Estimating The Postoperative Intraocular Lens Position Using Parameters Obtained By Optical Biometry.

The correct postoperative effective lens position (ELPpost) is a key factor in achieving emmetropy after cataract surgery. This parameter is the one used in “thin lens” methods. Mild errors in calculating ELP represent a common cause of refractive surprises. To improve these outcomes, newer formulae based on ray tracing try to predict the postoperative anterior chamber depth (ACDpost), forming the so-called “thick lens” methods. We propose two models for ELPpost and ACDpost estimation, adjusted by several factors measured by optical biometry. 

Ophthalmology Unit, Hospital Clínico Universitario Valencia, Valencia, Spain.

We included 118 eyes who underwent cataract surgery with three different types of IOL (Asphina409MP® (Zeiss), MI60® (Bausch&Lomb), QuadrimaxPC545® (Opthec). We performed an optical biometry using IOLMaster700 (Zeiss) 1 month before and 1 month after the surgery. We retrieved information about axial IOL position (ACDpost) and lens thickness. ELPpost was calculated using the solution to the vergence formula from the power of the IOL implanted and the postoperative measurements: axial length (AL), keratometry (Km) and refraction. We performed two models using multiple regression analysis to predict the ELPpost and ACDpost. The independent variables were AL, Km, anterior chamber depth (ACDpre), white-to-white (W-W) and IOL constant (kte A).

Mean ACDpost was 4.72+0.39mm. Mean ELPpost was 5.36+0.71mm. ELPpost was situated 0.88+1.18 mm posterior to the ACDpost. Multiple regression analysis showed that, for ELPpost prediction, both AL and Km had a negative significant effect (-3.15, p<0.001 and -1.2, p<0.001, respectively), whereas Kte A showed a positive effect (1.41, p<0.001). W-W and ACDpre were non-significant (p=0.68 and p=0.92). To predict ACDpost, all variables our model showed a positive effect, although only AL, ACDpre and Kte A were significant: AL 0.08,p=0.004; Km 0.03,p=0.18; ACDpre 0.25,p<0.001; W-W 0.03, p=0.73 and kteA 0.29, p=0.001.The goodness of fit of the model was higher for the ELPpost prediction (R²=0.96 vs 0.58).

There are 2 parameters to assess the postoperative lens position. ACDpost is used in ray tracing methods, whereas ELPpost in “thin lens” methods. We performed a multivariate analysis to predict these values using parameters measured by optical biometry. AL had the strongest effect in predicting ELPpost, while KteA was the main predictive factor for ACDpost estimation. Newer methods for IOL calculation are based on “thick lenses” and ray tracing, using the ACDpost. We propose the utility of multiple regression methods to predict this parameter, improving the accuracy of IOL power calculation, proposing KteA and ACDpost as the most valuable preoperative values. Further studies will be needed to assess the clinical application of our findings.