Guan J, Cameron DJ, Eng C. Quantifying visual acuity of Terrapene carolina triunguis utilizing optokinetic response.
Vet Ophthalmol 2022;
26:205-210. [PMID:
36214775 DOI:
10.1111/vop.13028]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/14/2022] [Accepted: 09/23/2022] [Indexed: 11/30/2022]
Abstract
OBJECTIVE
Quantify visual acuity of a semi-aquatic turtle species, Terrapene carolina triunguis (three-toed box turtles), utilizing optokinetic response/reflex/nystagmus.
METHODS
Ten turtles were placed on a custom platform and an image of white and black gratings of varying sized widths was projected onto a white screen in front of the turtles. Optokinetic response (OKR) was observed through a web camera as well as physically by an observer. The grating sizes were decreased until OKR could not be elicited. The size of grating was recorded and was used to calculate visual acuity.
RESULTS
The average visual acuity was 0.26 cycle per degree (cpd) with the highest recorded value being 0.43 cpd and lowest being 0.15 cpd. Neither sex nor weight were significantly associated with visual acuity (p = .24 and .98, respectively).
CONCLUSIONS
Visual acuity of these semi-aquatic turtles was much lower than previously reported visual acuities of aquatic turtles. This could be due to differences in refractive indices between water and air, behavioral adaptations for the different species and/or method of obtaining visual acuity.
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