Residency · Residency · Ophthalmology

Visual Field Interpretation and Neuro-Ophthalmic Localization

Automated Perimetry Basics

Humphrey Visual Field (HVF) -- Standard Automated Perimetry

The Humphrey visual field analyzer is the most commonly used instrument for perimetry in clinical practice. It performs static, automated, threshold perimetry, measuring the minimum light intensity detectable at each test point. The standard protocols are the 24-2, which tests the central 24 degrees of the visual field, and the 30-2, which extends to 30 degrees. The 10-2 protocol tests the central 10 degrees with 2-degree spacing between test points and is used for macular disease and advanced glaucoma where paracentral defects are of particular concern. The SITA Standard algorithm (Swedish Interactive Thresholding Algorithm) is faster than traditional full-threshold testing while maintaining comparable accuracy, and SITA Fast offers even quicker testing with slightly reduced precision, making it useful for screening purposes.

Key Components of the HVF Printout

Understanding the HVF printout is essential for accurate clinical interpretation. The raw sensitivity values are measured in decibels, with higher values indicating greater sensitivity. The greyscale map provides a visual representation of the field but should not be used for clinical decision-making, as it can be misleading. The total deviation plot shows the difference between the patient's sensitivity at each point and age-matched normal values, identifying overall sensitivity loss. The pattern deviation plot corrects the total deviation for generalized depression (such as that caused by cataract), isolating focal or localized defects. Probability maps display the statistical significance of deviations at each point, flagged at the p less than 5%, 2%, 1%, and 0.5% levels.

Three global indices summarize the overall field status. Mean deviation (MD) is the average deviation from normal across all test points -- more negative values indicate worse fields, and it serves as the primary measure of overall field loss. Pattern standard deviation (PSD) quantifies the variability of sensitivity across the field and is elevated when focal or localized defects are present. The visual field index (VFI) expresses the percentage of remaining visual field function, with 100% representing a normal field.

Reliability Indices

Before interpreting any visual field, the reliability indices must be checked. Fixation losses exceeding 20%, monitored by the Heijl-Krakau blind-spot method, indicate that the patient was not consistently fixating on the target. False positives above 15% suggest a trigger-happy patient who presses the response button without detecting a stimulus. False negatives above 33% may indicate unreliable responses but can also reflect genuinely severe field loss. Unreliable fields should be interpreted with caution and repeated if necessary.

<image>Annotated Humphrey visual field printout showing the key components: greyscale map, total deviation plot, pattern deviation plot, probability symbols, global indices (MD, PSD, VFI), and reliability indices</image>

Patterns of Visual Field Loss and Localization

Retinal/Optic Nerve Head Lesions

Arcuate Scotoma

An arcuate scotoma follows the course of the arcuate nerve fiber bundles from the optic disc and respects the horizontal meridian at the nasal raphe. It is the classic visual field defect of glaucoma, appearing as superior or inferior arcuate defects. Arcuate scotomas can also be caused by anterior ischemic optic neuropathy, branch retinal artery occlusion, and optic disc drusen.

Altitudinal Defect

An altitudinal defect involves loss of the entire superior or inferior hemifield, respecting the horizontal meridian. It is the characteristic visual field pattern of anterior ischemic optic neuropathy, with an inferior altitudinal defect being the most common presentation in NA-AION. Other causes include branch retinal vein occlusion and retinal detachment.

Central Scotoma

A central scotoma involves loss of the central fixation area and is seen in optic neuritis, macular disease, and toxic or nutritional optic neuropathy. A cecocentral scotoma, which connects the central scotoma to the blind spot, is particularly characteristic of toxic optic neuropathy from agents such as ethambutol or methanol.

Enlarged Blind Spot

An enlarged blind spot is most commonly caused by papilledema. Other causes include optic disc drusen, peripapillary atrophy, and acute idiopathic blind spot enlargement syndrome.

Generalized Depression

Generalized depression refers to diffuse sensitivity reduction across the entire field. The most common cause is cataract, which produces an artifactual reduction in sensitivity by reducing the amount of light reaching the retina. True causes include end-stage glaucoma and optic atrophy. Patient fatigue and malingering can also produce this pattern.

Chiasmal Lesions

Bitemporal Hemianopia

Bitemporal hemianopia -- loss of the temporal visual fields bilaterally -- respects the vertical meridian and localizes the lesion to the optic chiasm. The most common cause is a pituitary adenoma. Other causes include craniopharyngioma (especially in children, where the tumor compresses the chiasm from above), meningioma of the tuberculum sellae or diaphragma sellae, and rarely aneurysms, gliomas, or demyelination. A junction scotoma, consisting of an ipsilateral central scotoma combined with a contralateral superior temporal defect, localizes the lesion to the junction of the optic nerve and chiasm, attributed to the crossing fibers at the anterior chiasm (Wilbrand knee).

Binasal Hemianopia

Binasal hemianopia is very rare in practice. True binasal field loss could result from bilateral lateral chiasmal compression, such as from bilateral carotid aneurysms or bilateral optic nerve sheath meningiomas. More commonly, an apparent binasal pattern is artifactual or results from bilateral glaucomatous nerve fiber layer damage.

Retrochiasmal Lesions

Homonymous Hemianopia

A homonymous hemianopia is the loss of the same hemifield in both eyes -- for example, a right homonymous hemianopia involves loss of the right visual field in both eyes. It indicates a lesion in the contralateral optic tract, lateral geniculate nucleus, optic radiations, or occipital cortex. The most common cause is stroke in the posterior cerebral artery territory.

Localization Within the Retrochiasmal Pathway

The specific characteristics of the field defect help localize the lesion within the retrochiasmal pathway. An optic tract lesion produces an incongruous homonymous hemianopia (the defects in the two eyes differ in shape and extent), a contralateral RAPD, and characteristic optic atrophy -- band atrophy on the ipsilateral side and diffuse atrophy on the contralateral side. Lateral geniculate nucleus lesions are rare and produce sectoral or wedge-shaped hemianopias depending on the vascular territory involved. Temporal lobe lesions affecting Meyer loop produce a superior homonymous quadrantanopia ("pie in the sky") that is relatively incongruous, and these fibers are vulnerable during temporal lobe surgery. Parietal lobe lesions produce an inferior homonymous quadrantanopia ("pie on the floor") and may demonstrate asymmetry of optokinetic nystagmus. Occipital cortex lesions produce a highly congruous homonymous hemianopia; macular sparing may occur because the occipital pole receives dual blood supply from both the posterior cerebral artery and the middle cerebral artery.

Congruity

Congruity refers to how similar the visual field defects are between the two eyes. Greater congruity indicates a more posterior lesion, closer to the visual cortex. Optic tract lesions produce highly incongruous defects because fibers from the two eyes are not yet fully organized. Occipital cortex lesions produce highly congruous defects because the retinotopic map is precisely organized at this level.

<image>Diagram showing patterns of visual field loss with corresponding lesion locations along the visual pathway: optic nerve (central scotoma), chiasm (bitemporal hemianopia), optic tract (incongruous homonymous hemianopia), temporal lobe (superior quadrantanopia), and occipital cortex (congruous homonymous hemianopia with macular sparing)</image>

Glaucomatous Visual Field Patterns

Early Glaucoma

The earliest glaucomatous visual field changes include paracentral scotomas within the central 10 degrees near fixation, a nasal step (a sensitivity difference across the horizontal midline in the nasal field), and a temporal wedge defect.

Moderate Glaucoma

As glaucoma progresses, the classic arcuate scotoma (Bjerrum scotoma) develops, arcing from the blind spot toward the nasal horizontal meridian. Superior and inferior arcuate defects may appear individually or together as a double arcuate scotoma.

Advanced Glaucoma

In advanced disease, only a central island (the central 5 to 10 degrees) or a temporal island (the temporal periphery) of vision may remain, with generalized depression and possible residual islands. "Split fixation" occurs when field loss threatens to encroach on central vision.

Glaucoma Progression Analysis

The Humphrey instrument's Guided Progression Analysis (GPA) software detects statistically significant changes between serial fields. The MD rate of change, calculated by linear regression of MD values over time, provides a slope representing the rate of field deterioration. The VFI slope similarly tracks the rate of visual field loss per year. Clinically significant progression is generally defined as MD worsening of more than 1 dB per year or points flagged as progressing on GPA.

Special Considerations

Functional (Non-Organic) Visual Field Loss

Functional visual field loss can mimic organic disease. Key features include tunnel vision that does not expand when testing distance is increased -- organic visual field defects expand proportionally with distance. Spiraling fields, in which isopters progressively constrict on kinetic perimetry, are another hallmark. Inconsistency between the severity of reported field loss and the patient's daily function is an important clue. Monocular temporal hemianopia that respects the vertical meridian without an organic cause may also suggest functional disease.

Medications and Visual Fields

Several medications can produce characteristic visual field abnormalities. Vigabatrin causes bilateral concentric visual field constriction through irreversible GABA-mediated retinal toxicity. Hydroxychloroquine produces paracentral scotomas, best detected on the 10-2 field protocol with SD-OCT serving as the earliest detection modality. Ethambutol causes central or cecocentral scotomas from optic neuropathy.

<image>Humphrey visual field examples of common glaucomatous patterns: nasal step, superior arcuate scotoma, double arcuate defects, and advanced field loss with central and temporal islands</image>

Clinical Pearls

The reliability indices must always be checked first -- an unreliable field cannot be meaningfully interpreted. Pattern deviation is more clinically useful than total deviation for detecting focal defects because it corrects for generalized media opacity such as cataract. A bitemporal hemianopia indicates a chiasmal lesion, most commonly a pituitary adenoma, and warrants MRI of the brain with a sella protocol. A homonymous hemianopia indicates a retrochiasmal lesion, and the degree of congruity helps localize it along the visual pathway. In glaucoma, the 24-2 protocol is used for routine monitoring, while the 10-2 is added for advanced disease or when paracentral defects near fixation are suspected. Optimal clinical decision-making combines structural data from OCT with functional data from visual field testing -- the structure-function correlation is critical. MD is the single best metric for tracking glaucoma progression over time. Macular sparing in a homonymous hemianopia suggests an occipital cortex lesion with preserved dual blood supply to the macular cortical representation. A key localizing principle is that respect of the vertical meridian indicates a chiasmal or retrochiasmal lesion, while respect of the horizontal meridian indicates a retinal or optic nerve process. Functional visual field loss should be evaluated with tangent screen testing and careful correlation with the patient's daily visual function.

References

• Keltner JL, et al. Classification of visual field abnormalities in the Ocular Hypertension Treatment Study. Arch Ophthalmol. 2003;121(5):643-650.
• Walsh TJ. Visual Fields: Examination and Interpretation. 3rd ed. Oxford University Press; 2010.
• Kedar S, et al. Congruency in homonymous hemianopia. Am J Ophthalmol. 2007;143(5):772-780.
• American Academy of Ophthalmology. Basic and Clinical Science Course, Section 5: Neuro-Ophthalmology; Section 10: Glaucoma.

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