Microtropia

Question 1

what is the definition of microtropia and what do patients who got microtropia usually have

Answer 1

Unilateral small angle strabismus (10∆ or less)

Binocular single vision(BSV) with abnormal retinal correspondence develops (ARC)

Question 2

what does 10∆ correlate to in degrees

Answer 2

5-8 degrees

Question 3

list 6 features of microtropia

Answer 3

• Anisometropia: usually astigmatic or hyperopic and other eye plano
• Foveal suppression scotoma
• Amblyopia: as not fixing on best part of fovea
• Eccentric fixation: does not fix with fovea, but slightly less centrally
• Reduced fusional amplitudes: compared to what a non-microtropia px has
• Subnormal stereopsis: compared to what a non-microtropia px has

Question 4

what type of amblyopia does a microtropia px usually have

Answer 4

usually astigmatic or hyperopic and other eye plano

Question 5

why do patients with microtropia tend to have amblyopia

Answer 5

as not fixing on best part of fovea

Question 6

what 2 things does a microtropia px have less of in comparison to a normal px

Answer 6

• fusional amplitudes
• stereopsis

these are still present in a microtropia px, but to a lesser extent

Question 7

what is the prevalence of microtropia out of all squints

Answer 7

2.84% seen in general practice

Question 8

which direction of microtropia is more common than which and which direction is generally more rarer

Answer 8

Micro ET (more common) > XT (less common)

Vertical microtropia rare (no variability in size of squint)

Question 9

microtropia is _________ throughout life

Answer 9

microtropia is constant throughout life

Question 10

what is the aetiology of microtropia thought to be

Answer 10

Most common theory:
Anisometropia - Hyperopic +/- astigmatism

because they have anisometropia, they go on to develop microtropia

however microtropia is also thought to cause anisometropia, because the microtropic pc has effective vision from a squint which results in anisometropia

Question 11

what does anisometropia result in

Answer 11

Results in a defocused image to the more ametropic eye. As fixation reflex not fully developed patient uses a retinal point other than the fovea to fix (pseudo fovea)

the patient always accommodates to the least ametropic eye e.g. if its the right eye, then thats the eye that will govern the accommodation and if the left eye is hyperopic, then it will always be out of focus

Question 12

what 4 things could the result of anisometropia explain about microtropia

Answer 12

This could explain:

• Foveal suppression scotoma
• Amblyopia
• Eccentric fixation on border of scotoma
• ARC with reduced fusion, defective stereopsis

Question 13

what type of visual acuity does a person with microtropia have as a result of eccentric fixation on the border of the scotoma

Answer 13

6/7.5 or 6/9

as its very close to the fovea

Question 14

what type of condition is abnormal retinal correspondence ARC and what is it defined as

Answer 14

ARC is a BINOCULAR condition: it only happens when both eyes are open and is not there is using each eye individually i.e. if you cover the straight eye, the other eye won’t have ARC anymore and will use the fovea for fixation

The fovea of 1 eye corresponds to a non-foveal area in the other (squinting) eye

Question 15

what is microtropia the most comm form of
what does it allow
what does it ensure

Answer 15

Microtropia the most common form of ARC
allows binocular vision (i.e. allows fusion and stereopsis to develop)
ensures long-term stability of the alignment of the squint

Question 16

what type of condition is eccentric fixation EF and what is it defined as

Answer 16

EF is a UNIOCULAR condition: if you cover up the straight eye, the other eye will stay fixing with their eccentric point

There is fixation of an object by a point other than the fovea

Question 17

what is seeing someone with an eccentric fixation relevant in

Answer 17

differentiating between micro with and without identity

Question 18

what 2 things may co-exist in microtropia and explain how

Answer 18

ARC and EF may co-exist in microtropia

fix with different point on retina when affected eye viewing monocularly and binocularly

Question 19

explain the 2 things that can happen with a micro tropic patient’s foveal suppression scotoma when you cover the right eye

Answer 19

• when cover the right eye, the px will re-fixate and uses the left eye’s fovea, so they use that point binocularly to get ARC

or

• when cover the right eye, the left eye stays there at the same place and uses that point as their pseudo fovea eccentrically fixing

Question 20

what are the 2 classifications of a primary mictrotropia and what are they based on the outcome of

Answer 20

• with identity
• without identity

based on the outcome of a cover test

Question 21

what is seen in a ‘with identity’ microtropia px

Answer 21

NO manifest deviation
heterophoria may be present

i.e. px is using their eccentric point/pseudo fovea binocularly and uniocularly = don’t see any deviation on cover test

Question 22

what is seen in a ‘without identity’ microtropia px

Answer 22

Small constant manifest deviation
May be associated heterophoria with partial recovery to microtropia angle

i.e. will see a small convergent flick, when you do a CT, cover the fixing eye and you will go to the true fovea on CT

Question 23

what are the 3 aims of investigating a microtropia

Answer 23

• Diagnose the microtropia
• Assess quality of binocular single vision
  fusion
  stereopsis
• Differentiate from bifoveal fixation
  Anisometropic amblyopia

Question 24

why is it important to assess quality of binocular single vision when investigating someone with a microtropia

Answer 24

because a px with poor fusion and stereopsis means they’re more likely to decompensate to bigger squints

Question 25

why is it important to differentiate from bi foveal fixation when investigating someone with a microtropia

Answer 25

it makes a difference to what you expect to get for your end result treatment treatment is the same but when you stop will differ depending on whether they have got true bifocal fixation or if they fixate with a extra foveal point in the other eye

Question 26

give 3 possible causes (history) for a patient to visit you and are found to have a microtropia

Answer 26

- Referred with defective vision in one eye School nurse check (4.5 years of age) - May present with constant or intermittent squint (without glasses) Less common reason Px will have a bigger squint than 10^, you then do a cyclo refraction and prescribe glasses for hypertropia and px ends up with a microtropia Sometimes presents as adults - Occasionally present to A and E because child says cannot see out of one eye

Question 27

what is found and prescribed to a px with microtropia during refraction and fundus check

Answer 27

Anisometropia Hypermetropic with or without astigmatism Glasses for full-time wear: can give plano in the fixing eye and hyperopic correction in micro tropic eye, but if theres a lot of refractive error in the fixing/least ametropic eye, then they will have to be corrected there is a lot of improvement with glasses on most patients, but child may not find a big improvement with glasses, but they must wear them Review 2/12 (6-8 weeks) to check vision (if it has improved) and decide on future management

Question 28

what is the pre treatment vision of a micro tropic patient which type of test is best to use when measuring visual acuity and why what is the optimum vision in the micro tropic eye

Answer 28

Pre-treatment vision varies 6/60 to 6/9 Beware crowding phenomenon - so move onto crowded visual acuity test as soon as possible as uncrowded over estimates the visual acuity linear charts rather than single optotypes to detect small differences in visual acuity ensure child not peeping! Optimum vision in the microtropic eye is about 1 line lower than better eye (as not fixing with the true fovea)

Question 29

name 7 occupations you can do if visual acuity is no worse than 6/12 in the worse eye

Answer 29

- Police Officer / prison officer - Fire Officer - Train driver - Guard - Emergency or depot driver - Passenger carrier i.e. taxi - HGV driver

Question 30

name 2 occupations you can do if visual acuity is no worse than 6/9 in the worse eye

Answer 30

- Commercial pilot | - Air traffic Controller

Question 31

name an occupation you can do if visual acuity is no worse than 6/6 in the worse eye

Answer 31

Motor sport

Question 32

what is seen in Microtropia with identity when you occlude the right eye and what is explained by this what 3 things are identical in Microtropia with identity and why

Answer 32

No manifest deviation on cover test RE occluded, LE fixates with Pl – parafoveal fixation with same retinal area under binocular and monocular viewing (no manifest deviation on cover test, may see a phoria) Absence of manifest deviation is explained by presence of stable parafoveal fixation Angle of deviation Angle of eccentricity Angle of anomaly = all identical Because it is the same point they use i.e. ARC and absolute eccentric fixation point coincide with angle of squint

Question 33

up to what age will you see a successful microtropia treatment

Answer 33

in children up to 17 years old

Question 34

what is seen in microtropia without identity when you occlude the right eye and why

Answer 34

Small manifest deviation seen on cover test RE occluded, LE moves and fixates with retinal area between Nl and F and minimal ET seen on cover test as monocular fixation taken up. because eccentric fixation does not coincide with angle of squint in monocular and binocular conditions

Question 35

list 4 things you want to measure when investigating a micro tropic patient's binocular status and give examples of which tests you can use to carry them out which 3 of these are the same for with and without identity

Answer 35

- Sensory fusion Bagolini glasses - Quality of motor fusion Prism fusion range - Stereopsis TNO, Wirt, Frisby = Same for with and without identity: - Measurement of deviation Prism cover test / simultaneous prism cover test = Different for with and without identity

Question 36

which 3 forms of binocular status is the same for with and without identity microtropia

Answer 36

- Sensory fusion - Quality of motor fusion - Stereopsis

Question 37

describe how bagolini glasses are used to test sensory fusion and what a microtropia px will see and why

Answer 37

- Patient fixes light 1/3m or 6m away (sensory fusion) - As lenses have small striations (at right angles to each other), a white line is seen crossing through the light - Minimal dissociation as aware peripheral objects surrounding light - Ask patient to draw what they see - Microtropia patients may on questioning report a gap in the cross at the centre because of the parafoveal suppressing area ~5 deg - Difficult for patient to see - Does not assess motor fusion only sensory fusion

Question 38

what does measuring prism fusion range assess in a micro tropic px what should you check when doing it and what should you find what else may be required and why before deciding to treat how should you check your results on a child

Answer 38

- Assessment of motor fusion - Check BO and BI range often reduced level - Control such as Bagolini glasses may be required to confirm when fusion is lost as patient suppresses at break of fusion This is essential as you can decide to patch that child without breaking their fusion You have to check the patient's fusion objectively as a child won't tell you when they have diplopia

Question 39

what test is used to measure the amount of deviation in a microtropic px what does this test require what 2 types of angle is this test used to measure and what is this test used to differentiate

Answer 39

- Prism Cover Test (PCT) (as to have a microtropia, they have to have 10^ or less) - Requires good cooperation (e.g. not helpful if VA is poor) - Used to measure latent or manifest angle - Microtropia with and without identity

Question 40

what are the stereo results like in a micro tropic patient in which type of stereo test is there difficulty obtaining a response from and give 2 examples which type of stereo test do they tend to do better in and give an example

Answer 40

Often reduced have difficulty obtaining response from pure random dot tests e.g. Lang and TNO do better in something with better contour e.g. titmus fly

Question 41

what is a stereo test result NOT an indication of

Answer 41

NOT an indication of fusion

Question 42

``` list the results found from: Refraction Visual acuity Cover test OM PFR/Stereo 4^ test Fixation ``` in microtropia with identity and without identity

Answer 42

- Refraction: with = Anisometropia without = Anisometropia - Visual acuity: with = 6/60 to 6/9 without = 6/60 to 6/9 - Cover test: with = Phoria without = Tropia - OM: with = Full without = Full - PFR/Stereo: with = Reduced without = Reduced - 4^ test: with = Negative for bifoveal fixation without = N/A as already manifest squint - Fixation: with = Parafoveal without = N/A as already manifest squint

Question 43

for a patient who had microtropia with identity, how can you prove their reduced vision is due to microtropia and not any other cause

Answer 43

Prove there is foveal suppression by assessing - eccentric fixation - 4∆ prism test If you got a patient with reduced VA in one eye with defective stereopsis and fusion range, but can't see anything on CT, then you will know they have a microtropia with a central suppression area by using a 4^ or by looking with an ophthalmoscope for eccentric fixation

Question 44

how must the ophthalmoscope be set up to check for eccentric fixation in a patient who may have with identity microtropia

Answer 44

- light turned to green | - fixation target displayed

Question 45

list the steps of how you will carry out the assessment of eccentric fixation on a with identity microtropia px

Answer 45

- Undertake in dark room, patient may need to be dilated - Check good eye first to assess understanding & cooperation - Examiner projects the fixation target onto the fundus close to the fovea - Patient is instructed to look directly at the centre of the circle - Note the position of the fixation target on the fundus - There is a decrease in visual acuity with increasing distance from the fovea

Question 46

what results may you see in a px with eccentric fixation from testing it with an ophthalmoscope and which values show that the patient does not have microtropia

Answer 46

1 = Parafoveolar 2 = Parafoveal 3 and 4 = Peripheral: Not seen with microtropia

Question 47

what is the 4^ test used for what type of test is it what must the patient fixate on whilst being tested

Answer 47

- Shows if patient has foveal suppression i. e. microtropia with identity - Objective test - Fixate on small detailed target (and nothing around it e.g. a small spot in the distance on snellen chart or small house on budgie stick)

Question 48

describe what will be the normal bifoveal response from a 4^ BO test if placed in front of right eye

Answer 48

4Δ BO (if eso) Prism infront of RE/fixing eye, therefore image displaced away from fovea, RE adducts to maintain fixation (so will see movement of eye under prism, towards the apex of the prism) Due to Herrings Law, LE also moves. Now in LE image from letter falls on temporal retina and projects nasally resulting in diplopia Diplopia simulates nasal movement of LE to maintain BSV. This is the observed movement of the prism being overcome.

Question 49

describe what will be the response from a 4^ BO test of a patient with a Left Microtropia if the prism is placed before the RE

Answer 49

Place prism before RE, therefore image displaced away from the fovea, and RE adducts to maintain fixation Herrings Law: the LE moves. Now image falls within the suppression scotoma of the LE (i.e. brain is not aware that the target has moved), thus no diplopia results therefore NO nasal movement of the LE to maintain BSV = microtropia with identity i.e. NO disjugate movement to maintain fixation

Question 50

describe what will be the response from a 4^ BO test of a patient with a Left Microtropia if the prism is placed before the LE

Answer 50

Prism placed in front of LE, the image falls within the suppression scotoma, thus NO movement of either eye is seen = microtropia with identity

Question 51

what is the management the same for

Answer 51

with and without identity

Question 52

what is the 5 aims/steps of management for microtropia

Answer 52

- Optimise vision - Correct refractive error - Constant glasses wear - Glasses adaptation - Occlusion (patch/atropine)

Question 53

how long does the patient have to adapt to their glasses i.e. how long can it take and what needs to be done it adaptation does not occur

Answer 53

- up to 16 weeks for maximum for optimal vision with specs | - if no adaptation, then move onto patching/occlusion

Question 54

when will you decide to occlude a px with amblyopia and why how long is occlusion continues for what is the optimum post treatment VA what can be done if a px has good motor fusion what is the risk of occlusion for a patient who is over the age of 7

Answer 54

If VA is still down, done to treat px for amblyopia Occlusion continued until no further improvement over 2 or 3 visits (a couple of months apart) Optimum post treatment VA often 6/9 or 6/12 or one line below other eye If good motor fusion, can occlude after 7/8 year cut-off (compared to if px has poor motor fusion) If poor / absent motor fusion and over 7 years old = risk of INTRACTABLE DIPLOPIA if occluding as can eliminate suppression scotoma

Question 55

list the 5 HES criteria for discharge a micro tropic px has have what is this also a good level for

Answer 55

- Stable visual acuity - Up to date refraction - Gls / CL for long term - Static angle of deviation - Asymptomatic this is also a good level to retry occluding if previously poor compliance

Question 56

list what three things in a patient will make you want to investigate for microtropia

Answer 56

- Reduced uniocular vision - Anisometropia - Abnormal binocular vision