Tomography-based customized IOL calculation model.

PURPOSE

To provide a mathematical calculation scheme for customized intraocular lens (IOL) design based on high resolution anterior segment optical coherence tomography (AS-OCT) of anterior eye segment and axial length data.

MATERIAL AND METHODS

We use the corneal and anterior segment data from the high resolution AS-OCT and the axial length data from the IOLMaster to create a pseudophakic eye model. An inverse calculation algorithm for the IOL back surface optimization is introduced. We employ free form surface representation (bi-cubic spline) for the corneal and IOL surface. The merit of this strategy is demonstrated by comparing with a standard spherical model and quadratic function. Four models are calculated: (1) quadratic cornea + quadratic IOL; (2) spline cornea + quadratic IOL; (3) spline cornea + spline IOL; and (4) spherical cornea + spherical IOL. The IOL optimization process for the pseudophakic eye is performed by numerical ray-tracing method within a 6-mm zone. The spot diagram on the fovea (forward ray-tracing) and wavefront at the spectacle plane (backward ray-tracing) are compared for different models respectively.

RESULTS

The models with quadratic (1) or spline (3) surface representation showed superior image performance than the spherical model 4. The residual wavefront errors (peak to valley) of models 1, 2, and 3 are below one micron scale. Model 4 showed max wavefront error of about 15 µm peak to valley. However, the combination of quadratic best fit IOL with the free form cornea (model 2) showed one magnitude smaller wavefront error than the spherical representation of both surfaces (model 3). This results from higher order terms in cornea height profile.

CONCLUSIONS

A four-surface eye model using a numerical ray-tracing method is proposed for customized IOL calculation. High resolution OCT data can be used as a sufficient base for a customized IOL characterization.