Lecture 9-10 Flashcards
what are the characteristics of normal correspondence on the retina?
highly stable, not altered by image luminance, contrast, color, size or orientation
what is anomalous retinal correspondence (ARC)?
the centers of the fovea have different visual direction (oculocentric direction) - new corresponding points = fovea of straight eye and peripheral retina point in turned eye
is ARC the same thing as eccentric fixation?
no - EF is monocular and usually much smaller in size than ARC (ARC may be present with or without EF)
why does a patient develop ARC?
anti-diplopia sensory adaption if onset before age 6 - able to preserve rudimentary binocular vision
if a strabismic patient develops ARC - can they be cured?
less than 50/50 change of cure (if constant ET without ARC then 50/50 chance of cure)
in ARC, what is point z called?
zero measure point of the turned eye (sometimes the same as point a to restore single vision)
in ARC, what is point a called?
the PVD of the turned eye has moved to a non-foveal point (anomalous point) a and has the same oculocentric visual direction as the fovea of the straight eye
what does the displacement of point a from the fovea represent?
typically related to the size of the strabismus and “a” location usually co-varies with strabismic fluctuation
what is ARC influenced by?
luminance and contrast (unlike normal correspondence) - the more natural the test environment the more likely ARC will be found
what is angle H in ARC? how do you measure it?
the horizontal objective angle of the deviation - how much the eye is physically turned, measured by CT and prism
what is angle S in ARC? how do you measure it?
the subjective angle of directionalization - perceived angle of diplopia and measured by maddox rod, red lens test, or synoptophore
what is angle A in ARC? how do you measure it?
angle of anomaly - amount of shift of correspondence from fovea, it is measured by afterimage test or angle H - angle S
how are angles H (objective angle) and angle S (subjective angle) related in normal correspondence?
they are equal
H = S
how does a synoptophore (major amblyoscope) measure the subjective angle S?
present different images to each eye in stereoscope, the turned eye’s image is moved in until it is aligned with the other image of straight eye = angle S
what does a person with normal correspondence see in the synoptophore?
two diplopic images are separated by the same angle as the angle of esotropia (H = S) so anomaly A is zero (point a corresponds with f)
what is harmonious ARC?
sensory adaptation A completely compensates for angle of strabismus H and there is no subjective angle S (a coincides with zero point z)
what type of ARC does a patient have if they have 20PD RET on cover test and 10PD displacement on the synoptophore (angle S)?
unharmonious ARC
Angle A = 20PD - 10PD = 10PD (S < H and will have diplopia)
what type of correspondence will a patient have with angle S = 0, and A = H?
harmonious ARC
what type of correspondence will a patient have with angle A = 0 and H = S?
Normal correspondence
what does the Hering-Birlschowski afterimage test measure?
a direct measurement of angle A for ARC
how does the afterimage test work?
a horizontal afterimage is flashed for the straight eye and vertical for deviated eye - the position of the images doesn’t depend on whether the eyes are straight or crossed (test depends on fixation behavior - NRC vs. ARC)
what side will the vertical line be if the patient has left ET with HARC?
the afterimage will be seen to the right side of the horizontal line
what side will the vertical line be if the patient has a left XT with HARC?
the afterimage will be seen to the left side of the horizontal line
what will the afterimage look like if a patient has a right ET with NRC? (or adult onset)
crossed lines
