A lesion of the optic nerve causes vision loss in which pattern?

• A. Loss in the affected eye only with central vision loss
• B. Bilateral temporal field loss with central sparing
• C. Quadrantanopia in the temporal field of both eyes
• D. Loss in the contralateral visual field

Answer: (A)

A lesion of the optic nerve causes monocular vision loss because this nerve carries all visual information from one eye before it reaches the chiasm. When the nerve on one side is damaged, the entire input from that eye is lost, so vision is affected in only that eye. If the fibers serving the central retina (the papillomacular bundle) are involved, central vision can be lost as well, producing a central scotoma within that monocular field.

Patterns involving the other eye, the opposite eye, or the opposite visual fields point to lesions located at the optic chiasm or beyond (such as the optic tract, radiations, or occipital cortex). For example, a chiasm lesion tends to cause loss in the temporal fields of both eyes, and post-chiasm lesions produce homonymous field defects in the same side of both eyes.