Calculation of intraocular lens power: a review

Olsen, Thomas

doi:10.1111/j.1600-0420.2007.00879.x

Cited by 280 publications

(248 citation statements)

References 61 publications

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“…The error in measurements of the keratometric data can lead to unwanted postoperative refractive error. Although keratometric mistakes are not the first or most frequent source of error in today's biometric methods, 1 keratometry has an undisputed and important role in cataract surgery. Moreover, cases of implantation of toric IOLs require more precise keratometric readings and cylinder axis determination than ever before.…”

Section: O R I G I N a L A R T I C L Ementioning

confidence: 99%

Repeatability Data and Agreement of Keratometry With the VERION System Compared to the IOLMaster

Németh¹,

Szalai²,

Hassan³

et al. 2015

J Refract Surg

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he exact measurement of the radius of the curvature of the cornea is crucial for planning the diopter of the intraocular lenses (IOLs) for implantation during cataract surgery. The error in measurements of the keratometric data can lead to unwanted postoperative refractive error. Although keratometric mistakes are not the first or most frequent source of error in today's biometric methods, 1 keratometry has an undisputed and important role in cataract surgery. Moreover, cases of implantation of toric IOLs require more precise keratometric readings and cylinder axis determination than ever before.There are numerous papers showing that the repeatability of keratometric measurements is excellent in the case of the IOLMaster (Carl Zeiss Meditec, Jena, Germany), 2-4 although above 42.0 diopters (D), the cylinder axis has relatively low repeatability data.2 In the case of the Lenstar (Haag-Streit, Koeniz, Switzerland), the interclass coefficient of the variation of the astigmatism axis was 0.915 and the mean arithmetic difference between the two measurement sessions was 3.19°, with an absolute difference of a median of 9°. 5 The Lenstar keratometry has repeatable values, 6,7 but according to Zhao et al., 7 the Lenstar and the IOLMaster cannot be used interchangeably in relation to keratometric data. With regard to average keratometric data, it seems that the Lenstar is biometrically equivalent to the IOLMaster, 8 and the correlation between the cylinder axis measurements of the IOLMaster and the Lenstar is high.9 However, Rohrer et al. 9 observed that the differences between the axis value of the flattest meridian in the Lenstar and the IOLMaster in a large percentage of patients is unacceptably high. Besides these controversialTo analyze the repeatability of keratometric and white-to-white (WTW) distance measurements with the VERION Measurement Module (Alcon Laboratories, Inc., Fort Worth, TX) and to compare the measured data to the results of the IOLMaster (Carl Zeiss Meditec, Jena, Germany). METHODS:Three images were captured with the VERION and the flattest and steepest keratometric data, the astigmatism axis, and the WTW distance were recorded. Subsequently, the axial length, the keratometric data with axis, and the WTW distance were measured with an IOLMaster. The repeatability data of the keratometric value of the VERION System, converted to cross cylinder J 0 and J 45 vector components, were analyzed. The agreement data for keratometry obtained by the VERION System and the differences regarding keratometric data and WTW distance compared to IOLMaster were calculated. RESULTS:The measurements were conducted in 50 eyes of 50 healthy volunteers (median age: 50.32 years, range: 19.34 to 85.3 years). The flattest and the steepest keratometric data, the diopter of astigmatism, the J 0 and J 45 vector components, and WTW distance did not differ significantly between devices (P > .05). Intraclass correlation coefficients (range: 0.863 to 0.994) and Cronbach's alpha values (range: 0.950 to 0.998) were high for all p...

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Section: O R I G I N a L A R T I C L Ementioning

confidence: 99%

Repeatability Data and Agreement of Keratometry With the VERION System Compared to the IOLMaster

Németh¹,

Szalai²,

Hassan³

et al. 2015

J Refract Surg

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“…Our sample had a mean age (± SD) of 70.2 (± 10.7) years, over double that of Ho et al's sample at 34.4 (± 16.1) years; 6 given that ELP is positively correlated with age (ELP increases with age) 4 , this may account for the slight tendency towards overestimation with the SRK/T keratometry-independent ELP estimation method in our study, when compared with that of Ho et al 6 However, this relationship between ELP and age fails to explain the observed discrepancy between the slight underestimation seen when using the Holladay 1 keratometryindependent ELP estimation method in our study, when compared with that of Ho et al 6 While our sample was less myopic, with a mean spherical equivalent of -0.89 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 17 further in the differing axial lengths of the two studies [mean ± SD: current study:…”

Section: -24mentioning

confidence: 94%

Estimation of effective lens position using a method independent of preoperative keratometry readings

Dooley

Charalampidou

Nolan

et al. 2011

Journal of Cataract and Refractive Surgery

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Purpose To evaluate the validity of a keratometry-independent method of estimating effective lens position (ELP) prior to phacoemulsification cataract surgery. Setting Institute of Eye Surgery, Whitfield Clinic, Waterford, Ireland Methods The anterior chamber diameter (AGm) and corneal height (Hm) in 95 eyes (95 patients) scheduled for cataract surgery were measured with a rotating Scheimpflug camera. Hm and AGm were used to estimate the ELP in a keratometry-independent method (using the SRK/T [ELPrs] and Holladay 1 [ELPrh] formulae). Results The mean (± SD) ELP was calculated using traditional (mean ELPs ± SD: 5.59 ± 0.52 mm and mean ELPh ± SD: 5.63 ± 0.42 mm) and keratometry-independent (mean ELPrs ± SD: 5.55 ± 0.42 mm and mean ELPrh ± SD: 5.60 ± 0.36 mm) methods. Agreement between ELPs and ELPrs and between ELPh and ELPrh were represented by Bland Altman plots, with mean differences (± 1.96 SD; range; student's t-test) of 0.06 mm (± 0.65 mm; -0.59 to +0.71 mm; p = 0.08) in association with ELPrs and -0.04 mm (± 0.39 mm; -0.43 to +0.35 mm; p = 0.08) in association with ELPrh. The mean absolute error (MAE) for ELPs versus ELPrs estimation and for ELPh versus ELPrh estimation were 0.242 ± 0.222 mm (range: 0.001 to 1.272mm) and 0.152 ± 0.137 mm (range: 0.001 to 0.814 mm), respectively. ConclusionThis novel study confirms that this keratometry-independent ELP estimation method is comparable to traditional keratometry-dependent methods and may be useful in post-refractive surgery patients. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 Running titleUtilising Scheimpflug imaging to estimate effective lens position in a keratometryindependent fashion. PresentationsThis work has been presented at the Irish College of Ophthalmologist's annual meeting May 2010. FundingNo author received any funding for this study. DeclarationThe authors declare that they have no conflict of interest. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 Keywords Abstract PurposeTo evaluate the validity of a keratometry-independent method of estimating effective lens position (ELP) prior to phacoemulsification cataract surgery. SettingInstitute of Eye Surgery, Whitfield Clinic, Waterford, Ireland MethodsThe ResultsThe mean (± SD) ELP was calculated using traditional (mean ELP s ± SD: 5.59 ± 0.52 mm and mean ELP h ± SD: 5.63 ± 0.42 mm) and keratometry-independent (mean ELP rs ± SD: 5.55 ± 0.42 mm and mean ELP rh ± SD: 5.60 ± 0.36 mm) methods. ConclusionThis novel study confirms that this keratometry-independent ELP estimation method is comparable to traditional keratometry-dependent methods and may be useful in post-refractive surgery patients.

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“…The vergence equation was used to calculate the anterior corneal plane value of the posterior corneal astigmatism as follows [ 16 ]:…”

Section: Aq1mentioning

confidence: 99%

“…Total corneal power was calculated using a thick lens formula based on corneal thickness, anterior corneal radius, and posterior corneal radius [ 16 ].…”

Section: Aq1mentioning

confidence: 99%

Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position

Eom

Ryu

Kim

et al. 2016

Graefes Arch Clin Exp Ophthalmol

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Calculation of intraocular lens power: a review

Cited by 280 publications

References 61 publications

Repeatability Data and Agreement of Keratometry With the VERION System Compared to the IOLMaster

Repeatability Data and Agreement of Keratometry With the VERION System Compared to the IOLMaster

Estimation of effective lens position using a method independent of preoperative keratometry readings

Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position

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