Diseases of the Special Senses

Chapter 41 Diseases of the Special Senses



SNAKES


The ear has both auditory and vestibular function in the snake. In many reptiles, the ear is located in a shallow depression on the side of the head and is covered by a thin piece of tissue that is shed during ecdysis. Snakes lack an external ear and have no tympanic membrane or middle ear cavity. Although it has been the general belief that snakes have little hearing capability, they are able to hear sounds in the low-frequency range of 150 to 600 Hz.


The eye is different from that of mammals. The iris contains striated muscle and does not respond to common mydriatics. The pupil is round and relatively immobile in diurnal species and slitlike in nocturnal species. There is no consensual pupillary light reflex. Descemet’s membrane is absent from the cornea. A fusion of the lids to form a protective spectacle over the surface of the cornea allows tears to flow between the spectacle and the cornea to maintain moisture. The secretions drain into the lacrimal duct, which drains into the oral cavity. The retina is relatively avascular but contains the conus papillaris, a large vascular body that protrudes into the vitreous. Examination of the eye in reptiles is challenging.


Specialized infrared sensors called heat pits can be found in Booidea and pit vipers. The location of these sensors depends on the species. These allow the snake to navigate and find food in darkness and to sense small temperature variations.



Retained Spectacles


Spectacles cover the entire surface of the cornea in the snake. These spectacles undergo changes during the shedding cycle, becoming cloudy before the shed, then clearing after shedding is completed. Retention of the spectacles is a common condition seen in pet snakes and, in many cases, is a result of low humidity in the environment (Fig. 41-1).


image

Figure 41-1 A retained spectacle in a snake.


(From Mader DR: Reptile medicine and surgery, ed 2, St. Louis, 2006, Saunders. Courtesy S. Barten.)



CLINICAL SIGNS



• History of recent shed

• Blue–white cap over cornea of one or both eyes

• Behavior problems related to impaired vision; nervousness, striking when handled


DIAGNOSIS



• Physical examination


TREATMENT



• Removal of the retained spectacle without injuring the cornea can be done as follows:
Place snake in a warm container lined with damp paper or soak the animal in warm water to loosen the spectacle; some have used wet cotton balls over the spectacles to soak.

Apply ointment to soften and loosen the spectacle.

When loose, gently lift the spectacle from the cornea; if it will not lift easily, continue to soak until it comes loose or you may damage the cornea.

• Prevent by educating the owner in proper humidity required by the species.

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Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Special Senses
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