Maintaining a visual target on the fovea is largely achieved by three mechanisms:

(1) Stabilization of fixation, including via visual feedback mechanisms by which the visual system suppresses unwanted saccades and detects retinal drifts followed by corrective eye movements.
(2) Vestibuloocular reflexes which maintain eye position despite head and body movements.
(3) The neural integrators that maintain the eyes in a desired eccentric gaze position by counteracting the elastic pull of orbital tissues that draws the eyes back toward the center.

Key components of the ocular motility examination include:

  1. Assessment of fixation/gaze holding
  2. Assessment of monocular eye movements (ductions)
  3. Assessment of binocular eye movements (versions, pursuits, and saccades).

FIXATION/GAZE HOLDING IN PRIMARY POSTION.
The primary position of the eyes should be observed when the patient looks straight ahead: the primary position of gaze. Fixation should be evaluated by asking the patient to view a target of visual interest (the largest letter on an eye chart at distance, or the top of a near card) in primary viewing position1.
Careful attention should be paid to any instability of fixation, which may include square-wave jerks or nystagmus.
Ocular misalignment is a common clinical problem, and is confirmed with a cover test in primary gaze, and when the eyes are held in an eccentric position. 

DUCTIONS refer to monocular movements of each eye: abduction, adduction, elevation, depression, incyclotorsion, and excyclotorsion2.
Evaluation of ductions is completed by occluding one eye and asking the patient to follow a visual target through all cardinal gaze positions.  Assessment should be made of any apparent limitation or restriction of eye movements; subtle asymmetry in ocular alignment is sometimes easier to detect with testing of versions.

VERSIONS refer to binocular conjugate movements of both eyes, such that the visual axes of the eyes move in the same direction: dextroversion, levoversion, elevation, depression, dextrocycloversion, and levocycloversion2.
It is important to note that, under normal circumstances, when looking off center in the horizontal plane, the eyes and the head make one single movement to the target. In the somewhat artificial situation of purposefully keeping the head still, the normal range of eye motion is 10–200  for vertical gaze, with a moderate restriction of upward gaze commonly present in the elderly.

VERGENCES refer to binocular disjunctive movements, such that the visual axes of the eyes move in opposite directions. They include convergence, divergence, incyclovergence, and excyclovergence2.


 

Video 1. Evaluating the range of normal eye movements, and assessment of gaze holding, while looking for nystagmus 

 

(vv)Range_of_Eye_Movements_and_Evaluation_for_Nystagmus.mp4(tt)


 


Video 2. Assessing normal gaze

 

(vv)Gaze Test 2.mp4(tt)


 


Video 3. Examination of Gaze Holding Deficit and Gaze Evoked Nystagmus

 

(vv)Examination of Gaze Holding Deficit Gaze Evoked Nystagmus.mp4(tt)

 

 

References

  1. Glisson CC. Approach to Diplopia [published correction appears in Continuum (Minneap Minn). 2020 Feb;26(1):240]. Continuum (Minneap Minn). 2019;25(5):1362-1375. doi:10.1212/CON.0000000000000786
  2. Wong, A. M. (2008). Eye movement disorders. Oxford: Oxford University Press.