Foundations of Clinical Research: Applications to Practice, 2nd Edition, Leslie Gross Portney, Mary P. Watkins. Prentice Hall, Upper Saddle River, NJ (2000), 752 pages. $60

Purpose To assess the accuracy of 7 intraocular lens (IOL) power formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2) using IOLMaster biometry and optimized lens constants. Setting Public hospital ophthalmology department. Design Retrospective case series. Methods Data from patients having uneventful cataract surgery with Acrysof IQ SN60WF IOL implantation over 5 years were obtained from the biometry and patient charts. Optimized lens constants were calculated for each formula and used to determine the predicted refractive outcome for each patient. This was compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length (AL) as follows: short (≤22.0 mm), medium (>22.0 to Results The study included 3241 patients. The Barrett Universal II formula had the lowest mean absolute prediction error over the entire AL range ( P P P P Conclusion In eyes with an AL longer than 22.0 mm, the Barrett Universal II formula was a more accurate predictor of actual postoperative refraction than the other formulas. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Intraocular lens power formula accuracy: Comparison of 7 formulas.

Protocols for studies of intraocular lens formula accuracy.

Purpose To evaluate the repeatability and reproducibility of a newer swept-source optical biometer and to compare it with a standard partial coherence interferometry (PCI) biometer. Setting Siriraj Hospital, Mahidol University, Bangkok, Thailand. Design Prospective comparative study. Methods One hundred eyes from 100 cataract patients were enrolled in this study. Each patient was measured with 2 optical biometers, a newer swept-source optical biometer (IOLMaster 700) and a standard partial coherence interferometry biometer (IOLMaster 500) by 2 independent operators. The keratometry, axial length (AL), anterior chamber depth, white-to-white corneal diameter, and intraocular lens (IOL) power, calculated by the SRK/T and the Haigis formulas for each device, were recorded. Intraoperator repeatability and interoperator reproducibility of both devices were analyzed using intraclass correlation coefficients (ICCs). Agreement of ocular biometry and IOL power between the 2 devices was evaluated using the Bland-Altman method. Results The repeatability and reproducibility of the swept-source and standard biometers were high for all ocular biometry parameters (ICC, 0.93-1.00). The agreement between the 2 biometers was also high (ICC, 0.92-1.00). The IOL powers obtained from both devices were not distinct. Because of the density of the cataracts, the AL in 5 eyes could be measured only by the swept-source biometer. Conclusions Repeatability and reproducibility of a swept-source optical biometer was excellent and agreement with a standard biometer was very high. Better lens penetration ability and AL measurements were obtained with the swept-source biometer than with the standard biometer. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Clinical comparison of a new swept-source optical coherence tomography–based optical biometer and a time-domain optical coherence tomography–based optical biometer

Ophthalmology is a technologically advancing field with the constant production of new instrumentation. Instruments are usually released on the market with manufacturers claiming performance in various data formats, and this is typically followed by clinical evaluation studies by independent users. Ubiquitous issues in this area include, not least, the variety of methods, both practically and statistically, and the various terminology differences. It is becoming exceedingly difficult for clinicians and researchers to make sense of study results that have used nonstandard methodology in addition to confounding terminology. Terms such as consistency, precision, reliability, accuracy, repeatability, reproducibility, and agreement are just some examples of the many terms that frequently appear in the ophthalmic literature with inconsistent definitions and synonymous usage. The purpose of this editorial is to provide guidance to prospective authors conducting precision (repeatability and reproducibility) studies in terms of basic concepts, terminology, statistical methods, sample size considerations, study design, use of 1 eye or 2 eyes, and worked examples. A number of bodies in the scientific world have devised their own terminology and statistical recommendations, some of which are similar and others markedly different. An example is the International Organization for Standardization (ISO), an independent nongovernmental membership organization and the world's largest developer of voluntary International Standards. ISO has published more than 20 500 International Standards covering almost every industry, including ophthalmology. Examples include standards relating to contact lenses, contact lens care products, intraocular lenses, intraocular implants, spectacle lenses, and ophthalmic instruments. The ISO standardsmight differ markedly even within ophthalmic instruments, an example being differing statistical methods for tonometry and topography. A full list is available on the ISOwebsite (www.iso.org). Such ISO standards are developed by following a formal methodology involving a multi-stakeholder process. They are organic and dynamic, and developments might take years. This editorial is not set to replace any of the ISO standards or suggest that a single approach should be applied to every situation but rather provides a practical commentary on precision that draws

Precision (repeatability and reproducibility) studies and sample-size calculation

Purpose To compare the repeatability and reproducibility of ocular biometry and intraocular lens (IOL) power obtained with a new optical biometer (AL-Scan) and a standard optical biometer (IOLMaster 500). Setting Siriraj Hospital, Mahidol University, Bangkok, Thailand. Design Prospective comparative study. Methods Two independent operators measured eyes with cataract using both biometers. The keratometry values, axial length, anterior chamber depth, white-to-white (WTW) corneal diameter, and IOL power calculated using the Holladay 1 formula obtained with each device were recorded. Intraoperator repeatability and interoperator reproducibility of both devices were analyzed using the intraclass correlation coefficient (ICC). The agreement in ocular biometry and IOL power between the 2 devices was evaluated by the Bland-Altman method. Results The study recruited 137 eyes of 81 patients. The repeatability and reproducibility of both devices were high for all ocular biometry measurements (ICC, 0.87-1.00). Except for the WTW corneal diameter (ICC, 0.44), the agreement between the biometers was also high (ICC, 0.98-0.99). The IOL powers calculated by the Holladay 1 formula were similar between the 2 biometers. Conclusion The new optical biometer provided excellent repeatability and reproducibility for all ocular biometry. Agreement with the standard optical biometer was good except for the WTW corneal diameter. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

https://www.nidek-intl.com/archives/004/201411/55a8a25884bbb.pdf

Comparison of ocular biometry and intraocular lens power using a new biometer and a standard biometer.

To compare the refractive outcomes following cataract surgery using conventional keratometry (K) and total keratometry (TK) for intraocular lens (IOL) calculation in the SRK/T, HofferQ, Haigis, and Holladay 1 and 2, as well as Barrett and Barrett TK Universal II formulas. Sixty eyes of 60 patients from Siriraj Hospital, Thailand, were prospectively enrolled in this comparative study. Eyes were assessed using a swept-source optical biometer (IOLMaster 700; Carl Zeiss Meditec, Jena, Germany). Posterior keratometry, K, TK, central corneal thickness, anterior chamber depth, lens thickness, axial length, and white-to-white corneal diameter were recorded. Emmetropic IOL power was calculated using K and TK in all formulas. Selected IOL power and predicted refractive outcomes were recorded. Postoperative manifest refraction was measured 3 months postoperatively. Mean absolute errors (MAEs), median absolute errors (MedAEs), and percentage of eyes within ± 0.25, ± 0.50, and ± 1.00 D of predicted refraction were calculated for all formulas in both groups. Mean difference between K and TK was 0.03 D (44.56 ± 1.18 vs. 44.59 ± 1.22 D), showing excellent agreement (ICC = 0.99, all p < 0.001). Emmetropic IOL powers in all formulas for both groups were very similar, with a trend toward lower MAEs and MedAEs for TK when compared with K. The Barrett TK Universal II formula demonstrated the lowest MAEs. Proportion of eyes within ± 0.25, ± 0.50, and ± 1.00 D of predicted refraction were slightly higher in the TK group. Conventional K and TK for IOL calculation showed strong agreement with a trend toward better refractive outcomes using TK. The same IOL constant can be used for both K and TK.

Comparison of refractive outcomes using conventional keratometry or total keratometry for IOL power calculation in cataract surgery.

The accuracy of the Holladay 2 (H2) formula is well-documented. This formula requires seven variables to estimate effective lens position (ELP) for the IOL power calculation. The lens thickness (LT) value is one of the required variables. Interestingly, the IOLMaster, which is one of the most commonly used optical biometers, can provide all the required ocular variables except LT value. It has become a pertinent issue to evaluate the accuracy of theH2 formula when it is used without the LT value. The purpose of this study was to evaluate the results when using the H2 formula, without the LT value, and compare such results to those obtained using the Haigis formula and the Hoffer Q formula. The Institutional review board (IRB) gave their approval for the conduct of this prospective comparative study. One hundred and sixty-three eyes of 143 cataract patients from the Ophthalmology Department, Siriraj Hospital, Thailand were recruited. All eyes were measured using the IOLMaster (Carl Zeiss Meditec, Jena, Germany) for keratometry (K), axial length (AL), anterior chamber depth (ACD), and horizontal white-to-white (WTW) corneal diameter. Then, the LT measurement was obtained by A-scan ultrasonography (Quantel Axis-II, Quantel Medical, USA). Every patient underwent uncomplicated phacoemulsification by a single surgeon (NC) with a single technique using a single IOL model. Post-operative refraction was obtained at 3 months. The mean absolute errors (MAEs), median absolute errors (MedAEs) and percentage of the eyes within ±0.25, ±0.50, and ±1.00 D of predicted refraction was calculated for H2 formula both with and without LT input, Haigis, and Hoffer Q formula. The results were also classified into a group of short AL ( 24.5 mm). There was no statistically significant difference in either MAEs or MedAEs of all formulas in all AL groups including the H2 with and without LT. There was a trend toward lower MAEs and MedAEs for H2 in the long AL group. Percentage of the eyes within ±0.25, ±0.50, and ±1.00 D of predicted refraction were similar in all AL groups. The preliminary results of this study showed that the H2 formula performed well even without the LT value. It was comparable to the Haigis and Hoffer Q formulas.

Accuracy of Holladay 2 formula using IOLMaster parameters in the absence of lens thickness value.

Purpose To compare the corneal astigmatism (magnitude and axis location) derived by total corneal power (TCP), automated keratometry, and simulated keratometry. Setting Siriraj Hospital, Mahidol University, Bangkok, Thailand. Design Prospective comparative study. Methods Eyes with previous ocular surgery or abnormalities were excluded. All patients were examined with the ARK 730A autokeratometer and the Galilei analyzer. The steepest and flattest corneal power along with the steepest axis of the TCP, automated keratometry, and simulated keratometry were recorded. Vector analysis (J0 and J45) was calculated. Analysis of variance with Bonferroni correction was performed for multiple comparisons. Outcome measures were the magnitude and axis location of astigmatism. Results One hundred eyes of 100 cataract patients were randomly selected. There was no statistically significant difference in the mean steepest axis between TCP (93.31 ± 68.75 [SD]), automated keratometry (94.24 ± 64.78), and simulated keratometry (92.42 ± 64.30). However, the mean magnitude of astigmatism measured by TCP (1.23 ± 0.75) was significantly higher than that measured by automated keratometry (0.93 ± 0.68) ( P =.01) but not than that measured by simulated keratometry (1.08 ± 0.68) ( P =.43); there was no statistically significant difference in J0 or J45. Twenty two (40%) of 54 eyes with more than 1.00 diopter of TCP astigmatism had more than 10 degrees of axis difference from automated keratometry. Conclusions The magnitude of TCP astigmatism was higher than that of automated keratometry. The axis location was similar. However, there was more than 10 degrees of axis difference between automated keratometry and TCP in patients with high astigmatism. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Comparison of corneal astigmatism and axis location in cataract patients measured by total corneal power, automated keratometry, and simulated keratometry.

Chareenun Chirapapaisan

Papers

Clinical comparison of a new swept-source optical coherence tomography–based optical biometer and a time-domain optical coherence tomography–based optical biometer

Comparison of ocular biometry and intraocular lens power using a new biometer and a standard biometer.

Comparison of refractive outcomes using conventional keratometry or total keratometry for IOL power calculation in cataract surgery.

Accuracy of Holladay 2 formula using IOLMaster parameters in the absence of lens thickness value.

Comparison of corneal astigmatism and axis location in cataract patients measured by total corneal power, automated keratometry, and simulated keratometry.