Purchase this article with an account.
Lin He, Myoung Choi, Xin Hong, Ramesh Sarangapani; Correlation between clinical visual acuity and optical/visual metrics at varied defocuses in pseudophakic patients implanted with monofocal and multifocal IOLs. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2978.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Visual acuity and defocus curve are now commonly used as primary clinical endpoints to evaluate the efficacy of newly-developed intraocular lenses (IOLs). Simulation of visual acuity and defocus curve can potentially help to screen new IOL designs and estimate their clinical outcomes.
A two-surface reduced model eye was constructed with a corneal surface and an IOL surface. The corneal surface was reconstructed using averaged or individual high-order corneal aberration measured from the clinical studies. The IOL surface was extracted from theoretical design or bench measurement as a grid-sag profile with base curvature subtracted. Both surfaces were scaled and combined at the corneal plane where defocus was defined. One-hundred pupil sizes were randomly sampled from a normal distribution of 3.50±0.80 mm and were used for each iteration of simulation. Point spread function was derived by Fourier transform of the pupil functions. Three metrics, light-in-the-bucket (LIB), Strehl ratio (SRX) and visual Strehl ratio (VSOTF) were calculated at varied defocuses. The LIB metric was further explored using a range of multiples of bucket size (1 multiple of bucket size = 1 Airy disk). Simulation were performed in two Alcon monofocal IOLs and two Alcon multifocal IOLs under monochromatic conditions (λ=550nm) and were linearly correlated with binocular visual acuity from four clinical studies (n=104, 138, 116 and 130).
Standard LIB (with 1 multiple of Airy disk size) and SRX have shown good correlation with clinical visual acuity (R2=0.83 and 0.81). Increasing bucket size of LIB to 6 multiples of Airy disk size helped to achieve the best correlation (VA = -0.57 * logLIB - 0.08, R2=0.88, Figure 1). This improvement is more obvious for two diffractive multifocal IOLs with R2 increasing from 0.59 and 0.93 to 0.72 and 0.96. VSOTF has shown slightly worse and less linear correlation (R2=0.70) than LIB and SRX.
Two-surface model eye can serve as a useful tool to predict clinical visual acuity. Refining optical/visual metrics (e.g., increase bucket size for LIB metric) can better reflect the optical efficiency of complicated IOL designs and therefore achieve better clinical correlation. Polychromatic and binocular summation will be further implemented to also potentially improve the clinical correlation.
This PDF is available to Subscribers Only