7. Accommodation Flashcards
What is accommodation?
The ability of the lens to change shape to obtain a clear image of a near object
What lenses stimulate and relax accommodation?
Minus lenses stimulate accommodation
Plus lenses relax accommodation
How do you assess accommodation?
Amplitude of accommodation
Accommodative facility
Accommodative lag or lead
How do you measure amplitude of accommodation (AoA)?
Measure Near point using RAF rule
Minus lenses
How can you measure AoA using RAF rule?
Px wears full distance rx (max plus and minumum minus)
Use smallest target they can read eg. N5 and bring it closer to them until it blurs then pull back until its clear
Test monocularly and binocularly 3 times
Why does px need to wear full distance rx for measuring accommodation?
If px is hyperopic and not wearing their distance rx then they are already accommodating
What unit is AoA recorded in?
Measure in cm and covert to dioptres
What do you record for AoA?
If difference between the blur and clear is less than 1, record the mean, if greater than 1 record the range
If you are measuring AoA for a presbyope and if you gave them a +2.00 reading add, how do you calculate the final result?
Subtract the add from the final near point result
What is the normal value for AoA dependant on?
Age- AoA reduces with age
What is the normal value for AoA for px under 10
15 dioptres
What is the normal value for AoA for 11-20 yr old?
10 dioptres
What is the normal value for AoA for 11-21-30 yr old?
6 dioptres
Over 60 AoA?
Around 0
How to you record AoA?
AoA RAF: Binoc with rx 10D x3
Monoc, RE 8D, LE 8D x3
What is another way of measuring AoA?
Minus lenses
How do you use minus lenses to measure AoA?
Px wears full refractive correction, one eye occluded, hold near chart at 40cm, keep adding minus lenses in 0.25 steps
Encourage px to make print clear and stop when can no longer be cleared
Repeat with other eye and binocularly
When are minus lenses used as a method to measure AoA
In research as it’s too time consuming in practise
What is Accommodative facility?
The ability to change accommodation with demand i.e how quickly you can stimulate and relax accommodation
Give a real life example of change in accommodation
In a lecture hall looking at the board then looking at your notes infront of you
How do you measure accommodative facility?
Flipper lenses
How do you use flipper lenses to measure accommodative facility?
Give patient near chart , must wear full rx and put on 1 minute timer
Hold plus side flippers infront and say can you tell me when the print becomes clear then flip to minus and say again can you tell me when it’s clear
What do you record in accommodative facility?
Number of cycles per minute
What counts as 1 cycle?
The plus and minus 1 flip of each is one cycle
What dioptre flipper do you start with and what happens if px can’t do it?
Start with +2.00 flippers then reduce strength if px can’t do it
What is the normal values for accommodative facility for a normal young adult or child?
9/11 cycle per minute with +2.00 flippers
What do you record for accommodation facility result?
(full rx worn, size of print, cycles per minute, flipper size used
Is AoA and accommodative facility objective or subjective ways to assess accommodation?
Subjective
What are the disadvantages of subjective assessment of accommodation?
Unreliable
What is an objective way to assess accommodation?
Measuring accommodative lag or lead using dynamic ret
What is accommodative lag?
Under-accomdating
What is accommodative lead?
accommodating
What are the two methods of dynamic ret?
MEM
Nott
Describe how you would use MEM method to measure lag or lead?
Wear full distance rx, target same distance as ret at 40cm (attachment card that comes with retinosocpes)
A with movement indicates lag
An against indicates lead
Neutralise the movement you see
How do you know if their accommodation is perfect and accommodating exactly to the demand so no lag or lead?
Neutral reflex
What does AC/A mean?
Amount of accommodative convergence per dioptre of accomdation
Describe AC/A in more simpler terms
It’s how much your eyes converge when you accommodation by 1 diopters
Does AC/A ratio change with age?
No, the AC/A ratio we develop when we were young stays until presbyopia
What is a normal AC/A ratio?
3:1 to 5:1
If patient has 12 dioptres of exophoria, what lenses and power do you give so eyes pull in?
-3 as minus stimulates accom so eyes will pull in
What are the 3 different ways to measure AC/A ratio?
Heterophoria method
Gradient method
Fixation disparity method
Describe the Heterophoria method
Wear distance rx, measure hetrophoria or tropia and distance and near, measure the PD
Use this formula
AC/A= PD in cm+(AngleN- AngleD) /(Accommodative demand)
For eso use a + sign and for exo a minus sign
What is the accommodative demand?
It depends on where you hold the targer so if it’s head at 1/3m(33cm) then the demand is 3 dioptres
If it’s held at 50cm then the demand in 2 dioptres
