Page 1321 - Problem-Based Feline Medicine

64 – THE CAT WITH ABNORMAL GLOBE POSITION OR SIZE 1313

understood syndrome where the lens is positioned ● Anti-inflammatories can be used, especially
more anteriorly along the axis of the eye as a result of where the glaucoma has been secondary to chronic
aqueous being diverted into the vitreous. anterior uveitis.
– Topical prednisolone acetate 1% (Prednefrin
Signs of lens instability are typically present and include:
Forte, Allergan) 1 drop q 12–24 h.
● Aphakic crescent (crescent shape produced by the
– Oral prednisolone up to 1 mg/kg q 12 h.
clear space between the edge of the displaced lens
and the adjacent pupillary margin). Surgical therapy.
● Anterior or posterior luxation (dislocation). ● Cyclo-destructive procedures are used to selec-
● Iridonesis (wobbling of the iris). tively destroy parts of the ciliary body to reduce
aqueous production to match reduced outflow.
Signs of intra-ocular neoplasia such as mass lesions or
● Transcleral diode laser cyclo-photo-coagulation
discoloration of the iris may be present.
only works well where the ciliary body is well pig-
mented, and so tends not to work well for color
Diagnosis dilute cats, e.g. Burmese, Siamese, Himalayans.
– Transcleral cyclo-cryo-ablation. This is the ori-
Diagnosis is based on the appearance of buphthalmos
ginal technique described for cyclo-destruction,
with any or all of the other related signs of glaucoma,
and is a suitable alternative for use in cats where
chronic anterior uveitis, intraocular neoplasia or lens
laser surgery does not work well, i.e. Color
instability.
Point cats with minimal pigmentation of the
Measurement of intra-ocular pressure by tonometry uveal tract.
confirms the diagnosis. Normal range for intra-ocular ● Lens removal is suggested wherever the lens is
pressure in the cat is 15–25 mmHg. Readings over unstable because of chronic anterior uveitis.
30 mmHg are supportive of a diagnosis of glaucoma. Inflammation is sometimes easier to control by
removing the lens.

Treatment

There are no consistently reliable therapeutic proto- TRAUMATIC GLOBE PROPTOSIS**
cols which will lower intra-ocular pressure in all cats.
Monitoring is necessary to confirm that chosen treat- Classical signs
ment is working. Type of therapy chosen and its pre-
● Globe located cranially to eyelid margins.
dicted success will depend on several factors. These
● Subconjunctival hemorrhage.
include:
● Extra-ocular muscle tearing.
● Whether the angle is opened or closed. When the
angle is closed or obstructed, treatment regimes
involving cyclo-destruction to reduce production of
aqueous within the eye may not work as well as Pathogenesis
aqueous shunting procedures.
Proptosis occurs through excessive blunt trauma to
● Whether the glaucoma is primary or secondary
the globe or lateral orbit. The condition is uncommon
to other pathology. If glaucoma occurs secondary
in cats because of skull shape. The globe is located
to chronic anterior uveitis it is often more respon-
deeper in the orbit with more protection laterally than
sive to simple treatment with anti-inflammatories
in dogs, except in brachycephalic cats. Occasionally
alone, without the use of other ocular hypotensive
however, cats can be seen with this condition following
treatments.
motor vehicle trauma. Prognosis for the eye is usually
Medical therapy includes: poor because the forces required to proptose a feline
● Carbonic anhydrase inhibitors. globe are often so severe that severe globe trauma
– Dorzolamide 2% (Trusopt): one drop q 8 h occurs with resultant permanent loss of normal globe
topically. structure and function.