Abstract
Purpose :
To demonstrate the unrestrained combinations of values allowed by an FDA-approved variable toricity ratio toric intraocular lens (tIOL) calculator and the variability of toricity ratio for different input combinations.
Methods :
The tIOLcalculator under study was observed to accept for input, in addition to K values, both the IOL power and the axial length. Some such combinations correspond to emmetropia or near emmetropia, which is the general pattern of use of most surgeons for most patients worldwide. Other combinations however corresponded to extreme myopic or hyperopic refractive targets of myopia or hyperopia, with no corresponding warning generated. The toricity ratio that can be computed acccording to the methods we developed generated a matrix for each desired refractive target. We chose to compute it for some unusual, yet "reasonable" refractive targets.
Using the UniversIOL Calculator (and confirming results with IOLMaster and DGH6000 calculators), expected spherical equivalent target values of -2, -5, and -8 were entered for specific high, average, and low axial length values with high, average, and low mean corneal power values to generate three 3x3 matrices of paired values, one for each refractive target. The sphere power thus generated was entered in the manufacturer's toric calculator and a toricity ratio generated for each axial length and mean corneal power pair at each expected spherical equivalent target.
Results :
The toric calculator accepted every pair of values and suggested a toric lens, regardless of the expected spherical equivalent targets being unusual or extreme. The toricity ratio for each matrix was slightly different but generally followed the now recognized trend of monotonic increase with both axial length and mean corneal curvature.
Conclusions :
The FDA-approved calculator under study allowed for axial length and mean corneal power pairs resulting in unrealistic/generally undesirable surgical outcomes. For each given refractive target, its general trend for toricity ratio correlated with recognized trends. Variability for different refractive targets is under active investigation. Identifying the limitations of the method may lead to better surgical outcomes.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.