What is an arcuate scotoma and what causes it?

An arcuate (Bjerrum) scotoma is a curved, arc-shaped visual field defect that follows the path of the retinal nerve fiber bundles as they arch around the fovea. It is the most characteristic glaucomatous field defect, resulting from damage to the arcuate nerve fiber bundles at the optic disc. It typically affects the superior or inferior field and may connect to the blind spot on one end and the nasal meridian on the other (a ring scotoma if both arcuate areas are affected).

What causes a bitemporal hemianopia?

Bitemporal hemianopia is loss of the temporal (outer) visual field in both eyes. It results from a lesion at the optic chiasm, where the nasal retinal fibers from each eye cross. A lesion here damages fibers from both nasal retinas, eliminating the temporal visual field of each eye. The most common cause is a pituitary adenoma compressing the chiasm from below, but other chiasmal tumors and vascular abnormalities can produce this pattern.

What is the difference between congruous and incongruous homonymous hemianopia?

Congruity refers to how similar the defects are between the two eyes in a homonymous field loss. A congruous defect looks virtually identical in both eyes; an incongruous defect is similar in location but not identical in shape or density. More posterior lesions (occipital cortex) produce more congruous defects because fibers from corresponding retinal points are closely grouped in the visual cortex. More anterior post-chiasmal lesions (optic tract) produce more incongruous defects because fibers are less organized at that level.

Visual Field Defect Patterns: CPO Exam Guide

Why Field Patterns Matter

The pattern of a visual field defect localizes the lesion along the visual pathway. Different diseases produce characteristic field loss patterns that can be recognized on the printed Humphrey visual field report. As a CPO, understanding these patterns helps you recognize significant findings and communicate effectively with the physician.

The Visual Pathway

Understanding field defect patterns requires knowing the visual pathway anatomy:

Retina (each eye) → optic nerve → optic chiasm (nasal fibers cross) → optic tract → lateral geniculate body → optic radiations → occipital cortex

Lesions at different points along this pathway produce characteristic defect patterns because of how retinal fibers are organized at each level.

Common Glaucomatous Field Defect Patterns

Arcuate (Bjerrum) Scotoma

The most characteristic glaucomatous field defect. Retinal nerve fiber bundles arch around the fovea in an arcuate pattern. Glaucomatous damage to these fibers produces a curved arc-shaped defect that follows this arcuate course, typically in the superior or inferior field.

Nasal Step

A field defect that respects the horizontal meridian on the nasal side, producing a step-like discontinuity between the superior and inferior fields nasally. This occurs because the retinal nerve fibers above and below the horizontal raphe travel in separate bundles.

Paracentral Scotoma

Small defects near (but not involving) the central fixation point. These often precede larger arcuate defects and may be the earliest detectable glaucomatous field change.

Altitudinal Defect

A field defect affecting the entire upper or lower half of the visual field, respecting the horizontal midline. In glaucoma, dense inferior altitudinal defects reflect severe superior arcuate nerve fiber bundle damage.

Glaucomatous field defects are characteristically in the superior field (corresponding to inferior nerve fiber bundle damage, since the inferior disc rim is usually most affected in early glaucoma), respect the horizontal midline (nasal step), and are more pronounced nasally than temporally.

Neurological Field Defect Patterns

Pattern	Location	Lesion Site	Common Cause
Monocular loss	One eye only	Retina or optic nerve (pre-chiasmal)	CRVO, CRAO, optic neuritis, AION
Bitemporal hemianopia	Both temporal fields	Optic chiasm	Pituitary tumor
Homonymous hemianopia	Same side both eyes	Post-chiasmal (optic tract, radiation, cortex)	Stroke, tumor, trauma
Superior quadrantanopia	Upper quadrant, both eyes, same side	Temporal lobe optic radiation	Stroke in MCA territory
Inferior quadrantanopia	Lower quadrant, both eyes, same side	Parietal lobe optic radiation	Stroke in MCA territory
Congruous vs. incongruous	Varies	Cortical vs. tract lesions	More congruous = more posterior lesion

A key rule: field defects that affect both eyes in the same location (homonymous) are always caused by a lesion behind (posterior to) the optic chiasm. Field defects affecting only one eye (monocular) are always caused by a lesion in front of (anterior to) the chiasm — either in the retina or optic nerve.

Misidentifying a homonymous hemianopia as two separate monocular defects. Look at both fields together: if the same hemifield (left or right) is affected in both eyes, the defect is homonymous and post-chiasmal. This distinction changes the neurological workup completely.

Key Takeaways

Arcuate scotoma and nasal step are the hallmark glaucomatous field defect patterns
Monocular defects = lesion anterior to the chiasm (retina or optic nerve)
Bitemporal hemianopia = chiasmal lesion (most commonly pituitary tumor)
Homonymous hemianopia = post-chiasmal lesion (stroke, tumor)
More posterior lesions produce more congruous (symmetric) homonymous defects