Corneal topography, refractive state, and accommodation in harbor seals (Phoca vitulina)

Abstract

Corneal topography of a harbor seal measured with a Placido’s disc shows a central flattened stripe in the vertical meridian. Together with a pupil that can form a vertical slit, the flat vertical meridian can minimize the optical effects caused by the transition from water to air. Using infrared (IR) photoretinoscopy, we analyzed the refractive state of harbor seals and revealed a high degree of myopia and astigmatism in air, but emmetropia or slight hyperopia with little astigmatism underwater. The brightness distribution in the pupils suggest the presence of a multifocal dioptric apparatus in air and underwater. We found a first indication for accommodation by dynamic recordings underwater.