Supranuclear Control Systems for Eye Movement
Eye movements are directed and coordinated by several supranuclear systems. The saccadic system generates fast (up to 400°–500° per second) eye movements, such as eye movements of refixation. This system functions to place the image of an object of interest on the fovea or to shift gaze from one object to another. Saccadic movements require a sudden strong pulse of force from the EOMs to move the eye rapidly against the viscosity produced by the fatty tissue and the fascia in which the globe lies.
The smooth-pursuit system generates following, or pursuit, eye movements that maintain the image of a moving object on the fovea. Pursuit latency is shorter than saccade latency, but the maximum peak velocity of these slow pursuit movements is limited to 30°–60° per second. The involuntary optokinetic system utilizes smooth pursuit to track a moving object and then introduces a compensatory saccade to refixate. Tests of this system, performed with an optokinetic stimulus, are often used to detect visual responses in an infant or child with apparent vision loss, such as with ocular motor apraxia (see Chapter 12). The vergence system controls dysconjugate eye movement, as in convergence or divergence. Supranuclear control of vergence eye movements is not yet fully understood. There are also systems that integrate eye movements with body movements in order to stabilize the image on the retinas. The most clinically important of these systems is the vestibular-ocular system. Vestibular-ocular reflex responses are driven by the labyrinth, which involves the semicircular canals and otoliths (utricle and saccule) of the inner ears. The cervical, or neck, receptors also provide input for this reflex control. See BCSC Section 5, Neuro-Ophthalmology, for in-depth discussion of these systems.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.