What instrument is primarily used to measure the exact radius of curvature of the cornea?

The keratometer is the instrument specifically designed to measure the radius of curvature of the cornea. This measurement is crucial for various aspects of ophthalmic practice, particularly in fitting contact lenses and assessing corneal health. The keratometer provides precise readings of the corneal curvature, which helps eye care professionals understand how the cornea shapes light entering the eye, identify certain types of astigmatism, and plan for refractive surgery if needed.

Other instruments mentioned serve different purposes; for instance, the ophthalmoscope is primarily used for viewing the interior structures of the eye, allowing the clinician to assess conditions such as diabetic retinopathy or glaucoma. The tonometer measures intraocular pressure to assess for glaucoma, which is critical in monitoring eye health but does not provide information about the curvature of the cornea. The exophthalmometer is used to measure the degree of protrusion of the eyeball, often in conditions such as Graves' disease, but it too does not relate to the measurement of corneal curvature. Therefore, the keratometer is the appropriate choice for assessing the radius of curvature of the cornea.