Glaucoma is a progressive eye disease defined by characteristic damage to the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. This damage involves the gradual loss of retinal ganglion cells and their axons, resulting in irreversible vision loss, often beginning with the peripheral field. While frequently associated with elevated intraocular pressure (IOP), the damage is the defining feature of the condition. Doctors classify the severity of this chronic, progressive illness into distinct stages to standardize diagnosis and treatment planning, tracking its advancement from high risk to profound visual impairment.
Defining Glaucoma Staging
Doctors stage glaucoma to accurately gauge the severity of optic nerve damage, which determines the intensity of treatment and predicts the long-term visual prognosis. The process relies on measuring two primary aspects: structural damage to the optic nerve and functional vision loss. Structural assessment uses imaging like Optical Coherence Tomography (OCT) to measure the thinning of the retinal nerve fiber layer (RNFL). Functional testing is standardized through perimetry, specifically visual field tests, which map areas of vision loss.
These stages are defined by the extent of irreversible damage, not the patient’s current intraocular pressure (IOP) reading. Although lowering IOP is the main treatment goal, the stage reflects the cumulative, permanent harm inflicted on the visual system. Classifying severity allows clinicians to tailor the target IOP and the aggressiveness of therapy, providing a common language for ophthalmologists.
Stage 1: Glaucoma Suspect
The initial stage of concern is characterized by an elevated risk for developing the disease rather than confirmed, measurable damage. Individuals classified as a Glaucoma Suspect often present with ocular hypertension, meaning their intraocular pressure is consistently higher than average but they have no detectable changes to the optic nerve or visual field. A suspicious appearance of the optic nerve head, such as an increased cup-to-disc ratio, is another characteristic.
Other risk factors leading to this designation include a strong family history or thin central corneal thickness, which can falsely lower IOP readings. At this point, standard visual field testing shows no loss of function, and the patient is typically asymptomatic. Close monitoring is initiated, often involving repeated structural imaging and visual field tests, to establish a baseline and detect the earliest signs of progression.
Stages 2 and 3: Mild and Moderate Damage
The transition to Stage 2, or Mild Glaucoma, marks the first definitive diagnosis, where structural damage is accompanied by measurable, limited functional loss. This stage is characterized by early, localized defects in the visual field that are subtle, meaning the patient is largely unaware of them. The damage typically appears in the peripheral vision, away from the central point of fixation. Clinical metrics often show a Mean Deviation (MD) score on the visual field test that is better than or equal to -6.00 decibels (dB).
Progression to Stage 3, or Moderate Glaucoma, signifies a worsening of the visual field defect, which becomes more extensive and deeper. Functional loss is still primarily outside the central 5 degrees of vision. However, the defects are now present in one half of the visual field, either the upper or lower division. The Mean Deviation score is typically worse than -6.00 dB but better than -12.00 dB, reflecting a significant reduction in visual sensitivity. Patients may begin to notice impairment during complex visual tasks, though central acuity remains preserved.
Stages 4 and 5: Advanced Stages and Blindness
Stage 4, or Severe Glaucoma, represents deterioration where the patient experiences significant visual impairment due to widespread damage. Functional loss is defined by visual field defects present in both the upper and lower halves of the visual field. The damage has often encroached into the central 5 degrees of vision, which directly impacts reading and other fine visual tasks. The Mean Deviation score typically falls within the range of -12.01 dB to -20.00 dB, and the extensive loss limits daily activities and mobility.
The final stage, Stage 5, is often termed End-Stage Glaucoma, resulting in near-total or absolute loss of vision. The optic nerve has suffered near-complete atrophy, and the visual field may be reduced to only a small, isolated central island of vision. Functional blindness is common in the affected eye, and reliable visual field testing may no longer be possible. Treatment efforts shift toward preserving any remaining functional vision and managing chronic pain, as the accumulated damage is irreversible.