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Differentiating between Exophthalmos and Buphthalmos
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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; myositis of the extraocular muscles, and salivary cysts/mucoceles are also possible (though rare) causes of exophthalmos. Buphthalmos, on the other hand, is a normally-positioned globe that is enlarged due to elevated intraocular pressure (IOP), i.e., glaucoma. However, despite differences in globe size and causes, clinicians may find it difficult to differentiate between the two syndromes, as both present with an asymmetric appearance of the globe.
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 buphtlamous during examination, without resorting to other instrumentation. Signs that clinicians should evaluate include:
- 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.
- A history of acute vs. chronic, progressive presentation is not helpful in differentiating between exophthalmos and buphthalmos, as both presentations are possible in both syndromes. However, once the clinician has established the presence of exophthalmos, the history may help in determining the primary cause. A majority of retrobulbar tumors present with progressive exophthalmos, while a majority of retrobulbar abscesses present with acute exophthalmos.
- 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. Therefore, excess conjunctiva is usually not visible.
- Observe the animal from the top of the head. For the reasons just explained, exophthalmos may be readily visible from the top, as the lids are pushed forward. In buphthalmos, they should be in normal position.
- Evaluate the position of the third eyelid. This is normal in most cases of glaucoma (though severe pain may sometimes cause enophthalmos and passive elevation of the third eyelid). The third eyelid is usually elevated in exophthalmos, as the space occupying retrobulbar mass usually pushes against the third lid, causing its elevation.
- Estimate the diameter of the cornea. It is normal in exophthalmos, and increased in buphthalmos due to stretching of the globe. This examination sounds a little “far fetched”, but in fact it is a very sensitive test. In many cases you will be able to detect even a slight increase in corneal diameter, especially in unilateral cases, when you can compare the two corneas.
- 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. Note that this test is not a measurement of IOP, but of resistance.
- Are there signs of conjunctivitis? As noted in the “Red Eye” abstract elsewhere in these proceedings, glaucoma may present with a red “ciliary flush” and some lacrimation, but the conjunctiva is of normal consistency. The conjunctiva is also normal-appearing in most exophthalmos cases that are caused by a retrobulbar tumor. However, exophthalmos caused by a retrobulbar abscess/cellulitis is usually accompanied by conjunctivitis and purulent discharge. [...]
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