Introduction
A simple retweet of a turtle eye examination at the National Aquarium inspired a day of terrapin-friendly tweets by LafeberVet.com.
Rehab patient Kermit received an eye exam from Dr. Colin this morning. pic.twitter.com/DLtMS5OTon
— Jennifer Dittmar (@jenndittmar) December 4, 2014
Inspired by @jenndittmar @NatlAquarium eye exam photo to share turtle tweets all day long! #reptiles #turtles pic.twitter.com/Y1k44jksLg
— LafeberVet (@LafeberVet) December 8, 2014
Adnexa
Turtle Tweet 1: As in (most) lizards, the lower eyelid of Chelonia is larger & more mobile than the upper lid pic.twitter.com/FtWhXxr0EG
— LafeberVet (@LafeberVet) December 8, 2014
Turtle Tweet 2: Turtles and tortoises also possess a well-developed nictitating membrane.
Turtle Tweet 3: Eyelid trauma can be a common finding in RE sliders housed in groups #reptiles #turtles pic.twitter.com/bzSV3m5W1F
— LafeberVet (@LafeberVet) December 8, 2014
Turtle Tweet 4: Blepharedema is a common finding in aquatic turtles and is often associated with hypovitaminosis A.
Turtle Tweet 5: Neoplasia involving the reptile eyelids include herpesviral fibropapillomas in sea #turtles pic.twitter.com/U2FraBOHIq
— LafeberVet (@LafeberVet) December 8, 2014
Most Chelonia have a Harderian gland in the medial region and a lacrimal gland laterally.
Lacrimal system
The nasolacrimal duct is absent in all Chelonia that have been studied therefore tears naturally spill over the eyelids and down the sides of the face to eventually evaporate. Any fluorescein placed in the eye does the same.
“Tear-feeding” or lachryphagy: #turtles allow butterflies to drink their tears as they bask on a log #reptiles pic.twitter.com/u4S0CMugZY
— LafeberVet (@LafeberVet) December 8, 2014
Shown above, two Julia butterflies (Dryas julia) drinking the tears of turtles in Ecuador.
Globe
Turtle Tweet 7: Scleral ossicles are present in some Chelonia; there are 6-17 scleral bones in Testudo spp. pic.twitter.com/zLCEtYjtLT
— LafeberVet (@LafeberVet) December 8, 2014
The globe of most reptiles is almost spherical, and this holds true for turtles and tortoises. The globe is supported by a series of scleral ossicles or small bones that overlap to form a cup-like structure. Chelonia also possess a scleral cartilage that measures up to 1 cm thick. The scleral cartilage is a continuous band of cartilage that circles the posterior segment of the globe.
Turtle Tweet 8: Among Chelonia binocular vision is best in freshwater spp & most advanced in snapping #turtles pic.twitter.com/RToFgeVpyl
— LafeberVet (@LafeberVet) December 8, 2014
Intraocular pressure (IOP) has been shown to vary with eye position relative to the body. Loggerhead sea turtles (Caretta caretta) in dorsoventral and ventrodorsal positions have lower IOP than when the head is in a down position (Chittick 2001).
Looking for additional information on chelonian ophthalmology? Here are some additional facts:
- As in birds, the reptile iris contains skeletal muscle and is therefore under voluntary control.
- Turtles and tortoises possess an avascular retina.
- The conus papillaris is a vascular structure, similar to the pecten in birds, that projects into the vitreous in some chelonian species. A conus papillaris was not observed in thirty, adult red-eared slider turtles (Trachemys scripta elegans) (Somma 2014).
- Chelonia possess cones and rods, allowing significant color vision.
- Finally, some Chelonia have been shown to possess ultraviolet vision.
Follow Us
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References
References
Chittick B, Harms C. Intraocular pressure of juvenile loggerhead sea turtles (Caretta caretta) held indifferent positions. Vet Rec 149(19):587-589, 2001.
Chitty J, Raftery A. Essentials of Tortoise Medicine and Surgery. Malden, MA: Wiley-Blackwell; 2013.
Lawton MPC. Reptilian ophthalmology. In: Mader DR (ed). Reptile Medicine and Surgery, 2nd ed. St. Louis, MO: Elsevier Saunders; 2005:323-342.
Mader DR, Divers SJ. Current Therapy in Reptile Medicine and Surgery. St. Louis, MO: Elsevier Saunders; 2013.
Somma AT, Lima L, Lange RR, et al. The eye of the red-eared slider turtle: morphologic observations and reference values for selected ophthalmic diagnostic tests. Vet Ophthalmol 2014 [Epub ahead of print].