Exotis ISSN 2398-2985

Reptiles

Cataracts

Contributor(s): Vetstream Ltd, Mark Naguib

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Introduction

  • Cause: age-related, hibernation damage, congenital, systemic, nutritional, UV damage.
  • Signs: white opacity.
  • Diagnosis: clinical signs, direct ophthalmoscopy, slit lamp biomicroscopy, retroillumination.
  • Treatment: phacoemulsification.
  • Prognosis: good to guarded.
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Pathogenesis

Etiology

  • As with other species there are likely to be several factors involved in the generation of lens opacity.
  • Genetics seem to play a significant part in the etiopathogenesis of age-related cataract as well as directly inherited cataract in humans and canine patients, although there is limited information in reptiles.
  • Environmental factors, particularly UV exposure have been shown to be a significant cause in laboratory rodents via photo-oxidation of lens proteins:
    • This may be the case in reptiles too, although no direct evidence exists.
    • Although keratitis is more commonly seen with inappropriately high levels of UV exposure, it is possible that cataracts could occur as a result of this.
    • A varanid monitor lizard that was housed very close to an ultraviolet light source showed signs of an immature posterior cortical cataract.
    • Different species have skin adapted to different UV levels depending upon their natural environment and normal basking behavior and it is likely there is similar variation in their lenses.
  • Cataracts are thought to occur following freezing during hibernation in Testudo species. Although these were mature, blinding cataracts, they often cleared over time unlike in age-related ones.
  • Research investigating cataracts in older Testudo species has shown that by the age of 35 most, if not all, tortoises of this genus have some degree of nuclear cataract without any reported hibernational problems Hibernation.
  • While there is no direct evidence for ultraviolet (UV) light causing cataracts in reptiles, poor nutrition may predispose to cataract formation Nutritional requirements.
  • Systemic inflammation may result in uveitis and secondary cataract formation.
  • One study suggests Mycoplasma infection may play a role in cataract formation in Testudo spp.
  • In mammals, some drugs and toxins are known to be cataractogenic.
  • Trauma may induce cataracts as in mammals.

Predisposing factors

General

  • Age.
  • Genetics.
  • Nutrition.
  • Inappropriately high UV light exposure.
  • Freezing during hibernation.
  • Cataractogenic drugs.
  • Trauma.
  • Uveitis Uveitis.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Organisation(s)

Reproduced with permission from Bonnie Ballard & Ryan Cheek: Exotic Animal Medicine for the Veterinary Technician © 2017, Simon J Girling: Veterinary Nursing of Exotic Pets © 2013, and David L Williams: Ophthalmology of Exotic Pets © 2012, published by John Wiley & Sons.


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