APPENDIX: Cranial Nerve Testing

INTRODUCTION

Clinical testing of cranial nerves is quick and yields valuable information. Formal assessment of cranial nerve function is important for clinical diagnosis as well as tracking therapeutic progress after nervous system damage. Injury produces classic presentations based on the laterality of the lesion and the anatomic distribution of long pathways and CN nuclei at the injury site, allowing for precise localization of the damage based on clinical findings. Clinical assessment of cranial nerve function requires practice and a solid understanding of what is normal. A thorough examination includes observation for facial or postural asymmetry, and listening for difficulty with speech. These initial observations inform the selection of specific follow up questions regarding difficulty with basic function including vision, hearing, balance, eating, and speech production.

HOW TO TEST CN I, THE OLFACTORY NERVE

Cranial nerve I is responsible for the sense of smell. Each nostril detects odors independently and connects directly to the forebrain. Loss of CN I function may be one of the earliest sign of Alzheimer's or Parkinson's disease; periodic, in-office testing is advised.

Observation

There is no directly observable behavior of olfactory dysfunction. The patient may have reduced appetite or decreased enjoyment of meals, which may lead to weight loss or signs such as baggy clothing.

Screening

Ask whether loss of smell is present or if food tastes different than it did in the past. A history of smoking may confound the diagnosis; ask about smoking habits as part of the comprehensive history.

Examination

Test patency of the nostrils, listening for a clear passage while inhaling. Close a nostril and test the smell discrimination of each olfactory bulb by asking the patient to identify or name (if communication allows) scents such as vanilla versus citrus, or coffee versus chocolate.

HOW TO TEST CN II, THE OPTIC NERVE

Observation

Note behaviors such as bumping into or avoiding objects. Observe for squinting or an eye turn.

Screening

Inquire about blurry or dim vision. Ask about difficulty with peripheral vision such as bumping or walking into objects. Inquire about difficulty driving at night or during dusk. Ask about ease of reading and use of computer or tablet.

Examination

Evaluate visual acuity, contrast sensitivity, and visual fields as appropriate and critical to appropriate diagnosis.

Visual acuity

Measure the Snellen visual acuity of each eye at 20 feet (far) and at 16 inches (near), indicating function of the central (foveal) vision at distance (Figure A.1) and at near. Repeat the measurement, using a pinhole. If acuity improves to 20/30 or better, the patient ...