What is the typical visual field and acuity presentation with an anterior visual pathway (optic nerve) lesion?

• A. Monocular vision loss with decreased acuity and possibly an afferent pupillary defect in the affected eye.
• B. Bitemporal hemianopia due to chiasm involvement.
• C. Binocular field loss with preserved acuity.
• D. Only color vision loss.

Answer: (D)

An anterior visual pathway lesion affects only the eye with the damaged optic nerve because the damage is before the fibers cross at the chiasm. The typical presentation is monocular vision loss with reduced visual acuity in that eye, and an afferent pupillary defect is often present due to diminished input from the affected nerve. Color vision can be affected in optic neuropathies, but it is not the sole or primary deficit you’d expect; the hallmark is decreased acuity along with a corresponding monocular field defect.

The other patterns point to different sites: a lesion at the chiasm causes bitemporal field loss; lesions beyond the chiasm can produce binocular field losses with varying acuity depending on the exact location, but not the classic monocular loss with decreased acuity from an optic nerve issue.