148. Movements of the Eye – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• The six extraocular muscles are medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique and inferior oblique. They coordinate eye position, fixation and binocular vision.
• The nerve supply is remembered by SO4, LR6, all others III: superior oblique by trochlear nerve (IV), lateral rectus by abducens nerve (VI), and the remaining four muscles by oculomotor nerve (III).
• From the primary position, the medial rectus adducts and the lateral rectus abducts the eye. The superior rectus elevates the abducted eye, the inferior rectus depresses the abducted eye, the inferior oblique elevates the adducted eye, and the superior oblique depresses the adducted eye.
• Conjugate movement means coordinated movement of both eyes in the same direction while maintaining alignment of the visual axes. It requires integrated activity of the oculomotor, trochlear and abducens nuclei.
• The major types of ocular movements are saccades, smooth pursuit, vergence and vestibulo-ocular movements. Saccades rapidly shift gaze between targets, whereas smooth pursuit keeps a moving object focused on the fovea.
• Vergence movements are disconjugate movements. Convergence occurs when looking at a near object, while divergence occurs when looking at a distant object. They maintain single binocular vision and depth perception.
• The vestibulo-ocular reflex stabilizes vision during head movement. Signals from the semicircular canals produce compensatory eye movements in the direction opposite to head movement.
• Paralysis of an extraocular muscle produces characteristic diplopia and abnormal eye deviation. Lateral rectus paralysis causes inability to abduct and horizontal diplopia. Superior oblique paralysis causes difficulty depressing the adducted eye and vertical diplopia, especially while reading or walking downstairs. Complete oculomotor nerve palsy causes the eye to deviate downward and laterally.
• Nystagmus is an involuntary rhythmic oscillation of the eyes with slow and fast phases. Physiological nystagmus helps prevent prolonged stimulation of the same retinal receptors and supports continuous vision. Optokinetic nystagmus consists of slow pursuit followed by a rapid corrective saccade.
• Pathological nystagmus may result from disorders of the vestibular system, brainstem, cerebellum or ocular motor pathways and may impair visual stability and acuity.
• Diplopia occurs when the visual axes are misaligned and images fall on non-corresponding retinal points. Strabismus is persistent misalignment of the visual axes and may result from extraocular muscle weakness or paralysis.
• Depth perception depends mainly on binocular vision. Because the two eyes receive slightly different images of an object, the visual cortex fuses them to produce stereoscopic perception of depth. Loss of vision in one eye markedly reduces stereoscopic depth perception.
• Electro-oculography records changes in the electrical potential associated mainly with the retinal pigment epithelium and can help assess retinal pigment epithelial disorders.
• Electroretinography records retinal electrical responses to a flash of light. The a-wave mainly reflects photoreceptor activity, the b-wave reflects bipolar and Müller cell activity, and the c-wave arises from the retinal pigment epithelium. It is useful in evaluating retinal disorders.
• Visual evoked potentials record electrical activity along the visual pathway up to the visual cortex. The important P100 wave occurs at approximately 100 milliseconds after stimulation and helps detect disorders such as optic neuritis, optic atrophy and demyelinating disease.