Veterinarians confronted by an unsymmetrical appearance of the globe may have difficulties determining whether they are being confronted by a case of proptosis (an eye that is protruding outside the orbit, usually due to trauma), exophthalmos (an eye that is pushed forward relative to its normal position, but is still in the orbit) or buphthalmos (an enlarged, glaucomatic globe). This talk will help you diagnose and treat proptosis and exophthalmos, and differentiate them from buphthalmos.

Traumatic Proptosis - How Do I Treat? What Prognosis Can I Give the Owner?

Prognostic Indicators

Owners of pets with traumatic prolapse of the globe will want to know whether the eye can be salvaged. This question actually has two components, as in some cases vision may be salvaged, while in other cases the eye will be blinded, but the globe can be salvaged cosmetically (i.e., not be enucleated).

Criteria that will help the clinician answer these questions include:

1.  What is the skull conformation? Traumatic prolapse is common in brachycephalic dog breeds, due to the shallow orbit and poor lid closure. Therefore, in these breeds minimal trauma may cause prolapse. However, frequently there will be no additional injuries to the eye, skull or body. On the other hand, in cats and in mesocephalic and dolichocephalic dogs, the eye is situated in a deep orbit and is protected by tight lid closure. In these animals, traumatic prolapse is frequently accompanied by other intraocular or bodily injuries, and the prognosis is poorer.

2.  Duration of prolapse. Depending on the duration of the prolapse, animals may present with corneal ulceration, necrosis or perforation.

3.  Intraocular injury. Hyphema is a bad prognostic indicator, as it implies trauma to the uvea or globe rupture. An ultrasound examination may aid in imaging intraocular injuries.

4.  Pupils. Pupillary light reaction (PLR) is an important sign. If the pupil cannot be seen (due to hyphema), the consensual PLR should be checked.

5.  Strabismus and extraocular muscles. Clinicians should remember that ciliary arteries, which supply blood to the anterior segment of the eye, are carried in the extraocular muscles. Therefore, rupture of too many muscles will result in ocular ischemia.

Overall prognosis for vision is rather poor, with only 20% of dogs reportedly remaining visual. However, prognosis for cosmetic salvage is better. Unless prognostic indicators are very poor, you should attempt globe replacement at presentation.

Treatment

Owners who telephone regarding traumatic ocular prolapse should be instructed to keep the cornea moist, using water, moist gauze, Vaseline, ophthalmic lubricants, etc. Upon presentation, conduct the prognostic tests described. The cornea should be washed, cleaned and lubricated.

After the patient has been stabilized and anesthetized, the lids should be rolled/pulled out over the equator, using muscle/strabismus hooks, forceps, etc. The globe is pushed back into the orbit using gentle pressure. A lateral canthotomy may be required to facilitate replacement. A temporary tarsorrhaphy is performed to maintain lid closure. Depending on the size of the animal, 2–4 horizontal mattress sutures, using 2-0 to 4-0 nonabsorbable monofilament material are used, with stents for tension relief. Make sure that the suture passes through the lid margin (meibomian gland openings) and not through the palpebral conjunctiva. Compresses (to reduce swelling) and an Elizabethan collar should be applied.

Exophthalmos - What Is Pushing this Eye? What Should I Do About It?

Differentiating Between Exophthalmos and Buphthalmos

Exophthalmos is a normal-sized globe that is being pushed forward by a space occupying lesion in the orbit, most commonly a retrobulbar abscess/cellulitis or neoplasia. Buphthalmos, on the other hand, is a normally-positioned globe that is enlarged due to elevated intraocular pressure (IOP), i.e., glaucoma. Some tests, such as ultrasound or tonometry (discussed later), may provide a definitive diagnosis. However, frequently it may be possible to differentiate between exophthalmos and buphthalmos during examination, without resorting to other instrumentation.

Signs that clinicians should evaluate include:

1.  Glaucoma and buphthalmos may present as either a unilateral or a bilateral disease. However, in most cases exophthalmos will present as a unilateral problem. Therefore, bilateral presentation usually indicates that the primary problem is glaucoma.

2.  Amount of visible conjunctiva. In exophthalmos the eye is pushed forward, and therefore excessive conjunctiva is visible. In buphthalmos, the eye is stretched but remains in its normal position inside the orbit.

3.  Evaluate the position of the third eyelid. This is normal in most cases of glaucoma. The third eyelid is usually elevated in exophthalmos, as the space occupying retrobulbar mass usually pushes against the third lid, causing its elevation.

4.  Estimate the diameter of the cornea. It is normal in exophthalmos, and increased in buphthalmos due to stretching of the globe.

5.  Perform a retropulsion test. Use 2 fingers to gently push on the globe, through the upper eyelid. In buphthalmos, the eye may feel hard but it will sink readily into the orbit. In exophthalmos, there will be resistance to the retropulsion, caused by the presence of a retrobulbar, space occupying mass.

6.  If you succeed in opening the mouth, look behind the last upper molar. It will be normal looking in glaucoma. Retrobulbar disease may sometimes present with a draining fistula or changes in the color or consistency of the soft palate.

7.  Are there unique signs associated with either syndrome? For example, striate keratopathy or corneal edema are associated with glaucoma. On the other hand, mandibular lymph nodes may be enlarged in many cases of exophthalmos, but will be normal-size in glaucoma.

Two tests can give a conclusive answer:

1.  Tonometry, or measurement of IOP. Pressure will be normal in exophthalmos and elevated in glaucoma.

2.  Imaging. An ultrasound is very useful for imaging of retrobulbar masses in cases of exophthalmos. Advanced imaging techniques, such as CT or MRI, may yield additional diagnostic information in cases of exophthalmos.

Retrobulbar Cellulitis/Abscess

Clinical Signs & Diagnosis of Retrobulbar Abscess

The disease is characterized by acute onset and by severe pain. The pain is caused when the condyle of the mandible presses on the abscess whenever the animal opens its mouth. This leads to refusal to eat and great resistance to opening the mouth for examination. It is often necessary to sedate the animal in order to open its mouth. Once the mouth has been opened, it is often possible to see a red swelling, or even an open draining tract, in the oral mucosa, behind the last upper molar tooth. If no gross lesion is visible in the oral cavity, it is possible to use imaging techniques, such as ultrasound or CT that may also demonstrate foreign bodies, or allow to perform guided fine needle aspirations for cytological diagnosis.

Treatment of Retrobulbar Abscess

Treatment of a retrobulbar abscess requires general anesthesia. This is because the patient must be intubated to avoid aspiration of exudate when the abscess is drained. Make an incision in the mucosa behind the last upper molar, and slowly inset a pair of curved hemostats to blindly explore the orbit and open pockets of exudate. If a pocket of exudate is encountered, copious amounts of exudate will flow out. This can be collected for cytology, and culture & sensitivity. In cases of retrobulbar cellulitis, no massive drainage of exudate will be seen. However, the very act of establishing a draining tract is usually sufficient to achieve a cure.

After creating a draining tract, flush the orbit with saline and antibiotics. The wound is not sutured. Systemic antibiotics are administered for 10–14 days, and the animal fed soft food. Dramatic, and most rewarding, improvement is usually observed within 1–2 days.

Retrobulbar Tumor

Clinical Signs & Diagnosis

As noted, retrobulbar tumors share a number of signs with retrobulbar abscesses. However, in contrast to retrobulbar abscesses, retrobulbar tumors are usually very slowly progressive, and non-painful. Furthermore, patients with retrobulbar tumors are 10–11 years old, on average, significantly older than patients with retrobulbar abscesses.

A retrobulbar tumor can cause deformation of the posterior part of the globe which can be visualized ophthalmoscopically, or using an ultrasound. However, ultimate localization relies on ultrasonography, CT or MRI imaging. The final diagnosis is usually made by guided fine needle aspiration and cytology.

Treatment and Prognosis

Solitary tumors discovered in early stages may be removed surgically. In such cases, the best surgical approach is usually orbitotomy, and it may be possible to preserve the globe and vision. Advanced cases may require radical orbitotomy, combined with radiation therapy and/or chemotherapy. However, most tumors are discovered in advanced stages, and due to their malignant nature they carry a very poor prognosis. One retrospective study reported a mean survival time of 1 month in cats and 10 months in dogs, with 35% of patients euthanized at the time of diagnosis.