(G3) The Binocular Vision Examination Flashcards
Binocular Vision anomalies in terms of two broad categories:
(1) BV is maintained, often at the cost of an amount of stress— including phorias, fusional vergence anomalies, fixation disparity, & anomalies of accommodation)
(2) BV is absent— including strabismus (tropia or squint) & amblyopia.
convergence that is associated with accommodation
Accommodative convergence
determines, to a great extent the distance phoria
Tonic convergence
an excess of tonic convergence result in
Esophoria
deficiency of tonic convergence result in
Exophoria
Deficiency of accommodative convergence result in
Exophoria at near
For someone who is orthophoric at distance, excessive amount of accommodative convergence result in
Esophoria at near
convergence that compensates for any excess or deficit in tonic or accommodative convergence
Fusional convergence
can compensate for a deficiency of tonic or accommodative convergence
Positive fusional convergence
it prevents a person from seeing double, or prevents a phoria from being a tropia
Fusional convergence
To test proximal convergence, hold an object such as pencil at normal reading distance & slowly move it toward your nose until you see two pencils, this exercise is known as
Pencil pushup
can compensate for an excess of tonic or accommodative convergence
Negative fusional convergence
occurs because of awareness of nearness
Proximal convergence
method of eliminating stimuli to fusion routinely used for clinical phoria measurement involve use of
Dissociating prism
simplest method to eliminate stimuli to fusion
Occlude one eye, done in cover test
position of the eyes taken by two visual axes with respect to each other when all stimuli to fusion have been eliminated
The Phoria Position
used to measure a lateral phoria
Vertical dissociating prism
used to measure vertical phoria
Horizontal dissociating phoria
if visual axes are found to be parallel when px views a distant object & all stimuli to fusion have been eliminated
Orthophoria
if visual axes converge toward one another when eyes are dissociated the individual has
Esophoria
if visual axes diverge toward one another when eyes are dissociated the individual has
Exophoria
if one visual axis deviates above or below the other
Hyperphoria
stimulus to accommodation is approximately 6m & 40cm
0.17D (6m)
2.50D (40cm)
in routine optometric practice, phorias are measured at distances of
6m (far) and 40cm (near)
at ______, stimuli to both accommodation & convergence are considered to be zero
6m
stimulus to convergence is approximately
1△
at 40cm, the stimulus to accommodation is
2.50D
the stimulus to convergence for an individual with 64mm PD is
15△
most people are orthophoric at distance, thought to be due to
Fusion adaptation process
_______ described that most people are ortho at distance due to “fusion adaptation process”
Carter (1963,1965)
if an individual is found to have significant distance phoria, it is because he/she does not possess-or has a deficient “fusion adaptation process”
Fusion adaptation process theory
