Some diagnostic procedures (eg, ultrasonography, tonometry) may provide a definitive diagnosis; although, exophthalmos and buphthalmos can often be differentiated during examination without additional instrumentation.
Clinicians should consider the following questions when differentiating between exophthalmos and buphthalmos (ie, glaucoma).
Related Article: Exophthalmos in a Dog
Is the condition unilateral or bilateral?
Glaucoma may be unilateral or bilateral, but exophthalmos is typically unilateral. Therefore, bilateral presentation usually indicates glaucoma.
How much conjunctiva is visible?
In exophthalmos, the eye is pushed forward; therefore, excess conjunctiva is visible, especially when looking at the eye from the side. With buphthalmos, the eye is stretched but remains in normal position inside the orbit; therefore, excess conjunctiva is usually not visible.
What is the position of the nictitans?
The nictitans (ie, third eyelid) is positioned normally in most glaucoma cases, although severe pain may sometimes cause enophthalmos and passive elevation of the nictitans. The nictitans is usually elevated in exophthalmos, as the space-occupying retrobulbar mass pushes against the nictitans, causing the elevation.
What is the diameter of the cornea?
Figure 2. Unilateral glaucoma in an Afghan hound (4 years of age). Note the obvious difference in corneal diameter and corneal edema. Although vessels in the affected eye are more congested, the conjunctiva looks normal and the nictitans is not elevated, thus differentiating it from exophthalmus. Courtesy of Dr. Seth Koch