2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 3: Cranial Nerves: Central and Peripheral Connections
Cranial nerve (CN) II—Macular projections constitute 80%–90% of the total volume of the optic nerve. Nasal fibers, carrying input from the temporal visual field, cross at the optic chiasm whereas temporal fibers do not.
CN III—CN III subnuclei supply their respective ipsilateral extraocular muscles. Exceptions are the subnucleus for the superior rectus muscle, which innervates the contralateral superior rectus; and the single, central levator palpebrae subnucleus, which supplies both levator muscles.
CN IV fascicles completely decussate after leaving the nucleus, thus innervating the contralateral superior oblique muscle. CN IV has the longest intracranial course and is the only CN to exit dorsally from the brainstem.
CN V, the largest of the CNs, provides sensation to the face and eye, as well as other structures of the head.
CN VI is susceptible to injury from increased intracranial pressure.
CN VII provides the efferent limb of the tear reflex.
Cranial nerves I–VI are depicted in Figure 3-1 in relation to the bony canals and arteries at the base of the skull. In Figure 3-2, the nerves are shown in relation to the brainstem, cavernous sinus, and orbit. For further study, see BCSC Section 5, Neuro-Ophthalmology, which describes these nerves as they apply to specific clinical entities.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.