Check extraocular movements (eye movements) by having the patient look in all directions without moving their head and ask them if they experiences any double vision. Test smooth pursuit by having the patient follow an object moved across their full range of horizontal and vertical eye movements. Test convergence movements by having the patient fixate on an object as it is moved slowly towards a point right between the patient's eyes. Also, observe the eyes at rest to see if there are any abnormalities such as spontaneous nystagmus (see below)or dysconjugate gaze (eyes not both fixated on the same point) resulting in diplopia (double vision).
Saccades are eye movements used to rapidly refixate from one object to another. The examiner can test saccades by holding two widely spaced targets in front of the patient (such as the examiner's thumb on one hand and index finger on the other) and asking the patient to look back and forth between the targets.
Test optokinetic nystagmus (OKN) by moving a strip with parallel stripes on it in front of the patient's eyes and asking them to watch the stripes go by. Normally, rhythmic eye movements called nystagmus occur consisting of an alternating slow phase with slow pursuit movements in the direction of strip movement, and a rapid phase with quick refixations back to midline.
In comatose or severely lethargic patients, the vestibulo-ocular reflex can be used to test whether brainstem eye movement pathways are intact. The oculocephalic reflex, a form of the vestibulo-ocular reflex, is tested by holding the eyes open and rotating the head from side to side or up and down. These maneuvers obviously should not be performed in cases of head injury or other cases of suspected cervical spine trauma unless complete cervical spine films are normal. The reflex is present if the eyes move in the opposite direction of the head movements, and it is therefore sometimes called doll's eyes. Note that in awake patients, doll's eyes are usually not present because voluntary eye movements mask the reflex. Thus, the absence of doll's eyes suggests brainstem dysfunction in the comatose patient but can be normal in the awake patient. Another, more potent stimulus of the vestibulo-ocular reflex used to evaluate comatose patients is caloric stimulation (see Neuroanatomy Through Clinical Cases, Chapter 3).
Careful testing can often identify abnormalities in individual muscles or in particular cranial nerves (oculomotor, trochlear, or abducens) in their course from the brainstem to the orbit, in the brainstem nuclei, or finally, in the higher-order centers and pathways in the cortex and brainstem that control eye movements (for more details, see Neuroanatomy Through Clinical Cases, Chapter 14). Spontaneous nystagmus can indicate toxic or metabolic conditions such as drug overdose or alcohol intoxication, or peripheral or central vestibular dysfunction.