Optical development of the ocular lens of an elasmobranch, Raja elanteria

Abstract

The shape and focal properties (spherical aberration) of the ocular lens of hatchling, yearling and adult clearnose skates ( Raja eglanteria) were examined. In contrast to the spherical shape of the typical teleost lens, the lens of the clearnose skate is slightly aspherical; equatorial diameter being greater than axial diameter. The asphericity is approximately equal, in absolute measures, at all ages and is thus more obvious in younger skates. Lens spherical aberration is well corrected at all three levels of development. Yearling and adult lenses have relative focal lengths (Matthiessen's Ratio) which are close to the representative value of 2.55:1 expected for the teleost lens. However, the relative focal length of lenses from hatchling lenses is higher (about 2.75:1). This value approaches the upper limit of reports dealing with teleost lens focal characteristics. The difference between hatchling lenses and those of adult and yearling lenses may be due to the absence of extensive compression of central lens tissue by peripheral growth at early stages in development.