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The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence. A near object (for example, a computer screen) subtends a large area in the visual field, i.e. the eyes receive light from wide angles. When moving focus from a distant to a near object, the eyes converge.
Pupillary light reflex and accommodation reflex tests Argyll Robertson pupils ( AR pupils ) are bilateral small pupils that reduce in size on a near object (i.e., they accommodate ), but do not constrict when exposed to bright light (i.e., they do not react).
Convergence of the eyes, or the orientation of the visual axis of each eye towards an object in order to focus its image on each fovea, is the first of the three responses. This can be observed by the cross-eyed movement of the eyes when a finger is held up in front of a face and moved towards the face. Next, constriction of the pupil occurs.
Accommodation usually acts like a reflex, including part of the accommodation-convergence reflex, but it can also be consciously controlled. The main ways animals may change focus are: Changing the shape of the lens. Changing the position of the lens relative to the retina. Changing the axial length of the eyeball. Changing the shape of the cornea.
The Edinger-Westphal nucleus moderates pupil dilation and aids (since it provides parasympathetic fibers) in convergence of the eyes and lens adjustment. [21] Nuclei of the optic tract are involved in smooth pursuit eye movement and the accommodation reflex, as well as REM.
The pupil of the human eye can ... The vestibulo-ocular reflex is a reflex eye movement that stabilizes ... the eyes rotate 'towards each other' (convergence), ...
Clinically, accommodative convergence is measured as a ratio of convergence, measured in prism diopters, to accommodation, measured in diopters of near demand. The patient is instructed to make a near target perfectly clear and their phoria is measured as the focusing demand on the eye is changed with lenses.
Both of these mechanisms are neurally linked forming the accommodation-convergence reflex [1] of eyes. One can distinguish vergence distance — a distance of a point towards which both eyes are converging, and an accommodation distance — a distance of a region in space towards which the focus or refractive power of the ...