Bottle-nosed dolphin: double-slit pupil yields equivalent aerial and underwater diurnal acuity.

In bright daylight, and at best viewing distances, the bottlenosed dolphin resolves visual gratings approximately equally well in air and in water. Aerial resolution improves with increased viewing distance, while underwater resolution improves with decreased viewing distance. The double-slit pipil overcomes the gross myopia in air measured by ophthalmoscope and produces the indicated effects of viewing distance.