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Binocular vision- my one > 6. Measuring ocular deviations > Flashcards

6. Measuring ocular deviations Flashcards

1
Q

Give 3 reasons why you should measure the deviation

A

To diagnose

Decide when to manage

Monitor progression

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2
Q

How should the measurements be taken?

A

At distance, near and greater than 6m if deviation increases

With and without rx

With and without CHP if they have one

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3
Q

What are the objective methods of measuring deviation?

A

Using total dissociation= objective prism cover test (PCT)

Using corneal reflections: hirschberg and krimsky

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4
Q

When would you use objective methods?

A

Unreliable patient, very young, had a stroke

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5
Q

What are the subjective methods of measuring deviation?

A

Subjective prism cover test

Maddox rod

Maddox wing

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6
Q

Which method is the best and why?

A

Prism cover test as it reveals the maximum angle of the deviation i.e shows the px at their worst

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7
Q

PCT measures total deviation? What does this mean?

A

It measures tropia and phoria added up

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8
Q

How reliable is PCT?

A

Only as reliable as the clinician and required px co-operation

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9
Q

What target do you use for PCT?

A

Accommodative target so line above worst VA

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10
Q

What target should you use if px’s VA is worse than 6/60?

A

spotlight

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11
Q

What do you do first in PCT?

A

a cover/uncover test and alternating cover test to know what type of deviation it is

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12
Q

What eye do you place the estimated prism in front of if phoria? Tropia?

A

If tropia then the eye with the tropia

If phoria then either eye

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13
Q

What prism base do you select to correct?

A

Base opposite deviation

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14
Q

RSOT?

A

Base Out RE

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15
Q

LXOT?

A

Base in LE

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16
Q

Right hypertropia?

A

Base down RE

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17
Q

XOP

A

BI either eye

18
Q

How do you know if patient has crossed or uncrossed diplopia when they have a tropia, explain this for RSOT?

A

If they have RSOT then the fixation target stimulates the nasal retina of the RE and fovea of the LE

Nasal retina projects temporally

So px has uncrossed diplopia

19
Q

Describe how you would use prism cover test to measure/correct a RSOT

A

To alleviate diplopia, base opposite direction of deviation so base out in front of RE

20
Q

Which way does the eye move with a prism infornt?

A

Eye moves towards apex, image moves towards base

21
Q

Describe PCT routine

A

Head erect, measure VA, line above worst VA then discover what type of deviation it is

Perform alternating cover test slowly

Put prism of estimated strength in front of they eye with tropia or either eye if its a phoria

Increase prism till you see opposite movement, always look at the ye behind the prim, so if eso then continue increasing till exo is seen.

22
Q

What do you record?

A

Record prism dioptres the one before reversal

23
Q

How do you record results?

A

Near with rx. 10 prism dioptres BI

24
Q

What are the advantages of PCT?

A

Accurate measurement down to 2 prism dioptres

Measures full angle

25
Q

What are the disadvantages of PCT?

A

Dependant on px fixating properly, unreliable with poor VA, can’t be used in young children, can’t measure cyclodeviations

26
Q

What is simultaneous prism cover test used for? (how does it differ from PCT)

A

Measures manifest deviation only

27
Q

How do you do a simultaneous prism cover test?

A
  1. determine type of deviation
  2. place estimated prism strength infront of deviated eye whilst doing alternating cover test
  3. Keep increasing prism until reversal seen
  4. Record one before reversal
28
Q

How can you estimate the angle of a deviation?

A

Corneal reflections

29
Q

What are 3 ways of ESTIMATING the angle of deviation using corneal reflections?

A
  • Bruckner
  • Hirschberg
  • Krimsky
30
Q

Describe the Hirschberg test

A

Patient fixates of pentorch at 33cm

Compare corneal reflections in both eyes

31
Q

1mm corneal reflection displacement equals to how much prism of deviation?

A

1mm corneal reflection displacement= 20-22 prism dioptres deviation approximately

32
Q

Describe the krimsky test

A

Patient fixates of pentorch at 33cm

Compare corneal reflections in both eyes

Estimated prism strength placed infront of FIXING eye, base opposite deviation

Increase prism until corneal reflections are equal in both eye

33
Q

What are the advantages in using corneal reflections?

A

Good for uncooperative patients, infants, learning difficulties,

Good if blind or one eye poor VA

34
Q

What are the disadvantages in using corneal reflections?

A

Can not measure latent deviations (phorias)

Will not detect microtropias

Accommodation not controlled

35
Q

What is different in subjective PCT?

A

Same as objective PCT but ask patient if they notice image moving from

  • side to side or
  • up to down

Keep increase prism until movement of images neutralised

36
Q

When is subjective PCT useful?

A

In small symptom producing vertical deviations

37
Q

What is maddox rod?

A

Place striated red filter (can be clear or blue) in front of either eye if latent (not normally used with manifest)

Other eye views spot light in dark room and prism placed infront of it, apex of prism in the direction you want the spot to move

Increase prism until spot and image is coincident

38
Q

Why is it done in dark room?

A

As other light sources produce extra streaks

39
Q

When spot and image is coincident what does this mean?

A

Prism at this point is equal to the angle of deviation

40
Q

What are the advantages of maddox rod?

A

Easy to use

Detects and measure cyclodeviations

41
Q

What are the disadvantages of maddox rod?

A

Needs good VA, accommodation not controlled, can’t have suppression or ARC, slight head tilt may simulate vertical deviation

Binocular vision- my one (11 decks)

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