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Journal Français d'Ophtalmologie
Volume 38, n° 8
pages 717-722 (octobre 2015)
Doi : 10.1016/j.jfo.2015.03.006
Received : 14 January 2015 ;  accepted : 5 Mars 2015
Comparison of different formulas for intraocular lens power calculation using a new optical biometer
Comparaison de formules différentes pour le calcul de la puissance des implants intraoculaires par un nouveau biomètre optique
 

F. Kaya a, I. Kocak b, A. Aydin b, , H. Baybora a, Y. Karabela b
a Service d’ophtalmologie, hôpital de Nisa, Fatih Caddesi, Yenibosna, Istanbul, Turkey 
b Clinique universitaire d’ophtalmologie, faculté de médecine, université d’Istanbul Medipol, Ataturk Bulvari No. 27 Unkapani 34083 Fatih, Istanbul, Turkey 

Corresponding author. Özel Nisa Hastanesi, Göz Hastalıkları Servisi, FatihCaddesi, Yenibosna, Turkey.
Summary
Purpose

To evaluate and compare the predictability of different formulas for intraocular lens (IOL) power calculation using a new optical biometer (Aladdin).

Methods

This prospective cross-sectional study included 70 eyes of 70 patients who underwent uneventful phacoemulsification with IOL implantation. Preoperative IOL power calculations were performed using the Aladdin optical biometer. Postoperative actual refractive errors and errors predicted by the SRK/T, SRK II, Holladay 1, Hoffer Q and Haigis formulas were analyzed. The mean estimation error (EE), mean absolute estimation error (AEE) and the percentage of eyes within ±0.50 and ±1.00D of the target refraction for each of five formulas were calculated and compared. This analysis was also repeated in three groups formed based on axial length (AL) (group 1: <22.5mm, group 2: 22.5–24mm, group 3: >24mm).

Results

In the overall study group, the smallest mean AEE was provided by the Holladay 1 formula, however there was no statistically significant difference in the mean AEE's predicted by the five formulas (P =0.34). The highest percentage of eyes within ±0.50 and ±1.00D of the target refraction was also found by using Holladay 1 (71% and 97%). SRK/T provided smallest mean AEE for groups 1 (n =13) and 3 (n =16). In group 2 (n =41), the smallest mean AEE was obtained using Holladay 1.

Conclusions

Based on the Aladdin biometric data used in our study, better results can be obtained using SRK/T formula in eyes with short or long AL. The Holladay 1 formula may be preferred in eyes with moderate AL.

The full text of this article is available in PDF format.
Résumé
But

Évaluer et comparer la prévisibilité des formules différentes pour le calcul de la puissance des lentilles intraoculaires (LIO) en utilisant un nouveau biomètre optique.

Méthode

Soixante-dix yeux de 70 patients qui ont subi une phacoémulsification avec LIO implantation sans incident ont été inclus dans cette étude prospective transversale. Les calculs préopératoires de la puissance de LIO ont été effectués avec le biomètre optique : Aladdin. Les erreurs réelles postopératoires de réfraction et les erreurs prédites par les formules SRK/T, SRK II, Holladay 1, Hoffer Q et Haigis ont été analysées. L’erreur moyenne d’estimation (EE), l’erreur absolue moyenne d’estimation(EAE) et le pourcentage des yeux au sein de ±0,50 et ±1,00D de la réfraction cible pour chacune des cinq formules ont été calculés et comparés. Cette analyse a été répétée également en trois groupes constitués selon la longueur axiale (LA) (groupe 1 : < 22,5mm, groupe 2 : 22,5–24mm, groupe 3 : >24mm).

Résultats

Dans le groupe global d’étude, la plus petite EAE moyenne a été fournie par la formule Holladay 1, cependant il n’y avait pas de différence statistiquement significative dans les EAE moyennes estimées par les cinq formules (p =0,34). Le pourcentage le plus élevé des yeux au sein de ±0,50 et ±1,00D de la réfraction cible a également été trouvé en utilisant Holladay 1 (71 % et 97 %). SRK/T a fourni la plus petite EAE moyenne pour les groupes 1 et 3. Dans le groupe 2, la plus petit EAE moyenne a été obtenue en utilisant Holladay 1.

Conclusion

Selon les données biométriques d’Aladdin utilisées dans notre étude, de meilleurs résultats peuvent être obtenus en utilisant la formule de SRK/T dans les yeux avec une LA courte ou longue. La formule de Holladay 1 peut être préférée dans les yeux avec une LA modérée.

The full text of this article is available in PDF format.

Keywords : Aladdin optical biometer, Axial length, IOL power, Calculation formula

Mots clés : Biomètre optique d’Aladdin, Longueur axiale, Puissance de LIO, Formule de calcul


Introduction

The postoperative refractive expectations of patients having cataract surgery have been increased due to the advances in technology. Therefore, accurate intraocular lens (IOL) power calculation is very important to attain the postoperative target refraction. Accuracy and consistency of postoperative refractive outcomes require ongoing effort. IOL power is calculated using preoperatively measured keratometric (K) value, axial length (AL), A constant of IOL [1, 2, 3]. IOL power is estimated by means of several formulas [1, 2, 3]. Latest formulas show similar refractive outcomes with average AL [3]. However, in eyes with long or short AL, the accuracy of these formulas may vary and deviate from postoperative refractive target [4, 5]. Formulas such as Holladay 1, Hoffer Q, SRK/T, SRK II calculate the estimated IOL power using AL, K value, and a constant as variables [6]. Latest formulas such as Haigis use additionally the anterior chamber depth (ACD) [7].

It has been shown that applanation and immersion ultrasound biometry may lead to erroneous measurements of AL, depending on the globe compression and off-axis evaluation [2]. With the introduction of optical biometry, IOL power calculation problems caused by the AL measurement errors have been greatly reduced [3]. The Aladdin is a new optical biometry device released in 2012, which produces valid and reproducible results [8].

The aim of this study is to evaluate and compare the predictability and accuracy of five IOL power calculation formulas (SRK/T, SRK II, Holladay 1, Hoffer Q and Haigis) for IOL power calculation using the Aladdin optical biometer.

Materials and methods

Subjects enrolled in this prospective cross-sectional study were patients with cataract who underwent uneventful phacoemulsification with IOL implantation at Ophthalmology Department of Nisa Hospital, Istanbul, Turkey between August 15 and October 30, 2014. The study was explained to each patient and written informed consent was obtained. The study project was approved by Institutional Ethical Board of Istanbul Medipol University. All research and data collection adhered to the tenets of the Declaration of Helsinki.

Patients with good quality Aladdin biometry measurements and best-corrected visual acuities (BCVA) greater than 20/40 after cataract surgery were included in the study. Exclusion criteria were history of traumatic or uveitic cataracts, previous intraocular or corneal surgery (e.g. refractive surgery or glaucoma surgery), intraoperative complications (e.g. anterior or posterior capsule ruptures, vitreous loss or zonule dehiscence), or postoperative complications (e.g. tilted or decentrated IOL).

Preoperatively all patients had a complete examination including manifest refraction, BCVA testing, intraocular pressure (IOP) measurements with applanation tonometry, slit lamp, and dilated fundus examinations. Each patient underwent biometry measurement on Aladdin optical biometer (Topcon, Tokyo, Japan) by the same examiner. After carefully positioning of patient, Aladdin biometer was focused as determined by a clear view of anterior segment and the display of a ‘green eye’ quality control image. Six AL measurements, three K values and three ACD readings were obtained. IOL power was calculated using the SRK/T, SRK II, Holladay 1, Hoffer Q and Haigis formulas. The goal in IOL power selection was a value that would provide a postoperative refraction nearest to plano, staying on the side of myopia. The power selection of implanted IOLs was determined based on the SRK/T formula.

All phacoemulsification and IOL implantations were performed under topical anesthesia by one of two experienced surgeons (F.K. and I.K.). A standard phacoemulsification was performed through a 2.8mm temporal clear corneal incision. The monoblock foldable hydrophobic acrylic IOL (Focus force F260, A-constant of 118.4, Zarracom, Turkey) was inserted into the capsular bag using an injector system.

By the end of first postoperative month, ophthalmological examination was carried out for all patients. Postoperative objective refractive error was measured by using Topcon KR 8800 autorefractometer (Topcon, Tokyo, Japan). Uncorrected visual acuity (UCVA) and BCVA were also evaluated.

The estimation error (EE) was defined as the difference between the postoperative objective refractive error (spherical equivalent) and the preoperative refractive error predicted by the Aladdin optical biometer using different formulas(SRK/T, SRT II, Holladay 1, Haigis and Hoffer Q) for the power of IOL implanted. The absolute estimation error (AEE) was defined as the absolute value of the EE. For example, if postoperative objective error is −0.50 D and preoperative predicted error is −0.12 D, the EE is calculated as −0.50–(−0.12)=−0.38 D. The AEE (the absolute value of EE) is [−0.38]=0.38 D.

The Friedman Anova (comparing multiple related samples) Test was used to evaluate differences in mean EE and mean AEE between five formulas in entire study group. This assessment was repeated also in three groups formed based on the axial length (AL) (group 1:<22.5mm, group 2: 22.5–24mm, group 3:>24mm). Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS) version 12.0 (SPSS Inc, Chicago, Illinois, USA). P values<0.05 were considered to be statistically significant.

Results

Seventy eyes of 70 patients were included in the study. The mean patient age was 68.4±11.6 years (range, 26–95 years). The mean K value was 43.66±1.63D (range, 40.16–46.64D). The mean AL was 23.3±1.06mm (range, 20.69–26.59mm). The mean preoperative corneal astigmatism was -0.73±0.65 D (range, 0–(–1.88) D). Characteristics of patients are shown in Table 1.

The results of overall study group concerning the EE, AEE, and percentages of eyes within target refraction for five formulas are shown in Table 2. In overall study group, the smallest mean AEE was obtained by using Holladay 1 formula (0.39D±0.32), however there was no statistically significant difference in the mean AEEs predicted by the five formulas (P =0.34). Regarding the comparison of mean EEs, mean EE predicted by SRK II was significantly greater than other formulas (P <0.001). If SRK II is excluded, there is no significant difference between the mean EEs of other formulas (P =0.15). The highest percentage of eyes within±0.50 and±1.00 D of target refraction was also found by using Holladay 1 (71% and 97%).

In group 1 (n =13), mean AL was 22.02±0.60mm (range, 20.69–22.48mm). The results of this group are shown in Table 3. The smallest mean AEE was calculated by using SRK/T (0.50 D±0.46) comparing with other four formulas, however the difference was not statistically significant (P =0.68). The smallest EE was obtained by using SRK II formula (P <0.05). The SRK/T and Holladay 1 predicted more eyes with EE within±0.50 and±1.00D of target refraction compared to other formulas (61% and 92%).

In group 2 (n =41), mean AL was 23.24±0.37mm (range, 22.67–23.95mm). The results of this group are presented in Table 4. The smallest mean AEE was obtained by using Holladay 1 (0.38±0.27). However, no significant difference of mean AEE was found between five formulas (P =0.27). There was also no significant difference of mean EE between five formulas (P =0.97). The Holladay 1 formula predicted more eyes with EE within ±0.50 and ±1.00D of target refraction when compared to other formulas (78% and 97%).

In group 3 (n =16) mean AL was 24.77±0.89mm (range, 24.01–26.59mm). The results of this group are presented in Table 5. Although there was no significant difference of mean AEE between five formulas (P =0.13), the smallest mean AEE was calculated by using SRK/T (0.28D±0.19). Regarding the comparison of mean EEs, mean EE predicted by SRK II was significantly greater than other formulas (P <0.05). If SRK II is excluded, there is no significant difference between the mean EEs of other formulas (P =0.17). The highest percentage of eyes within ±0.50 and±1.00D of target refraction was also found by using SRK/T (87% and 100%).

Discussion

The Aladdin optical biometer is one of the most recently released optical biometry device that is able to assess six biometry parameters simultaneously (AL, kerotmetry, corneal topography, ACD, white to white corneal diameter, and pupillometry). AL measurement is obtained using an optical low coherence interferometer with 820nm superluminescent diode. ACD is measured using a blue light emitting diode (LED) horizontal slit projection. Keratometric values are obtained through a 24 placido disk ring reflection. In a recent study evaluating the validity and repeatability of the Aladdin ocular biometer [8], it has been reported that the Aladdin produces valid and reproducible results that are comparable with those provided by the IOLMaster 500. Similarly in our study, satisfactory refractive results have been obtained with Aladdin optical biometer.

IOL power estimation results have varied, depending on the formula used for optical biometry analyses [3]. In a study comparing optical biometry to ultrasound biometry, no significant difference was found between refractive outcomes of the Holladay1, Olsen and SRK/T formulas, using optical biometry [9]. In another study evaluating refractive results of IOLMaster biometry, Eleftheriadis [10] has reported that Holladay 1 formula had better results than the SRK/T, SRK II and Hoffer Q, in eyes with an average AL of 23.36mm. In a more recent study evaluating refractive results of IOLMaster in a large series of 8108 eyes, there were no significant differences in AEEs of different formulas (Hoffer Q, Holladay 1, and SRK/T) for ALs from 21.50 to 23.50mm [11]. In our entire study group, Holladay 1 provided the smallest mean AEE, however the difference was not statistically significant. This result may be due to the fact that the largest group of our study (n =41) consisted of average sized eyes (AL: 22.5–24mm).

Some of previous studies of IOLMaster biometry have shown that the accuracy of the IOL power calculation in eyes with short AL was better with Hoffer Q [12, 13], or Haigis formulas [14]. Eom et al. [15] have reported that Hoffer Q and Haigis had similar success in 75 eyes with AL shorter than 22mm. Nevertheless, the Haigis formula was significantly more accurate than Hoffer Q in patients with an ACD less than 2.40mm [15]. In the study of Aristodemou et al. [11], it has been reported that more predictable outcomes were achievable using the Hoffer Q formula for eyes with AL shorter than 21.50mm. In our study, in short eyes (AL<22.5mm, n =13) the smallest mean AEE was calculated by using SRK/T (0.50 D±0.46) comparing with other four formulas, however the difference was not statistically significant.

There are several studies assessing different IOL power calculation formulas in eyes with long AL using optical biometry [11, 16, 17, 18]. Aristodemou et al. have found that SRK/T formula was better than the Holladay 1 and Hoffer Q for eyes with ALs of 27mm or longer [11]. Roessler et al. have reported that the Haigis had better outcomes than the Holladay 1 and SRK/T formulas for eyes with AL longer than 26.5mm [16]. In another study evaluating the accuracy of IOL power calculation formulas in high myopic eyes using the IOLMaster, it has been found that the Haigis performed better than the Hoffer Q, Holladay 1, SRK/T formulas [17]. In the study of Wang et al, the lowest AEE was obtained using the IOLMaster data in the Haigis formula in 68 eyes with an AL longer than 25mm [18]. In our study, although there was no significant difference of mean AEE between five formulas, the smallest mean AEE was calculated by using SRK/T (0.28D±0.19) in eyes with long AL.

In conclusion, the Aladdin optical biometer produces satisfactory refractive results. Although the difference of mean AEE between five formulas was not statistically significant, Holladay 1 formula can be preferred in eyes with moderate AL, based on the Aladdin biometric data used in our study. Better results can be obtained using SRK/T formula in eyes with short or long AL. However, this conclusion should be interpreted with caution due to the small number of study patients with short or long AL.

Disclosure of interest

The authors declare that they have no conflict of interest concerning this article.

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