Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

OV2018 binocular vision > measurement of ocular deviations > Flashcards

measurement of ocular deviations Flashcards

1
Q

why should we measure the deviation ?

A

. enable us to diagnose
. to ensure consistency between examiners
. find maximum deviation - decide when to manage
. monitor progression - improvement/deterioration
. relate size to fusion range or other clinical features
. to calculate AC/A ratio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are different points the measurement of ocular deviation taken at?

A

. measurements taken at:

  • at 1/3 metre (near)
  • 6 meters
  • at > 6 meters plus of increase in the distance
  • 8 positions of gaze- HES
  • with and without refractive correction
  • with and without head posture
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the three objective methods of calculating deviation ?

A

. using total dissociation
1. objective prism cover test

. using corneal reflections

  1. Hirschberg
  2. krimsky
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the three methods of calculating subjective deviation ?

A
  1. subjective prism cover test
  2. maddox rod
  3. maddox wing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what method to use on unreliable patients ?

A

objective methods- comes from clinician

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

which patients are unreliable ?

A

. younger children
. children and adults with learning difficulty
. patients who had a stroke and find communication hard

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

which methods is maximally dissociative ( gives maximum angle )?

A

. important to consider when thinking about surgery

. objective prism cover test - allows you to see maximum angle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is prism cover test (PCT)?

A

. best test to use
. method of choice in all suitable deviations
. requires patient co-operation
. only as reliable as the clinician
. PCT measures total deviation (manifest and latent )
. accommodative target required
- line above weakest eye R6/18 , L. 6/12 use 6/24
- but spot light if less than 6/60

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

why is the prism cover test rarely used ?

A

. only as reliable as the clinician

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what to do before carrying out prism cover test ?

A

. carry cover test to see if patient has SOT or XOT or SOP or XOP
. if patient has a phoria you can put prism bar in front either eye
. if patient has a tropia you must put prism bar in front of manifest eye
. estimate deviation
. the base of the prism bar is always opposite the deviation
- RSOT base out in RE
-L XOT base IN LE
- right hyper eye base-down RE
- XOP BI in front of RE or LE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why is the base of the prism always opposite to the deviation ?

A

. patient has right SOT - because the right eye is turned in
. fixation target stimulates fovea of the LE and nasal retina RE
. nasal retina projects temporally
. uncrossed diplopia
. to alleviate diplopia from RSOT
. base out prism moves image towards the apex- to resolve the double vision
. to correct base always opposite the deviation
. base the same direction as the deviation to moves images further apart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how to carry prism cover test (PCT)?

A

. head erect
. perform alternating cover test slowly ( slower = easier to determine )
. start with prism close to estimate ( large deviation use a higher prism )
. carry on performing alternating cover test
. always look at the eye behind the prism bar
. increase prism strength until no movement seen
. then increase prism until opposite movement is seen
( if eso increase until exo movement seen)
. record results in prism dioptres as the prism before reversal seen
. PCT
- near with RX: 10 △ BI
- distance with Rx: 6 △ BI

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are advantages of prism cover test ?

A

. accurate measurement, down to 2△

. measures full angle ( manifest and latent component)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are the disadvantages of prism cover test?

A

. dependent upon ability to fixate accurately
. can not be used to measure cyclodeviations
. unreliable in the presence of poor visual acuity
. cannot be used young children

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is a simultaneous cover test (SPCT)?

A

. used in manifest strabismus with a latent component
. PCT measures both manifest and latent
. SPCT measures manifest deviation only
. perform cover test to determine type and estimate angle of deviation
. prism of estimated strength paled before deviated eye while occluder simultaneously covers fixing eye ( cover/uncover cover test)
. keep increasing strength until neutral movement achieved
. you add the px manifest and latent strabismus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what tests do we use to estimate angle/size of deviation by corneal reflections ?

A

. Bruckner
. Hirschberg test
. Krimsky test

17
Q

what is bruckner ?

A
  • a test that will allow you to detect manifest deviation
  • will not allow you to measure manifest deviation
  • screening test
  • compare red reflex on both eyes using an ophthalmoscope
  • normal: same reflex in both eyes
  • if red reflex is slightly less bright in one eye compared to other- mean they got a refractive error large in one eye
  • diminished red reflex in LE: could mean cataract
  • LE has some black speckled flex: means corneal abrasion or foreign body in the eye
  • eye with manifest strabismus has a brighter reflex
18
Q

what is Hirschberg test ?

A
  • patient fixes on pen torch at 33 cm
  • corneal reflections noted in fixing eye and compared with other eye
  • displacement estimated 1mm displacement = 12 (20-22△ ) deviation approximately
19
Q

what is Krimsky test ?

A
  • patient fixes on light at 33 cm
  • corneal reflections noted in both eyes
  • estimated prism placed in front of fixing eye
  • base opposite to deviation
  • strength increased until the corneal reflexes in deviated eye equal to position in fixing eye initially- i.e corneal reflection central eventually
  • can be used with prism before deviating eye ( prism reflection test)
20
Q

what is prism reflection test (prt)?

A
  • used on patient with good vision in both eyes
  • opposite prism base direction is put in front of manifest eye
  • increase the prism bar strength until you find that the corneal reflection in the deviated eye is approximately equal to where the corneal reflection is in the fixing eye
21
Q

what are the advantages of using corneal reflections ?

A

PRT- good for uncooperative patients e.g. infants, learning difficulties
Krimsky - good for blind or one eye with very poor vision

22
Q

what are the disadvantages of using corneal reflection?

A

. can not measure latent deviations
. will not detect microtropias (small angle manifest deviations )
. accommodation not controlled

23
Q

what is subjective prism cover test (PCT)?

A

. head straight - target same size as before
. carry out cover test to work out type of deviation
. place prism of estimated strength before:
- strabismic eye in manifest deviation
- either eye if latent
. base opposite deviation RSOT base Out RE
. carry out alternating cover test ensuring one of the eyes is always covered
. ask the patient if they notice image moving from
- side to side
- up to down
- is deviation getting less
- tell me when deviation is getting less
. find prism strength to neutralise movement of images as cover is moved from one eye to the other
. make deviation reverse then record prism before reversal
. useful in small symptoms producing vertical deviation
-if image is moving with occluder then its exo
-you can ask px - is the image moving side to side getting bigger and that would mean you put the prism up in the wrong direction (base in or out) and then would change it and ask is the movement getting smaller and smaller until there is no longer any movement

24
Q

what is maddox rod ?

A

. high powered cylinders are always placed in front of one eye
. high powered cylinders blur spot of light into streak 90deg to direction of grooves
. other eye views spot light
. traditionally red but sometimes clear or blue
. lens added to trial frame
. placed before
- either eye in latent
- not normally used in manifest deviations
. conducted in darkened room
. additional light sources produce additional streaks
. prism placed before other eye
. apex of prism in the direction
you want the spot light to move
. increased until spot and image coincident
. prism at this point is equal to the angle of deviation
. put the apex in the direction that you want the light to move in

25
Q

what are the advantages of maddox rod?

A

. relatively easy to use

. detects and measures torsion in cyclodeviations

26
Q

what are the disadvantages of maddox rod ?

A

. accommodation not controlled
. can’t have suppression or ARC
. slight head tilt may simulate vertical deviation
. needs fairly good V-A either eye

27
Q

how does maddox double rod test cyclodeviations ?

A

. patient reports line is tilted or torsion suspected
. two (vertical) maddox rods are inserted into trial frame
. one before each eye
. if little separation between lines insert vertical prism
. patient or practitioner rotates rods so that they appear straight and parallel
. amount of cyclodeviation is measured on trial frame in degrees
. used for distance and near viewing in primary position

28
Q

what is maddox wing?

A

. held in reading position
. allow patient time to dissociate
. patients asked what number
- white arrow pointing to
- red arrow pointing to
. caution if arrow falls between two numbers i.e. 9 and 11 patient may report 10
- even numbers suggest and exo deviation - crossed
- odd numbers suggest and eso deviation
. torsion indicated if red horizontal arrow not parallel with the white horizontal grading scale
. patient asked to adjust arrow themselves until it is parallel

29
Q

what are the advantages of maddox wing?

A

. easiest
. quickest
. measures latent horizontal , vertical and cylodeviations

30
Q

what are the disadvantages if maddox wing?

A

. near only
. set distance of 33 cm
. septa bend easily not fully preventing peripheral fusion
. accommodation effects results PD fixed
. can’t have suppression or RC
. unreliable in the presence of poor visual acuity

31
Q

how should all tests be carried ?

A

. all tests should be carried with and without correction if it influences their deviation

32
Q

when would spectacles not impact the deviation?

A

. presbypic patients who don’t have accommodation

33
Q

How would you describe what a prism cover test measures in simple language to your patient ?

A
  • explain what you are measuring
  • e.g if exophoria- eyes are straight however when I put an occluder infront of your eye , it moves and I want to measure that
    e. g if they have a right esotropia- say that your right eye is turned into towards your nose and I want to measure how much is turned in by .

OV2018 binocular vision (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions