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Investigations > Hess/Lees charts > Flashcards

Hess/Lees charts Flashcards

1
Q

What is the principle of how Hess and Lees charts work?

A

for investigation of strabismus - the eyes are dissociated and the position of the non-fixing eye is plotted as the fixing eye adopts different positions of gaze determined by the examier

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2
Q

How is Hess testing performed?

A

dissociation is achieved by colour filters
* red (appearance) filter before fixing eye
* green (appearance) filter before non-fixing eye
* examiner presents red or white target
* subject perceives with fixing eye (only) target and grid
* subject perceives their green target with non-fixing eye (only)
* position of non-fixing eye is revealed by projection of green target and plotted
* procedure repeated, reversing laterality for other eye

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3
Q

What visual angle is subtended by the horizontal and vertical lines of the grid in Hess testing?

A

5 degrees

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4
Q

What is the size of each square in the Hess chart?

A

5 degrees

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5
Q

What area size is represented by the inner field of the Hess chart?

A

15 degrees

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6
Q

What area is represented by the outer field of the Hess chart grid?

A

30 degrees

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7
Q

What is the patient asked to do in the Hess chart testing?

A

asked to superimpose their green light on the examiner’s red light

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8
Q

Can the Hess chart differentiate between manifest and latent deviations?

A

no

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9
Q

What is seen by each eye in Hess chart testing?

A

eye under red goggle sees red light, eye under green goggle sees green light

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10
Q

What is the fixing eye and what is the indicating eye when the examiner shines a red light in Hess chart testing?

A

the eye under the red goggle is the fixing eye, the other eye will be the indicating eye from which deviation is measured

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11
Q

What is directly represented by what is mapped on a Hess chart?

A

the position of the eye

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12
Q

What is the rule for retinal correspondence for Hess testing and why?

A

patient MUST have normal retinal correspondence (NRC) - if have ARC, measurement of deviation will be incorrect

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13
Q

What are 3 contraindications to Hess testing?

A
  1. abnormal retinal correspondence (ARC)
  2. suppression
  3. red-green colour blindness
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14
Q

How far should the patient sit from the chart in Hess testing?

A

50cm

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15
Q

What are the 4 conditions for assessing gaze in Hess testing?

A
  1. fixing R and L eye
  2. in all positions of gaze
  3. for inner (15 degree) field
  4. for outer (30 degree) field - if required
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16
Q

Which order should Hess chart testing be performed in?

A
  • assess left eye first - fix right eye (red filter on R eye + red light)
17
Q

Which goggle should be used for fixing?

A

where possible should always use red light for fixing - i.e. examiner moves red light and patient moves green light over it

18
Q

Which goggle is over which eye when assessing L vs R eye?

A

L eye: red filter over R eye, green filter over L eye
R eye: red filter over L eye, green filter over R eye

19
Q

When is it useful to use the outer 30 degrees of gaze with Hess chart testing?

A

for small/subtle under/overactions

20
Q

What principle does Hess testing rely on that means that the mapped gaze corresponds to the position of the eye?

A

foveal projection

21
Q

How is Lees testing performed?

A
  • dissociation achieved by mirror between subject’s eyes
  • mirror bisects two facing Lees screens 90 degrees apart
  • operator presents target to fixing eye
  • subject’s non-fixing eye position is revealed by their projected perception of a corresponding point in the opposite Lees screen
22
Q

What are 3 advantages of Lees testing over Hess testing?

A
  1. constant illumination L vs R
  2. greater contrast
  3. easier test for usbject to understand and perform
23
Q

What does the smaller field of movement for Hess and Lees charts usually indicate?

A

smaller field of movement indicates affected eye

24
Q

What does inward displacement indicate in Hess and Lees testing?

A

underaction

25
Q

What does outward displacement indicate in Hess and Lees testing?

A

overaction

26
Q

What does similarity of fields L vs R indicate with Hess and Lees testing?

A

concomitance

27
Q

What does a compressed field with asymmetry L vs R with Hess and Lees testing indicate?

A

(incomitance) - mechanical defect

28
Q

What do sloping fields indicate with Hess/Lees charts?

A

A or V patterns (not torsion)
* **A-pattern **strabismus describes a deviation that is more convergent or less divergent in upgaze.
* Conversely, a V-pattern strabismus exists when the magnitude of deviation is less convergent or more divergent in upgaze

29
Q

What is shown in this Hess chart?

A
  • limitation of L upgaze and abduction, with right upgaze and overaction and lesser right adduction overaction
  • suggests asymmetrical thyroid eye disease (L worse than R) related to disease of left inferior rectus and medial rectus
30
Q

What does the Hess chart show?

A
  • underaction of R superior oblique and overaction of L inferior rectus
  • consistent with recent right 4th nerve palsy
31
Q

What are 2 types of tests which test for binocularity i.e. simultaneous perception?

A
  1. Worth 4-dot test
  2. Bagolini glasses
32
Q

What are 3 tests for suppression?

A
  1. Worth 4-dot test
  2. 4 prism dioptre base-out prism test
  3. Bagolini glasses
33
Q

What are 3 tests that can detect anomalous retinal correspondence (ARC)?

A
  1. Worth 4-dot test
  2. Bagolini glasses
  3. after-image test
34
Q

What are 5 tests of stereopsis?

A
  1. titmus (polarised glasses)
  2. TNO (red green glasses)
  3. Lang (no glasses)
  4. Frisby (no glasses)
35
Q

What is the difference between binocularity vs stereopsis?

A

stereopsis is the highest level of binocular vision - binocular vision consists of simultaneous perception->fusion->stereopsis, which is 3D perception

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