Chapter 8: Cranial Nerve Screening

INTRODUCTION

8.1 INTRODUCTION TO CRANIAL NERVE SCREENING

Cranial nerves (CN) 2, 3, 4, and 6 are all either directly or indirectly assessed during routine eye examination. However, patients will often present to their eye care provider with neurologic dysfunction involving one or more of the other eight CNs because many of the diseases that affect these nerves present with visual or ocular symptoms such as diplopia, blurry vision, or reduced peripheral vision. For example, a patient with a new-onset Bell’s palsy may present to their optometrist because they are experiencing ocular dryness or observed a new onset ptosis in the mirror. In situations such as this, optometrists need to be able to determine if their patient’s condition warrants monitoring, treatment, or referral. If monitoring is called for, the optometrist must be confident that no harm will come to the patient while they wait and watch the patient’s condition over an extended period of time.

If treatment of neurologic dysfunction is required and falls within the optometrist’s scope of practice, appropriate testing is necessary to accurately diagnose the condition and prescribe appropriate therapy. If the treatment falls outside the optometrist’s scope of practice, they need to decide the type of specialist the patient will be referred to and within what time frame. In order to make these decisions, the optometrist uses data about the neurological status of the patient through problem-specific tests such as the chair-side procedures described in this chapter.

A thorough exposition of the entire general neurological examination is beyond the scope of this text and can be found in other sources (see References for Chapter 8). This chapter is limited to problem-specific procedures for assessing the functions of the CNs, because ocular or visual symptoms that are likely to motivate a patient to see an eye care specialist are likely to affect the functions of the CNs. The reader should remember that many of the routinely performed entrance tests also assess the function of certain CNs. For example, tests of visual acuity, color vision, visual fields, and ophthalmoscopy assess the structure and function of the optic nerve, while extraocular muscle movement testing and cover test assess the oculomotor, trochlear, and/or abducens nerves.

The techniques described in this chapter require no unusual or special instrumentation. They are easy to perform and use equipment and supplies that are readily available in most optometric settings.

8.2 LID AND PTOSIS MEASUREMENTS

Purpose