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Takashi Miyai, Yosai Mori, Ryohei Nejima, Masato Honbo, Kazunori Miyata, Mariko Shirayama, Tomohiko Usui, Shiro Amano; Intraocular Lens Power Calculation after Excimer Laser Phototherapeutic Keratectomy; Comparison of the Calculating Methods without Prior Data to the Excimer Laser Treatment. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6557.
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© ARVO (1962-2015); The Authors (2016-present)
Phototherapeutic keratectomy (PTK) was a treatment to remove corneal opacity locating in the epithelial or subepithelial layer. The calculation of intraocular lens (IOL) after PTK is difficult because the refractive data before PTK could not be obtained due to corneal opacity and irregularity in several cases. The aim of the current study is to retrospectively evaluate the IOL calculating methods for the eyes after PTK by applying those for myopic laser vision correction without prior data to the excimer laser treatment.
Eleven eyes of 11 cases were included in the current study that undertook phacoemulsification and posterior IOL implantation after PTK and were available of the following data; post PTK keratometric data, axial length, anterior chamber depth,and Pentacam Scheimplufg camera data and manifest refractive spherical equivalent 1 month after cataract surgery. From these data, IOL power was calculated with Shammas no history methods with Double-K Holladay 1 fomula (43.86D was used as keratometric value before excimer laser treatment), Haigis-L fomula and Pentacam Equivalent K readings (EKR) with SRK/T fomula (single K). The accuracy of IOL power calculation using these methods was assessed by calculating the mean absolute prediction error (MAE) with standard deviation, and the percentage of eyes with prediction errors within 0.5, 1.0 and larger than 3.0D were also investigated.
The MAEs were 2.38±2.59D in Shammas methods, 2.27±2.62D in Haigis-L and 1.84±2.53D in Pentacam EKR, respectively and there were no statistically significant difference among these methods (paired t-test with Bonferroni correction). The percentages of eyes with prediction errors in Shammas methods, Haigis-L and Pentacam EKR were respectively 9%, 9%, 36% within 0.5D, 18%, 36%, 54% within 1.0D, and 18%, 9%, 18% more than 3.0D. One eye showed more than 8D hyperopic shift in all the methods. Only the case had longer axial length than 27mm.
The application of IOL calculation methods for myopic laser vision correction to post PTK eyes showed inadequate clinical results. Further investigation is necessary to reduce refractive errors of IOL calculation for the eyes after PTK, especially, with long axial length.
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