Accommodation and Convergence

Question 1

how is the near point assessed?

Answer 1

convergence
- near point and fusional reserves

accommodation
- near point, facility and lag

relationship between accommodation and convergence
- AC/A ratio
–> +ve and -ve relative accommodation/convergence
+ve = increasing accommodation but keeping vergence fixed
-ve = relaxing accommodation with a fixed vergence

near pupil response

Question 2

what does accommodative facility mean?

Answer 2

facility is the ability to change accommodation quickly - therefore rapid changs in accommodative effort

Question 3

what does accommodative lag mean?

Answer 3

lag is a measure of how accurate your accommodation is.

may have lots of accommodation but it is over-excessive or under-accommodative

Question 4

what is the AC/A ratio?

Answer 4

it is the amount of accommodative convergence per dioptre of accommodation

Question 5

what is does the RAF rule do and what are the methods of measurement using it?

what units is diplopia measured in?

Answer 5

The RAF rule measures the near point of convergence. It has a dot which provided a fixation point and a single high contract line which helps to know when diplopia occurs.

methods:
push target towards patient - record the break point when the line is seen as being two

push target away from px - watch for when the lines are fused and record the recovery point

repeat.

diplopia is measured in cm’s

Question 6

what happens during a subjective NPC and an objective NPC?

Answer 6

subjective: the px reports diplopia - bring up towards px’s nose
objective: watch the px’s eyes. make note when the convergence breaks. make note of which eye diverges first and the distance of the target from the face and does the px report diplopia or not.

Question 7

is NPC done with or without correction and why?

Answer 7

if the px normally wears specs for reading then do with glasses on. if they dont, then do without specs. - done in the condition the px is in for NV.

• high hypermetropes, presbyopes and moderate myopes whilst wearing glasses.

in high minus lenses the base in prism due to the -ve lens will assist the convergence.

with specs the lens edge and frame may obscure the target.

Question 8

how is accommodation assessed?

Answer 8

accommodative amplitude or range
- near point with RAF rule - and keep adding minus lenses until blurred as will accommodate through the first set of minus lenses

accommodative facility
- using flipper lenses and flipping between + and -

accommodative lag/lead

• carrying out dynamic retinoscopy - using ret to judge the accommodation
• using the Monocular Estimation Method or the Nott Method

Question 9

how do you do the minus lenses test for accommodation?

Answer 9

• full rx is worn
• the target is a near card at 40cm
• done monocularly and then binocularly
• negative lenses are placed in front of the eye
• increased in 0.25 steps
• encourage the px to make the print clear
• end point is when the px cannot make the letters clear
• repeat for the other eye

the point where the px says its blurred is the limit of accommodation.

Question 10

how is accommodative facility tested?

Answer 10

tested using flipper lenses.
spheres of + and -
requires rapid changes in accommodative demand whilst keeping the vergence fixed

in a normal adult/child with a plus or minus 2 they are able to do 9-11cycles per minute.

= good method

Question 11

how is dynamic retinoscopy done?

Answer 11

ret is used to look at the accuracy
lights stay on and target is being looked at in the place of the ret - budgie stick or cards

if the accommodation is equal to the stimulus accommodation then there should be a neutral reflex seen.

Question 12

what is dynamic retinoscopy?

Answer 12

it is the difference between accommodative demand and plane of neutralisation, in Dioptres

Question 13

how the dynamic retinoscopy done for the Nott method and the MEM (monocular estimate method)?

Answer 13

Nott method:
change distance of retinoscope to neutralise

MEM method:
neutralise using lenses

Question 14

what is the Nott method and how is it done?

Answer 14

when you change the distance of retinoscope to neutralise - keep the target at a fixed distance, 33cm, and move ret back and forth to neutralise and then calculate the measurement.

• px fixates details on the target
• accommodative lag = with movement therefore move ret back
• accommodative lead = against movement therefore move ret forward

e.g. target at 33cm which is 3D.
ret reflex neutral at 40cm which is 2.5D
therefore the lag is 0.5D

a normal lag is between 0 and 0.75 dioptres

Question 15

what is the MEM method and how is it done?

Answer 15

neutralise using lenses - keep the target at a fixed distance, 33cm, and neutralise

• px fixates on details on the target
• accommodative lag = with movement therefore add +ve lenses
• accommodative lead = against movement therefore add -ve lenses

Question 16

what are the 3 methods to measure the AC/A ratio?

Answer 16

• heterotropia method
• gradient method
• fixation disparity method

Question 17

what does a high AC/A ratio signify?

Answer 17

• excessive change in angle of deviation between neara and distance fixation
• near eso = excess convergence
• distance exo = excess divergence

if ortho at near - means divergent at distance - exo.

Question 18

what does a low AC/A ratio signify?

Answer 18

• insufficient change in angle between near and distance fixation

near exo = weak convergence
ditance eso = weak divergence

if ortho at near - means convergent at near - eso.

Question 19

how is a near pupil response done?

Answer 19

• px’s face should be well illuminated
• keep light on face constant during eye movement
• use UV lamp to see pupil better if dark irises
• observe pupil response
• rapidly shift the fixation from distance to near or from near to distance using a detailed target
• ensure there is pupillary miosis when looking from distance to near.