stereo/diplopia Flashcards
word problem CT for EP
when the paddle is moved, the previously covered eye will move out
the covered eye will move behind the paddle on unilateral cover test
Hirschberg
measure of gross alignment. the Patient views a light source held at 50cm on his midline. The examiner observes the corneal reflex and each eye compared to the pupillary axis
what is considered normal for Hirschberg
0.5mm nasal
angle lambda
what is measured on Hirschberg under monocular conditions
normal is 0.5mm nasal
1mm shift in the corneal light reflex
22PD
contour stereo testing
monocular clues
a patient without stereopsis could still do well
uses laterally displaced targets with monocular cues
-titmus fly, wirt circles, animals
-better at detecting peripheral stereopsis
global stereo testing
random dot targets that have NO monocular cues ( the patient must have bifocal fixation to detect shapes within random dot targets.) These targets are very good for detecting constant strabismus
must have bifocal fixation to appreciate
normal stereopsis
20s of arc with contour testing and an appreciation for gross random dot targets
phi
subjective CT
-ask the direction they see the target move
anismetropic amblyopia
due to a significant difference in uncorrected refractive error between the two eyes
anisometropic hyperopia vs anisometropic myopia
aniso hyperopia is more likely to lead to amblyopia. In myopia, each eye will have a clear retinal image at some distance, reducing the risk of developing amblyopia (although stereopsis will still be decreased because the eyes never learn to work together). In contrast, in hyperopia, the eye will accommodate the smallest amount possible in order to obtain a clear image, resulting in the less hyperopic eye having a clear retinal image while the more hyperopic eye ALWAYS has a blurred retinal image
isometric amblyopia
due to high refractive error in BOTH eyes. BC the refractive error is so high, neither eye receives a clear retinal image, resulting in poor connections between each eye and the visual cortex
meridional amblyopia
characterized by reduced acuity for stimuli in a certain orientation due to uncorrected astigmatism during the critical period. The reduced acuity persists even after correction of the astigmatism
how should glasses be worn to reduce the risk of amblyopia
full time
anisometropic myopia value
> 3D
isometropic myopia value
> 8D
anisometropic hyperopia value
> 1D
isometropic hyperopia value
> 5D
anisometropic astigmatism value
> 1.50D
isometropic astigmatism value
> 2.50D
mallet box
binocular cues for motor fusion and therefore measures the associated phoria (fixation disparity) . the majority of the field of view is seen by both eyes, which serves as a fusion lock to prevent the eyes from dissociating.
associated tests
mallet box AO vectograph Bernell lantern Wesson fixation card Sheedy disparameter
used for FD
decompensated phoria
a large phoria that the patient can no longer compensate for, resulting in an acute intermittent or constant tropia that causes diplopia
ARC
develops prior to the age of 5 in patients with a constant unilateral strabismus. The fovea f of the non deviated eye becomes linked to a new retinal point fn of the deviated eye so that the image seen by both eyes is in the same visual direction. This adaptation prevents diplopia and visual confusion
congenital nystagmus
present at birth or before the age of 6. it generally does not cause complaints of oscillopsia that can be seen with acquired cases of nystagmus
saccadic suppression
occurs when the visual cortex suppresses vision during a saccade in order to minimize image blur, Suppression prevents diplopia and oscilopsia
fixation disparity
measured in minutes of arc
the small misalignment of the visual aces of the two eyes under associated conditions, meaning it DOES NOT cause diplopia. Although there is a small misalignment of the eyes, the object falls within Panums Fusional Area for the corresponding retinal points in each eye, resulting in the object being seen as single
horopter
image here is single
panums
slightly behind/infront of the horopter but still single image
when is fixation disparity indicated
if the patient has symptoms of asthenopia but no complaints of diplopia. If a fixation is noted, prism can be prescribed to neutralize the small ocular misalignment. The magnitude of prism necessary to neutralize the fixation disparity is termed the associated phoria. Clinically, the smallest amount of prism that is necessary to relieve the patient symptoms is prescribed
type 1 FD curve
most common with a sigmoidal shape, patients are asymptomatic
“large comfy chair”
type 2 FD curve
due to an eso disparity
type 3 FD curve
due to an eco disparity
type 4 FD curve
unstable BV system. Patients may not have ab associated phoria but may have symptoms of aniseikonica and poor sensory fusion
a FD that is opposite direction to the associated phoria
paradoxical fixation disparity
