Point diffraction interferometry for the rotational symmetry analysis in fish lenses

Abstract

It is generally assumed that teleost fish lenses are spherically symmetrical. Our purpose is to evaluate this symmetry by means of point diffraction interferometer (PDI) which is an accurately technique to evaluate very aberrated optical elements as eye lenses. Several lenses of two different fish were evaluated in vitro with a PDI, they were placed over a ring inside a glass cell filled with Medium 199. Measurements were performed for ten different positions of the lens, from a position with equatorial plane orthogonally to optical axis of the system to a position with equatorial plane quasi-parallel with optical axis. Based on the assumption of a spherically symmetrical refractive index, they should yield radially-symmetric interferograms regardless of their position. With PDI measurements we are able to test visually and numerically this assumption. We found that only when the fish lens is positioned with equatorial plane orthogonally to the optical axis of the system shows a quasi-spherical symmetry. This technique allows quantify the deviation from the spherical symmetry commonly assumed for teleost fish lenses.