Tl. Litwiler et Tw. Cronin, No evidence of accommodation in the eyes of the bottlenose dolphin, Tursiops truncatus., MAR MAMM SC, 17(3), 2001, pp. 508-525
Bottlenose dolphins (Tursiops truncatus) are aquatic mammals that must come
to the surface to breathe. As a result, it might be expected that their ey
es are adapted for both aerial and underwater vision. Earlier studies sugge
st that dolphins are emmetropic (i.e., focused at infinity) in water, and i
n some cases, emmetropic in air, although the mechanisms chat permit these
animals to see well in both media are not well understood. Nor is it known
whether they can accommodate to focus sharply on objects at different dista
nces. We employed video photoretinoscopy to investigate the possibility of
an active accommodative mechanism in the eyes of the bottlenose dolphin in
water. Measurements of the refractive state in water indicated near emmetro
pia for two individuals and slight myopia (nearsightedness) for the third i
ndividual. No clear cases of accommodation were observed underwater in any
of the subjects examined. Vision underwater may be used to supplement echol
ocation. If so, such a role might not require an accommodative mechanism.