accommodation & convergence Flashcards
list the things which assessment of near point measures
- convergence
- accommodation
- relationship between accommodation and convergence
- near pupil response
which ways can convergence be measured
- near point (bringing target to px)
- fusional reserves
which ways can accommodation be measured
- near point (bring target towards px until blurred)
- facility (measure of how accurate accommodation is)
- lag (ability to change accommodation quickly)
what are you measuring when measuring the facility of accommodation
how accurate your accommodation is, e.g. at 25cm you should accommodate by 4D etc
- speed of change in accommodation
- rapid refixation from near to distance viewing
which ways can you measure the relationship between accommodation and convergence
- AC/A ratio
- +ve and -ve relative accommodation/convergence
what is +ve relative accommodation
increasing our accommodation whilst keeping our vergence fixed
what is -ve relative accommodation
relaxing our accommodation whilst keeping our accommodation fixed
what is used to measure the near point of convergence
RAF rule
- dot provides a fixation point
- single high contrast line helps recognition of diplopia
- use cm scale for measurement to measure near point convergence (when lines just go into two)
what does the dot target on the RAF rule provide
a fixation point
what does the high contrast line provide on the RAF rule
helps recognition of diplopia
what is a subjective example of measuring near point convergence
patient reports diplopia
when can a subjective method of near point convergence i.e. patient reporting diplopia not reliable
- on young children
- on adults - as we have physiological diplopia so we can learn to ignore when a target splits into two
what are the objective examples of measuring near point convergence
- watch the patients eyes
- when convergence breaks note:
which eye diverges first
at which distance from the face
does the patient report diplopia
what must be noted when objectively measuring near point convergence by when convergence breaks
- which eye diverges first
- at which distance from the face
- does the patient report diplopia
what is the reason for when convergence breaks, when objectively measuring near point convergence
they have reached the limit of their convergence
list the steps of how you would do the push up and back of the target of the RAF rule when measuring near point convergence
- push target towards patient - record break point - bring target away from patient - watch for fusion record recovery point - repeat - normal 6-10cm - record NPC 5cm (subjective)left eye convergence breaks
which patients should wear rx when measuring near point convergence
high hypermetropes
high myopes
presbyopes
what reasons may wearing rx when measuring near point convergence not a good idea
- for myopes - base in prisms due to -ve lens will assist in convergence
- lens edge and frame contours may obscure target
what is the assessment of accommodation measured with
RAF rule
list which aspects of accommodation is measured when measuring the assessment of accommodation
- accommodative amplitude or range
- accommodative facility
- accommodative lag or lead
how is the accommodative amplitude measured as an assessment of accommodation
- near point -
bring target towards until it becomes blurred - minus lenses -
keep adding minus lenses until they can no longer accommodate through them, and report its blurred = reached limit of accommodation
how is the accommodative facility measured as an assessment of accommodation
flipper lenses - ability to change accommodation rapidly by using +/- confirmation test lenses
how is the accommodative lag or lead measured as an assessment of accommodation
- dynamic retinoscopy
monocular estimation method
nott method
list the steps of how you would measure near point
- test monocularly and binocularly
- ensure full distance rx is worn
max +ve or least -ve - find nearest point of clear vision
measure in cm and convert into dioptres
use dioptric scale - target
N5 or smallest visible print or target - technique
push up target until patient reports target blur
pull back until patient reports target is clear
repeat push up and pull back
if difference is less than 1D - record mean
if difference is more than 1D - record range
when measuring near point how do you record your results if there is a difference of less than 1D between readings
record mean
when measuring near point how do you record your results if there is a difference of more than 1D between readings
record range
when measuring near point, is it done monocularly or binocularly
both
is rx worn when measuring near point
yes full distance rx
what is the target viewed on the RAF rule when measuring near point
N5 or smallest visible print or target
what is the technique when measuring near point with an RAF rule
- push up target until patient reports target blur
- pull back until patient reports target as clear
- repeat push up/pull back
why is it important to select the smallest visible line of text on the RAF rule when measuring near point
printed text is more demanding target than single letter presentation
what must you do if the amplitude is less than 2D (50cm) on the RAF rule when measuring near point
- include binocular near add e.g. +2.00DS
- find near point and subtract add from final result
e. g. if measure accommodation with +2.00DS add, if you find +6.00D of accommodation, they actually have +4D
which type of person may have an amplitude less than 2D (50cm) and why do you need to give them an add e.g. +2D when using the RAF rule to measure near point
presbyopes, so that their range is brought towards the middle of the RAF unit
when measuring accommodative amplitude or range via minus lenses, which rx should be used
full refractive correction (must do when measuring accommodation)
what target and at which distance must be used when measuring accommodative amplitude or range with minus lenses
near card at 40cm
list the steps of how you would measure accommodative amplitude or range with minus lenses
- one eye occluded
- negative lenses are placed infront of eye
- increased in 0.25DS steps
- encourage patient to make print clear
- end point when letters cannot be cleared (reached limit of accommodation)
- repeat for other eye and binocularly
when measuring accommodative amplitude or range with minus lenses, is it done monocularly or binocularly
both
monocularly first them do binocularly
which ways are there to measure amplitude of accommodation subjectively
- near point
or - far point through minus lenses
when is recording near point as a subjective measure of amplitude of accommodation slightly better and why
binocularly as convergence strives accommodation
when is recoding far point through minus lenses as a subjective measure of amplitude of accommodation slightly better
monocularly
what are the disadvantages of measuring amplitude of accommodation subjectively i.e. by recording near point and far point through minus lenses
- an unreliable end point
- large differences between stimulus and response accommodation
depth of field increased by small pupils (accommodate more than they actually accommodate) - changing subjective criteria
- cannot do on children
define accommodative facility
change in accommodative effort with change in accommodative demand
how are flippers/confirmation test used to measure accommodative facility
- binocular + and - spheres
ask to look through +ve lenses, when clear flip round to -ve lenses and ask them to make it clear, so they’re exerting and relaxing accommodation whilst keeping their vergence fixed - rapid change in accommodative demand
- number of cycles per minute
normal young adult or child with ±2.00 lens 9-11 cyc/min
what is the normal range of cycles per minute with ±2.00DS lenses, when measuring the accommodative facility
9-11 cyc/minute
what are the objective techniques of measuring accommodation
- accommodative lag
- dynamic retinoscopy
which two ways in accommodative lag measured, as an objective technique of measuring accommodation
- stimulus accommodation distance of fixation target in D sphere if their accommodation is equal to the stimulus accommodation = neutral reflex - response accommodation objective assessment of accommodation
how can dynamic retinoscopy measure accommodation
- nott method
changing distance of retinoscope to neutralise - MEM (monocular estimate) method
use lenses to neutralise - difference between accommodative demand and plane of neutralisation, in dioptres
when using dynamic retinoscopy MEM to measure accommodation, where must the target be placed
same distance as ret, normally 1/3rd metre
px fixates of detailed target e.g. pictures for children
when does neutralisation occur when using dynamic retinoscopy MEM to measure accommodation
when back focal plane of the eye is conjugate with back focal plane of retinoscope
what movement shows lag in ret reflex, when using dynamic retinoscopy MEM to measure accommodation
with movement
what does an against movement in ret reflex show, when using dynamic retinoscopy MEM to measure accommodation
accommodative lead
how do you neutralise, when using dynamic retinoscopy MEM to measure accommodation
using appropriate spheres in one meridian only very briefly
what does it mean when theres an accommodative lag/with movement in ret reflex, when using dynamic retinoscopy MEM to measure accommodation
accommodation is falling slightly behind the target, need to hold up +ve lens in front of eye until it becomes neutral.
can have an exo deviation larger than normal
what does it mean when theres an accommodative lead/against movement in ret reflex, when using dynamic retinoscopy MEM to measure accommodation
accommodating too much & can have an eso deviation
what distance must the target be when using dynamic retinoscopy Nott to measure accommodation
same distance as ret, normally 1/3rd metre
px fixates on detailed target
when does neutralisation occur when using dynamic retinoscopy Nott to measure accommodation
when back focal plane of eye is conjugate with back focal plane of retinoscope
what does a with movement in ret reflex show when using dynamic retinoscopy Nott to measure accommodation
accommodative lag
what must you do to neutralise, when there is an accommodative lag/with movement in ret reflex, when using dynamic retinoscopy Nott to measure accommodation
move ret backwards until back focal plane of eye and ret are conjugate
what must you do to neutralise, when theres an accommodative lead/against movement in ret reflex, when using dynamic retinoscopy Nott to measure accommodation
move ret forwards
how do you measure neutralisation when using dynamic retinoscopy Nott to measure accommodation
lag is the dioptric difference in distance of ret and target
eg
- target at 33cm (3D = stimulus of accommodation)
- if ret reflex neutralised at 40cm (2.5D = response accommodation)
- lag = 0.5D
- normal lag is between 0-0.75 dioptres
what is normal lag, when using dynamic retinoscopy Nott to measure accommodation
0-0.75D
what does the AC/A ratio as a measure of relationship between accommodation and convergence stand for
amount of convergence per dioptre of accommodation
(amount you converge per unit of accommodation)
prism dioptre/DS
when using +ve and -ve relative convergence as a measure of relationship between accommodation and convergence, what is kept constant and what changes
- accommodation constant
- change in vergence demand
when using +ve and -ve relative accommodation as a measure of relationship between accommodation and convergence, what is kept constant and what changes
- vergence constant
- change in accommodative demand
list the three different methods of measuring AC/A ratio
- heterophoria method
- gradient method
- fixation disparity method
what is the heterophoria method of AC/A ratio, finding the difference in
difference in angle of deviation (phoria or tropia) on near and distance fixation
what measurement do you take when using the heterophoria method of AC/A ratio
- pd (cm)
- prism cover test at distance & near
- angle of deviation on distance fixation
- angle of deviation on near fixation
what is the AC/A calculation for the heterophoria method
pd + ((angleN - angleD)/accommodative demand)
in the heterophoria method of calculating the AC/A ratio, what sign does a eso and exo prism dioptres deviation have
eso +ve
exo -ve
what does the heterophoria method of calculating the AC/A ration make no allowance for
proximal convergence
give an example of the heterophoria method of measuring AC/A ratio
- distance viewing: 2 prism dioptres XOP (-ve)
- 1/3rd m viewing: 8 prism dioptres XOP
- pd = 64mm (6.4cm)
- pd + ((phoriaN - phoriaD)/accomm demand)
- 6.4 = ((-8 - (-2)/3) = 6.4 - 2
- = 4.4:1
what is the normal AC/A range when using the heterophoria method
3:1 to 5:1
what does the gradient method of measuring AC/A ratio measure
the change in angle or heterophoria when viewing through +ve or -ve spheres
when measuring the change in angle or heterophoria when viewing through +ve or -ve spheres, in the gradient method of AC/A ratio, what is altered and what is kept the same
- accommodative demand altered
- vergence demand kept the same
when using the gradient method to measure AC/A ratio, list what type of fixation is required and which types of prism cover tests are required
- near fixation
- near PCT
compare near PCT with +3.00DS binocularly or without +3.00DS - distance PCT
compare PCT with -3.00DS binocularly or without -3.00DS
to get angle of deviation
what is the calculation of the AC/A ration with the gradient method
PCT with accomm - PCT without accomm/accomm demand
give an example of the gradient method of measuring AC/A ratio
PCT at near (0.33m)
24^ base out
3^ base out with +3.00DS
(exo deviations = -ve value)
AC/A = 24^ - 3^/3 (as used +3DS lens) = 7:1
what is considered a normal AC/A ratio
3-5:1
3-5 convergence to 1D of accommodation
what does a high AC/A ratio indicate
excessive change in angle of deviation between near and distance fixation i.e. when we accommodate/converge excessively when we’re emmetropic
- near eso called covergence excess (nv probs)
- dist exo called divergence excess (dv probs)
what does a low AC/A ratio indicate
insufficient change in angle between near and distance fixation when we’re emmetropic
- near exo called convergence weakness
- distance eso called divergence weakness
what happens when you don’t have a good fusion range and give an example of someone who is orthoptic at near but has a high AC/A ration at distance
will have uncontrolled phorias which may become manifest
if orthoptic at near but have high AC/A ratio at distance, at DV will have poorly controlled exophoria and can become manifest i.e. exotropia
what can +ve and -ve relative convergence measure
how much we can change convergence with keeping accommodation fixed (by looking at 40cm target)
what is used to measure +ve and -ve relative convergence
prism bar or flipper prisms
how do you measure +ve relative convergence
- use base out prisms (to increase their convergence = positive relative convergence)
- eso deviation of visual axis
- measure to blur point (point where can no longer increase convergence & keep accommodation static/fixed = keeping one thing constant and changing the other)
how do you measure -ve relative convergence
- use base in prisms (so converge less but keep accommodation the same)
- exo deviation of visual axis
- measure to blur point or break point if breaks prior to blur
what can +ve and -ve relative accommodation measure
how much we can change accommodation whilst keeping vergence fixed (by looking at a fixed target)
which flipper lenses are used when measuring +ve relative accommodation
-ve
what accommodation does +ve flipper lenses measure
-ve relative convergence
what happens to the accommodation when placing +2.00DS flipper lenses infront of eyes whilst it focuses on a target to keep convergence fixed
accommodation relaxes
what happens to the accommodation when placing -2.00DS flipper lenses infront of eyes whilst it focuses on a target to keep convergence fixed
accommodating twice as much
how can dynamic ret high neutral objectively measure -ve relative accommodation
patient looks at the target and the plane of the ret & add +ve lenses until get neutralisation, then keep adding +ve lenses until get an against reflex and try to see the point where they can no longer keep their accommodation fixed
list how to measure with the near pupil response of assessing near point/accommodation
- patients face should be well illuminated
- keep light on face constant during eye movement
isolate near reflex from light responses - use of UV lamp assists visibility of pupil
- observe pupil réponse
- rapidly shifting fixation
from a distance to a near target or vice versa
use detailed target for near and distance
looking for pupillary miosis when looking from distant target to near
