Refractive techniques in amblyopia

Question 1

what is the definition of amblyopia

Answer 1

reduced visual acuity in one or both eyes. with no pathological cause for the reduced VA.

Question 2

what visual acuity is usually taken to be amblyopia

Answer 2

6/9 or Logmar 0.2 approx, or worse

Question 3

what is amblyopia caused by

Answer 3

abnormal visual development during the ‘critical period’ for visual development
(children in first 7-8 years old, when their va is supposed to improve i.e. deprived of a clear retinal image)

Question 4

how much % of the population does amblyopia affect

Answer 4

between 1 and 4% of the population

Question 5

list 3 different types of amblyopia

Answer 5

• refractive
• stimulus deprivation
• strabismic

Question 6

describe how refractive amblyopia occurs

Answer 6

results from uncorrected refractive error in one or both eyes (during the critical period of first 7-8 years)
e.g. anisometropia RE: +4.00 LE:emmetropic
if the left eye is covered and the right eye wants to see clearly in the distance, it will have to accommodate by +4D. if the right eye is covered, the emmetropic eye (LE) doesn’t need to accommodate to see clearly.
when both eyes are open, the right eye won’t accommodate by +4D and the left eye won’t accommodate at all, as both eyes always accommodate by the same amount and in this case the eyes won’t accommodate at all, so right eye will have +4D of blur and if this happens during the critical period, the px’s va’s cannot develop properly = amblyopic for both DV and NV

Question 7

describe how refractive amblyopia occurs

Answer 7

results from uncorrected refractive error in one or both eyes (during the critical period of first 7-8 years)
e.g. anisometropia RE: +4.00 LE: emmetropic
if the left eye is covered and the right eye wants to see clearly in the distance, it will have to accommodate by +4D. if the right eye is covered, the emmetropic eye (LE) doesn’t need to accommodate to see clearly.
when both eyes are open, the right eye won’t accommodate by +4D and the left eye won’t accommodate at all, as both eyes always accommodate by the same amount and in this case the eyes won’t accommodate at all, so right eye will have +4D of blur and if this happens during the critical period, the px’s va’s cannot develop properly = amblyopic for both DV and NV

Question 8

describe how stimulus deprivation amblyopia occurs

Answer 8

occlusion e.g. ptosis (affected eye has no clear retinal image during critical period)

Question 9

list 7 refractive techniques required to be carried out properly in a amblyopic px

Answer 9

• choice of dioptric interval
• crossed cyl target
• crossed cyl power
• fan and block
• pinhole disc
• binocular balancing
• retinoscopy in strabismic amblyopia w

Question 10

what is the problem with a dioptric interval that is too small on an amblyope

Answer 10

invites the wrong results and wastes time e.g. for a +4D with 6/12 va & using a +0.25D for bsv will always look the same to px, as they can’t see a significant enough difference, for a long time

Question 11

what is the best choice of powers to use whilst doing bvs in a bracketing approach on a amblyopic patient

Answer 11

• using higher dioptric powers as it gives a clearer response e.g. for a 6/12 px, use ±1.00D or ±0.50D lens, and don’t give -ve lenses if the patient reports that the letters look the same
• use higher power spheres to begin with
• choice of power depends on patients acuity and ability to discriminate change
• may use +1.00DS or +2.00DS initially, especially those with a visual impairment

Question 12

when will you know which choice of power for bvs on an amblyope is best to use

Answer 12

choice of power depends on patients acuity and ability to discriminate change

Question 13

which powers may you initially use on a px that is visually impaired when doing bvs

Answer 13

+1.00DS or +2.00DS initially

Question 14

when may you refine your bvs with smaller dioptric intervals

Answer 14

if noticed by the px e.g. +1.00D or +0.50D, use +0.25D spheres last or if at all, it is up to us to decide, but not really needed for an amblyope

Question 15

what is the usual target for cross cyl

Answer 15

concentric rings

Question 16

what is the inner ring of the concentric rings of a cross cyl target equivalent to

Answer 16

approx 6/6 snellen letter

Question 17

what is the outer ring of the concentric rings of a cross cyl target equivalent to

Answer 17

approx 6/15 snellen letter

Question 18

which level of vision is best to use the cross cyl ring targets

Answer 18

vision 6/12 or better

if worse than 6/12, concentric rings is not a good target

Question 19

which choice of concentric ring targets for cross cyl will you choose or a 6/18 px, and explain why it still isn’t essential

Answer 19

use a 6/24 round target for cross cyl, so go one line worse.

but sometimes this is not available on all charts

Question 20

describe the 4 steps of cross cyl bracketing approach

Answer 20

• use a higher powered cross cyl (±0.50DC is usually the only one available) to begin with
• use ±0.25DC crossed cyl, but only if changes produced by this cross cyl are appreciated by the patient
• may use ±0.75DC or even ±1.00DC initially with visually impaired patients
• refine results with smaller powers, but only if changes produced by these cross coyly are appreciated by the patient

Question 21

which powers of cross cyl will you initially use on a visually impaired px

Answer 21

±0.75DC or even ±1.00DC initially

Question 22

what are the lines on the fan and block chart approx equivalent to

Answer 22

6/15 snellen

Question 23

when should you not consider using fan and block

Answer 23

when a px’s va’s are worse than 6/12

Question 24

how is a pinhole disc useful in amblyopes

Answer 24

to distinguish between poor acuity/vision due to a bad refraction or poor acuity/vision due to amblyopia (or eye disease)
if acuity/vision does not improve with a pinhole, then you are unlikely to improve acuity during your refraction

Question 25

what does a pin hole disc cause on a px with normal pupil size

Answer 25

smaller blur circles

Question 26

what does smaller blue circles caused by a pinhole allow for

Answer 26

a clearer image

Question 27

where in relation to the retina does the image come if a px is over plussed and the image is at infinity

Answer 27

infront of the retina

Question 28

what contributes to larger blur circles, hence a less clearer image

Answer 28

peripheral rays

Question 29

which patients are suitable for binocular balancing

Answer 29

all patients with binocular vision and good acuity in each eye

Question 30

list 6 types of patients that you should not binocular balance on

Answer 30

• with a squint
• with amblyopia
• who are monocular
• with VA differences of 3 or more lines
• who are presbyopes (60 years or over)

Question 31

explain why there will not be any point on a px who is 6/5 in one eye and 6/18 in the other to do binocular balancing on

Answer 31

because by using a +0.75 or +1.00DS lens to blur then in the good eye, it is not going to make the acuity as bad as the amblyopic eye

Question 32

what is a possible theoretical method of binocular balancing on an amblyope

Answer 32

using the septum method - Turville’s infinity balance test or TIB test

Question 33

explain the idea of the Turville’s infinity balance test or TIB test

Answer 33

• to push the septum (stick) across the mirror right in-between the left and right circles on the duo chrome
• so when correctly positioned, the patient sees the black ring on the red and green by the left eye on the left side, & on the right hand side black rings against the red & green by the right eye ONLY
• if you equalise the rings on the left side & clarify them & do the same on the right side whilst each eye is covered, then you have balanced them
• if left eye = 6/9 (amblyopic) you can still equalise the circles on the red & green and won’t be as clear as seen by right side of right eye
• but your only trying to equalise the left side circles as seen by the left eye

Question 34

when is it worth binocular balancing in monocular amblyopia

Answer 34

when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/9 then MAYBE try it

Question 35

when is there no point in binocular balancing in monocular amblyopia

Answer 35

when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/12, 6/18, 6/24 and worse

Question 36

when is it worth maybe binocular balancing in binocular amblyopia

Answer 36

when va’s = 6/9 R+L eye

Question 37

when is there no point in binocular balancing in binocular amblyopia

Answer 37

when va’s = 6/12 or worse R+L eye

Question 38

when can you get binocular amblyopia

Answer 38

if a patient has had uncorrected astigmatism in both eyes, making them amblyopic in both eyes

Question 39

when is it difficult to carry out retinoscopy (distance fixation)

Answer 39

in strabismus, on the squinting eye, and you must do ret on the patient’s visual axis, if not can produce astigmatic errors

Question 40

what can be a possible solution and possible drawback of this solution, of carrying out ret (distance fixation) on a px with a squint

Answer 40

occlude the fixing eye (brings squinting eye back into fixation) - but optometrist’s head now gets in the way of the target AND px will also accommodate

Question 41

when is it worth doing retinoscopy (distance fixation) on a px with a strabismus and occluding the non-deviated eye and what is a possible drawback to this method

Answer 41

• if the eye is not off axis that much
• but patient is more likely to accommodate monocularly (because with the two eyes open, convergence helps to keep accommodation steady)
• probably worth doing if squint is greater than 10 prism dioptres (to cover the good eye, but px more likely to accommodate & will slightly be off-axis)

Question 42

explain how you would carry out retinoscopy with someone who has a strabismus with near fixation and the drawbacks to this method

Answer 42

• occlude fixing eye - but not recommended as accommodation is very unstable
• position ret where two axes meet - but location may change during retinoscopy

Question 43

how is using a cycloplegic drug the best method for doing retinoscopy

Answer 43

e. g. cyclopentolate
- this will paralyse or partially paralyse accommodation
- you can occlude the fixing eye as required and the patient can directly fixate the ret light
- may be acceptable for children but a bit drastic for other (e.g. who don’t have accommodation)