image vergence

image vergence 

at a refracting surface is equal to
L′ = n′/l
where n′ is the index of refraction of the second medium and l′ the distance between the image plane and the refracting surface in metres. The unit of vergence is the dioptre. 2. Disjunctive movements of the eyes such as convergence, divergence, cyclovergence, infravergence or supravergence. See image distance; object distance; duction; fundamental paraxial equation; refractive power.
v. accommodation See convergence accommodation.
accommodative v. See accommodative convergence.
disparity v. See motor fusion.
v. facility Ability of the eyes to make fusional vergence movements in a given period of time. Clinically, this is measured by introducing a relatively large prism in front of one or both eyes of a patient fixating a target until it appears single. The operation is repeated many times and the results are commonly presented in cycles per minute (one cycle indicates that single vision was reported both with the prism and after removing the prism). See fusional convergence; motor fusion; lens flippers.
v. formula See fundamental paraxial equation.
fusional v. See relative convergence.
v. power See refractive power.
proximal v. See proximal convergence.
v. reflex See vergence reflex.
relative v. See relative convergence.
tonic v. The passive state of vergence of the eyes in the absence of a stimulus, i.e. when the eyes are in total darkness or when looking at a bright empty field. This position is maintained by the tonus of the extraocular muscles. Only at death or when paralysed do the eyes return to their anatomical position of rest and tonic vergence disappears. Syn. dark vergence; tonic convergence. See resting state of accommodation; physiological position of rest; tonus.
vertical fusional v. Movement of the eyes upward until an object that was imaged on slightly disparate vertical parts of the retina falls on corresponding retinal points.
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