Assessing Monocular Fixation Flashcards
Why assess monocular fixation?
Determine which part of the retina is used to fixate under monocular conditions
What does eccentric fixation influence?
VA, objective angle, correspondence
Visual Direction
Direction in subjective space asociated with retinal receptor
temporal retinal receptors associated with nasal space
Principle Visual direction
the direction from which other visual directions are referenced
subjectively associated with the point of fixation
Retinomotor Value
Value assigned to retinal location indicating angular distance and direction from the fovea (or other point of reference)
Zero Retinomotor Value
Value representing amount of electrical signal used to put the part of the retina used for fixation (normally the fovea) on target
Match the following:
a) normal fixation
b) eccentric fixation
c) eccentric viewing
1) PVD at fovea
2) PVD and ZRMV at fovea
3) PVD and ZRMV not at fovea
a2, b3, c1
EF: no subjective awareness that fovea is not aimed at the target
eccentric viewing: subjective awareness that fovea is not aimed at the target
What type of visual condition MUST be present if a patient has eccentric fixation?
amblyopia
Which theory of EF etiology has been debunked by research?
Scotoma hypothesis
Location for anomalous correspondence is much bigger/smaller than eccentric fixation
larger
AC and EF can happen seperately or together
Motor origin theory: what happens when the non-deviated eye is occluded?
excessive motor tonus remains
results in a small amount of misalignment of the eye that is not perceived in the motor coordination centers
MAR: minimum angular ___________
resolution
the smallest thing you can resolve
What is the calculation for MAR?
MAR = EF (PD) +1
20/x= 1/ MAR
2 contributing components to amblyopic vision?
- sensory due to poor development of visual system
- improper location of the retina used for fixation
Why can’t we predict EF from VA?
amblyopia may be ALL due to poor development and have no EF component
What could be the problem if measured VA is better than what should be possible based upon EF finding?
measurement of EF location or measurement of VA
What are the three characteristics of eccentric fixation?
location, magnitude, stability
location typically same direction of strab
magnitude in PD, independent of strab magnitude
What is/ are objective procedures for assissing eccentric fixation?
visuoscopy
What are subjective procedures for assessing eccentric fixation
Haidinger’s Brush/ MIT; Brock-Givner afterimage transfer
Purpose of visuoscopy?
determine presence, location, magnitude and stability of EF
done monocularly with DO (star target on Heine)
what is the magnitude of EF?
2PD nasal OS
first circle = 2pd; 2nd= 3pd; 3rd= 4pd
Where is the brush in releation to the fovea when performing Haidinger’s Brush?
Brush is always at the location of the fovea
What is the distance for Haidinger’s Brush/ MIT?
40 cm (4mm= 1PD)
if NOT 40cm, remember 1 cm devation at 1m = 1PD
Brock-Givner determines the presence, direction and magnitude of EF, but the patient must have anamalous/ normal correspondence
normal
