Lesions are rare, causing vertical diplopia and a compensatory tilt of the head that could be mistaken for dystonia. The trochlear nerve (CNIV), also originating in midbrain, innervates the contralateral superior oblique, enabling the eye to point down while it is pointed medially. Partial lesions of CNIII are rare, so a lesion of the nucleus or nerve will result in a unilateral failure of almost all eye movements (as well as dilated pupil and ptosis). The oculomotor nerve (CNIII) innervates all but two of these, ipsilaterally. There are six extraocular muscles: four rectus muscles (superior, inferior, lateral, medial) and two oblique (superior and inferior). Unequal pupils (anisocoria) are due to the efferent (motor) system, which includes CNIII, somatic and parasympathetic components, sympathetic nerves originating in the cervical spine, and the smooth muscle of the iris. Even a blind eye should constrict in response to light shined on the other eye. Because projections from the pretectal to the Edinger-Westphal nuclei are bilateral, the pupils should respond about equally to light shined on either eye. The Edinger-Westphal nucleus sends efferent projections through CNIII to the ciliary ganglion, then to the pupil. The optic tract synapses in the pretectal nucleus, which projects equally to the Edinger-Westphal nucleus (part of CNIII) on both sides. As discussed in the previous article of this series, light energy is transduced into neural activity in the retina, courses through the optic nerve (CNII), through the optic chiasm (where the nasal retinal projections, containing information from the lateral visual fields, cross over), and then the optic tract (containing all information from the opposite visual hemifield). As such, they are informative in common psychiatric conditions. 1, 2 Motor activity controlling the direction of gaze, the elevation of the eyelids, and the size of the pupils also reflect higher cortical activity, and are sensitive to drug effects. For example, even minor weakness in one extraocular muscle can cause diplopia, and the eyelids reveal even mild variations in the activity of skeletal or smooth muscle. In addition to their value in localizing lesions, these three oculomotor nerves (sensory function is limited to proprioception) can reveal subtle changes in general skeletal and smooth muscle activity. Because these features of the eyes can have so many causes, it is more useful to start with specific observations (e.g., frequent, rapid, spontaneous, lateral eye movements) rather than an inference (e.g., appears to be responding to internal stimuli) and then consider explanations.Ĭranial nerves III (CNIII) (oculomotor), IV (trochlear), and VI (abducens) control the position of the eyeballs CNIII influences the position of the eyelids and the size of the pupils. Frequent lateral gazes (“shifty eyes”) sometimes implies anxiety or deception, but also may be assumed to reflect hypervigilance, paranoia, or hallucination. A lack of direct eye contact is taken to indicate a lack of confidence, authenticity, or interest excessive eye contact can be taken as intimidating. Spontaneous eye movements also have conventionally accepted implications. Eyes that are “glazed” (appearing to be unfocused) or reddish (due to conjunctival injection) elicit suspicions of fatigue and/or the use of intoxicating substances. We tend to associate sunken eyes, prominent folds beneath the eyes, discoloration beneath the eyes, and conjunctival injection with distress and fatigue. As seen most often in Victorian fiction, close observation of the eyes can reveal much about the mental state of healthy adults. The general appearance of the eyes often conveys impressions about physical and mental condition.
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