What Does an Increase in Cup-to-Disc Ratio Mean?
An increased cup-to-disc ratio indicates progressive loss of optic nerve fibers and is a major risk factor for glaucoma, signaling either early glaucomatous damage or increased risk of developing primary open-angle glaucoma (POAG). 1
Primary Clinical Significance
An enlarging cup-to-disc ratio represents actual structural damage to the optic nerve:
- The increase reflects loss of retinal ganglion cells and their axons, combined with physical tissue rearrangements at the optic nerve head 2
- A larger cup-to-disc ratio is an established independent risk factor for developing POAG in patients who are glaucoma suspects 1
- In patients already diagnosed with glaucoma, an increasing cup-to-disc ratio is a risk factor for disease progression 1
What the Increase Actually Represents
The pathophysiology involves two distinct components:
- Prelaminar thinning: A shallow form of cupping related to loss of retinal ganglion cells 3
- Laminar damage: Involves damage to the lamina cribrosa and peripapillary scleral connective tissue, representing deeper structural changes 3
Cupping begins as soon as nerve fiber loss begins, making it potentially more sensitive than visual field testing for detecting early glaucomatous damage 2
Critical Diagnostic Considerations
When It Suggests Glaucoma
The following features point toward glaucomatous cupping:
- Progressive enlargement over time with elevated intraocular pressure 1
- Asymmetric cupping between eyes (difference >0.2 in cup-to-disc ratio) 2
- Associated findings: disc hemorrhages, retinal nerve fiber layer defects, or visual field changes consistent with glaucoma 1
- Preserved pink neuroretinal rim color (as opposed to pallor) 3
When It May NOT Be Glaucoma
An increased cup-to-disc ratio can occur in non-glaucomatous optic neuropathies, including 3:
- Compressive optic neuropathies
- Arteritic anterior ischemic optic neuropathy
- Hereditary optic neuropathies
- Optic neuritis
The key distinguishing feature: non-glaucomatous cupping typically shows pallor of the neuroretinal rim, whereas glaucomatous cupping maintains rim color until late stages 3
Important Pitfall: Small Optic Discs
In eyes with small optic discs, glaucomatous damage may occur with misleadingly low cup-to-disc ratios 4. In these cases:
- Parapapillary chorioretinal atrophy becomes a more sensitive indicator than the cup-to-disc ratio itself 4
- Loss of visible retinal nerve fiber bundles may be more apparent than cupping 4
- Do not falsely reassure patients with small discs and "normal" cup-to-disc ratios if other signs of glaucoma are present 4
Clinical Action Required
When you observe an increased or increasing cup-to-disc ratio:
Immediate assessment should include 1:
- Intraocular pressure measurement
- Gonioscopy to assess anterior chamber angle
- Visual field testing (automated perimetry)
- Optical coherence tomography of retinal nerve fiber layer and ganglion cell layer
- Assessment for disc hemorrhages
- Central corneal thickness measurement
Follow-up frequency depends on risk stratification 1:
- High-risk patients (multiple risk factors including large cup-to-disc ratio, elevated IOP, thin cornea, family history): every 6-12 months
- Lower-risk patients: every 12-24 months
- Any documented progression: convert to glaucoma management with target IOP reduction of at least 20% from baseline 1
Risk calculators are available at https://ohts.wustl.edu/risk/ to quantify 5-year risk of conversion to glaucoma using cup-to-disc ratio combined with age, pattern standard deviation, central corneal thickness, and IOP 1