Monocular Polyplopia Predicted by Point Spread Function Caustics

Monocular polyplopia may be expected when the point spread function (PSF) has multiple intensity cores (a dense concentration of a large portion of the radiant flux contained in the PSF) relatively separated from each other, each of which contributes to a its own image, according to research published in Ophthalmic and Physiologic Optics. Multiple PSF cores most likely result from the presence of hyperbolic umbilic caustics which form on the retinal surface and are associated with cusps of Gauss (where the gradient of a curvature function vanishes).  

Investigators used the wavefront error (WFE) function to characterize caustics generated at the retina due to the structure’s ability to define regions of ray crossings and therefore higher flux density. They used catastrophe theory to show that computation of fertile cusps of Gauss from the eye’s wavefront aberrations can predict the generation of PSF cores responsible for polyplopia. 

The team suggests that eliminating the WFE regions giving rise to PSF cores could be applied to correct polyplopia. “The number and location of cores in the PSF is thus a potentially useful metric for the existence and severity of polyplopia in spatial vision,” according to the researchers. “These examples also help explain why physiological pupil constriction might reduce the incidence of ghosting and multiple images of daily objects that affect vision with dilated pupils. This mechanistic explanation suggests a possible role for optical phase-masking as a clinical treatment for polyplopia and ghosting.”

The report also discussed potential strategies to reduce the visual asthenopia associated with ghosting. Investigators state that polyplopia is a common experience of presbyopic or pseudophakic patients fitted with multifocal corrections, but it can be reduced by controlling levels of spherical aberration within multifocal lens designs, according to the report. Pupil-masking may be instrumental in avoiding multiple images and can be implemented using artificial apertures included within contact lenses, the cornea (corneal inlays or tattoos), or intraocular lenses containing opaque outer regions. 

Reference

Barbero S, Bradley A, López-Gil N, Rubinstein J, Thibos L. Catastrophe optics theory unveils the localised wave aberration features that generate ghost images. Ophthalmic Physiol Opt. Published online May 27, 2022. doi:10.1111/opo.13008