Lecture 21 microtropia

Question 1

What is a microtropia?

Answer 1

*A constant small angle unilateral strabismus
*Measures less than 10 prism dioptres or 5 degrees
*Prescence of subnormal single vison

Question 2

What are the clinical characteristics of a microtropia?

Answer 2

*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

Question 3

What is the aetiology of a microtropia?

Answer 3

*Anisometropia: results in defocused image in more ametropic eye. Most px with microtropia have this.
*Hereditary
*Unknown

Question 4

What is eccentric fixation?

what is the relationship between ARC and eccentric fixation?

Answer 4

*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

Question 5

How can you classify a microtropia?

Answer 5

1. Microtropia with identity
2. Microtropia without identity

(identity refers to fixation)

Question 6

MICROTROPIA WITH IDENTITY

1.Describe the cover test
2. Describe fixation
3. describe retinal correspondence
4. is there any stereopsis?

Answer 6

1. no manifest movement. may have heterophoria on ACT.
2. eccentric fixation (stable parafoveal fixation)
   -amount of eccentricity=angle of deviation
3. ARC
4. gross stereoacuity

Question 7

why is there no movement on cover test in microtropia with identity?

Answer 7

*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.

Question 8

MICROTROPIA WITHOUT IDENTITY

1. describe cover test
2. describe fixation
3. describe retinal correspondence
   4.How do they appreciate BSV?

Answer 8

1. -small manifest deviation less than 10D on CT
   
   • large latent component on ACT
2. central fixation
   -eccentric fixation does not coincide with the angle of deviation
3. ARC or NRC
4. • If they have ARC:
     -able to achieve BSV

*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

Question 9

What test is required to diagnose microtropia with identity?

Answer 9

4 D test

Question 10

How else can you classify microtropia?

Answer 10

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)

Question 11

What is the range of VA in someone with microtropia?

Answer 11

0.2-1.00 logMAR

Question 12

How can you assess fixation?

Answer 12

*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.

Question 13

How do you carry out the D4 test and what does it test for?

Answer 13

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

1. prism is placed in front of RE. RE adducts to take up fixation.
2. LE moves out. image falls in impression scotoma so there is no double vision
3. no movement seen

Question 14

What is the management of a micotropia?

Answer 14

*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

Question 15

What is the visual outcome after treatment?

Answer 15

*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.