In POAG, which visual change is typically affected first?

• A. Central acuity
• B. Peripheral vision
• C. Night vision
• D. Color vision

Answer: (B)

In primary open-angle glaucoma, the earliest change is loss of peripheral (side) vision. Glaucoma damages retinal ganglion cells and their optic nerve fibers in a pattern that first affects the outer parts of the visual field, so the center remains clear while the edges fade. Central visual acuity, which depends on the fovea, stays good until the disease is quite advanced. Night vision and color vision are not typically affected early because the initial damage is to the peripheral visual pathways rather than the mechanisms that govern night vision (rods) or color discrimination. As a result, patients often notice “tunnel vision” later in the disease, after peripheral vision has deteriorated.