refractive techniques in amblyopia

Question 1

what is amblyopia ?

Answer 1

. reduced VA in one or both eyes with no pathological cause for reduced VA
. usually 6/9 ( logMAR = approximately 0.2 ) or worse

Question 2

what is amblyopia caused by ?

Answer 2

. caused by abnormal visual development during the ‘critical period’ for visual development
. critical period is usually 7-8 years old

Question 3

how much of the population does amblyopia affect?

Answer 3

. affects between 2% to 5% of the population

Question 4

what are the types of amblyopia ?

Answer 4

1. refractive
2. stimulus deprivation
3. strabismic

Question 5

what is refractive amblyopia ?

Answer 5

. results from uncorrected refractive error in one or both eyes
e.g. anisometropia

RE= +4.00DS
LE= emmetropic
when both eyes are open they will accommodate by the same amount and the visual system will choose to not accommodate

Question 6

what is the perfect recipe for the development of amblyopia ?

Answer 6

. when both eyes are open there is a clear retinal image in the emmetropic eye but a blurred image in the hyperopic/myopic eye
. when the eye is deprived of a clear retinal image this results in amblyopia

Question 7

what is stimulus deprivation?

Answer 7

. another cause of amblyopia

. monocular ptosis or droopy lid

Question 8

why is it important to choose the right dioptric interval in an amblyopic patient ?

Answer 8

. choosing a dioptric interval that is too small invites the wrong result and wastes time

. amblyopic patients can’t appreciate the changes that 0.25 steps introduce as the changes in clarity are too small and patient doesn’t notice any change

. holding a lens such as +1.00 / 0.50 will be more appreciated by the patient

Question 9

what is the bracketing approach ?

Answer 9

. use a higher powered sphere to begin with
. the choice of power depends on patient’s acuity and ability to discriminate changes
. may use +1DS or even +2DS initially with some patients, especially those with visual impairment
. refine the result with smaller powers, if these are appreciated by the patient
. use +/-0.25 DS sphere last of all

Question 10

when is it recommended to use concentric ring targets ?

Answer 10

. inner ring is approximately equivalent to 6/6 snellen letter
. outer ring is approximately equivalent to 6/15 snellen letter
. crossed cylinder can reduce the vision in one position
. so it is recommended to use ring target when vision 6/12 or better

Question 11

what crossed cyl target to use for amblyopic patients?

Answer 11

. 6/18 - use 6/24 round letter
. 6/24 - use 6/36 round letter
. 6/36- use 6/60 round letter

Question 12

what crossed cyl powers to use for amblyopic patient ?

Answer 12

. higher powered crossed cyl
( +/-0.50DC )
. only use +/-0.25 if changes produced by this crossed cyl appreciated by the patient
. may use +/- 0.75DC or +/- 1.00DC initially with visually impaired patients

Question 13

what is the VA of fan and block?

Answer 13

. lines on chart are approximately equivalent to 6/15 snellen
. so fan and block should not be used if vision is worse than 6/12

Question 14

what is use of pinhole disc in amblyopes ?

Answer 14

. very useful in amblyopes to distinguish between poor acuity/vision due to a bad refraction or poor acuity/vision due to amblyopia

. if acuity/vision does not improve with a pinhole, then you are unlikely to improve acuity during your refraction

Question 15

which patients are suitable for balancing ?

Answer 15

. all patients with binocular vision and good acuity in each eye

Question 16

which patients should you not balance ?

Answer 16

. with squint
. with amblyopia ( some people disagree) 
. who are monocular
. with VA difference of 3 or more lines 
. who are presbyopes 
( 60 years or over)

Question 17

how do some people binocular balance amblyopic patients?

Answer 17

. possible in theory using the septum method ( turville infinity balance test)
. a septum is moved across the mirror until right eye only see right hand side and left eye only sees the left hand side
. then you equalise the clarity of black circles on red and green on right side and left side

Question 18

when would you binocular balance an amblyopic patient?

Answer 18

. 6/5 and 6/9 ( maybe )

. 6/9 and 6/9 ( maybe )

Question 19

what is the issue with ret in strabismus ?

Answer 19

. difficult to work on-axis when retinoscopy is carried out on the squinting eye

Question 20

how to do ret in an eye with a strabismus ?

Answer 20

. place occlude in eye that is straight so eye with strabismus can be straight
. the problem produced is the optom head is in the way of target so you need to move your head and ret so patient can see the target so you will be off-axis

Question 21

when is distance fixation with ret in strabismus worth doing ?

Answer 21

. if angle beta with one eye occluded is less than the angle alpha with both eyes open
. but the patient is more likely to accommodate monocularly

. probably worth doing if squint if greater than 10 prisms dioptres

Question 22

how to do near fixation with ret in strabismus ?

Answer 22

. occlude fixing eye - not recommended as accommodation is very unstable

Question 23

what is the another solution for unstable accommodation ?

Answer 23

. use cycloplegic drug
. this would 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 others