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Light from a single point of a distant object and light from a single point of a near object being brought to a focus. The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, lens shape (accommodation) and pupil size.
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.
Incorrect vergence response can cause double vision. Accommodation is the eye’s focusing mechanism and it is engaged to produce a sharp image on a retina. Both of these mechanisms are neurally linked forming the accommodation-convergence reflex [1] of eyes.
However, errors in this relationship can cause problems, such as hyperopic individuals having a tendency for crossed eyes because of the over exertion of their accommodation system. Clinically, accommodative convergence is measured as a ratio of convergence, measured in prism diopters, to accommodation, measured in diopters of near demand.
Gaze-stabilising movement may include the vestibulo-ocular reflex and optokinetic reflex, and gaze-shifting mechanisms as saccades and pursuit movements. Vergence movement or convergence is the movement of both eyes to make sure that the image of the object being looked at falls on the corresponding spot on both retinas.
The two different types of near response are caused by different underlying disease processes. Adie's pupil is caused by damage to peripheral pathways to the pupil (parasympathetic neurons in the ciliary ganglion that cause pupillary constriction to bright light and with near vision). The pathophysiologic mechanism which produces an Argyll ...
Accommodative excess may occur secondary to convergence insufficiency also. In convergence insufficiency near point of convergence will recede, and positive fusional vergence (PFV) will reduce. So, the patient uses excessive accommodation to stimulate accommodative convergence to overcome reduced PFV. [5]
Convergence insufficiency is a common problem with the eyes, and is the main culprit behind eyestrain, blurred vision, and headaches. [9] [unreliable source?] This problem is most commonly found in children. Near point of convergence (NPC) is measured by bringing an object to the nose and observing when the patient sees double, or one eye ...