Which instrument is utilized to measure the forward protrusion of the eye?

The instrument used to measure the forward protrusion of the eye is the exophthalmometer. This device specifically assesses the amount of protrusion of the eyeball from the orbit, which can be crucial in diagnosing conditions such as Graves' disease or thyroid eye disease, where there is an abnormal increase in eye bulge. An exophthalmometer provides a quantifiable measurement that can help healthcare providers monitor changes in orbital volume over time.

The other instruments listed serve different purposes: a pachymeter measures corneal thickness, which is important for assessing risk for glaucoma and other corneal diseases. A slit lamp is used for a detailed examination of the anterior segment of the eye, allowing for the observation of structures like the cornea, lens, and conjunctiva. A keratometer measures the curvature of the cornea, which is vital in fitting contact lenses and assessing refractive errors. Each of these tools has its unique application in ophthalmic practice, but only the exophthalmometer is specifically designed to gauge protrusion of the eye itself.