Many see a prominent eye, and think it must be an enlarged (buphthalmic) globe and jump to a diagnosis of glaucoma. This is one possible cause, but there are other possible aetiologies for a prominent eye.
The globe looks prominent. In severe cases this is quite obvious, but in early cases this can be hard to define. Try looking from on top, even slight proptosis can usually be identified.
Chemosis: swelling of the conjunctiva is seen when orbital disease leads to reduced venous return. The swollen conjunctiva can dry out, and can also reduce eyelid movement resulting in corneal exposure. A prominent eye with chemosis of the eyelid and or third eyelid conjunctiva suggests retrobulbar disease.
Corneal Exposure: when the globe is quite prominent, the cornea can develop exposure problems. This may be seen as slow healing ulceration, vascular keratitis, and/or pigmentary keratitis.
Reduced Retropulsion: with orbital disease eg tumour, or abscess, or cellulitis, the eyeball cannot be pushed back into the orbit. Compare the affected eye with the normal eye.