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Figure 1


Fig. 1. Schematic representation of the experimental setups used to measure harbour seal lenses. (A) IR-Photoretinoscopy under water. A retinoscope (R) with 13 IR-LEDs arranged eccentrically and a knife edge (edge of metal shield in the lens aperture; KE) arranged horizontally was attached to a video camera (C). IR-light entered the eye, was partly reflected and caused variation in brightness in the pupil. The seals were trained to lower their heads into an aquarium from an elevated platform. (B) Schlieren photography. White light (point source, cold light laboratory lamp, 3200 K) was reflected by a beam splitter into the optical axis. The lens, immersed in PBS (pH=7.4, 290 mosmol, 20°C), focused the light beam on a diffuse reflector. Reflected light was focused by the lens on the pinhole and recorded by a camera. (C) Laser scan. The lens was positioned on a holder in the middle of the immersion bath filled with PBS to which a small amount of microparticles was added. A 5 mW green (537 nm) diode-pumped, solid-state laser was used to scan through a meridional plane of the lens. The upwards scattered light was recorded by a video camera.





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