W7 accommodation & convergence

what is convergence

simultaneous rotation of the eyes inwards

methods of measuring near point of convergence

pen to nose

RAF rule

subjective test for convergence

when px reports diplopia

objective test for convergence

watch px eyes for convergence to break

note which eye diverges first

note distance and whether they were able to maintain convergence

note if diplopia was noticed

define accommodation

ability to change the convexity of the crystalline lens in order to obtain a clear image of a near object

3 ways to assess accommodation

accommodative amplitude / range

accommodative facility

accommodative lag / lead

how to assess accommodative amplitude / range

near point

minus lenses

what is accommodative facility

speed to change in accommodation

rapid refixation from near to distance viewing

how to measure accommodative facility

flipper lenses

+/- 2.00

disadvantages of subjective assessment of accommodation

unreliable endpoint

large difference between stimulus and response accommodation

objective techniques to measure accommodation

accommodative lag

dynamic retinoscopy

Dynamic Retinoscopy (MEM)

what does a 'with' movement show

accommodative lag

Dynamic Retinoscopy (MEM)

what does a 'against' movement show

accommodative lead

dynamic retinoscopy (Nott)

how to neutralise

move ret backwards for lag

move ret forwards for lead

define AC/A ratio

amount of accommodative convergence per dioptre of accommodation

what the AC/A ratio

for every D of accommodation

there is a certain amount of accommodation convergence

what are the 3 methods of measuring AC/A ratio

heterophoria method

gradient method

fixation disparity method

describe the heterophoria method when measuring AC/A ratio

wear distance rx

measure: PD, angle of deviation on distance and near fixation

calculate AC/A

REMEMBER

eso = +

exo = -

Accom Demand = the distance of target at near

what is the equation for working out AC/A ratio with the heterophoria method

PD + (AngleN - AngleD) / Accom Demand

describe the gradient method for working out AC/A

wear distance rx

for near: compare PCT with +3.00DS binoc and without

for distance: compare PCT with -3.00DS binoc and without

what is the equation for working out Ac/A ratio with the gradient method

(PCT with accom - PCT without accom) / Accom demand