I’m going to touch on a topical that I think many people find confusing.

Buphthalmia is the term for an enlarged globe.

Exophthalmia is the term for a globe that is being pushed forward.

Both buphthalmia and exophthalmia cause the eye to appear bulgy.

So, what causes each thing?

Buphthalmia occurs secondary to glaucoma. This is the only way the eye will physically enlarge. When the pressure inside the eye is sustained at a level outside of normal for any significant time, the outer collagenous ocular tunic (cornea and sclera) will stretch. This results in the eye becoming larger or stretching.

This will cause other ocular changes including Haab’s stria (corneal stretch marks), lens subluxation, optic nerve cupping, and possibly exposure keratitis. This is due to CHRONIC glaucoma and is not seen with acute pressure elevations.

A big eye=blind. The exception is rarely for cats, horses, and puppies. Cats and horses tolerate high pressures a bit better than dogs but usually a big eye will still be blind. Young animals have more elastic skin and sclera so they may have a big eye that still has some functional vision.

Exophthalmia happens if anything pushes the eye forward. It can be acute and profound, like in a proptosis scenario. It can also be somewhat acute and painful like in an orbital abscess/cellulitis situation. Cases of orbital neoplasia are typically more chronic with a gradual progressive bulging of the eye noted over several weeks or months. Autoimmune disease can also cause exophthalmia (i.e. extraocular myositis, masticatory myositis). Depending on the cause and location of the driving force of the exophthalmia, the eye may be pushed directly forward, deviate medially or laterally, or be pushed dorsally or ventrally.

There is a lot of tissue in the orbit including fat, nerves, muscle and glandular tissue. Neoplasia, cyst formation, vascular anomalies (orbital varix), trauma, inflammation, and infection can all cause the eye to become exophthalmic.

How can you tell if an eye is buphthalmic or exophthalmic?

If there is another eye to compare, you can measure the size of the globe using a Schirmer tear test strip or by utilizing ocular ultrasound.

Retropulsion is the process of gently pushing on the globes when the eyelids are closed to see if they squish back into the orbit. Retropulsion should be symmetrical for both eyes. Note if the globe retropulses the same amount as the contralateral eye or if you detect any resistance to that movement. Pro tip: It sometimes helps to close your eyes and do both eyes at the same time!

Also, when evaluating a patient for exophthalmia, look at the patient from many angles including from above and the side.

If you still can’t tell or the patient only has one eye, use other clues like looking for evidence of lens subluxation, Haab’s stria, or blindness. Remember a big eye is usually a blind eye but an eye pushed forward will very likely still have vision!

Remember that brachycephalic skulls are basically flat and therefore physiologically somewhat exophthalmic, and you may not be able to retropusle them much compared to a deep orbited dog like a retriever.