Eccentric fixation Flashcards
What is the definition of eccentric fixation?
Uniocular, squinting eye uses extrafoveal point on retina to fixate when fixing eye is covered.
Affected eye does not move as much on CT to take up fixation.
Where can fixation be?
Foveal
Parafoveal
Peripheral
Wandering
What is the treatment for eccentric fixation?
Inverse occlusion (deviating eye) to change fixation, then occlude fixing eye to improve VA.
What is the definition of ARC?
Binocular condition where the fovea of one eye corresponds with an extrafoveal point in the other eye, to achieve BSV when a squint is present.
Not present on occlusion.
What is the angle of anomaly?
Difference between objective and subjective angle of deviation
(Measured angle larger than px’s interpretation)
What happens in ARC when the fixating eye is covered?
Fovea takes up fixation in squinting eye
What is harmonious ARC?
Objective angle = angle of anomaly
Subjective angle = 0
Form of BSV is present
Brain thinks eye is straight but deviation found on PCT
What is inharmonious ARC?
Subjective angle smaller than objective angle (but not 0)
Brain thinks deviation is smaller than PCT finds
What is the definition of a microtropia?
Small angle tropia, under 10D with a form of BSV
Why does a microtropia develop?
Fovea of more ametropic eye is suppressed in anisometropia, fixation occurs on edge of suppression scotoma
What are the classifications of microtropia?
Primary
Secondary
Primary decompensated
What is primary microtropia?
Microtropia is the initial defect
What is secondary microtropia?
Angle was originally larger
Reduced due to surgery, refractive correction of orthoptic exercises
What is primary decompensated microtropia?
A microtropia which has increased in size
What is a microtropia with identity?
Harmonious ARC or absolute eccentric fixation present
No movement on CT due to pseudo-fovea taking up fixation
Gross stereopsis
One eye has reduced VA
Asymmetrical corneal reflections (small)
No movement of suppressed eye on 4^BO
What is a microtropia without identity?
ARC and possible eccentric fixation present
OR
NRC with central suppression and peripheral fusion
Small CT movement
Gross stereopsis
What is the treatment for microtropia?
Correct refractive error
Treat amblyopia
(Usually conservative as good cosmesis and some stereopsis present)
What are the characteristics of a microtropia?
Angle less than 10D
Anisometropic
Unilateral VA reduction
Deviated eye foveal suppression
Eccentric fixation
ARC
Reduced fusion and stereopsis
Usually eso
Vertical deviation rare
