Aberrant corneal occlusion or pseudopterygium
Esther van Praag, Ph.D.
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A variety of names - pseudopterygium, precorneal membranous occlusion, aberrant conjunctival overgrowth, or conjunctival centripetalization - have been given to the aberrant growth of conjunctival membrane tissue. The condition is progressive and extends from the bulbar conjunctiva onto the cornea of the rabbit eye. The condition is very poorly described in veterinary literature.
The etiology of the disease is unknown. It appears the result of an inflammatory process that leads to the adherence of a fold of the conjunctiva to the cornea, near the border of the cornea and the sclera (corneal limbus) or more centrally. Breed, age, and sex of the rabbits seem to play a role, as male dwarfs, aged between 5 and 12 months are more particularly affected. It appears congenital in some cases. A further possible cause for pseudopterygium may be ultraviolet radiation.
"Pseudo" in the term pseudopterygium refers to the fact that the conjunctival membrane is not adhering to the underlying cornea, but growing over it. In rare cases, the membrane may be loosely attached to the cornea, but can be easily separated without causing damage. It can cover only a small part of the cornea with an annular peripheral opacification of the cornea, or cover it almost fully, leading to blindness. When the membrane is sectioned from the outer edge to the corneal limbus, it usually retracts back to its normal position. The condition can be unilateral or affect both eyes.
Pseudopetrygium can be accompanied by pain if the cornea is damaged by, e.g., a foreign body or a piece of hay stuck under the membrane.
Two cases of pseudopterygium in rabbits have been described by Arnbjer. In the first case, the conjunctival membrane was detached with a blunt instrument from the underlying cornea, followed by injection of methylprednisolone acetate in the subconjunctival membrane. The eye was treated with steroid/antibiotic eye drops during 3 week. In the second case, the only treatment was topical antibiotics after the detachment of the membrane; it grew back within weeks.
As surgical removal of the overgrown conjunctiva leads to recurrence, the condition can be left untreated if it does not hinder the sight of the rabbit, and does not cause pain.
The surgical procedure that leads to the best results includes suturing the fold back to the eyelid, to the sclera, or to the loose arching folds connecting the conjunctival membrane lining the inside of the eyelid with the conjunctival membrane covering the eyeball (fornix conjunctivae) on a fully anesthesized rabbit. This can be done with resorbable Dexon or Vicryl sutures 5.0 or 6.0. Post-surgical care includes the daily administration of topical cyclosporine 0.2% and corticosteroids (e.g. dexamethasone 0.1%) during a few weeks.
Rarely, the condition may become chronic, with repeated re-growth of the membrane; life-long follow-up is needed to minimize regrowth of the conjunctival membrane.
My gratitude goes to Akira Yamanouchi (Veterinary Exotic Information Network, Japan), for the permission to use his pictures.
Arnbjer, J. Pseudopterygium in a pygmy rabbit. Vet. Med. Small Anim. Clin. 74,737-738 (1979).
Bourne D. Aberrant conjunctival overgrowth in rabbits. http://wildlife1.wildlifeinformation.org/S/00dis/Miscellaneous/AbConjunctOvergrowthRabbit.html
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