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When the optic nerve is damaged, the sensory (afferent) stimulus sent to the midbrain is reduced. The pupil, responding less vigorously, dilates from its prior constricted state when the light is moved away from the unaffected eye and towards the affected eye. This response is a relative afferent pupillary defect (or Marcus Gunn pupil). [1]
The absence of this lens left the patient highly hyperopic (farsighted) in that eye. For some patients the removal was only performed on one eye, resulting in the anisometropia / aniseikonia. Today, this is rarely a problem because when the lens is removed in cataract surgery, an intraocular lens, or IOL is left in its place. [citation needed]
Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image forming and the more newly discovered photosensitive ganglion cells. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones.
Gaze is held steadily on a location by producing eye movements in the direction opposite that of head movement. For example, when the head moves to the right, the eyes move to the left, meaning the image a person sees stays the same even though the head has turned.
More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation. Mydriasis is frequently induced by drugs for certain ophthalmic examinations and procedures, particularly those requiring visual access to the retina .
In a sixth nerve palsy one would expect that, over the 6 month observation period, most patients would show the following pattern of changes to their ocular muscle actions: firstly, an overaction of the medial rectus of the affected eye, then an overaction of the medial rectus of the contraletral eye and, finally, an underaction of the lateral ...
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Ocular dominance, sometimes called eye preference or eyedness, [1] is the tendency to prefer visual input from one eye to the other. [2] It is somewhat analogous to the laterality of right- or left- handedness ; however, the side of the dominant eye and the dominant hand do not always match. [ 3 ]