Meridional analysis for calculating the expected spherocylindrical refraction in eyes with toric intraocular lenses

Fam, Han Bor; Lim, Kooi Ling

doi:10.1016/j.jcrs.2007.07.034

Cited by 46 publications

(23 citation statements)

References 9 publications

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“…Intraocular lens toricity is calculated at the corneal plane considering the influence of ELP according to meridional analysis. 12,13 Remaining calculations are the same as for model 4.…”

Section: Concepts and Definitionsmentioning

confidence: 99%

An Analysis of the Factors Influencing the Residual Refractive Astigmatism After Cataract Surgery With Toric Intraocular Lenses

Savini

Næser

2015

Investigative Ophthalmology & Visual Science

130

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Citation: Savini G, Naeser K. An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses. Invest Ophthalmol Vis Sci. 2015;56:827-835. DOI:10.1167/ iovs.14-15903 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 ¼ À0.59 6 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 6 0.42 D, P ¼ 0.01). When total corneal astigmatism was used instead of keratometric astigmatism (model 2), the ERA meridional power decreased in WTR (À0.13 6 0.42 D) and ATR (0.07 6 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.Keywords: astigmatism, toric IOL, mathematics, polar values T oric intraocular lenses (IOLs) are a common choice to correct corneal astigmatism at the time of cataract surgery. Several articles have shown good results, but the refractive outcome is not yet perfect.1-3 Over-or undercorrection of the cylinder may be related to the influence of several factors, including posterior corneal astigmatism. [3][4][5][6] To evaluate the optical results of surgery and the influence of each factor, we developed a set of equations describing the astigmatism along the steeper corneal meridian of each eye. For this purpose, we first performed a standard analysis based on keratometric astigmatism and a mean estimated surgicallyinduced corneal astigmatism (SICA). The influence of the remaining factors was assessed by progressively adding information related to posterior corneal astigmatism, actual SICA, IOL orientation, and the effective lens position (ELP) of the individual case. METHODSA sample of consecutive patients undergoing phacoemulsification and toric IOL implantation was p...

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“…Intraocular lens toricity is calculated at the corneal plane considering the influence of ELP according to meridional analysis. 12,13 Remaining calculations are the same as for model 4.…”

Section: Concepts and Definitionsmentioning

confidence: 99%

An Analysis of the Factors Influencing the Residual Refractive Astigmatism After Cataract Surgery With Toric Intraocular Lenses

Savini

Næser

2015

Investigative Ophthalmology & Visual Science

130

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“…For calculation of IOL toricity, the Pentacam AXL offers meridional analysis method, which uses total corneal power in a 3-mm zone [27,28]. For the spherical equivalent power, anterior corneal curvature values are applied.…”

Section: Discussionmentioning

confidence: 99%

Comparison of anterior segment parameters and axial length measurements performed on a Scheimpflug device with biometry function and a reference optical biometer

Muzyka−Woźniak¹,

Oleszko

2018

Int Ophthalmol

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Purpose To compare measurements of axial length (AL), corneal curvature (K), anterior chamber depth (ACD) and white-to-white (WTW) distance on a new device combining Scheimpflug camera and partial coherence interferometry (Pentacam AXL) with a reference optical biometer (IOL Master 500). To evaluate differences between IOL power calculations based on the two biometers. Methods Ninety-seven eyes of 97 consecutive cataract or refractive lens exchange patients were examined preoperatively on IOL Master 500 and Pentacam AXL units. Comparisons between two devices were performed for AL, K, ACD and WTW. Intraocular lens (IOL) power targeting emmetropia was calculated with SRK/T and Haigis formulas on both devices and compared. Results There were statistically significant differences between two devices for all measured parameters (P \ 0.05), except ACD (P = 0.36). Corneal curvature measured with Pentacam AXL was significantly flatter then with IOL Master. The mean difference in AL was clinically insignificant (0.01 mm; 95% LoA 0.16 mm). Pentacam AXL yielded higher IOL power in 75% of eyes for Haigis formula and in 62% of eyes for SRK/T formula, with a mean difference within ± 0.5 D for 72 and 86% of eyes, respectively. Conclusions There were statistically significant differences between AL, K and WTW measurements obtained with the compared biometers. Flatter corneal curvature measurements on Pentacam AXL necessitate formulas optimisation for Pentacam AXL.

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“…The meridional IOL power calculation was used to determine the toricity of the IOL (the IOL cylinder), as suggested by Fam et al 18 The Holladay 1 formula 19 was used for this calculation.…”

Section: Methodsmentioning

confidence: 99%

Comparison of corneal astigmatism measurements of 2 optical biometer models for toric intraocular lens selection

Srivannaboon

Chirapapaisan

Chonpimai

et al. 2015

Journal of Cataract and Refractive Surgery

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Meridional analysis for calculating the expected spherocylindrical refraction in eyes with toric intraocular lenses

Abstract: Calculation of the expected spherocylindrical refraction with toric IOLs was achieved using meridional analysis.

Cited by 46 publications

References 9 publications

An Analysis of the Factors Influencing the Residual Refractive Astigmatism After Cataract Surgery With Toric Intraocular Lenses

An Analysis of the Factors Influencing the Residual Refractive Astigmatism After Cataract Surgery With Toric Intraocular Lenses

Comparison of anterior segment parameters and axial length measurements performed on a Scheimpflug device with biometry function and a reference optical biometer

Comparison of corneal astigmatism measurements of 2 optical biometer models for toric intraocular lens selection

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