Impact Of Phakic Intraocular Lens On Preoperative Biometric Measurements Using Swept-Source Optical Coherence Tomography Biometry: A Retrospective Cohort Study

Our study intends to evaluate the impact of anterior chamber (AC) phakic intraocular lens (pIOL) on Swept-Source optical coherence tomography (SS-OCT) biometric measurements and intraocular lens (IOL) power calculation for cataract surgery with third and fourth generation formulas (SRK/T, Haigis (H), Barrett Universal II (B), Hoffer QTS (HQ), Cooke K6 (C), EVO, Kane (K), and Pearl DGS).

Refractive Surgery Unit of the Ophthalmology Department of Centro Hospitalar Universitário de Santo António, a tertiary hospital in Oporto, Portugal.  

We conducted a retrospective analysis of patients with previous AC pIOL implantation. All patients underwent SS-OCT biometry (IOL Master 700, Zeiss Corp). We analyzed the accuracy of automatic AC depth and lens thickness (LT) segmentation and its impact on IOL power calculation. Eyes with inaccurate measurements comprised the inaccurate (I) group, where ACD and LT were manually corrected using ImageJ (National Institutes of Health) software. Preoperative IOL power was calculated using third and fourth formulas for both corrected/uncorrected measurements. Target spherical equivalent (SE) and mean prediction error (PE, difference between subjective postoperative SE and target SE) and standard deviation were calculated for both measurements.  

We included 73 eyes of 54 patients. The anterior surface of the crystalline lens was misidentified in 18 (24.7%) eyes. ACD was underestimated (mean difference (MD) -0.85±0.33 mm, p<0.001) and LT was overestimated (0.81±0.25, p<0.001). Target SE with the corrected measurements was significantly different only for H (-0.14±0.14, p=0.002) and B (-0.04±0.05, p=0.019) formulas, and K formula showed the lowest difference (0.01±0.09 D, p=0.791). Mean PE for corrected and uncorrected measurements was significantly different in H (0.15±0.14, p=0.002) and B (0.04±0.05, p=0.019) formulas. C formula showed the lowest PE for both uncorrected (-0.03±0.38 D) and corrected (0.01±0.35 D) measurements.  

SS-OCT biometry misidentifies the anterior surface of the crystalline lens in a significant proportion of patients with previous anterior chamber pIOL implantation. It results in a significant IOL power calculation error in the H and B formulas, underestimating lens power. The C formula seems to be more predictable in misidentified cases and may provide additional accuracy in IOL power calculation of these patients. SRK/T formula is not affected by ACD or LT and may be valuable in these cases. Manual proofing of segmentation of SS-OCT biometry is mandatory in these patients.