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F. D. Hanke, R. H. H. Kröger, G. Dehnhardt; What Affects Eye Temperature in Harbor Seals (Phoca vitulina)?. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2018.
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In swordfishes, the eye is heated by the eye heater muscle. Fritsches et al. (2005) showed that warming the retina drastically improves temporal resolution in these animals. Marine mammals could also benefit from regulating eye temperature in correlation to ambient luminance and temperature. If ambient luminance is low, it would be advantageous for them to have cold eyes, thus reducing background noise and improving absolute light sensitivity. If ambient luminance is high, there is no need to suppress noise since the signal-to-noise ratio is good, and a warm eye would provide the high temporal resolution necessary for the detection and pursuit of fast moving prey. This is especially valuable when foraging in bright but cold waters.
In order to test the hypothesis of a regulation of eye temperature in harbor seals, we determined eye temperatures using an infrared-thermographic camera. Air and water temperature, ambient luminance and exact daytime were recorded for each measurement. For measurements, the seals were brought into a dark chamber to achieve constant pupil dilatation, independent of the ambient luminance outside. The first measurement was always taken 1 min after the animal had left the water.
Eye temperature seems to increase with increasing ambient luminance in general and at dawn in particular, but no clear decline could be observed during dusk. Eye temperature also changes over the day with the lowest temperature just before dawn. During one measurement, eye temperature increased continuously reaching a steady state after approximately 10 min. There is preliminary evidence that eye temperature increases with attention.
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