Lecture 21 microtropia Flashcards
What is a microtropia?
*A constant small angle unilateral strabismus
*Measures less than 10 prism dioptres or 5 degrees
*Prescence of subnormal single vison
What are the clinical characteristics of a microtropia?
*Manifest monocular strabismus measuring 10 dioptres or less
*Anisometropia present in nearly all cases (commonly hypermetropia/hypermetropia with astigmatism)
*Reduced VA in affected eye (amblyopic, can occur post amblyopic treatment)
*Abnormal BSV-sensory and motor fusion, reduced stereovision and rarely no stereovision
*May have foveal suppression scotoma
*May have eccentric fixation
*Can have NRC or abnormal retinal correspondence
PX CAN ACHIEVE BSV with a microtropia
What is the aetiology of a microtropia?
*Anisometropia: results in defocused image in more ametropic eye. Most px with microtropia have this.
*Hereditary
*Unknown
What is eccentric fixation?
what is the relationship between ARC and eccentric fixation?
*The eye fixates with an area outside the fovea
-Both EF and ARC coexist in microtropia
*Dependant on whether eyes are viewing monocularly or binocularly
*The eye will fix with different points of the retina
How can you classify a microtropia?
- Microtropia with identity
- Microtropia without identity
(identity refers to fixation)
MICROTROPIA WITH IDENTITY
1.Describe the cover test
2. Describe fixation
3. describe retinal correspondence
4. is there any stereopsis?
- no manifest movement. may have heterophoria on ACT.
- eccentric fixation (stable parafoveal fixation)
-amount of eccentricity=angle of deviation - ARC
- gross stereoacuity
why is there no movement on cover test in microtropia with identity?
*under binocular and monocular viewing:
*RE uses this parafoveal area of retina to fix with so no movement if you cover LE. This is why you don’t notice a change in fixation under cover test.
MICROTROPIA WITHOUT IDENTITY
- describe cover test
- describe fixation
- describe retinal correspondence
4.How do they appreciate BSV?
- -small manifest deviation less than 10D on CT
- large latent component on ACT
- central fixation
-eccentric fixation does not coincide with the angle of deviation - ARC or NRC
- If they have ARC:
-able to achieve BSV
- If they have ARC:
*If they have NRC:
-diplopia as nasal retina doesn’t correspond to fovea of other eye
-there has been an expansion of panums fusional area allowing px to maintain BSV with a small angle squint
What test is required to diagnose microtropia with identity?
4 D test
How else can you classify microtropia?
Primary microtropia
* Microtropia is the initial defect
* Accompanies other concomitant deviations
Secondary microtropia
*Residual
*Seen after treatment for a larger angle manifest deviation (infantile esotropias often corrected to microtropia)
What is the range of VA in someone with microtropia?
0.2-1.00 logMAR
How can you assess fixation?
*Can use ophthalmoscope or visuscope
*Have px fixate on centre of target. Show on the wall so px knows what they are looking at.
*Cover the px non fixing eye
*Comment on location of fixation and if its steady/wandering.
How do you carry out the D4 test and what does it test for?
tests for suppression scotoma
Same process as 20 BO test but moves images over a smaller area
*For px with NRC
*Done on px without identity
- prism is placed in front of RE. RE adducts to take up fixation.
- LE moves out. image falls in impression scotoma so there is no double vision
- no movement seen
What is the management of a micotropia?
*Need to optimise visual acuity:
-do a cycloplegic refraction
-fully correct anisometropia
-glasses worn full time for full refractive adaptation period (16-22 weeks)
-if there is still a difference in vision after glasses given, start part time occlusion therapy-cease once no further improvement of visual acuity
-continually monitor fixation/suppression throughout treatment
What is the visual outcome after treatment?
*Equal vision is seen to be achievable after amblyopia treatment
*Often there can be a 0.1-0.3-line difference intraocularly
*Fixation, degree of anisometropia and compliance with treatment effects visual outcome
*In px with anisometropic amblyopia in the Prescence of a microtropia can be treated a little over the age of 7. GUIDED PROGONSIS (unlikely to get vision equal in eyes)
*flick movement in microtropia without identity is because fixation changes under uniocular and binocular viewing conditions.
