Aberrant corneal occlusion or pseudopterygium
Esther van Praag, Ph.D.
Warning: this file contains pictures that may be distressing for
people.
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.
Clinical signs
"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.
Treatment
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.
Acknowledgement
My gratitude goes to Akira Yamanouchi (Veterinary Exotic Information Network, Japan),
for the permission to use his pictures.
Further
information
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
Delaney, K.H. Diagnostic exercise: Apparent
corneal occlusion in a New Zealand white rabbit. Contemp. Top. Lab. Anim.
Sci. 34,76-77 (1995).
DuPont, C., Carrier, M. & Gauvin, J. Bilateral precorneal
membranous occlusion in a dwarf rabbit. J. Small Exotic Anim. Med. 3,41-44 (1995).
Fehr, M. Eye anomalies in dwarf rabbits. [German]. Kleintierpraxis 29, 129-130, 132 (1984).
Matros, L.E., Ansari,
M.M. & Van Pelt, C.S. Eye anomaly in a dwarf rabbit. Avian Exotic Pract.
3,13-14 (1986).
Roze, M., Ridings, B.
& Lagadic, M. Comparative morphology of epicorneal conjunctival membranes in rabbits and human pterygium.
Vet. Ophthalmol. 4,171-174 (2001).
Schoofs, S. & Hanssen,
P. Epicorneal conjunctival membrane in the rabbit:
a clinical case and surgical therapy. Vlaams Diergeneeskundig
Tijdschrift 67,344-346 (1998).
Wagner, F., Heider, H.J.,
Gorig, C. & Fehr, M. Ophthalmic diseases in dwarf rabbits. Part 1: eye examination, anatomy, diseases of
the eyelids, the conjunctiva and of the nasolacrimal
duct. [German]. Tierarztl. Prax. 26,205-210 (1998).
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