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Chúng tôi biết điều này đúng với kính áp tròng mềm-4.0-D mềm liên lạc với ống kính cung cấp D -4 quyền lực trên một giác mạc bằng phẳng hoặc dốc, mặc dù độ cong của ống kính là khác nhau. Lý do là cả hai bề mặt thay đổi tương ứng. Một khả năng khác là vị trí trục của ICL là lớn hơn nhiều so với dự đoán preoperatively (nó phải sâu hơn so với dự đoán sẽ làm giảm sức mạnh của ống kính có hiệu lực) | Chapter 4 net change in the total power should be zero. We know this is true for soft contact lenses where a -4.0-D soft contact lens provides the same -4 D of power on a flat or steep cornea even though the overall curvature of the lens is different. The reason is that both surfaces change proportionately. Another possibility is that the axial position of the ICL is much greater than that predicted preoperatively it must be deeper than predicted to reduce the effective power of the lens . This possibility cannot explain a 15 difference because the axial position would need to be more than 2 mm deeper to explain a 15 error. Postoperative A-scans and high-resolution B-scans have shown the exact position of the lens to be close to the anatomic anterior chamber depth proving that the axial position of the lens is not the explanation. In any case back-calculated constants for the ICLs using the phakic IOL formula above result in lens constant ELPs that are 5.4713.86 mm even though the average measured ELP is 3.6 mm. In the data sets that we have analyzed when the optimized back-calculated ELP is used the mean absolute error is approximately 0.67 D indicating that 50 of the cases are within 0.67 D. This value is higher than the 0.50 D typically found with standard IOL calculations following cataract surgery. The ICLs should be better than ACLs since the exact location of the lens can be predicted from the anatomic anterior chamber depth preoperatively. This difference is puzzling not only because of the better prediction of the ELP but also because any errors in the measurement of the axial length are irrelevant because it is not used in the phakic IOL formula. 4.7 Bioptics LASIK and ACL or ICL When patients have greater than 20 D of myopia LASIK and ICLs have been used to achieve these large corrections. Although Intraocular Lens Power Calculations 37 only a few cases have been performed by a few surgeons the results have been remarkably good. The surgeon performs the
