(a) Open-angle glaucoma reproduced from [1], with permission from Elsevier

Suspect	One or two of the following: (1) IOP > 21 mm Hg (2) Suspicious disc or C/D asymmetry of >0.2 (3) Suspicious 24-2 (or similar) VF defect
Early	(1) Early glaucomatous disc features (e.g., C/D∗ < 0.65) (2) Mild VF defect not within 10° of fixation (e.g., MD better than −6 dB on HVF 24-2)
Moderate	(1) Moderate glaucomatous disc features (e.g., vertical C/D∗ 0.7–0.85) (2) Moderate VF defect not within 10° of fixation (e.g., MD from −6 to −12 dB on HVF 24-2)
Severe	(1) Advanced glaucomatous disc features (e.g., C/D∗ > 0.9) (2) VF defect within 10° of fixation† (e.g., MD worse than −12 dB on HVF 24-2)

C/D, cup-to-disc; HVF, Humphrey visual field; IOP, intraocular pressure; MD, mean deviation; VF, visual field.

∗ refers to vertical C/D ratio in an average size nerve. If the nerve is small, then a smaller C/D ratio may still be significant; conversely, a large nerve may have a large vertical C/D ratio and still be within normal limits. † also considers baseline 10-2 VF (or similar).

Recent evidence indicates that ganglion cell loss should also be taken into consideration when staging/classifying glaucoma [2].