Assessing Monocular Fixation

Question 1

Why assess monocular fixation?

Answer 1

Determine which part of the retina is used to fixate under monocular conditions

Question 2

What does eccentric fixation influence?

Answer 2

VA, objective angle, correspondence

Question 3

Visual Direction

Answer 3

Direction in subjective space asociated with retinal receptor

temporal retinal receptors associated with nasal space

Question 4

Principle Visual direction

Answer 4

the direction from which other visual directions are referenced

subjectively associated with the point of fixation

Question 5

Retinomotor Value

Answer 5

Value assigned to retinal location indicating angular distance and direction from the fovea (or other point of reference)

Question 6

Zero Retinomotor Value

Answer 6

Value representing amount of electrical signal used to put the part of the retina used for fixation (normally the fovea) on target

Question 7

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

Answer 7

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

Question 8

What type of visual condition MUST be present if a patient has eccentric fixation?

Answer 8

amblyopia

Question 9

Which theory of EF etiology has been debunked by research?

Answer 9

Scotoma hypothesis

Question 10

Location for anomalous correspondence is much bigger/smaller than eccentric fixation

Answer 10

larger

AC and EF can happen seperately or together

Question 11

Motor origin theory: what happens when the non-deviated eye is occluded?

Answer 11

excessive motor tonus remains

results in a small amount of misalignment of the eye that is not perceived in the motor coordination centers

Question 12

MAR: minimum angular ___________

Answer 12

resolution

the smallest thing you can resolve

Question 13

What is the calculation for MAR?

Answer 13

MAR = EF (PD) +1

20/x= 1/ MAR

Question 14

2 contributing components to amblyopic vision?

Answer 14

1. sensory due to poor development of visual system
2. improper location of the retina used for fixation

Question 15

Why can’t we predict EF from VA?

Answer 15

amblyopia may be ALL due to poor development and have no EF component

Question 16

What could be the problem if measured VA is better than what should be possible based upon EF finding?

Answer 16

measurement of EF location or measurement of VA

Question 17

What are the three characteristics of eccentric fixation?

Answer 17

location, magnitude, stability

location typically same direction of strab

magnitude in PD, independent of strab magnitude

Question 18

What is/ are objective procedures for assissing eccentric fixation?

Answer 18

visuoscopy

Question 19

What are subjective procedures for assessing eccentric fixation

Answer 19

Haidinger’s Brush/ MIT; Brock-Givner afterimage transfer

Question 20

Purpose of visuoscopy?

Answer 20

determine presence, location, magnitude and stability of EF

done monocularly with DO (star target on Heine)

Question 21

what is the magnitude of EF?

Answer 21

2PD nasal OS

first circle = 2pd; 2nd= 3pd; 3rd= 4pd

Question 22

Where is the brush in releation to the fovea when performing Haidinger’s Brush?

Answer 22

Brush is always at the location of the fovea

Question 23

What is the distance for Haidinger’s Brush/ MIT?

Answer 23

40 cm (4mm= 1PD)

if NOT 40cm, remember 1 cm devation at 1m = 1PD

Question 24

Brock-Givner determines the presence, direction and magnitude of EF, but the patient must have anamalous/ normal correspondence

Answer 24

normal