Do small‐aperture presbyopic corrections influence the visual field?

Abstract

To explore the effect of small-aperture optics, designed to aid presbyopes by increasing ocular depth-of-focus, on measurements of the visual field. Simple theoretical and ray-tracing models were used to predict the impact of different designs of small-aperture contact lenses or corneal inlays on the proportion of light passing through natural pupils of various diameters as a function of the direction in the visual field. The left eyes of five healthy volunteerswere tested using three afocal, hand-painted opaque soft contact lenses (www.davidthomas.com). Two were opaque over a 10mm diameter but had central clear circular apertures of 1.5 and 3.0mm in diameter. The third had an annular opaque zone with inner and outer diameters of 1.5 and 4.0mm, approximately simulating the geometry of the KAMRA inlay (www.acufocus.com). Afourth, clear lens was used for comparison purposes. Visual fields along the horizontal meridian were evaluated up to 50° eccentricity with staticautomated perimetry (Medmont M700, stimulus Goldmann-size III; www.medmont.com). According to ray-tracing, the two lenses with the circular apertures were expected to reduce the relative transmittance of the pupil to zero at specific field angles (around 60° for the conditions of the experimental measurements). In contrast, the annular stop had no effect on the absolute field but relative transmittance was reduced over the central area of the field, the exact effects depending upon the natural pupil diameter. Experimental results broadly agreed with these theoretical expectations. With the 1.5 and 3.0mm pupils, only minor losses in sensitivity (around 2dB) in comparison with the clear-lens case occurred across the central 10° radius of field. Beyond this angle, sensitivity losses increased, to reach about 7dB at the edge of the measured field (50°). The field results with the annular stop showed at most only a slight loss in sensitivity (≤3dB) across the measured field. The present theoretical and experimental results support earlier clinical findings that KAMRA-type annular stops, unlike circular artificial pupils, have only minor effects on measurements of the visual field.