Abstract
The optical quality of a set of IOLs (modeling set: one monofocal and two bifocals) was assessed through focus by the area under the modulation transfer function (MTFa) metric and related to the visual acuity (VA) defocus curves of pseudophakic patients implanted with said IOLs. A non-linear relationship between the MTFa and clinical VA was obtained with an asymptotic limit found to be the best VA achievable by the patients. Two mathematical fitting functions between clinical VA and MTFa were derived with high correlation coefficients (R2≥0.85). They were applied to the MTFa obtained from a different set of IOLs with advanced designs (trial set: one extended range of vision -ERV-, one trifocal ERV and one trifocal apodized) to predict VA versus defocus of patients implanted with these IOLs. Differences between the calculated VA and the clinical VA for both fitting models were within the standard deviation of the clinical measurements in the range of -3.00 D to 0.00 D defocus, thus proving the suitability of the MTFa metric to predict clinical VA performance of new IOL designs.
Highlights
The optical quality of an intraocular lens (IOL) is a key parameter contributing to a patient’s visual performance after cataract or refractive surgery, and has drawn the attention of increasing number of researchers in the last years (e.g., [1,2,3,4])
Alarcon et al [4], in their comprehensive paper proposed up to four metrics based on optical-bench data, three of them, using modulation transfer function (MTF) based values integrated in a spatial frequency range, and a fourth, using the cross-correlation coefficient image quality metric (IQM) to correlate with binocular visual acuity (VA) clinically tested in pseudophakic patients implanted with six different IOL designs including two monofocals, three bifocals and one extended-range-of-vision (ERV), all of them from Abbott Medical Optics (Santa Ana, California)
3.1 Mathematical relationship between VA and MTFa using the IOL modeling set Figure 3 depicts experimental results obtained with IOLs of the modeling set (Table 1): Figs. 3(a, b) show the mean clinical values of VA in the range −5.00 D to + 3.00 D measured in pseudophakic patients and Figs. 3(c, d) the through focus MTFa, obtained in-vitro in the model eye under green illumination
Summary
The optical quality of an intraocular lens (IOL) is a key parameter contributing to a patient’s visual performance after cataract or refractive surgery, and has drawn the attention of increasing number of researchers in the last years (e.g., [1,2,3,4]). The difficulty lies in finding imaging quality metrics derived from objective measurements on optical bench (for example, metrics based on the optical transfer function) that highly correlates with subjective quality metrics of visual performance as measured by clinical tests (for example, visual acuity and contrast sensitivity) If these highly correlated metrics were found, it would be possible to predict the relative change in the clinical outcomes from a given change in the optical component (intraocular lens) tested on optical bench for a pupil range and different alignment conditions. Lang et al built up a model to predict the visual acuity (VA) and contrast sensitivity outcomes of clinical tests from in-vitro measurements of the modulation transfer function (MTF) taking into account a simple model of human threshold detection [1] They computed and plotted graphs to predict VA versus defocus from through-focus MTF measurements at certain spatial frequencies and compared their theoretical results with the visual function measured clinically in pseudophakic (monofocal and bifocal) patients. Alarcon et al [4], in their comprehensive paper proposed up to four metrics based on optical-bench data, three of them, using MTF based values integrated in a spatial frequency range, and a fourth, using the cross-correlation coefficient IQM to correlate with binocular VA clinically tested in pseudophakic patients implanted with six different IOL designs including two monofocals, three bifocals and one extended-range-of-vision (ERV), all of them from Abbott Medical Optics (Santa Ana, California)
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