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M. Prevor, G. Zaidman; Do phakic anterior chamber intraocular lenses (PAC–IOL) affect ocular biometry and IOL power calculations? . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2866.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine if a phakic anterior chamber intraocular lens alters the biometric measurement of axial length (AL), thereby affecting calculation of IOL power. Methods: We report a case of cataract formation in a patient with a PAC–IOL. Using a 2–staged surgical approach, we first explanted the PAC–IOL and 8 weeks later performed uncomplicated phacoemulsification. We measured the axial length prior to and after the removal of the PAC–IOL. IOL power calculations (using the SRK formula) were compared using each measurement of AL. We also performed a retrospective analysis of 9 similar patients in the literature looking at axial length measurement prior to PAC–IOL placement and after PAC–IOL placement. Results: In the case study, AL measured through the PAC–IOL was 22.18 mm. AL measured after explantation of the PAC–IOL was 22.84 mm. The first AL gave an IOL power of 23.0 diopters for a posterior chamber IOL. The second AL gave an IOL power of 21.9 diopters. This 1 diopter difference is a clinically important difference. The retrospective analysis of 9 similar patients showed that mean axial length was 31.5 mm when measured through the crystalline lens, but was only 30.29 mm when measured through the PAC–IOL. Using a paired samples t–test, this difference of >1mm is statistically significant (t=5.86, p<0.0005). Conclusions: PAC–IOLs systematically affect biometric measurement of axial length. This can lead to clinically significant errors in IOL power calculation in eyes that subsequently develop cataracts and require extraction. To correct for this systematic error, surgeons should preserve a database of patient ALs measured prior to PAC–IOL surgery. If this data is not available, a 2–staged surgical approach may be needed to obtain the correct IOL power.
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