Physiological Optics of the Eye of the Juvenile Lemon Shark (Negaprion brevirostris)

摘要

A schematic eye for the eye of the average juvenile lemon shark inhabiting Florida Bay, a shallow marine environment marked by high turbidity, was constructed. The crystalline lens in this eye is the sole refractive element, with an overall equivalent refractive index of 1.664 and a principal power of approximately +140 diopters. The eye is hypermetropic by nearly +3 diopters in seawater, although retinoscopic measurements of the refractive state of this eye average +7.5 diopters. Sources of this discrepancy are evaluated. Retinal magnification factor (RMF) in this eye is 164 micrometres per deg visual angle; minimum separable angle (MSA) predicted from the RMF and average intercone distance is approximately 4.1 ft, but this type of visual acuity will be adversely affected by the hypermetropia. Even so, the slight hypermetropia and observed intraocular opacity of these eyes are probably secondary to the poor quality of their photic environment. (Author)