OCT-based IOL power calculation for eyes with previous myopic and hyperopic laser vision correction

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1 American Academy of Ophthalmology Annual Meeting Orlando, Florida, October 2011 OCT-based IOL power calculation for eyes with previous myopic and hyperopic laser vision correction Weeks Professor of Ophthalmic Research Prof. of Ophthalmology & Biomedical Engineering Casey Eye Institute, Oregon Health & Science University Portland, Oregon Financial Interests: Optovue, Inc.: stock options, patent royalty, grants, speaker honorarium & travel support Carl Zeiss Meditec, Inc.: patent royalty Financial Disclosure I have the following financial interests or relationships to disclose: Dr. D. Huang has a significant financial interest in Optovue, a company that may have a commercial interest in the results of this research and technology. This potential individual conflict of interest has been reviewed and managed by OHSU. 1

2 The problem with keratometry after laser vision correction Measurement Extrapolation Pre-LASIK Post-LASIK The extrapolation no longer works! OCT Net Corneal Power combines anterior & posterior curvature measurements from OCT meridional scans FDA approved October mm 1.5mm 8 meridians D n 0 = 1 Fourier-domain OCT (RTVue, Optovue Inc.) R p R a n 1 = Tang M, Chen A, Li Y, Huang D. Corneal power measurement with optical coherence tomography. J Cataract Refract Surg 2010; 36: n n 2 1 K p Rp n n 1 0 Ka Ra n 2 =

3 OCT Net Corneal Power Is Lower Than Conventional Keratometry in Normal Eyes Bland Altman Plot of Net Corneal power % limits of agreement (1.96 SD) OCT_K Auto_K Mean difference = D (OCT_K + Auto_K) / 2 Tang M, Chen A, Li Y, Huang D. Corneal power measurement with optical coherence tomography. J Cataract Refract Surg 2010; 36: OCT net corneal power is lower than conventional keratometry because: Different reference plane OCT: first principal plane (anterior to cornea) Conventional keratometry: back vertex Conventional keratometry underestimates posterior corneal power in normal eyes Keratometric index of is too high OCT net corneal power should not be used with standard IOL power formula A special IOL power formula is needed 3

4 OCT-based IOL power formula IOL power ECP Position Vergence V 1 V 1 V 2 V 2 Back of IOL V 1 = 1000 / (AL-ELP-CCT-0.15)/n 2 Front of IOL V 1 = V 1 IOL power Back of cornea V 2 = 1000/ [1/V 1 + (ELP+CCT)/n 2 ] Front of cornea V 2 = V 2 ECP ELP = * (ACD-CCT) 0.25 * Pp * AL adj + pacd 8.11 ACD = Anterior chamber depth (mm) n 2 = refractive index of vitreous and aqueous (1.336) CCT = Central corneal thickness (mm) Pp = posterior corneal power AL = axial eye length (mm) ELP = effective lens position (mm) AL adj = sqrt(al) = sqrt(al+0.8*(al-24.4)), pacd = ACD-constant if AL < 24.4mm if AL > 24.4mm CCT = central corneal thickness (mm) = [(A-constant*0.5663) ]/ ECP, effective corneal power = * net corneal power (for myopic laser vision correction) 1 = 1.1 * net corneal power (for hyperopic laser vision correction) 2 1. Tang M, Li Y, Huang D. An intraocular lens power calculation formula based on optical coherence tomography: a pilot study. J Refract Surg 2010; 26: Tang M et al, Intraocular lens power calculation after previous myopic laser vision correction based on corneal power measured by Fourier-domain optical coherence tomography, Journal of Cataract & Refractive Surgery, 2011 in press. Input variables Partial coherence biometer (e.g. IOL-Master, Carl Zeiss Meditec) or ultrasound A-scan 1) ACD anterior chamber depth 2) AL axial eye length 3) Net corneal power 4) Anterior corneal power 5) Posterior corneal power 6) Central corneal thickness Fourier-domain OCT (RTVue, Optovue, Inc.) ; 4

5 Prospective clinical study on post-laser vision correction cataract surgery Clinical Site Myopic LVC (eyes) Hyperopic LVC (eyes) Cullen Eye Institute 12 6 Doheny Eye Institute 10 3 Total 22 9 LVC = laser vision correction Postoperative manifest refraction spherical equivalent was evaluated at 1 month Tang M et al, Intraocular lens power calculation after myopic and hyperopic laser vision correction using optical coherence tomography, Saudi Journal of Ophthalmology, 2011 in press OCT scan #1 Two OCT scans were averaged in the clinical study OCT scan #2 Average over 2 repeat scans Net corneal power Anterior power Posterior corneal power Central Corneal thickness 5

6 Accuracy of OCT-based IOL power calculation compared with Haigis-L after myopic LVC Keratometry Method IOL Formula Prediction Error Range MAE Within 1D IOL-Master Haigis-L ± 0.94 (-2.32, 1.30) % OCT OCT 0.07 ± 0.80 (-1.24, 2.15) % p = n = 22 eyes of 16 subjects. Accuracy of OCT-based IOL power calculation compared with Haigis-L and other methods after myopic LVC at the Doheny Eye Institute Keratometry Method IOL Formula Prediction Error Range MAE Clinical History Hoffer-Q 0.31 ± to * CL Overrefraction Holladay II 0.01 ± to * IOL-Master Haigis-L ± to Orbscan II Holladay II 0.17 ± to OCT OCT-based 0.49 ± to *p<0.05 compared to OCT. N = 10 eyes. The standard IOL formula that provided the smallest MAE was used for all keratometry methods except OCT. OCT-based IOL calculation was significantly better than clinical history and contact lens over-refraction methods. 6

7 Accuracy of OCT-based IOL power calculation compared with Haigis-L after hyperopic LVC Keratometry Method IOL Formula Prediction Error Range MAE Within 1D IOL-Master Haigis-L 0.36 ± 0.72 (-0.61, 1.71) % OCT OCT ± 0.34 (-0.64, 0.44) % p > n = 9 eyes of 8 subjects. Conclusion The predictive accuracy of OCT-based IOL power calculation is equal to or better than current standards for post-lvc eyes. 7

8 Acknowledgements R01 EY Guiding The Treatment of Anterior Eye Diseases with Optical Coherence Tomography Optovue, Inc. Douglas D. Koch, MD Li Wang, MD, Cullens Eye Institute Baylor College of Medicine The formula will be posted on 8

9 David Huang, MD, Ou Tan, Yimin Wang, Maolong Tang, Yan Li, Xinbo Zhang, Yali Jia, Michelle Montalto Janice Van Norman, COT Jason Tokayer, MS Matthew Bald Kathleen S. Torok, MA 9

IOL Power Calculation After Myopic LASIK. Hany Helaly, Lecturer of Ophthalmology, Faculty of Medicine, Alexandria University.

IOL Power Calculation After Myopic LASIK Hany Helaly, Lecturer of Ophthalmology, Faculty of Medicine, Alexandria University. SUPERVISORS Prof. Dr. Mohammad El-Hifnawy Professor of Ophthalmology Faculty