What is the best test for diagnosing glaucoma?

Tonometry is the best test for diagnosing glaucoma because it measures the intraocular pressure (IOP) within the eye, which is a critical factor in the development of glaucoma. Elevated IOP is one of the primary risk factors associated with the disease, and regular measurements can help identify patients at risk or those who may already have glaucoma.

Fluorescein staining is primarily used to assess the surface of the eye, particularly in cases of corneal abrasions or foreign bodies, and does not provide information about intraocular pressure or the condition of the optic nerve, which are crucial in diagnosing glaucoma.

The Snellen vision exam is designed to assess visual acuity and is not specific to glaucoma. While patients with advanced glaucoma may have reduced visual acuity, this test does not evaluate the intraocular pressure or other factors relevant to diagnosing glaucoma.

The refractive index pertains to the bending of light in relation to the eye's structure and is used in optometry to determine corrective lens prescriptions. It does not relate to the diagnosis or assessment of glaucoma.

Thus, tonometry is the gold standard diagnostic test for evaluating glaucoma due to its direct measurement of IOP, making it essential for early detection and management of the condition.