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Binocular Vision - Year 2 > Manifest & Latent Strabismus > Flashcards

Manifest & Latent Strabismus Flashcards

1
Q

What does Heterotropia refer to?

A

Manifest strabismus

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2
Q

What does Heterophoria refer to?

A

Latent Strabismus

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3
Q

What does it mean to have no tropia?

A

The fovea of both eyes can simultaneously look at an object

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4
Q

What is Manifest strabismus/heterotropia?

A

The fovea of both eyes cannot simultaneously look at an object - there will be one eye that will view the object using the fovea and the other will not.

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5
Q

What is the fixing eye?

A

The unaffected eye or the eye using the fovea to view things.

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6
Q

When noting a squint how must you note it?

A

Name the eye - you lose all marks if you don’t name the eye!

Then mention what it is e.g. esotropia , exotropia , hypertropia,incyclotorpia,excylcotropia.

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7
Q

What is esotropia?

A

Eye is turned in nasally

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8
Q

What is exotropia?

A

Eye is turned outwards temporally

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9
Q

What is hypertropia?

A

Eye deviates upwards

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10
Q

In the case of the left eye being lower than the right eye how do we note this?

A

Right hypertropia ( Not left hypotropia) .

Convention in optometry is that you must always name the higher eye.

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11
Q

Can a patient have exotropia and hypertropia (of the same eye)?

A

Yes and you have to name both to get the mark.

Look at the image attached of the girl that has Right exotropia and hypertropia.

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12
Q

Can all strabismus/ tropias be identified by simply viewing the patients eyes?

A

No- Not all tropias large enough to be cosmetically noticeable

Smaller angle tropias can appear normal

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13
Q

How do you identify whether someone has ‘normal’ eyes or a small angle tropia?

A

A Cover test is required to determine if they have a tropia or not

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14
Q

What is a psuedostrabismus?

A

An eye that gives the appearance of a tropia but in actuality is normal.

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15
Q

How do you determine that a psuedostrabismus is in fact a psuedostrabismus?

A

A cover test is required

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16
Q

What often gives the appearance of a psuedostrabismus in children?

A

In children the nose bridge isn’t fully formed so they have extra skin around the nose called the epicanthus. This extra skin can slightly overlap blocking the sclera on one side, giving the appearance of a strabismus.

This can be seen in the picture attached- where it looks like the baby has a right esotropia but in actuality does not. ( An indication that the baby doesn’t have an esotropia is the corneal reflection - look at how they are central and eual in both eyes).

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17
Q

A flashcard to show the impact of an epicanthus in the appearance of a psuedostrabismus.

What tropia does it look like the child has?

A

Notice how the extra skin gave the appearance of a psuedostrabismus. To confirm whether this is the case - we always need to do a cover test.

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18
Q

What are the different reasons for the appearance of a psuedostrabismus?

A

◦Epicanthal folds

◦Wide interpupillary distance

◦Unilateral myopia or exopthalmos

◦Facial asymmetry

◦Variation of angle kappa

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19
Q

What is an angle of Kappa?

A

The angle of kappa is the angle between the visual axis and the optical/pupillary axis.

K= angle of kappa

So if you cut the eye in half you would be going across the optical axis. Now if you actually wanted to view anything you would view it using your fovea - we call this the visual axis.

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20
Q

How can corneal reflections look and why?

A

For most of us the fovea lies temporal to the posterior pole of the eye [keep in mind corneal reflex is shown on visual axis point] . Thus there is a positive angle of kappa of usually 3 degrees as a result the corneal reflection is esotropic. This corneal reflection can be seen in the brown eyes in the image.

Some people may have an angle of kappa that is zero i.e. that the fovea aligns with the posterior pole. In this case the corneal reflection is central. This is shown by the green pair of eyes in the photo.

Very rarely - some people have a fovea that is nasal to the posterior pole and so have a negative angle of kappa. Thus corneal reflection is temporal and is noted to be exotropic.

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21
Q

What can a large angle of Kappa give the appearance of?

A

A psuedostrabismus

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22
Q

How do we conduct a corneal reflections test?

A

-hold a pen-torch 30 cm from the patient’s eyes and look to see if the corneal reflections are symmetrical

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23
Q

Name a benefit and a disadvantage of a corneal reflection/reflex test?

A

Benefit:

Useful in uncooperative children and adults

◦When cover test not possible or as an adjunct.

Disadvantage:

They are a gross test i.e.

-They can only be used in moderate large deviations

◦Small deviation need cover test

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24
Q

What is a cover test used to find out?

A

Whether its a:

◦Pseudostrabsmus

◦manifest (tropia) deviation

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25
Q

What two parts can the cover test be broken down into?

A

1.Cover/Uncover Test:

◦Used as a test to detect manifest strabismus (tropias)

2.Alternating cover test:

◦Best test to detect heterophorias as it fully dissociates (makes the deviation as large as possible)

26
Q

What are the conditions of a cover/uncover test?

A

•It needs to be Carried out at three distances:

—1/3m (to test near vision)

—6m (distance vision)

— 6m if deviation increases distance

•With an accommodative target

—Line above worst V-A

—The beak of the bird

  • If you find an esotropia at near also use a light

•It needs to be tested With and without spectacle prescription

  • If the patient has a head tilt needs to be tested at that tilt too.
27
Q

Background context: When doing the cover test - we first do it with a pentorch and look for the change in corneal reflections. Then you do the cover test without the pen torch and now you are looking for the eye movement.

When doing a cover/uncover test why should you always check the corneal reflex in the cover test first?

Which type of patients may have given you a false no tropia diagnosis if you weren’t checking corneal reflections in the cover test first?

A

Sometimes when we are doing our cover/uncover test the patient might not actually be focussing on the image we have asked them to and so we wouldn’t see the pupil movement we are looking for - this would give us a false diagnosis of no tropia, however we wouldve still been able to see a tropia via the corneal reflex/reflection.

Patients that are likely to do this are:

Young children or Adults with learning difficulties who didn’t understand you properly.

Equally…

Patients may have a visual impairment which means they can’t focus on the image we have asked them to and so again we would see no tropia if we had done the cover test without the pen torch first.

Finally …

It’s important to check corneal reflections in the cover test as patients with an eccentric fixation ( i.e. where the patient chooses to use the psuedofovea monocularly rather than the real fovea) won’t have shown a tropia (based on just eye movement).

28
Q

What should the accomodatitive target be for an infant in a cover/uncover test?

A

A toy

29
Q

What should the accomodative target be in an older child?

A

A line above their worst VA

30
Q

What is the biggest reason for misdiagnosis in a cover test?

A

Poor Patient fixation

Your cover test is only as good as your patient’s fixation.

31
Q

How do you force the patient to fixate for long (rather than lose focus)?

A

You ask the patient questions about the target e.g. What’s the first letter on the line? What’s the leter next to that? and so forth.

32
Q

What are the steps of the cover/uncover test and what movements of the eye are asscoiated with what diagnosis?

A
  • Ensure head straight and still
  • Cover the right eye and observe left eye
  • If the left eye is deviated, it will move to take up fixation. If it moves:

◦Out, it was convergent = left esotropia

◦In, it was divergent = left exotropia

◦Down, it was elevated = left hypertropia

◦Up, it was depressed = left hypotropia

-Repeat by covering left eye and observing right eye

ALWAYS LOOK AT HOW THE UNCOVERED EYE IS MOVING TO TAKE UP FIXATION

33
Q

What is a brief explaination of herring’s law of equal innervation?

A

-When a muscle in one eye contracts a muscle in the opposite eye also contacts in order for both eyes to work together

34
Q

What is important to remember in the cover/uncover test?

A

Look at the uncovered eye as you COVER the other one ( not as you take away the cover from the other one - as this messes up your diagnosis big time).

35
Q

How can we identify a CONSTANT tropia?

A

The fixing eye does not change whether the other eye is covered or not.

36
Q

What does herring’s law mean in terms of the cover test - how does the occluded eye behave?

A

Due to herring’s law, the occluded eye moves the same as the unoccluded eye e.g. if the left eye moves out then behind the occluder the right eye will also be doing the same thing. If the left eye moves down then from behind the occluder the right eye shall be doing the same.

37
Q

How can you identify an ALTERNATING tropia?

A

You identify an alternating tropia by paying attention to the following steps:

You occlude the fixing eye ( the one that appears normal) - naturally when you do this you will see the tropic eye fixate and move.

You then uncover the occluded eye and shall see that it no longer goes back to normal (i.e. to the centre) but rather that the eye you assumed to be the tropic one now appears central as if its the fixing eye.

38
Q

How do we record an alternating tropia?

A

If the eye is alternating 50/50 then we record it as an alternating tropia e.g. ALT SOT.

However if the eyes show a preference to fix with a particular eye e.g. the left one in a case of esotropia, then we would record this as L ALT SOT.

39
Q

How do we record results for tropia?

A

-Which eye?

◦Right, left or alternating

  • With or without Rx?
  • What distance was it measured?

◦Distance (D), near (N), Far distance (FD)

-Degree of movement

◦Minimal, small, moderate or large (experience)

-Target used

◦Accommodative or non-accommodative (light)

40
Q

What does XOT stand for?

A

Exotropia

41
Q

What does SOT stand for?

A

Esotropia

42
Q

What’s the difference between Manifest Strabsimus (heterotropia) and Latent Strabismus (heterophoria)?

A

In a manifest strabismus when both eyes are uncovered only one eye can use fovea the other cannot.

In a latent strabismus when both eyes are uncovered, the visual axes of both eyes are directed towards the target when focussing (i.e. both eyes using fovea) however, when you occlude one eye - that occulded eye deviates from the fixation point.

The image attached shows the difference.

[Side note - latent strabismus is different from normal vision because the eyes only look ‘normal’ when focusing on something otherwise normally they look like a strabismus patient).

43
Q

What are you looking out for with a heterophoria?

A

How long it takes the eye that was previously covered to go back to normal - this is called the recovery time - obviously as well as what direction the eye moved.

44
Q

What are the types of heterophoria?

A
45
Q

When testing for heterophoria what must you always do?

A

You must always carry out a cover uncover test initially to confirm no manifest deviation before moving onto alternating cover test

46
Q

Filler Card

A

Filler Card

47
Q

Why is alternating cover test the best test for heterophoria?

A

-Alternating Cover Test is the best method to detect heterophoria as it fully dissociates (makes the deviation bigger so its easier to see from a clincial POV).

48
Q

If you find a tropia in the Cover/uncover test will you see a tropia on the Alternating cover test?

A

Ofcourse - the alternating cover test just makes the deviations bigger.

49
Q

How can you be sure a patient has heterophoria?

A

There is no tropia in the Cover/Uncover test, however, a tropia is found in the alternating cover test. This is an indication the patient has heterophoria.

50
Q

What are the conditions of the Alternating cover test?

A

}Patient sits with their head erect

}

}Patient fixates suitable target

}

}Alternate the occluder between the two eyes

}

  • The patient must NEVER be able to see the target with both eyes
  • Continue alternating the occluder until the deviation no longer increases in size
  • Move the cover at an appropriate speed

The slower the better

51
Q

When deciding on what type of heterophoria a patient has what do you focus on as you occlude one of the eyes?

A

The movement of the eye that was previously occluded is noted as you occlude the other eye.

e.g. If the previosuly occluded eye moves outwards to take up fixation then it was esophoric before hand and thats what you record the patient to be!

52
Q

In the alternating cover test, if the previosuly occluded eye moves outwards to take up fixation then when phoria does the patient have?

A

If the previosuly occluded eye moves outwards to take up fixation then it was esophoric before hand and thats what you record the patient to be!

53
Q

What are we looking to note about recovery from the alternating cover test?

A

If the eye moves back to take up fixation their eyes have recovered to a phoria (straight eyes) when no eyes are occluded.

◦Note whether the recovery was fast or slow or whether they needed to blink to recover

54
Q

What happens if you don’t spot a recovery?

A

You have misidentified:

If the eye does not move back in to take up fixation then it is now a manifest strabismus e.g. XOP on ACT (alternating cover test) breaks down into a RXOT (right exotropia)

55
Q

What does XOP stand for?

A

Exophoria

56
Q

What does ACT stand for?

A

Alternating cover test

57
Q

What happens in an alternating cover test of right hyperphoria?

A

}Occluder placed in front of RE (fusion suspended) RE elevates

}Cover moved from RE to the left eye the right uncovered eye moves downwards to take up fixation

}As the eye needs to moves downwards to take up fixation then it was elevated to begin with (right hyperphoria)

}LE now occluded- as RE moved down to fixate due to Hering’s law the left eye also moved down ( it is a left hypophoria)

}If you were to move occluder from LE to the RE the LE would move up (left hypohoria

58
Q

What do we record when recording latent strabismus/ heterophoria?

A

}Record direction of deviation

◦Esophoria is NOT a Right or left

◦Exophoria is NOT a right or left

◦Right hyperphoria

◦Left hyperphoria

–In optometry record as right or left hyperdeviations rather than hypodeviations

}Record degree of deviation:

◦Minimal, small, moderate or large (experience) or othophoria

}Record speed of recovery

◦Rapid recovery (r.r), moderate recovery (m.r.) or slow recovery (s.r.) or to blink

}Distance:

◦Distance, intermediate or near

}Target:

}Accommodative or non-accommodative (light)

}Whether spectacles worn

59
Q

Why is speed of recovery important to note when recording results of an alternating cover test?

A

Speed of recovery is important as the faster the speed of recovery, the better the control of the deviation

60
Q

What is orthophoria?

A

Binocular Vision - Year 2 (15 decks)

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