Predictability and accuracy of IOL formulas in high myopia

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1 ARTICLE Predictability and accuracy of IOL formulas in high myopia Mohamed Yasser Sayed Saif, MD 1 ; Mohamed Othman Abdel Khalek, MD 1 ; Ahmed Tamer Sayed Saif, MD 2 ; Passant Sayed Saif, MD 3 ; Sherif Kamel Safina, MSc 4 PURPOSE: To study the predictability and accuracy of different intraocular lens calculation formulas in high myopia patients with axial length (AL) 26. mm or spherical equivalent (SE) refraction of more than 6 diopters, undergoing phacoemulsification. SETTING: Multicenter study in Beni Suef University hospital, Fayoum university hospital and MUST hospital in Egypt. METHODS: This prospective comparative study comprised 21 eyes of cataract patients divided into group A: AL less than 26 mm; and group B: AL more than 26 mm. All eyes had SE refraction of more than 6 diopters. A-scan ultrasound biometry and autokeratometry were performed. The IOL power was calculated using the Haigis, SRK-T, Holladay, Hoffer-Q, Binkhorst and SRK-II formulas. Differences between achieved postoperative refraction and target refraction was calculated using different formulas. P value <. was considered statistically significant. RESULTS: Mean age was 4. ± 8. years and 4. ± 11. years for group A and B, respectively. Mean AL was ± 2.42 mm. The average k reading was ± 1.82 and ± 2.74; pre-se was 9.78 ± 3.24 D and 12. ± 4.21 D (from. to D); mean were Haigis.46 ±.8 D and +.12 ±.73 D, Holladay.34 ±.83 D and.66 ±.77 D, SRK/T.23 ±.6 D and.24 ±.8 D, Hoffer-Q.1 ±.76 D and.69 ±.74 D, Binkhorst.7 ±.78 D and.69 ±.73, and SRK-II.4 ±.74 D and.46 ± 1.6 D. CONCLUSION: The Haigis formula showed the best result in myopic eyes with axial length of more than 26 mm, while SRK-II was best in axial lengths of less than 26 mm. J Emmetropia 16; 1: Pathologic myopia is classified as a high, progressive myopic refractive error that generally presents in early in childhood. In pathologic myopia, the spherical equivalent (SE) is more than 6. diopters, or axial length (AL) more than 26. mm 1. Patients with high axial myopia frequently present lens opacities and develop cataracts at an earlier age than emmetropes 2. Intra-Ocular Lens (IOL) power calculation in high myopes is challenging for cataract surgeons 3. Submitted: 9//1 Revised: 12/3/1 Accepted: 2/17/16 1 Beni-Suef University, Beni-Suef, Egypt. 2 Fayoum University, Fayoum, Egypt. 3 Misr University for Science and Technology, October, Egypt. 4 Embaba Hospital, Giza, Egypt. Financial Disclosure: The authors have no commercial or proprietary interest in the products mentioned herein. Corresponding Author: Mohamed Yasser Sayed Saif Beni-Suef University Salah Salem st, Beni Suef, Egypt ysaif@med.bsu.edu.eg The two main problems encountered are correct measurement of the AL to be used in calculations, due to posterior staphyloma, and lack of accuracy of available intraocular lens calculation formulas for cases of high myopia 4,. The aim of this study is compare and evaluate the accuracy of different intraocular lens calculation formulas in patients with high myopia. METHODS This was a prospective comparative study approved by the board of the Beni Suef ophthalmology and the research ethics committee. The study adhered to the tenets of the Declaration of Helsinki. Patients This study comprised 21 eyes of patients scheduled to undergo phacoemulsification in the Beni Suef University hospital, Fayoum university hospital and MUST hospital who presented with cataracts, AL 26 mm or refraction SE of over 6 diopters. 16 SECOIR Sociedad Española de Cirugía Ocular Implanto-Refractiva ISSN:

2 18 ASSESSMENT OF IOL FORMULAS IN HIGH MYOPIA Patients with refraction SE less than 6 D or AL less than 26 mm, history of previous ocular surgery, posterior segment disorders, eventful cataract surgery, keratoconus, endothelial dystrophy, and glaucoma were excluded. Procedures Preoperative examination included best corrected visual acuity, slit lamp biomicroscopy, indirect ophthalmoscopy, and Goldman applanation tonometry. In all cases, AL was measured using A-scan ultrasound biometry (E-Z SCAN AB Ophthalmic ultrasound scanner; Sonomed Escalon, Lake Success, NY, USA). Corneal power (k) was measured using autokeratometry (Topcon autokeratometer KR 89; Topcon Medical Systems, Inc. Paramus, NJ, USA). Preoperative IOL power calculations were performed using Haigis, SRK-T, Holladay, Hoffer-Q, Binkhorst and SRK-II formulas in all patients. The IOL formula that provided a lens power with the foregoing postoperative refraction was selected. Phacoemulsification was performed and AcrySof foldable IOL (Alcon, Fort Worth, TX, USA) was implanted within the capsular bag. Patients were followed up for 6 weeks postoperatively at the following intervals: 1 week, 3 weeks, and 6 weeks. At each visit, the patient underwent a complete examination of the anterior segment using slit lamp, cycloplegic refraction with retinoscopy, and auto refractometry. The following calculations were used: spherical equivalent (SE) = sphere + half the cylinder; error formula = post-operative SE predicted formula error. Statistical analysis At the end of this study, data were statistically described in terms of mean ± standard deviation (SD), median, minimum, maximum, correlation and percentages. Anova was used to compare numerical variables between the study groups. All statistical calculations were done using IBM SPSS Statistics 21 (Statistical Package for the Social Science). P-values of less than. were considered significant. RESULTS In total, 21 eyes of myopic patients with a mean age of ±.1711 years were included, 12 from men (8.14%) and 9 from women (41.86%). Patients were divided into 2 groups: A) axial length less than 26. mm; B) axial length more than 26.1 mm. The mean age was 4. ± 8. years for group A and 4. ± 11. years for group B, with no statistical significance between both groups. The age range was from 32 to 7 years; there were 1 (6.98%) women in group A and 7 (34.88%) in group B, as shown in Table 1. Table 1. Pre and postoperative results. Group A n = Group B n = 16 Group Mean Median SD Maximum Minimum Age (years) A B Pre-VA A..... B Post-VA A B Pre-IOP A B Post-IOP A B Average K A B Lens thickness A B ACD A B Vitreous length A B Power A B Pre-SE A B Post-SE A B ACD, anterior chamber depth; IOP, intraocular pressure; SD, standard deviation; SE, spherical equivalent; VA, visual acuity.

3 ASSESSMENT OF IOL FORMULAS IN HIGH MYOPIA 19 The mean preoperative VA in both group was.2 ±.1, which improved to.7 in group A and.8 in group B, as shown in Table 1. The mean preoperative IOP was 17. ± 3. mmhg and 16. ± 2. mmhg in both groups, which decreased to 14. ± 3. mmhg and 14. ± 2. mmhg, respectively, as shown in Table 1. The mean axial length was ± 2. mm, with a range of mm to 33.2 mm. The mean K reading was ± 1.82 D and ± 2.74 D in groups A and B, with a range of 34.7 D to D. The SE refraction was 9.78 ± 3.24 D for group A, and 12. ± 4.21 D for group B, with a range of. to D. The postoperative mean SE was.98 and.4, respectively, with a range of +3. to 4.7, as shown in Table 1. The error of each formula was calculated as the difference between the target or desired postoperative refraction and the actual or achieved refraction. The statistical differences between different formulas is shown in Table 2. As regards the mean error of deviation, Hoffer-Q formula in group A is the best, while the Haigis formula is the best in group B, as shown in Table 2. There was no statistically significant difference between both groups as regards the Haigis formula, while the SRK-T, Holladay, Hoffer-Q, Binkhorst and SRK-II formulas showed a statistically significance between both groups, as shown in Tables 3 and 4. Table 2. Statistical analysis of in the formulas. Group A n = Group B n = 16 Group Mean Median SD Maximum Minimum Haigis A B SRK T A B SRKII A B Holladay A B Hoffer Q A B Binkhorst A B SD, standard deviation. Table 3. Analysis of differences between groups for all formulas. Mean SD Maximum Minimum P value Haigis SRK-T * SRK-II * Holladay * Hoffer Q * Binkhorst * SD, standard deviation; *Significant differences. Table 4. Results of comparison between both groups for all formulas using other statistical tests. Haigis SRK-T SRK-II Holladay Hoffer Q Binkhorst Mann-Whitney U Wilcoxon W Z Asymp. Sig. (2-tailed).683

4 ASSESSMENT OF IOL FORMULAS IN HIGH MYOPIA > < > < Haigis SRK-T SRK-II Holladay Figure 1. The postoperative error in group A with axial length less than 26 mm. (y = number of eyes). Haigis SRK-T SRK-II Holladay Figure 2. The postoperative error in group B with axial length more than 26 mm (y = number of eyes). In Group A: SRK-II showed the best result, followed by the Holladay, SRK-T and Hoffer-Q, and Haigis and Binkhorst formulas. The Haigis formula showed more tendancy toward myopic shift, as shown in Figure 1. For Group B: the Haigis formula showed the most accurate results, followed by the SRK-T, Holladay, Binkhorst and Hoffer-Q formulas. The SRK-II showed myopic shift and the poorest results in this group, as shown in Figure 2. DISCUSSION This study is a prospective comparative analysis of 21 eyes presenting with cataracts, with AL 26 mm or SE of more than 6 diopters. The mean postoperative refractive SE when implanting a plus power IOLs was.3 ±.1 D (p <.1). A Pentacam examination was performed in patients with a K reading above 46, revealing no keratoconus or suspected keratoconus. Patients with short axial lens showed an SE refraction ranging from 6.63 to D. However, the Haigis formula showed the least deviation in group B (axial length of over 26 mm), while SRK-T showed the least deviation in group A (axial length of less than 26 mm). In, Raouf et al. 6 studied 3 eyes to compare 3 IOL calculation formulas in high myopia, and found no statically significant difference between them. In this study, the SRK/T formula caused the lowest mean error (.17D), and the Haigis formula showed a higher mean error (.21D), with post-operative hyperopic shift. The foregoing authors found the SRK/T formula to be the most accurate in high myopia compared with Haigis, and that the Haigis formula tended to cause a hyperopia shift. Our study, meanwhile, shows the Haigis formula to be the most accurate, with minimal post-operative myopia shift. These contrasting results may be due to the grouping criteria: Raouf et al. divides eyes into 3 subgroups according to AL, with fewer cases and a difference in A-scan biometry and keratometry. Saif et al. in 7, analyzed 3 formulas, SRK/T, SRK-II and Holliday s, in IOL calculations, and found the SRK/T formula to be better in high myopia. They did not evaluate the Haigis, Hoffer-Q or Binkhorst formulas, and the results were based on spherical error. Jia Wang et al. 8, studied eyes divided into 3 groups according to AL (Group 1 = 33 eyes, Group 2 = 92 eyes, and Group 3 = 7 eyes). The Haigis had a significantly lower mean error in all patients compared with the other formulas (<.). In Groups 1 to 3, the mean error calculated by the Haigis was either significantly lower or comparable to that calculated by the other formulas. Compared with other formulas using IOL Master biometric data, the Haigis formula yielded superior refractive results in eyes with various AL. This is consistent with our findings, in which the Haigis formula was the most accurate in higher axial length, and the least accurate in short axial length. Ganesh et al. in 4 9, compared the accuracy of IOL power calculation in high myopia using the Haigis and SRK II formulas, and found the Haigis formula to be very effective in eyes with AL ranging from 2 to 32 mm. However, a comparison of the SRK II and Haigis formulas did not clarify the accuracy of the Haigis formula, as all recent studies have shown that the SRK II formula does not accurately predict IOL power in high axial myopia patients. Roessler et al. showed the Haigis to be superior to the Holladay 1 and SRK/T formulas in predicting postoperative refractive outcomes in 37 eyes with AL > 26. mm. Terzi et al. 11 studied extremely high myopic eyes and extremely high hyperopic eyes, finding that the Haigis performed better than the Holladay 2, Hoffer Q and SRK/T formulas in 44 eyes with AL > 26 mm undergoing myopic refractive lens exchange. Bang et al. 12 concluded that the Haigis formula was the most accurate in predicting postoperative refractive error compared with the Holladay 1, Holladay 2, Hoffer Q and SRK-T formulas in 3 eyes with AL > 27 mm.

5 ASSESSMENT OF IOL FORMULAS IN HIGH MYOPIA 21 In conclusion, the Haigis formula showed the best result in high myopic axial cataractus eyes with minimal shift to myopia, while the SRK-II formula show the best results for short axial length. REFERENCES 1. Friedman NJ, Kaiser PK. Essentials of Ophthalmology. Philadelphia, PA: Elsevier Inc; 7: Kaufman BJ, Sugar J. Discrete nuclear sclerosis in young patients with myopia. Arch Ophthalmol. 1996; 114: Olsen T, Corydon L, Gimbel H. Intraocular lens power calculation with an improved anterior chamber depth prediction algorithm. J Cataract Refract Surg. 199; 21: Hafez A. Accuracy of A and B modes in myopic biometry. Bull Ophthalmol Soc Egypt, 4; 97: Ghanem AA, El-Sayed HM. Accuracy of intraocular lens power calculation in high myopia. Oman Journal of Ophthalmology ; 3: El-Nafees R, Moawad A, Kishk H, Gaafar W. Intra-ocular lens power calculation in patients with high axial myopia before cataract surgery. Saudi J Ophthalmol. ; 24: Saif SEH, Ahmed MH, Amer SK, Saif MYS. Comparison between IOL Formulae. Bull Ophthalmol Soc Egypt. ; 98: Wang JK, Shang SW. Optical biometry intraocular lens power calculation using different formulas in patients with different axial lengths. Int J Ophthalmol, 13; 6: Eom Y, Kang S, Song JS, Kim YY, Kim HM. Comparison of Hoffer Q and Haigis Formulae for Intraocular Lens Power Calculation According to the Anterior Chamber Depth in Short Eyes. American Journal of Ophthalmology. 14; 17: e2.. Roessler GF, Dietlein TS, Plange N, et al. Accuracy of intraocular lens power calculation using partial coherence interferometry in patients with high myopia. Ophthalmic Physiol Opt. 12; 32: Terzi E, Wang L, Kohnen T. Accuracy of modern intraocular lens power calculation formulas in refractive lens exchange for high myopia and high hyperopia. J Cataract Refract Surg. 9; 3: Bang S, Edell E, Yu Q, Pratzer K, Stark W. Accuracy of intraocular lens calculations using the IOL Master in eyes with long axial length and a comparison of various formulas. Ophthalmology. 11; 118:3-6. First author: Mohamed Yasser Sayed Saif, MD Beni-Suef University. Beni Suef, Egypt.