Ocular Ultrasonography and Effect of Topically Applied Rocuronium Bromide in Louisiana Pine Snakes (Pituophis ruthveni)

Abstract

Louisiana pine snakes (Pituophis ruthveni) are a threatened species with a range limited to portions of Louisiana and Texas. There are captive reproduction programs that aim to assist in the recovery of this species. Therefore, obtaining information that can aid in maintaining their health, such as a complete ocular examination, is a critical component in conservation efforts. Examination of the snake ocular posterior segment is challenging due to the presence of striated uveal musculature which is unresponsive to anticholinergic agents, and the presence of the spectacle which may create a barrier to topical mydriatics. The objectives of this study were to document normal ocular biometric measurements (axial globe length (AP), lens thickness (LT) and vitreous chamber depth (VCD)) in this species using ultrasonography (US) and to assess the effects of topically applied rocuronium bromide (RB) solution (1- and 2-drop protocol, 20 μl and 40 μl, respectively) to facilitate non-invasive examination of the fundus. The ocular biometric measurements were then correlated to morphometric data including snout-vent length (SVL), tail length (TL), total body length (SVL + TL), sex and body condition score (BCS). We found that US, using an 8-18 MHz linear array probe, provided adequate image quality to measure the above parameters in all snakes (n = 8), and that there were no significant correlations between the morphometric data and ocular biometric US measurements (P > 0.05). RB solution applied topically to the healthy, intact spectacle did not induce mydriasis in a subset of this same population (n = 6) (P > 0.05) using either the 1- or 2-drop protocol. In conclusion, ocular US can be utilized as a non-invasive diagnostic tool in Louisiana pine snakes and further studies are needed to evaluate non-invasive methods of inducing mydriasis in this species.