Visual and physiological optics: introduction to the Journal of the Optical Society of America A feature issue.

The 9th European Meeting on Visual Physiological Optics (VPO2018) was held August 29-31, 2018, in Athens, Greece. This issue of the Journal of the Optical Society of America A (JOSA A) is a dedicated feature, including numerous articles that span a large range of visual optics related topics, ranging from geometrical optics to visual psychophysics and from optical metrology to ophthalmic diagnostic technologies. The next VPO meeting will be held August 2020 in Cambridge, UK.

Method of locating the visual axis objectively.

PURPOSE: To locate the visual axis of the eye objectively. METHOD: Based on three-beam scanning laser radar microprofilometry, a technique is proposed to objectively locate the visual axis of the eye. The laser beam consists of three components, two of them being shifted relatively to the central one by differing frequencies, filtered in spatially orthogonal directions. The centre of the foveola is defined as the crossing of steepest inclinations determined in the specific beam positions on the trajectory of scanning. The position of the cornea crossing by the visual axis is designated by the optical axis of the measuring instrument. RESULTS: Nanometer sensitivity was confirmed in a preliminary test. CONCLUSIONS: The proposed technique can be incorporated into any clinical wavefront sensing instrument and can be used for centration-sensitive vision correction, as well as for other instances when knowing the exact position of the fovea is important.

Damped least-squares approach for point-source corneal topography.

An optimization algorithm to be used in point-source corneal topographers is developed for the reconstruction of the topography of aspheric corneal surfaces. It is based on the damped least-squares technique. The reconstructions obtained with a topographer comprising 48 or 90 point sources for corneas having different forms (spherical, conicoidal, complex) and apical radii (5-16 mm) were simulated numerically. Zernike polynomials up to the seventh radial order were used for the description of the shape of the anterior corneal surface. With no noise, i.e. uncertainty in the position of the image of each object point, it is shown that this approach allows reconstruction of the surface with a root-mean-square (RMS) error of <5 x 10(-7) microm for the elevation map and 3 x 10(-7) diopter for the refraction map. With noise, to get an averaged surface elevation RMS error of <1 microm, or an averaged refraction RMS error of <0.25 diopter, each spot must be located (in the image plane) with an error <1 microm.