabriele Vestri, Pietro Ducoli, Kristian NaeserAbstract:Purpose To evaluate the influence of posterior corneal Astigmatism on total corneal Astigmatism in patients with 1.00 diopter (D) or more of corneal Astigmatism. Setting Private practice, Bologna, Italy. Design Prospective case series. Methods Corneal Astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric Astigmatism, anterior corneal Astigmatism, posterior corneal Astigmatism, and total corneal Astigmatism were evaluated. Vector analysis was performed according to the Naeser method. Results One hundred fifty-seven eyes were enrolled. Keratometric Astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal Astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal Astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal Astigmatism, keratometric Astigmatism overestimated WTR Astigmatism by a mean of 0.22 D ± 0.32 (SD), underestimated ATR Astigmatism by 0.21 ± 0.26 D, and overestimated oblique Astigmatism by 0.13 ± 0.37 D. In the whole sample, a difference in Astigmatism magnitude of 0.50 D or more was detected between keratometric Astigmatism and total corneal Astigmatism in 16.6% of cases and the difference in the location of the steep meridian was greater than 10 degrees in 3.8% of cases. Conclusion In patients who are candidates for surgical correction of Astigmatism, measuring only the anterior corneal curvature can lead to inaccurate evaluation of the total corneal Astigmatism. Financial Disclosure Mr. Versaci and Mr. Vestri are employees of Costruzione Strumenti Oftalmici Srl. No author has a financial or proprietary interest in any material or method mentioned.
Li Wang - One of the best experts on this subject based on the ideXlab platform.
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Astigmatism induced by intraocular lens tilt evaluated via ray tracing
Journal of Cataract and Refractive Surgery, 2018Co-Authors: Mitchell P Weikert, Abhinav Golla, Li WangAbstract:Purpose To evaluate Astigmatism induced by aspheric and toric intraocular lens (IOL) tilt using a ray-tracing model. Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Experimental study. Methods Ray-tracing eye models with aspheric IOLs (16.0 diopters [D], 22.0 D, and 28.0 D) and toric IOLs (16.0 D, 22.0 D, and 28.0 D each with toricities of 1.50 D, 3.75 D, and 6.00 D) were used. The IOLs were tilted from 1 to 10 degrees horizontally around a 90-degree vertical meridian. Toric IOLs were aligned at 90 degrees and 180 degrees to correct with-the-rule (WTR) and against-the-rule (ATR) corneal Astigmatism, respectively. Astigmatism at the corneal plane induced by IOL tilt was calculated. Results Induced Astigmatism increased with increasing IOL tilt and power. Horizontal tilt around a vertical meridian induced ATR Astigmatism. For 5 degrees of tilt, induced Astigmatism was 0.08 D, 0.11 D, and 0.14 D for 16.0 D, 22.0 D, and 28.0 D aspheric IOLs, respectively. Ten degrees of IOL tilt produced 0.33 D, 0.44 D, and 0.56 D of induced Astigmatism for 16.0 D, 22.0 D, and 28.0 D aspheric IOLs, respectively. Tilting toric IOLs aligned at 90 degrees around a vertical meridian increased the magnitude of induced ATR Astigmatism. Tilting toric IOLs aligned at 180 degrees decreased the magnitude of induced WTR Astigmatism. Conclusions Tilting aspheric IOLs horizontally around a vertical meridian induced ATR Astigmatism. Tilting toric IOLs aligned at 90 degrees increased ATR Astigmatism, resulting in overcorrection. Tilting toric IOLs aligned at 180 degrees decreased WTR Astigmatism, producing undercorrection.
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contribution of posterior corneal Astigmatism to total corneal Astigmatism
Journal of Cataract and Refractive Surgery, 2012Co-Authors: Douglas D Koch, Mitchell P Weikert, Mariko Shirayama, Richard Jenkins, Li WangAbstract:Purpose 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. Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Case series. Methods 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. Results 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. Conclusions 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. Financial Disclosure 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.
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correction of Astigmatism during cataract surgery toric intraocular lens compared to peripheral corneal relaxing incisions
Journal of Refractive Surgery, 2010Co-Authors: Jed T Poll, Douglas D Koch, Li Wang, Mitchell P WeikertAbstract:PURPOSE: To compare the efficacy of astigmatic correction achieved at the time of cataract surgery using toric intraocular lens (IOL) implantation versus peripheral corneal relaxing incisions. METHODS: A retrospective review assessed the outcomes of phacoemulsification cataract surgery performed between January 2006 and January 2008 by a single surgeon. Patients receiving a toric IOL (toric IOL group) or peripheral corneal relaxing incisions (relaxing incisions group) were included in the study. Main outcome variables included postoperative uncorrected distance visual acuity (UDVA) and manifest refractive cylinder. Each treatment modality was stratified by amount of preoperative keratometric Astigmatism into three groups (low, moderate, and high Astigmatism) for comparative analysis. RESULTS: A total of 192 eyes were included in the study; 77 received a toric IOL and 115 received peripheral corneal relaxing incisions. Preoperative data were not significantly different between the two groups except regarding keratometric Astigmatism, which was higher in the toric IOL group (P<.05). Average postoperative Astigmatism was 0.42 diopters (D) and 0.46 D in the toric and relaxing incisions groups, respectively. In subgroup analysis, no statistical significance separated the two treatment options in terms of amount of surgically induced Astigmatism or residual Astigmatism. Eyes with Astigmatism ≥2.26 D were more likely to achieve 20/40 UDVA from a toric IOL. CONCLUSIONS: Toric IOL implantation and peripheral corneal relaxing incisions yielded similar results regarding surgical correction of Astigmatism at the time of phacoemulsification cataract surgery. Both treatment modalities achieved comparable results with mild-to-moderate Astigmatism. Higher degrees of Astigmatism favor use of a toric IOL.
Mitchell P Weikert - One of the best experts on this subject based on the ideXlab platform.
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Astigmatism induced by intraocular lens tilt evaluated via ray tracing
Journal of Cataract and Refractive Surgery, 2018Co-Authors: Mitchell P Weikert, Abhinav Golla, Li WangAbstract:Purpose To evaluate Astigmatism induced by aspheric and toric intraocular lens (IOL) tilt using a ray-tracing model. Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Experimental study. Methods Ray-tracing eye models with aspheric IOLs (16.0 diopters [D], 22.0 D, and 28.0 D) and toric IOLs (16.0 D, 22.0 D, and 28.0 D each with toricities of 1.50 D, 3.75 D, and 6.00 D) were used. The IOLs were tilted from 1 to 10 degrees horizontally around a 90-degree vertical meridian. Toric IOLs were aligned at 90 degrees and 180 degrees to correct with-the-rule (WTR) and against-the-rule (ATR) corneal Astigmatism, respectively. Astigmatism at the corneal plane induced by IOL tilt was calculated. Results Induced Astigmatism increased with increasing IOL tilt and power. Horizontal tilt around a vertical meridian induced ATR Astigmatism. For 5 degrees of tilt, induced Astigmatism was 0.08 D, 0.11 D, and 0.14 D for 16.0 D, 22.0 D, and 28.0 D aspheric IOLs, respectively. Ten degrees of IOL tilt produced 0.33 D, 0.44 D, and 0.56 D of induced Astigmatism for 16.0 D, 22.0 D, and 28.0 D aspheric IOLs, respectively. Tilting toric IOLs aligned at 90 degrees around a vertical meridian increased the magnitude of induced ATR Astigmatism. Tilting toric IOLs aligned at 180 degrees decreased the magnitude of induced WTR Astigmatism. Conclusions Tilting aspheric IOLs horizontally around a vertical meridian induced ATR Astigmatism. Tilting toric IOLs aligned at 90 degrees increased ATR Astigmatism, resulting in overcorrection. Tilting toric IOLs aligned at 180 degrees decreased WTR Astigmatism, producing undercorrection.
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contribution of posterior corneal Astigmatism to total corneal Astigmatism
Journal of Cataract and Refractive Surgery, 2012Co-Authors: Douglas D Koch, Mitchell P Weikert, Mariko Shirayama, Richard Jenkins, Li WangAbstract:Purpose 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. Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Case series. Methods 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. Results 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. Conclusions 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. Financial Disclosure 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.
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correction of Astigmatism during cataract surgery toric intraocular lens compared to peripheral corneal relaxing incisions
Journal of Refractive Surgery, 2010Co-Authors: Jed T Poll, Douglas D Koch, Li Wang, Mitchell P WeikertAbstract:PURPOSE: To compare the efficacy of astigmatic correction achieved at the time of cataract surgery using toric intraocular lens (IOL) implantation versus peripheral corneal relaxing incisions. METHODS: A retrospective review assessed the outcomes of phacoemulsification cataract surgery performed between January 2006 and January 2008 by a single surgeon. Patients receiving a toric IOL (toric IOL group) or peripheral corneal relaxing incisions (relaxing incisions group) were included in the study. Main outcome variables included postoperative uncorrected distance visual acuity (UDVA) and manifest refractive cylinder. Each treatment modality was stratified by amount of preoperative keratometric Astigmatism into three groups (low, moderate, and high Astigmatism) for comparative analysis. RESULTS: A total of 192 eyes were included in the study; 77 received a toric IOL and 115 received peripheral corneal relaxing incisions. Preoperative data were not significantly different between the two groups except regarding keratometric Astigmatism, which was higher in the toric IOL group (P<.05). Average postoperative Astigmatism was 0.42 diopters (D) and 0.46 D in the toric and relaxing incisions groups, respectively. In subgroup analysis, no statistical significance separated the two treatment options in terms of amount of surgically induced Astigmatism or residual Astigmatism. Eyes with Astigmatism ≥2.26 D were more likely to achieve 20/40 UDVA from a toric IOL. CONCLUSIONS: Toric IOL implantation and peripheral corneal relaxing incisions yielded similar results regarding surgical correction of Astigmatism at the time of phacoemulsification cataract surgery. Both treatment modalities achieved comparable results with mild-to-moderate Astigmatism. Higher degrees of Astigmatism favor use of a toric IOL.
Noel Alpins - One of the best experts on this subject based on the ideXlab platform.
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Role of Hemidivisional Corneal Topographic Astigmatisms (CorTs) in the Regularization and Reduction of Irregular Astigmatism.
Cornea, 2017Co-Authors: Noel Alpins, George StamatelatosAbstract:To demonstrate how the concept of hemidivisional corneal topographic Astigmatism (hemiCorT) enables the planning of hemidivisional corneal treatments to reduce irregularity and overall Astigmatism.Whole-of-cornea corneal topographic Astigmatism (CorT) is calculated from topography data derived from a corneal topographer or tomographer. The cornea is conceptually divided into 2 hemidivisions along the flat meridian of the CorT. For each hemidivision, hemiCorTs are calculated. The regularization treatment for each hemidivision is the treatment required to target the whole-of-cornea CorT, which is a symmetrical orthogonal corneal Astigmatism. The regularization is then combined with Astigmatism reduction treatment, which could be a conventional refractive treatment or a vector-planned treatment. For each hemidivision, the combined astigmatic effect of the regularization treatment and reduction treatment can be determined through double-angle vector summation. The 2 hemidivisional treatments together regularize and reduce corneal Astigmatism.A theoretical pair of hemidivisional treatments is derived from an actual example of a cornea displaying idiopathic asymmetric nonorthogonal Astigmatism.HemiCorTs allow for the design of hemidivisional corneal treatments of asymmetric nonorthogonal Astigmatism. Such treatments should be suitable in the routine treatment of commonly occurring irregular Astigmatism, while also allowing the spherical refractive error to be treated concurrently.
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Astigmatism analysis by the alpins method
Journal of Cataract and Refractive Surgery, 2001Co-Authors: Noel AlpinsAbstract:Abstract Purpose To determine the effectiveness of correcting Astigmatism by laser refractive surgery by a vectorial Astigmatism outcome analysis that uses 3 fundamental vectors: target induced Astigmatism vector (TIA®), surgically induced Astigmatism vector, and difference vector, as described by the Alpins method. Methods A data set of 100 eyes that had laser in situ keratomileusis to correct myopia and Astigmatism (minimum preoperative refractive Astigmatism 0.75 diopter) was analyzed. The data included preoperative and 3 month postoperative values for manifest refraction and standard keratometry. Using the ASSORT® or VectrAK® analysis program, individual and aggregate data analyses were performed using simple, polar, and vector analysis of Astigmatism and an analysis of spherical change. Statistical analysis of the results was used for means and confidence limits, as well as to examine the differences between corneal and refractive Astigmatism outcomes. Results At an individual patient level, the angle of error was found to be significant, suggesting variable factors at work, such as healing or alignment. A systematic error of undercorrection of Astigmatism is prevalent in the treatment of these 100 patients by a factor of between 15% and 30%, depending on whether refractive or corneal values are examined. Spherical correction showed systematic undercorrection of 11%, and parallel indices demonstrated it to be more effective than the astigmatic correction. Conclusion This method of Astigmatism analysis enables the examination of results of Astigmatism treatment measured by both refractive and corneal measurements using vector analysis. By examining individual vector relationships to the TIA (ie, the correction index, index of success, and flattening index), a comprehensive Astigmatism analysis is completed. Each index provides information necessary for understanding any astigmatic change. Astigmatic outcome parameters are more favorable when measured by subjective refractive than objective corneal methods.
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Management of irregular Astigmatism.
Current Opinion in Ophthalmology, 2000Co-Authors: Michael Goggin, Noel Alpins, Leisa M. SchmidAbstract:Abstract Using a liberal definition of corneal irregularity, modern videokeratoscopy may define approximately 40% of normal corneas with a toric refractive error as possessing primary irregular Astigmatism. The causes of secondary forms of irregular Astigmatism include corneal surgery, trauma, dystrophies, and infections. Internal refractive surface and media irregularity or noncorneal Astigmatism (ocular residual Astigmatism) contribute to irregular Astigmatism of the entire refractive path of which crystaline lenticular Astigmatism is usually the principal contributing component. Treatment options have increased in recent years, particularly, though not exclusively, through the advent of tailored corneal excimer laser ablations. However, discussion continues concerning the systematic approach necessary to enable treatment to achieve an optimal optical surface for the eye. Discussion also continues as to what constitutes the optimal corneal shape. Some refractive procedures may increase higher order aberrations in the attempt to neutralize refractive Astigmatism. The way to further refinement of the commonly performed refractive techniques will ultimately lie in the integrated inclusion of a trio of technologies: topographic analysis of the corneal surface, wavefront analysis of ocular refractive aberrations, and vector planning to enable the appropriate balance in emphasis between these two diagnostic modalities. For the uncommon, irregularly roughened corneas, the ablatable polymer techniques show some promise.
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Treatment of irregular Astigmatism
Journal of Cataract and Refractive Surgery, 1998Co-Authors: Noel AlpinsAbstract:Abstract Purpose: To treat irregular Astigmatism by applying separate appropriate treatments in each of the two distinct hemidivisions of the cornea. Setting: Cheltenham Eye Centre, Melbourne, Australia. Methods: Two general surgical strategies are presented. The first applies the principles of optimization separately to each corneal hemidivision to achieve the maximum reduction in Astigmatism when measured topographically and refractively. The second is for targeting symmetrical orthogonal topographic goals for each semimeridian to create the regular state in differing ways. These are performed in one of the following ways: without changing refractive Astigmatism; by reducing the associated ocular residual Astigmatism; by shifting the less favorably placed topography semimeridian to the other more favorably located one; by shifting both topographic semimeridians to more favorably located sites. This is an alternative when a potential improvement in the best corrected visual acuity is sought and the maximum reduction of Astigmatism is not the priority. Results: The calculated treatments necessary to achieve various improved astigmatic states, together with each of their respective separate refractive Astigmatism targets, are presented. A single refractive Astigmatism value for the entire cornea is also calculated by vector summations Conclusion: Consideration of each of the two distinct hemidivisions of the eye enables improved treatment of irregular Astigmatism, potentially resulting in improved visual outcomes.
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new method of targeting vectors to treat Astigmatism
Journal of Cataract and Refractive Surgery, 1997Co-Authors: Noel AlpinsAbstract:Abstract Purpose: To describe a method for optimizing the treatment of Astigmatism using vector analysis of both refractive and corneal topographic values. Setting: Cheltenham Eye Centre, Melbourne, Australia. Methods: This study evaluated a method of vector analysis for planning surgery that uses both preoperative topographic and refractive values and determined how to select the relative treatment emphasis to be given to each. In addition, the significance of the phenomenon of ocular residual Astigmatism (ORA) was explored. Its presence provides an inherent limitation on eliminating Astigmatism from the eye's optical system. Results: Various comparisons of preoperative and ORA values are plotted in a series of 100 excimer laser photoastigmatic refractive keratectomy patients. These ORA values are equivalent to the expected corneal Astigmatism resulting from surgery where treatment is performed by refractive Astigmatism values alone. A theoretical example is given in which the corneal Astigmatism remaining from surgery is reduced by giving less emphasis to completely eliminating refractive Astigmatism and consequently greater emphasis to completely eliminating topographic Astigmatism. Conclusion: Using vectors in Astigmatism surgery enables the incorporation of topography and refractive values into the surgical plan. This would achieve a greater reduction in corneal Astigmatism and potentially a better visual outcome than using refractive Astigmatism values alone.
