Abstract
Purpose :
DIMS (defocus incorporated multiple segments) is a novel designed spectacle lens for myopia control of children. Besides the treatment efficacy, optical performance is also important. However traditional method cannot evaluate the optical effects due to the segments. The purpose of this study is to define new evaluation indices and find out the relationship between segment distribution pattern and optical performance.
Methods :
The optical property through DIMS area is not constant but changes from one position to another because the alignment of segments within a pupil sized circle depends on its position on lens. This variation gives special effect which is different from a normal lens and needs to be quantified and evaluated. To do that, a map of performance index that shows the variation on DIMS area is necessary. Besides the absolute value of an optical performance index, the amplitude of its variation across the DIMS area is of more importance. This amplitude relates to the distribution pattern of segments. The more even the segments distribution, the smaller the amplitude of variation.
PSF (point spread function) varies with its position on lens. At all positions within DIMS area, PSF do not have rotational symmetricity about its principal position. According to these properties, four indices are defined and mapped. First index is local light intensity (LLI). LLI map is generated convoluting all PSFs with a flat intensity. Second index is local target shift which is defined as the quantity of PSF gravity center shifts from its principal position. Third and fourth indices are mean MTF and amplitude of MTF variation over all azimuth angles. Both are defined to quantify the azimuth dependence of MTF.
Results :
Two designs, honeycomb design as even distribution design and concentric rings design as an uneven distribution design, are examined. Table 1 shows a part of statistical values of each index within DIMS area in situation of 4mm pupil size. Except average value of mean MTF, honeycomb design gives smaller variations in all indices than concentric rings design.
Conclusions :
Four new indices are defined to evaluate DIMS lens. Compared to their absolute value, variation of these indices across DIMS area is more important to evaluate the special effect due to the segments. Evenly distribute the segments on lens is effective to reduce the variation.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.