Which statement is NOT true regarding visual field defects?

Which statement is NOT true regarding visual field defects?

• A. Pituitary adenomas commonly cause bitemporal VF defects
• B. Post chiasmal lesions cause posthemispheric VF defects
• C. A complete visual field defect is easy to localize
• D. Incongruous defects are caused by lesions more anterior in the visual pathway

Answer: (C)

Understanding where a visual field defect fits along the visual pathway is all about pattern recognition. Pituitary tumors pressing on the optic chiasm especially affect the crossing nasal fibers from both eyes, producing a bitemporal field loss. When the lesion is behind the chiasm—in the optic tract, radiations, or occipital cortex—the same part of the field is lost in both eyes, giving a homonymous defect. As you move deeper into the posterior pathway, defects become more congruent between the two eyes; lesions that are more anterior, like in the optic nerve, tend to produce defects that are less like each other between eyes (incongruent). A complete visual field defect doesn’t localize as precisely as one might think. If the entire field in one eye is lost, that points to a problem in the eye or its immediate nerve supply (retina or optic nerve), but this pattern alone doesn’t pin down the exact site within that anterior segment. Different structures before the chiasm can produce a total field loss in that eye, so you need additional clues and testing to specify the exact location. That’s why the statement claiming a complete visual field defect is easy to localize isn’t reliable. Localization relies on the overall pattern across eyes and fields, not on a single complete-field finding in isolation.

Understanding where a visual field defect fits along the visual pathway is all about pattern recognition. Pituitary tumors pressing on the optic chiasm especially affect the crossing nasal fibers from both eyes, producing a bitemporal field loss. When the lesion is behind the chiasm—in the optic tract, radiations, or occipital cortex—the same part of the field is lost in both eyes, giving a homonymous defect. As you move deeper into the posterior pathway, defects become more congruent between the two eyes; lesions that are more anterior, like in the optic nerve, tend to produce defects that are less like each other between eyes (incongruent).

A complete visual field defect doesn’t localize as precisely as one might think. If the entire field in one eye is lost, that points to a problem in the eye or its immediate nerve supply (retina or optic nerve), but this pattern alone doesn’t pin down the exact site within that anterior segment. Different structures before the chiasm can produce a total field loss in that eye, so you need additional clues and testing to specify the exact location.

That’s why the statement claiming a complete visual field defect is easy to localize isn’t reliable. Localization relies on the overall pattern across eyes and fields, not on a single complete-field finding in isolation.