Chapter 7: Examination of the Visual Motor System

CHAPTER OUTLINE

• OVERVIEW AND TERMINOLOGY

• GENERAL OBSERVATIONS

• OCULAR MOTILITY

  • Fixation

  • Ocular versions and ductions

  • Vergence

  • Pursuit

  • Saccades

  • Ancillary methods

  • Assessing ocular alignment

  • Forced duction testing

  • Nystagmus

  • Eye movement recording

• PUPILS

• EYELIDS

  • Examination techniques

  • Ptosis

  • Eyelid retraction

  • Facial nerve disorders

• ORBIT AND ADNEXA

  • Inspection

  • Palpation

  • Auscultation

• ADDITIONAL ASSESSMENTS

  • Cranial nerve V

  • Cranial nerve VII

• KEY POINTS

INTRODUCTION

This chapter expands the discussion of examination techniques summarized in Chapter 1 and is a companion to Chapter 2, which discusses examination of the afferent visual system. In this chapter, methods for examining the pupil and cranial nerves (CNs) III, IV, V, VI, and VII are presented, with greater detail provided in other chapters regarding examination of the pupil (chapter 11), CN VII (chapter 12), and CN V (chapter 13).

OVERVIEW AND TERMINOLOGY

The purpose of the ocular motor system is to aim the visual axis of each eye at an object of interest. This function places an image of the object on the area of greatest retinal sensitivity: the foveola. Ideally, the motor system keeps the eyes steady and aligned with the fixation object even when the object is moving in three-dimensional space. The smooth tracking of a moving object is called pursuit. When a new object of interest is encountered, the motor system can quickly redirect gaze with a rapid movement to fixate on a new object of interest. This rapid refixation movement is called a saccade. Generally, when following or finding objects, both eyes move in the same direction (conjugate gaze). However, objects that move toward or away from the observer require a disconjugate eye movement (vergence). For example, an object approaching the observer's nose from a distance requires the eyes to converge, or turn in (right eye turns to the left, left eye turns to the right) to maintain fixation. Divergence occurs in the opposite setting: When the fixation object moves from near to far the eyes move outward—from a converged state to a more parallel alignment. Additional complexity is introduced when the observer is moving or when both the observer and the object are moving in space. Even in this complex situation, eye movement systems can provide stability of fixation, compensating for movement of the observer as an object is tracked.

When binocular fixation occurs, the brain can synthesize depth information from the slightly disparate views of the object (stereopsis). If the motor system fails to provide alignment, the brain cannot reconcile the two images, potentially resulting in confusion and diplopia (Box 7–1).