Retinal Correspondence, ARC And Microtropia Flashcards
What happens if strabismus develops before 3 years old
- adaptation to normal development occurs to prevent symptoms
- leads to abnormal unconditioned reflexes developing by age 6
- usually no symptoms
What happens if strabismus acquires from 6 to adulthood
- binocular vision is well established
- symptoms very likely to occur
Develops between 3-6 years
- symptoms will occur
- but the system is unstable and readily breaks down
- adaptations will develop
How can binocular vision be embarrassed
- diplopia
- confusion
How does the visual system cope
- in young px, sensory adaptations overcome diplopia and confusion
- these adaptations are suppression and abnormal retinal correspondence
What is anomalous retinal correspondence
Condition in which originally non-corresponding retinal areas of the 2 eyes co-operate to produce a form of binocular single vision
2 types of abnormal retinal correspondence
- Harmonious (HARC)
- UNHARMONIOUS (UN-HARC)
What is Harmonious ARC
If the angle of anomaly = angle of strabismus
- new position is angle of deviation is the same with subjective and objective measurements
What is Un-Harmonious
- if angle of anomaly is greater than zero but less than the angle of deviation
- objective measures different from subjective measures
- present in retinal area perceiving the peripheral image in strabismic eye
- convergence of nerve fibres means no point to point correspondence, ie loss of resolution
- produces pseudo-panums area on point receiving the image
- no diplopia and low grade BSV
Classic ARC characteristics
- occcurs in long standing deviations
- small angled deviation less than 20 degrees
- microtropia less than 10 degrees
- usually convergent
- only mild amblyopia
- Rare in exotropia
- provides useful BSV in manifest strabismus
- may revert to original angle after surgery
ARC investigations
Binocular tests possible in manifest strabismus
- bagolini glasses
- lang 2 pen test
- worths lights 4 lights
- stereotests
Synoptophore
- compare objective and subjective angles
- look for fusion at smaller subjective angle
Prism adaptation test
Implications of ARC
- generally an advantage
- explains unexpected clinical findings
- may cause poor surgical results if not assessed correctly
- intractable diplopia
Characteristics of a microtropia
- small angle less than 10 dioptres
- common
- stable
- anisometropia, usually >1.50D
- always mildly amblyopic
- central suppression
- good but not perfect BSV
- strong motor fusion
- differs from classic ARC because associated with eccentric fixation
- may prevent successful orthoptic exercises
What is a microtropia without identity
- small manifest angle
- less than 10 dioptres
- mostly esotropia
What is a microtropia with identity
- ARC and eccentric fixation at the same retinal point, so no movement on cover test
- diagnosed with fixation with ophthalmoscope and 4 dioptre prism test
