Alejandro Bayón del Río, DVM PhD
Hospital Clínico Veterinario. Universidad de Murcia
Diseases of reptile's eyes are frequently seen in veterinary practice. The causes of these lesions are often identical to those responsible for inducing ophthalmic disease in mammals and birds. Although the approach to treatment is similar to that in mammals, anatomic differences in the reptile eye cause special conditions to reptiles. Because ciliary muscles of reptiles are composed of striated muscle rather than smooth muscle fibers, conventional mydriatic agents (parasympatholytics) such as tropicamide and atropine are ineffective in producing pupillary dilation. The second difference is that in those reptiles lacking movable eyelids, the corneas are covered by a clear protective epidermally derived structure called spectacle. This structure appears impervious to topical medications, thus making treatment of the globe difficult. The spectacle is periodically replaced during molting cycles (ecdysis).
Congenital ocular malformations (especially microphthalmos) occur with some frequency in captive breed reptiles possibly as consequence of inbreeding, or environmental conditions. Other congenital abnormalities include cyclopia and anophthalmos. These frequently occur with skeletal abnormalities.
Blepharitis, usually bacterial or fungal etiology occurs commonly in reptiles, occasionally extending to involve and destroy the globe. Swelling of the eyelids and conjunctiva are seen in lizards and chelonians. Conjunctivitis may be associated with these infections. Orbital abscesses are commonly encountered in some groups of lizards (especially chameleons). Cultures of eyelid abscesses are indicated and surgical curettage required to remove inspissated pus from lesions. Most of these infections are associated with Gram-bacterial isolates and they are very difficult to manage. Topic and systemic antibiotics (based of sensitivities) are administered for long periods. Some of these animals may be immunosuppressed and susceptible to infection with a range of pathogens. Systemic involvement resulting in inappetence, malaise and eventually death often occurs.
The spectacle of snakes and some lizards presents peculiar problems unique to these animals. The spectacle may fail to be shed at ecdysis. This mostly occurs in snakes kept in excessively dry conditions or which are dehydrated or nutritionally deficient. Also is caused by a lack of suitable scabrous substrates upon which a snake can rub its cin and rostrum to initiate the molting process. Occasionally the problem is exacerbated by ectoparasites (mites and ticks) feeding at the peripheral margin of the spectacle. Usually correcting the animal's hydration and environmental moisture just prior to shedding corrects the abnormality at the next shed. Treatment involves soaking the retained spectacle to aid its removal, some times with artificial tears (hypromellose) or hard contact lens wetting solution. This is best done using a wet cotton bud and rubbing from the medial and lateral canthi towards the center of the spectacle. Tightly adherent spectacles can be loosened using mucolytic agent acetyl-cysteine applied topically to the retained spectacle. Physical removal of the spectacle should be avoided initially since without care the underlying normal spectacle is easily torn loose. Although a partially lost spectacle will heal with successive ecdysis, exposure keratitis will develop if the entire spectacle is lost.
Blockage of the nasolacrimal duct (which cannot occur in chelonians because it is absent) results in a backup of tear secretion in reptiles with a spectacle. Most notably this occurs in snakes and geckos. The nasolacrimal duct can also be congenitally absent or become blocked by pressure from adjacent tissue (granulomas or neoplasia) or by fibrosis (burn injuries to the roof of the mouth). The fluid content may initially be clear but later become turbid and flocculent. Often culture of the fluid reveals bacteria such Aeromonas spp and Pseudomonas spp. The presence of protozoa in these infections of the corneospectacular space has been demonstrated repeatedly although their role in the disease is uncertain. Although some of these blockages and infections will clear spontaneously, in many cases the infection is unrelenting and progresses to panophthalmitis or extends into the periocular tissue spaces. Affected animals should be investigated for evidence of systemic infections. Fluid beneath the spectacle should be aspirated for cytology (bacterial and protozoa) and culture/sensitivity. Fluid can be drained through an incision in the ventral spectacle and antibiotics applied to the eye at this site. Another approach is to create a new drainage route between the subspectacle space and the mouth (conjuntivoralostomy). Systemic antibiotics are often required.
Corneal disease (ulcers, lipid dystrophies) occurs occasionally and where possible are treated empirically as in mammals. Corneal ulceration may be associated with foreign bodies or trauma as in other species. Traumatic lacerations can be sutured and a course of topical antibiotic provided. Severe ulcerations in chelonia and lizards may be treated by performing a third eyelid flap. Keratitis in tortoises (Testudo spp.) is seen as a white corneal mass. Such keratitis is contagious and should be considered a herd problem. Treatment consists of removal of the plaque from the cornea under general anaesthesia. Samples should be sent for culture and sensitivity. Topical treatment using a suitable antibiotic such as ciprofloxacin usually cures any infection.
Uveitis is rarely diagnosed in reptiles although it occurs associated with systemic infectious disease, post hibernation disease (hyphema and hypopyon), trauma and neoplasia. Treatment utilizes topical (where applicable) and systemic antibiotic therapy and both steroid and non-steroidal anti-inflammatory drug therapy.
Cataracts in tortoises (Testudo spp.) have been associated with freezing episodes. The chelonian lenses are extremely soft and almost fluid like in consistency. It is hypothetised that because of this they are particularly prone to damage from low temperatures. In some cases these changes are reversible, although it may take up to 18 months for the lens to clear. Also cataracts often occur in older reptiles (etiology unknown). Cataract surgery in reptiles can be performed with current technology.
Vitamin A deficiency occurs frequently in chelonians kept in captivity. Although this is often reported in young, rapidly growing aquatic species fed meat diets deficient in vitamin A (skeletal muscle meat) and dried insects, it also occurs in terrestrial species (box-turtles) inappropriately kept in captivity. This nutritional disease causes squamous metaplasia of the orbital glands and their ducts. Epithelial desquamation blocks the ducts, and the glands increase in size, resulting in orbital and eyelid edema and secondary conjunctivitis and blepharitis. Occasionally there is secondary bacterial infection. If animals are still eating oral supplementation is the best means of therapy. Commercial trout pellets are a good balanced diet for young turtles and should be fed routinely to aquatic turtles. Squamous metaplasia of the renal, pancreatic, gastrointestinal and respiratory epithelium contributes to the animal's demise in untreated cases. If inappetant, cautious use of parenteral Vitamin A will resolve the condition. Topical applications of antibiotics may be required in cases complicated by bacterial infection.
Neoplasms (fibropapillomas, fibrosarcomas, fibromas, papillomas) occur around the eyelids with some frequency-the occurrence of epizootics in chelonia and lizards have suggested that there is probably an underlying infectious (viral) etiology. Surgical debulking is rarely effective in curing these diseases.
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Alejandro Bayón del Rio, DVM, PhD