Quantifying visual acuity of Terrapene carolina triunguis utilizing optokinetic response

Area of Science:

• Herpetology
• Animal Vision
• Comparative Physiology

Background:

• Understanding visual acuity in reptiles is crucial for ecological and behavioral studies.
• Terrapene carolina triunguis (three-toed box turtles) are semi-aquatic, presenting unique visual challenges.
• Optokinetic response (OKR) is a standard method for assessing visual acuity in various species.

Purpose of the Study:

• To quantify the visual acuity of the semi-aquatic turtle, Terrapene carolina triunguis.
• To establish a baseline for visual performance in this species.
• To compare visual acuity with aquatic turtle species.

Main Methods:

• Ten three-toed box turtles were tested using projected gratings of varying widths.
• Optokinetic response (OKR) was monitored via webcam and direct observation.
• Grating size was reduced until OKR was no longer elicited, determining visual acuity in cycles per degree (cpd).

Main Results:

• The average visual acuity was 0.26 cpd.
• Individual visual acuity ranged from 0.15 cpd to 0.43 cpd.
• Neither sex nor weight significantly correlated with visual acuity.

Conclusions:

• Three-toed box turtles exhibit lower visual acuity compared to aquatic turtles.
• This difference may stem from adaptations to terrestrial vs. aquatic environments, including refractive index variations.
• Methodological differences in visual acuity testing could also contribute to observed disparities.