Background
Intraocular lenses are typically calculated based on a pseudophakic eye model, and for toric
lenses (tIOL) a good estimate of corneal astigmatism after cataract surgery is required in
addition to the equivalent corneal power. The purpose of this study was to investigate the differences between the preoperative IOLMaster (IOLM) and the preoperative and postoperative Casia2 (CASIA) tomographic measurements of corneal power in a cataractous
population with tIOL implantation, and to predict total power (TP) from the IOLM and CASIA
keratometric measurements.
Methods
The analysis was based on a dataset of 88 eyes of 88 patients from 1 clinical centre before
and after tIOL implantation. All IOLM and CASIA keratometric and total corneal power measurements were converted to power vector components, and the differences between preoperative IOLM or CASIA and postoperative CASIA measurements were assessed.
Feedforward neural network and multivariate linear regression prediction algorithms were
implemented to predict the postoperative total corneal power (as a reference for tIOL calculation) from the preoperative IOLM and CASIA keratometric measurements.
Results
On average, the preoperative IOLM keratometric / total corneal power under- / overestimates the postoperative CASIA keratometric / real corneal power by 0.12 dpt / 0.21 dpt. The
prediction of postoperative CASIA real power from preoperative IOLM or CASIA keratometry shows that postoperative total corneal power is systematically (0.18 dpt / 0.27 dpt) shifted
towards astigmatism against the rule, which is not reflected by keratometry. The correlation
of postoperative CASIA real power to the corresponding preoperative CASIA values is better than those as compared to the preoperative IOLM keratometry. However, there is a
large variation from preoperative IOLM or CASIA keratometry to the postoperative CASIA
real power of up to 1.1 dpt (95% confidence interval).
Conclusion
One of the challenges of tIOL calculation is the prediction of postoperative total corneal
power from preoperative keratometry. Keratometric power restricted to a front surface measurement does not fully reflect the situation of corneal back surface astigmatism, which typically adds some extra against the rule astigmatism
