Retinal Images with Catenary-Curved Contact Lenses [Letter]

The recent publication of a clinical trial of lenses with catenary curved power profile by Tuan et al 1 is an example of expandedfocus contact and intra-ocular lenses.The report is rare in that it includes the actual curvature specification, which allows independent evaluation of their diffraction-mandated resolution limit.Using the computational approach to the retinal image light distribution that had been applied to other non-traditional surface configurations, 2 this problem is explored here.After converting the curvatures to phase deviations of the wavefront converging on the retina, the diffraction image on the retina was calculated for monochromatic light, a round pupil of 4mm, and defocus in half-diopter steps from -1D to +4D, ie, target distances from 1m virtual to 25 cm real.To relate this information to the clinical reports, the computed point-spread functions were used to derive the light spread across the width of a 2 arcmin bright bar, the basic component of 20/40 (0.3 logMAR) letters on visual acuity charts.Because of its easy visualization of how defocus degrades the image through contrast reduction and light spread, this is a good measure for comparing patient data with the best performance allowed by physical theory.Figure 1 is the computationally generated through-focus display in the -1D to +4 diopter target vergence range, sideby-side for three conditions: left, normal viewing (with a plane wavefront) and a 4mm pupil, middle, with the catenary-Figure 1 Through-focus depiction of computed light spread in the retinal image of a 2 arcmin-wide bright bar in aberration-free eye with monochromatic light, for (left) normal vision with plane wavefront and 4mm pupil diameter, (middle) wearing catenary -curved contact lens and 4mm pupil, and (right) catenary curved lens and 6 mm pupil.Target vergence from bottom up in diopter steps from -1D (1m virtual) to 4D (25cm real).