Based on simulations performed using an innovative model eye, Xu et al. detail interesting relationships between diffraction, aberrations, retinal-illuminance-dependent neural contrast sensitivity, and pupil diameter that could provide a better understanding of current treatments for presbyopia and impact future design strategies. Multiple studies have used schematic eyes to examine the impact of diffraction and optical aberrations on retinal image quality for normal eyes, traditionally finding that small pupil diameters (2–3 mm) provide optimal retinal image contrast and quality for photopic lighting conditions. However, the potential deleterious impact of decreased light levels (i.e., increased photon noise) on visually relevant
image quality (or neurally weighted image quality) due to the use of small pupils under mesopic and scotopic lighting conditions is not fully understood. Therefore, questions exist over whether small artificial pupils can be an effective option for presbyopic correction. To better understand these questions, Xu et al. developed a presbyopic schematic eye that incorporated the effects of diffraction, monochromatic and chromatic aberrations, and a retinal-illuminance-dependent
neural contrast sensitivity function to examine three image quality metrics under conditions in which retinal illuminance or
stimulus luminance was held constant. When stimulus luminance remained constant as pupil size was changed (similar to real-word conditions) and the model eye was best-focused on the target, the pupil size yielding optimal visual image quality tended to become larger with decreasing luminance levels. However, the authors found that smaller pupils typically provided optimal visual image quality when the presbyopic model eye was defocused (such as when a presbyope would try to visualize a near target), despite its decreased performance due to higher quantal fluctuations. These results suggest that an effective presbyopic correction for photopic and mesopic light levels should consider a pupil diameter that balances improvements in image quality for near (or defocused) targets with potential losses in image quality at best focus. This paper sets the stage for future work that can probe the effectiveness of using small pupils as a presbyopic correction option under an increased range of light levels, including nighttime conditions.
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