Field Defects in Glaucoma
& Correlation with Optic Disc Morphology
Examination question · ~800 words
What are the characteristic visual field defects in glaucoma? Discuss their anatomical basis, correlation with optic disc morphology, staging, and progression analysis.
Try to outline your answer mentally before expanding sections below.
Glaucoma is a progressive optic neuropathy characterised by a stereotyped pattern of retinal ganglion cell (RGC) death and corresponding visual field (VF) defects that bear a precise anatomical relationship to optic disc morphological changes. Understanding this structure-function correlation is fundamental to glaucoma diagnosis, staging, and monitoring. The visual field is the mirror of the optic nerve: each sector of the neuroretinal rim (NRR) and each bundle of the retinal nerve fibre layer (RNFL) maps to a predictable region of the visual field, and loss in one predicts loss in the other with remarkable topographic fidelity. The characteristic arcuate, nasal step, and paracentral scotomas of glaucoma arise from the unique architecture of the RNFL as it converges on the optic disc, and can be correlated with focal NRR notching, RNFL defects on OCT, and disc haemorrhages.
The RNFL is composed of axons from RGCs that course towards the optic disc in a highly organised, arcuate pattern. Key anatomical principles governing VF defect morphology:
- Horizontal raphe: Temporal retinal fibres above and below the horizontal meridian do NOT cross. This creates the horizontal midline of VF defects (nasal step).
- Papillomacular bundle (PMB): Fibres from the fovea travel directly to the temporal optic disc. PMB occupies the temporal NRR and is vulnerable late; central VF preserved until advanced disease.
- Baring of the blind spot: Historically described as an early glaucomatous sign (enlargement of the physiological blind spot as superior/inferior disc margin fibres are lost), but now considered non-specific with limited diagnostic value — it can be elicited in normal subjects with threshold targets.
- Superior and inferior arcuate bundles: Fibres from superior and inferior retina arc around the fovea, entering the disc at superior and inferior poles — the zones of greatest vulnerability in glaucoma (thinner lamina cribrosa, fewer supporting astrocytes, higher IOP sensitivity).
| RNFL Region / Disc Sector | VF Correlate | Earliest Sign |
|---|---|---|
| Superotemporal NRR / superior pole | Inferior arcuate scotoma (inf. nasal VF) | Inferior nasal step / arcuate |
| Inferotemporal NRR / inferior pole | Superior arcuate scotoma (sup. nasal VF) | Superior nasal step / arcuate |
| Temporal NRR (PMB) | Central / paracentral scotoma | Late — paracentral cluster |
| Nasal NRR | Temporal VF loss | Uncommon early |
| Overall NRR thinning (diffuse) | Generalised constriction / tubular VF | Advanced / end-stage |
A. Paracentral Scotoma
One of the EARLIEST glaucomatous VF defects. Appears within 10° of fixation, often in the superior nasal paracentral area. Results from focal loss of RNFL fibres entering the superior or inferior disc poles that subserve the paracentral area (not the PMB itself). Detected on 30-2 grid; missed on 24-2 — hence 10-2 testing is critical when paracentral loss is suspected.
Paracentral scotomas can precede arcuate defects and may be the only early finding. The 24-2 test grid has only 4 test points within the central 10°, risking false negatives.
B. Arcuate (Bjerrum) Scotoma
The hallmark glaucomatous VF defect. Follows the arc of the RNFL from the blind spot, sweeping around fixation to terminate at the horizontal raphe nasally. Arises from focal loss of the superior or inferior arcuate RNFL bundle.
- Seidel scotoma: Comma-shaped extension from the blind spot — earliest form of arcuate defect.
- Bjerrum area: Region 10°–20° from fixation where arcuate defects are most common.
- Full arcuate: Complete arc from blind spot to nasal horizontal raphe.
- Ring (double arcuate): Both superior and inferior arcuates merge — indicates bilateral hemidisk involvement; advanced disease.
C. Nasal Step
A step-like asymmetry at the horizontal midline (nasal VF) between superior and inferior hemifields. Results from differential loss of superior vs. inferior arcuate fibres respecting the horizontal raphe. Highly specific for glaucoma. The nasal step is the reason the superior and inferior hemifields must always be compared independently in HPA staging.
D. Temporal Wedge
Rare; corresponds to nasal RNFL loss. Seen in NTG and superior segmental optic hypoplasia. Temporal VF defect respecting the vertical meridian.
E. Advanced Loss Patterns
- Tubular (gun-barrel) vision: Only central and/or temporal island remains. Corresponds to near-total NRR loss with sparing of PMB and temporal fibres.
- Temporal island: Final island at the far temporal periphery (temporal retinal fibres enter disc nasally — last to be lost). Patient has no central vision but can detect peripheral movement.
- Total field loss: Corresponds to complete optic atrophy with cup-to-disc ratio approaching 1.0.
The Hodapp-Parrish-Anderson (HPA) criteria are the standard staging system for glaucomatous VF loss using the Humphrey 30-2 SITA-Standard test:
| Stage | Mean Deviation (MD) | Criteria |
|---|---|---|
| Early | Better than −6 dB | MD > −6 dB; no point in central 5° ≤ 15 dB; ≤1 hemifield point ≤15 dB |
| Moderate | −6 to −12 dB | MD −6 to −12 dB; no point in central 5° ≤0 dB; ≤1 hemifield point ≤0 dB |
| Advanced / Severe | Worse than −12 dB | MD worse than −12 dB; OR point in central 5° ≤0 dB; OR both hemifields have points ≤0 dB |
Glaucoma Staging System (GSS-2) by Mills et al. and the Glaucoma Hemifield Test (GHT) are also used. GHT zones divide the VF into 5 corresponding superior-inferior zone pairs and flag asymmetry as: Within Normal Limits / Borderline / Outside Normal Limits (GHT-ONL).
A VF defect is considered significant (reproducible glaucomatous defect) if ANY of the following are met on a reliable Humphrey VF (false positives <15% — stricter glaucoma-grade cutoff; manufacturer default is <33% — false negatives <33%, fixation losses <20%):
- Cluster of ≥3 contiguous non-edge points on the pattern deviation (PD) probability map, all depressed at P < 5%, with at least 1 point depressed at P < 1% — in a location consistent with RNFL anatomy.
- Glaucoma Hemifield Test (GHT) result: Outside Normal Limits.
- Corrected Pattern Standard Deviation (CPSD) or Pattern Standard Deviation (PSD) outside 95% probability limits on the PD map.
These criteria require reproducibility on at least 2 reliable fields before diagnosing progression. A single abnormal VF in the absence of disc changes should be treated with caution — artefacts, media opacity, and learning effect all cause false positives.
A. Normal Optic Disc Parameters
| Parameter | Normal Value | Glaucomatous Change |
|---|---|---|
| Vertical C:D ratio | <0.6 (population mean 0.4) | >0.7; asymmetry >0.2 between eyes |
| NRR width (ISNT rule) | Inferior > Superior > Nasal > Temporal | Violation of ISNT rule |
| Disc area | Typically 1.8–3.4 mm² depending on ethnicity and measurement method (planimetric ~2.7 mm² in whites; HRT ~1.8 mm²) | Large discs — larger physiological cup |
| Cup shape | Round / oval | Vertically oval cup; focal notch |
| RNFL visibility | Bright striations on fundus | RNFL wedge defects; attenuation |
B. Glaucomatous Disc Changes and Their Field Correlates
Each glaucomatous disc change corresponds predictably to a specific VF sector:
| Disc Sign | Mechanism | VF Correlate |
|---|---|---|
| Inferior NRR notch (6 o'clock) | Focal RGC loss in inf. pole RNFL bundle | Superior arcuate scotoma |
| Superior NRR notch (12 o'clock) | Focal RGC loss in sup. pole RNFL bundle | Inferior arcuate scotoma |
| Disc haemorrhage (Drance) | RNFL infarct at disc margin — often inferotemporal | Paracentral / arcuate scotoma; precedes VF loss by ~1 yr |
| Bayonetting of vessels | Vessels angulate at cup margin — advanced cupping | Arcuate / tubular vision |
| Laminar dot sign | Posterior laminar cribrosa pores visible — deep cupping | Advanced / severe VF loss |
| Vertical cup elongation | Vertical cup ovoid due to superior/inferior NRR loss | Arcuate scotomas both poles |
| Nasal shifting of vessels | Cup expansion displaces vessels nasally | Advanced VF loss |
| Peripapillary atrophy (PPA) Zone Beta | Absence of RPE/photoreceptors — RNFL loss | Correlated with arcuate defect side |
| Temporal RNFL wedge defect | Dark streak on red-free photography | Localised arcuate / paracentral |
Optical coherence tomography (OCT) of the RNFL and the macular ganglion cell complex (GCC) provides structural quantification that can be correlated with VF sectors:
| OCT RNFL Clock Hour | Disc Sector | VF Region |
|---|---|---|
| 6-8 o'clock (inferior) | Inferior pole | Superior arcuate / nasal VF |
| 10-12 o'clock (superior) | Superior pole | Inferior arcuate / nasal VF |
| 3-4 o'clock (temporal/PMB) | Temporal NRR | Central / paracentral |
| 9 o'clock (nasal) | Nasal NRR | Temporal VF |
Structure precedes function: OCT can detect RNFL thinning approximately 5–8 years before reproducible VF defects appear on SAP (standard automated perimetry). This is because ~25–35% of RGCs must be lost before a reproducible VF defect manifests (Kerrigan-Baumrind LA et al., Invest Ophthalmol Vis Sci. 2000;41:741–748). Hence OCT-guided glaucoma management is increasingly preferred in early disease.
The 'floor effect': In advanced glaucoma, RNFL OCT reaches a measurement floor (~40–50 µm — residual glial and vascular tissue) and cannot detect further progression, whereas VF continues to deteriorate. At this stage, VF MD becomes the primary progression metric.
| Glaucoma Type | Characteristic VF Feature | Disc Morphology Clue |
|---|---|---|
| Normal Tension Glaucoma (NTG) | Denser scotoma; closer to fixation; steeper edge | Disc haemorrhages; focal inf. notch; PPA-beta |
| Pseudoexfoliative glaucoma | Asymmetric arcuate; rapid progression | Disc haemorrhages; asymmetric C:D |
| Pigmentary glaucoma | Heterogeneous — contemporary OCT series often show superior / superonasal RNFL thinning (distinct from POAG's inferior predominance); field defects may be steeper and localised | Variable notch location; reversal of the usual inferior-predominance on OCT is a clue |
| Juvenile OAG | Advanced loss at young age; arcuate | Large cup; thin NRR |
| Acute AACG | Generalised constriction (ischaemic) | Diffuse NRR atrophy; pale disc post-attack |
| Secondary NVG | Diffuse early loss + VF constriction | Cupping with underlying retinal disease signs |
VF progression can be assessed by event-based or trend-based analysis:
- Event-based (Guided Progression Analysis – GPA): Compares each test to baseline. Flags 'Possible Progression' (1 confirmation) or 'Likely Progression' (2 confirmations) using pattern deviation probability maps.
- Trend-based (VF Index – VFI; MD slope): Linear regression of MD or VFI over time. Rate of progression: MD loss >1.0 dB/year = fast; indicates need for aggressive intervention. VFI of 100% = normal; 0% = complete loss.
- Pointwise Linear Regression (PLR): Trend analysis at individual test locations — detects localised progression before global MD changes.
AGIS, CIGTS, EMGT, OHTS, and CNTGS are landmark trials that have established MD progression thresholds, IOP targets, and the predictive value of disc haemorrhages for VF progression.
The visual field and optic disc in glaucoma are inseparable partners — each change in the NRR, RNFL, or OCT maps precisely to a predictable VF sector by virtue of the strict retinotopic organisation of the RNFL. Mastery of this structure-function correlation enables the clinician to predict unseen VF loss from disc morphology, validate a suspicious VF defect against structural data, guide perimetric testing strategy (24-2 vs. 10-2), and interpret OCT progression in the context of functional status. In the era of OCT-guided glaucoma, this anatomical understanding remains the foundation of all clinical decision-making.
Trap 1 — FALSE
“Inferior NRR notch causes inferior arcuate scotoma”
Inferior NRR loss causes a SUPERIOR arcuate scotoma, because the inferior RNFL bundle subserves the superior visual field (strict retinotopic organisation).
Trap 2 — FALSE
“OCT RNFL is always more sensitive than VF for detecting glaucoma”
Context-dependent. In early glaucoma, OCT is superior (detects RNFL loss ~5–8 years before VF defects appear). In advanced glaucoma, OCT hits the floor (~40–50 µm — residual glial and vascular tissue) and cannot detect further progression; VF remains sensitive and becomes the primary progression metric.
Trap 3 — TRUE
“Temporal island is the last VF area preserved in advanced glaucoma”
True in most cases. Temporal retinal fibres enter the nasal aspect of the disc and are most resistant to glaucomatous damage — hence the peripheral temporal island is the final area preserved, often alongside a small central (papillomacular) island.
Trap 4 — FALSE
“The 24-2 grid is sufficient for all glaucoma monitoring”
Central 10-2 testing is required when 24-2 shows threat to fixation (within 5° of fixation), because 24-2 tests only 4 points within the central 10° and can miss progressive central loss.
Trap 5 — FALSE
“Disc haemorrhage is diagnostic of glaucoma”
Not exclusive. Disc haemorrhages are also seen in NTG, anterior ischaemic optic neuropathy (AION), and papilloedema. In the context of glaucoma, however, a disc haemorrhage (Drance haemorrhage) predicts impending VF progression — often within ~1 year.
Trap 6 — FALSE
“VFI is better than MD for end-stage glaucoma monitoring”
VFI overweights the central VF. In advanced glaucoma with a preserved central island, VFI appears deceptively good. MD slope is preferred for end-stage monitoring because it reflects the full 24-2/30-2 field.
A 58-year-old patient on maximum tolerated medical therapy for POAG has an MD of −14.2 dB on the right with a reliable 24-2 SITA-Standard VF showing a superior arcuate with threat to fixation and an inferior complete arcuate. The inferotemporal RNFL OCT is at the measurement floor (42 µm). How would you monitor this patient for progression, and what VF testing strategy would you employ? Justify your choice of metrics.
Monitoring strategy when OCT hits the floor
When inferotemporal RNFL OCT reaches the measurement floor (~40–50 µm), further structural thinning cannot be reliably detected. At this stage, VF becomes the primary progression metric. OCT should not be abandoned but should be supplemented with macular GCC analysis, which retains sensitivity slightly longer than peripapillary RNFL in advanced disease.
VF testing strategy
Given MD −14.2 dB with threat to fixation, the 24-2 grid is insufficient — it has only 4 test points within the central 10° and will miss progressive central loss. I would add a 10-2 SITA-Standard test to map the central 10° in detail and monitor the preserved island. Both tests should be performed at each visit (ideally every 4–6 months given rapid potential progression).
Progression metrics
I would use MD slope (linear regression) rather than VFI, as VFI overweights the central field. In this patient with a threatened but still-present central island, MD slope would more accurately reflect functional deterioration. Pointwise linear regression (PLR) would be used to detect localised progression within the preserved island. A rate faster than −1 dB/yr MD on 24-2 or any new absolute scotoma in the central 10° on 10-2 would trigger surgical intervention.
Surgical decision
Given maximum medical therapy, failure to control MD deterioration warrants trabeculectomy with MMC or a tube-shunt procedure, with an IOP target of ≤12 mmHg (IOP reduction ≥30%). The CIGTS and AGIS trials support aggressive IOP control in advanced disease to slow functional loss.
References
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- European Glaucoma Society Terminology and Guidelines for Glaucoma. 5th ed. 2021.
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- Kerrigan-Baumrind LA, Quigley HA, Pease ME, Kerrigan DF, Mitchell RS. Number of ganglion cells in glaucoma eyes compared with threshold visual field tests in the same persons. Invest Ophthalmol Vis Sci. 2000;41(3):741–748.
- Advanced Glaucoma Intervention Study (AGIS). The relationship between control of IOP and visual field deterioration. Am J Ophthalmol. 2000;130(4):429–440.
- Collaborative Initial Glaucoma Treatment Study (CIGTS). Comparison of initial treatment for glaucoma. Arch Ophthalmol. 1999;117:1341–1357.
- Early Manifest Glaucoma Trial (EMGT). Heijl A, et al. Reduction of IOP and glaucoma progression. Arch Ophthalmol. 2002;120(10):1268–1279.
- Leske MC, et al. Factors for glaucoma progression and the effect of treatment: the EMGT. Arch Ophthalmol. 2003;121(1):48–56.
- Garway-Heath DF, et al. Mapping the visual field to the optic disc in normal tension glaucoma eyes. Ophthalmology. 2000;107(10):1809–1815.
- Fingeret M, et al. Five rules to evaluate the optic disc and retinal nerve fibre layer for glaucoma. Optometry. 2005;76(11):661–668.