Comparison Of Through-Focus Binocular Visual Acuity With A Small Aperture And Monovision

Investigative Ophthalmology & Visual Science
Silvestre Manzanera; Christina Schwarz; Enrique J. Fernandez; Juan Tabernero; Pedro M. Prieto; Pablo Artal

Purpose: Corneal small aperture inlays provide extended depth of focus as a solution to presbyopia. As this procedure is becoming more popular, it is interesting to compare its performance with traditional approaches, such as monovision. In this study, we compared through focus binocular visual acuity (VA) using an adaptive optics visual analyzer to benchmark both approaches.
Methods: We used a binocular adaptive optics visual analyzer to measure binocular VA as a function of object vergence. The instrument allows for modifying the magnitude and phase of the eye’s complex pupil function. It incorporates two liquid-crystal spatial light modulators for both for wavefront shaping and to create the artificial pupil. A micro-display presents high contrast letters through the controlled eye’s optics. Three subjects were tested under a series of visual conditions with the accommodation paralyzed (simulating complete presbyopia). The experiments were performed for two luminance levels (photopic and mesopic) and for the following conditions: 1) normal reference case (4 mm pupil in each eye and in focus); 2) monovision (4 mm pupil each eye, one in focus, the other with -1.25 D); 3) small aperture inlay (1.6 mm pupil one eye, 4 mm the fellow eye, both in focus), and 4) small aperture inlay combined with micro-monovision (1.6 mm pupil and -0.75 D in one eye, the fellow eye 4 mm in focus).
Results: Both approaches increased depth of focus as compared with the normal baseline condition. We defined depth of focus as the dioptric range with VA larger than 0.18 LogMAR (J2). In the photopic case, the average values were 0.8 D for the normal case, 1.8 D for the monovision case, 1.6 D for the in focus small aperture case and 2.3 D for the small aperture inlay and micro-monovision. For distance vision, the small aperture approach provided better VA while for objects at 1.25 D vergence, VA with monovision was higher. A similar behavior was observed for mesopic conditions, although with an overall reduction in VA around 40%. Subjects reported some visual discomfort with monovision that was not evident from the VA data.
Conclusions: We compared through focus VA for controlled optical conditions simulating monovision and the small aperture inlay for two conditions. Both approaches were effective to extend depth of focus. The largest range was obtained with the small aperture in a micro-monovision type configuration. In addition, this latter approach also induces a reduced binocular disparity resulting in less visual discomfort as compared with monovision.