The snow leopard (i.e., Panthera uncia) is a threatened species, according to the International Union for Conservation of Nature Red List and Appendix I by the Convention on International Trade in Endangered Species of Wild Fauna and Flora. The snow leopard population in North American zoos has been in decline since 2015, and The Association of Zoos and Aquariums Snow Leopard Species Survival Plan (SSP) program manages breeding for 53 different zoos to help maximize genetic diversity. 

One SSP program project is preventing colobomas, a long-standing health issue in captive snow leopards. Our Veterinary Vision Center team explains this condition and how it affects snow leopards.

Coloboma overview

Coloboma comes from the Greek word “curtailed.” The condition occurs when the normal tissue in or around the eye does not develop properly and is missing at birth. The eye develops quickly as a fetus grows, and a gap, known as the choroidal fissure, emerges at the bottom of the stalk that eventually becomes the eye. Normally, the fissure closes during pregnancy, but if not, a coloboma or space forms. 

Colobomas can affect one or both eyes and many areas of the eye, such as:

  • Eyelid — An eyelid coloboma results in a missing piece of the upper or lower eyelid. This is the most common coloboma form identified in captive snow leopards and can cause recurrent corneal irritation.
  • Lens — A lens coloboma is a missing area in the parts of the eye (i.e., ciliary body and zonules) that hold the lens in place.
  • Macula — This coloboma type interferes with the macula’s development.
  • Optic nerve — An optic nerve coloboma can cause a smaller eye than normal and reduce vision.
  • Uvea — The uvea is the eye’s middle layer. A uveal coloboma can affect the iris, which is the eye’s colored portion, leaving a keyhole or cat-eye appearance.
  • Retina — This coloboma type results in a missing piece of retinal tissue.

Coloboma history in snow leopards

The first ocular abnormalities in zoo-born snow leopard cubs were described in Europe in the late 1960s. Additional colobomas in cubs were described in Europe, the United States, and Australia in the late 1970s and 1980s. The lesions ranged in severity and affected numerous eye areas, and researchers believe they likely represent a spectrum of the same syndrome. The lesions were classified under an umbrella term—multiple ocular coloboma syndrome. Most lesions had some effect on the snow leopard’s vision.

Coloboma causes in snow leopards

Identifying the underlying cause of colobomas in snow leopards is important to help resolve this medical issue that has significant animal welfare implications when lesions are so severe that they cause corneal trauma or vision impairment. While no definitive cause has been identified, hypotheses include:

  • Genetics — Affected snow leopards often have an affected parent or closely related family member, which suggests the condition is heritable. However, no genetic cause has yet been proven. 
  • Nutrition — Vitamin A is important in the embryonic development of eyes in mammals, and a vitamin A deficiency or toxicity has been proposed as a possible cause. Thresholds for vitamin A deficiency and toxicity have not been established for snow leopards, but measured vitamin A levels in snow leopards affected by colobomas didn’t seem to correlate.
  • Infectious disease — Infectious disease exposure during pregnancy has also been considered a potential trigger for coloboma development, but no infection has been linked to the condition.

Coloboma treatment in snow leopards

In some cases, corrective procedures can repair defects in the eyelids caused by colobomas, but colobomas affecting other eye areas can be managed only to prevent discomfort. If the eye causes problems, removal may be the best option, especially if the eye is not visual. Fortunately, captive blind snow leopards tend to do well, because they can acclimate to their familiar habitat. 

If your pet has an ocular abnormality that concerns you, contact our Veterinary Vision Center team. We will evaluate their condition and determine an appropriate treatment strategy.