BOT section clinical and theory Flashcards
(224 cards)
1
Q
as measuring unaided VA in patients who wear glasses is optional, in what cases should it be measured?
A
in patients who
-have lost/ broken their spectacles
-dont wear spectacles for some distance viewing tasks
-need the info for a report
-wear their spectacles all the time for distance and yet you suspect they may not need to
2
Q
how is LogMAR superior to the snellen chart?
A
-results from LogMAR charts have shown to be twice as repeatable as snellen chart
-results from logMAR have been shown to be over 3x more sensitive to interocular differences in VA
3
Q
How can the letters on a snellen and logmar chart be measured?
A
-each gap in the letter is 1min arc and hence the whole letter is 5min arc high
4
Q
What are the advantages of the cover test?
A
-quick and easy to carry out
-objective hence no verbal response is required: good for babies, people with speech difficulties
-minimal cooperation is required
-gives an idea of the presence of amblyopia/ poor vision
5
Q
what are the disadvantages of the cover test?
A
-poor fixation may make results inaccurate
-small deviations may not be recognised
-difficult to see strabismus if associated with nystagmus
-corneal reflections may not give an accurate guide to the size of deviation
6
Q
what is the patient’s MAR? what is it equal to
A
the smallest line they can read on the letter chart
MAR = y/x where y is the line red and x is the distance from the chart hence inverse of the snellen fraction
7
Q
what are the advantages of the snellen chart?
A
-commonly used and portable
8
Q
what are the disadvantages of the Snellen chart?
A
-different number of letters on each line hence recording and crowding issues
-unequal size progression per line
-only half as repeatable as LogMAR
-a third less sensitive to interocular differences in vision
9
Q
what are the advantages of LogMAR chart?
A
-same number of letters on each line
-even line spacing and crowding
-standardised recording
10
Q
what are the disadvantages to LogMAR?
A
-it’s big
11
Q
why is it important to get VAs in normal lighting
A
because in the dark, the pupil constricts and so vision becomes better than expected
12
Q
what is the purpose of near vision testing?
A
to measure function instead of the minimum size the patient can see
13
Q
How does a near vision chart use a point system?
A
each point is equal to a letter of size 0.35mm
14
Q
what are the limitations to measuring VA?
A
-unnatural conditions
-measures central vision only
-contrast sensitivity is not measured
-not measured at infinity, at 6m, vergence of light is -0.167D
15
Q
what are the 5 types of astigamtism?
A
-simple myopic
-compound myopic
-simpe hyperopic
-compound hyperopic
-mixed
16
Q
how can you control accomodation in ret?
A
-use the longest WD possible
-WD lens
-use a non accommodative target such as the green light on the duochrome
17
Q
how can you deal with small pupils in ret?
A
-move closer
-dim the light slightly
-use tropicamide to dilate
18
Q
What is habitual VA?
A
this is the ‘presenting’ or ‘walk in’ vision with the patient’s own glasses if they wear them or no glasses if they don’t wear them
19
Q
how do you find the LogMAR equivalent of the snellen fraction?
A
so you fist have to find the MAR which is the inverse fraction of the snellen e.g. MAR of 6/3 is 0.5 and then do Log(MAR) e.g. Log(0.5) on the calculator
20
Q
what is VAR =? (visual acuity rating)
A
VAR = 100 - 50 logMAR
21
Q
what do VAsc or Vsc mean
A
visual acuity measured without a correction
22
Q
what does VAcc mean?
A
visual acuity measured with a correction
23
Q
what does PHNI mean?
A
pin hole provided no improvement
24
Q
how is with and against movement affected by WD in ret?
A
-the closer the WD becomes, the more with movement
-the further the WD, the more against movement
25
how do you calculate the WD lens?
1/ distance (m)
26
in a presbyopic patient when doing ret, how can you make sure the patient will not accommodate?
by quickly scoping the left eye so that if with movement is observed you add positive lenses until against movement is obtained
27
in ret when correcting astigmatism, what should you be using to set your cyl?
the orientation of the streak of the least plus/ most minus meridian
28
in ret, how can you cope with a dim reflex in older patients?
-perform ret at a closer distance such as 25cm or 33cm for a brighter reflex
-use the least number of lenses in the trial frame
-use the large aperture sight hole where avaliable
29
What are the components that contribute to the amplitude of accommodation when measuring monocularly?
reflex + tonic + proximal
30
What is the goal to make patients more comfortable with subjective refraction?
to give patients as few decisions as possible as patients worry they'll give wrong answers or get frustrated by the limited difference in the options given
31
why do you use duochrome before JCC if there is a cyl?
to make sure the circle of least confusion is on the retina
32
after you finish subjective refraction, you compare your patients new VA with age matched normal data. what should you do if the VA is worse than expected or worse in one eye compared to the other?
re-measure the VA with a pinhole aperture. If the VA does not improve with the ph then either subjective refraction is not as good as possible and needs to be redone or the patient has some kind of media opacity most likely being in the lens being cataract
33
what could a subjective refraction result that is significantly less positive than the ret result indicate?
latent hyperopia or pseudomyopia so cycloplegic refraction may be needed
34
in best vision sphere, when adding the initial +0.25 what should you do:
if it blurs?
if it remains the same or improves?
-dont add
-add
35
in best vision sphere, how should you exchange the lenses in a young hyperope? why is this?
-keep the current plus lens in until you've inserted the new one at which point you can take the old one out
-this is because accommodation can be stimulated and hence makes the results inaccurate
36
in best vision sphere, when do you reach your end point in a hyperope?
at the most plus/ least minus lens that does not blur the VA
37
in best vision sphere when adding a -0.25 lens after the intial -0.25, what should you do if the the patient reports:
no change?
worsening vision?
-dont add
-dont add
38
what does it mean if in the +1.00 blur test, the VA doesnt get blurred by 2-4 lines?
the patient may have been over minused/ under plussed
39
what is the MPMVA best vision sphere test designed to do?
take advantage of a patient's depth of focus to provide the maximum range of clear vision
40
why can older patients be easily overplussed and what can indicate that they have been overplussed?
they can be easily overplussed because they have a larger depth of focus due to them having smaller pupils
this can be indicated when the measured addition in best vision sphere is lower than expected
41
what is a drawback to the best vision sphere MPMVA technique?
-patients end up being slightly over plussed by 0.16D as the distance VA chart is at 6m and not at infinity
42
what principle does the duochrome test rely on?
the principle of axial aberration where light of shorter wavelength is refracted more by the eye's optics
43
in duochrome, what will an eye that is slightly overplussed see?
the target on the red filter will look more clear so add more minus
44
in duochrome, what will an eye that is slightly overminussed see?
the target on the green filter will look more clear so add more plus
45
in a hyperopic eye in duochrome, which colour looks clearer and why
the green because the green is closer to the retina than the red
46
In ret, what should you get the patient to focus on? why is this?
the red and target on the duochrome, this is to control accommodation.
47
how does duochrome work?
-the purple side of the visible light spectrum gets refracted more than the red because it has a longer wavelength
-this means that the red gets refracted less because of its shorter wavelength
-the purple side falls in front of the retina and the red falls behind the retina
-in an emmetropic eye on the duochrome, the green is in front of the retina the same distance away that the red is behind the retina
-this means the clarity of the targets on the duochrome are the same
-in a myopic eye, because the eye ball is longer, the red will appear clearer as the red wavelegths get refracted more than the green and so are closer to the retina and so more minus should be added to make them equal
-in a hyperopic eye, because the eyeball is shorter, the green wavelengths get refracted less and so the green is closer to the retina than the red hence the green looks clearer so more plus needs to be added to make them equal
48
what are the limitations to duochrome?
-the round targets are usually constructed of ring thickness equivalent to 6/9 (inner) and 6/12 (outer) snellen equivalent taregts and so it will not work if the vision is >6/12
-difference in focal position due to chromatic aberration is 0.5DS so wont work if prescription is significantly incorrect
-small pupil will reduce the size of the blur circles causing the difference in clarity between the red and the green to be reduced
49
how would you adapt duochrome for patients with red green colour blindness?
just refer to the chart as 'top and bottom targets' instead of 'red and green'
50
what is the interval of sturm?
the distance between the focal lines produced when light enters an uncorrected astigmatic eye
50
What is the blur circle?
the point of overall focus that is formed on the retina of an astigmatic eye from the focal lines of light entering an eye as each of the meridians form their own focal point
51
what is the circle of least confusion?
its the point between the two focal points formed in an astigmatic eye where the blur circle is the smallest
51
when is astigmatism visually insignificant?
when the circle of least confusion is small enough to see small letters clearly
51
when is the circle of least confusion smallest?
when the interval of Sturm is the smallest
52
what needs to happen before you can correct astigmatism with cross cyl?
you need to do duochrome to make sure the blur circle is on the retina
53
what is simple hyperopic astigmatism?
where one of the focal points us on the retina and the other is behind it
53
what is simple myopic astigmatism?
Where one of the focal points are on the retina and the other one is in front of it
54
what is compound hyperopic astigmatism?
where both the focal points are behind the retina
54
what is simple myopic astigmatism?
Where both the focal points are in front of the retina
55
what is mixed astigmatism?
where one of the focal points is in front of the retina and the other one is behind the retina
55
how could you do JCC on a patient with vision that is 6/12 or worse compared to a patient that's 6/9 or better?
-use the 0.50DC cross cyl instead of the 0.25DC.
-use a larger target until the vision improves such as a larger circular letter
56
how do you adjust the sphere based on the cyl in JCC? why adjust?
-for each -0.5D0C change, add +0.25DS
-for each +0.50DC change, add -0.25DS
to make sure the circle of least confusion stays on the retina
56
why should you check the sphere for the last time after doing cross cyl?
becuase the patient is most likely still accommodating so we need to relax the accommodation by pushing the plus monocularly
56
how do you work out the prescription from snellen VAs?
-by doing 0.25DS for sphere
-by doing 0.50DC for cyl
per line of vision
57
what problems does an over misused prescription cause?
-headaches and tired eyes
-some studies have shown this may cause the potential to induce myopia
This is due to the patient having to accommodate to see clearly even in distance
57
what kind of patients are most vulnerable to being overplussed?
patients with smaller pupils so mainly elderly patients
57
what is the stage of refraction where you could probably overplus a patient?
in x cyl as the cyl findings are probably wrong. You know they were over-plussed in cyl if you find more minus is needed in the final stages
58
why do media opacities make it easy to be overplussed?
because they create problems detecting 0.25DS changes
59
why is binocular balancing used in refraction?
-to equalise both vision and accommodative demand
-to check sphere under binocular conditions as monocular conditions could mean over minussing as occlusion can stimulate accommodation
60
what do you do if you find your binocular balance is unequal?
-cyl is probably incorrect if sphere was incorrect
-so recheck sphere and then re check cyl
61
what are the limitations to binocular balance?
-it will not work if the unfogged is worse than 6/12
-its less likely to work if one eye is heavily dominant
62
when should you not use binocular balance?
-when the patient has strabismus
-when the patient is ablyopic or has another cause for significant visual reduction
-uneven acuities of more than one snellen line
62
when should you be wary of binocular balancing?
-in patients with compromised binocularity e.g. evidence of a poorly compensated phoria
-anismetropia
63
when does BVD need to be taken into account?
in patients with a prescription of more than +-5.00DS, and so if this is the case you need to measure it and record it at the end of the refraction routine
64
In duochrome, what does it mean if more than +-0.50DS is needed to balance the clarity of the rings?
this means the duochrome test is unreliable and should be ignored
65
how do you make sure a patient is ready for JCC
-make sure the red and green are equal
-if the clarity of the rings changes from red to green, make sure you give them the lens that leaves the patient on the green
66
give 2 ways fan shaped tests have an advantage over JCC
-accommodation is well controlled as the patient is fogged prior to the procedure
-they do not require patients to memorise two pictures presented sequentially and compare them
67
what do you need to rely on to measure astigmatism in patients where where subjective assessment is poor/ not possible?
-ret
-autorefraction
-keratometry
68
what does the zero mean power of the cross cylinder ensure?
that the circle of least confusion remains on the retina for both presentations of 'lens 1' and 'lens 2'
69
In JCC, when is the effective axis shift greater relative to power?
when the power of the correcting cylinder is lower so when making changes based on the patient response to jcc, amount of rotation should take into effect the cyl power
70
for each correcting cyl, when using a +-0.25 JCC, what are the recommended initial axial rotations?
0.25DC
0.50DC
0.75DC
1.00-2.00DC
2.25+DC
-30
-20
-15
-10
-15
71
how many JCC comparisons are most ideal in practise to limit patient difficulty
3-7
72
in JCC when adjusting the power and the patient reports no difference for the first time what should you do?
-do not assume you have the correct power
1. remove -0.25 from the cylinder
2. now repeat the comparison
3. stop at the lowest cylinder power for which the patient indicates their preference
73
when determining cyl whats wrong with the 'nudge nudge same' technique
-it is inefficient as it typically requires many more presentations than necessary
-it can be inaccurate as a 'same' response from a patient can indicate an incorrect cylinder axis
74
why can a patient's same response indicate an inaccurate cyl axis in JCC?
-you may be incorrect by 90 degrees
-patients can provide unreliable responses and 'same' could just be an incorrect result so you can be far more confident that you've obtained the correct cylinder axis if you've bracketed it
-some patients have a range of axes over which they believe the two JCC images look the same and in this case, the axis should be placed in the middle of the range
75
what is the with rule astigmatism? what kind of patients is it typically found in and why?
where the vertical meridian is steeper.
mainly found in younger patients. This is because it is most likely caused by pressures in the eyelids and so this tension decreases slowly with age hence the with the rule astigmatism slowly disappears and older patients instead typically have against the rule astigmatism
76
what occular pathologies could cause significant changes in astigmatism over a 1-3 year period?
-keratoconus
-cortical cataract
-chalazion
77
when does the binocular balance of accommodation test not need to be performed?
in patients that do not have binocular vision or accommodation e.g. patients of over 60 and pseudophakes
78
In binocular balance tests such as polarisation balance, monocular fogging and humphriss immediate contrast test, what do they all have in common and what do they aim to determine?
they are all minimally dissociated
the spherical correction in conditions similar to the patient's normal viewing situation so that vergence and pupil size are in their normal binocular state
79
in binocular balance, explain when polaroid tests on computer based systems are best
-they are best if they include 3 lines of VA with fusion lock line that is seen by both eyes
-this is because with only 2 lines, one seen with the right and one with the left, the lines may float freely and cause confusion
80
give some examples of common errors in binocular balancing
-attempting to balance the accommodation in patients who do not have binocular vision or accommodation
-failure to modify the fogging lens when +0.50DS or more has been added to the fellow eye
-presenting the +0.25 DS and -0.25DS for an equal amount of time
81
what is the NPC?
the point where the visual axes intersect under the maximum effort of convergence whilst still maintaining binocular single vision
82
what kind of target should you use in patients when doing NPC? Why?
an accommodative target because it may make a clinical difference in patients with convergence insufficiency (scheiman et al.)
83
In NPC why should you avoid a target with fine detail?
because patients especially presbyopes often confuse blur with diplopia
84
In NPC, when might you start thinking the patient is confusing diplopia with blur?
-if the patient reports diplopia with blur yet both eyes appear to be converging to the target
-if the subjective NPC is much larger than the objective NPC
85
what do NPC values 7cm or above suggest?
possible convergence insufficiency and should be investigated further through
-jump convergence
-distance and near heterophoria
-near fusional reserves
-near fixation disparity
86
give 6 common NPC errors
-relying on subjective NPC measures instead of using objective estimates from watching the eyes converge
-carrying out the test only once, should do it at least twice
-moving the target too quickly or too slowly
-not encouraging the patient enough to keep the NPC target single
-testing the eyes in primary gaze instead of downwards
-testing individuals who have near strabismus
87
in NPC what could happen if you move the target too slowly?
it could cause the patient to loose interest especially in children
88
In NPC, what could happen if you move the target too quick?
it could lead to an overestimation of convergence ability
89
what happens to AoA with age?
it falls with age
90
what is measurment of AOA used for in early presbyopes?
to get an estimate of a potential reading addition
91
what ages does the objective AoA become 0?
between 55-60
92
why do some clinicians prefer the pull away method for measuring the AoA?
because the patient responds by naming the letter as soon as they can identify it rather than when they first notice the blur. this is because blur is a subjective impression
93
what do accommodative lag and lead indicate?
wether the patient's accommodation level to a near target is less (lag) or more (lead) than expected
94
why are accommodation accuracy measurments useful in young hyperopes?
Because they help to decide whether or not to prescribe low-moderate corrections
95
in AoA, how are pull away values different to push up values?
pull away values tend to be lower
96
what could indicate a patient having an accommodative insufficiency?
if the measured amplitude is significantly lower than the age matched normal values (>1.50D)
97
explain if binocular or monocular values are higher in accommodation?
binocular values are usually a little higher because convergence response helps to induce additional accommodation
98
how does AoA get used to diagnose presbyopia?
if the patient (who's aged 40+) has an AoA of 5D or below and has difficulties seeing clearly at near whilst wearing an appropriate distance correction
99
what does it mean that most young patients have a small accommodative lag? What does the lag depend on?
that the accommodative response to a target is slightly less than the accommodative stimulus, depends on the accommodative demand so when demand is higher, lag is higher
100
in accommodation when the accommodative demand is 4.00D, what is the mean estimated lag in children aged 4-15 years?
estimated at 0.30D using the nott method
101
give 4 of the most common errors when testing AOA
-not stressing to the patient to say as soon as the target goes blurry
-carrying out the test without the patients glasses when they are habitually worn as it overstimulates the amplitude un myopes and underestimates in hyperopes
-moving the fixation stick too quickly from the patient too quick leading to an underestimation of AoA
-using an innapporpriate target (one that doesnt require accommodation
102
why do our eyes converge when they focus on a near object?
-because the two visual axes on our eyes are parallel for a distant object
-this means the image falls directly on each fovea allowing the brain to process both images as one object
-this means that in order to see a near object the eyes need to turn inwards because otherwise the image would fall elsewhere causing diplopia
103
what is tonic convergence?
the baseline amount of convergence and is due to the tonus in the extraocular muscles hence does not need a stimulus to work
104
what is proximal convergence? When does it happen?
-when the stimulus is the perceived distance of the object
-happens when a present stimulus/ object closer than infinity causes our eyes to automatically converge
105
What is accommodative convergence?
when our eyes automatically converge when we accommodate and the amount of convergence that occurs per dioptre of accommodation differs between people
106
what is fusional convergence?
the involuntary movement used to correct the retinal disparity in images created by both accommodative and proximal convergence
107
what is voluntary convergence?
it is the ability to converge beyond the tonic position without a stimulus i.e. going cross eyed
108
what does NPC actually check?
if the patient is capable of converging more than they need
109
what are the limitations to the push up test for AoA?
-the angular size of letters increase as the target is moved closer to the patient meaning the test gets easier and easier hence the test overestimates the amount of accommodation present
-the patients vary in their ability to notice blur hence results can be variable
110
what is the normal break and recovery in convergence for children and young adults?
-break less than or equal to 7cm
-recovery less than or equal to 11cm
abnormal if its anymore than either of these or the patient seems to struggle to converge e.g. the pupils are jumping
111
why does the eye need to accommodate?
as for a near object, because the light coming from it is divergent, without accommodation, the image would end up falling behind the eye making the image look blurred
112
How does activation of accommodation happen?
1. contraction of ciliary muscle relxaes tension on the zonules of Zinn between the lens and ciliary muscle allowing the lens to become more spherical
2. mostly the front surface and partly the back surface become more convex
3. the crystalline lens becomes more positive and its refractive power is increased
113
how does relaxation of accommodation occur?
1. the relaxation of the ciliary muscle increases tension on zonules of Zinn. pulling outwards on the lens and making it flatter and therefore less positive
2. when there's no contraction of ciliary muscle, accommodation is fully relaxed
114
What is tonic accommodation?
the amount of accommodation present when in resting state i.e. when there's no stimulus to accommodation present such as in total darkness usually around 1D in young adults
115
what is proximal accommodation?
when there's a stimulus present (perceived distance of the object) and is closer to us than infinity and our eyes automatically adjust accommodation
116
what is vergence accommodation?
the accommodation that automatically happens when our eyes convergence due to a near stimulus
117
What is reflex accommodation? when does it work best?
the automatic response of accommodation that is stimulated by retinal blur to maintain a clear retinal image.
it works best if the other parts of the accommodation system leave <2D to correct
118
what aspects of accommodation do we measure when we are testing
-monocularly?
-binocularly?
-monocular = tonic + proximal + convergence
-binocular = tonic + proximal + reflex + vergence
119
In AoA, why do the values for monocular and binocular accommodation differ?
binocular measurement is usually higher than either of the monocular measurements due to the extra contribution from vergence accommodation
120
what is the normal range of accommodation for people aged
-20
-40
-50
-20: 12-13D
-40: 3.75-5.5D
-50: around 2.5D
121
What are we checking in motility testing?
-extent and quality of eye movements
-to check for comitant and incomitant deviations
122
label the extraocular muscles `
check screenshots
123
be able to fill out the direction of action table
check screenshots
124
what does sheington's law of reciprocal innervation state?
one muscle contracts and the other relaxes
125
what does herring's law of equal innervation state?
innervation of the synergist muscle pairs is equal
126
what are three features of comitant strabismus?
-the angle of deviation is constant in all directions of gaze
-typically congenital or long-standing
127
what are 4 features of incomitant deviations?
-angle of deviation is not constant in all directions of gaze
-may be long standing
-can occur in new deviations arising from trauma or pathology such as nerve damage, space occupying lesions and vascular issues (need immediate referral if theyre new)
128
give two example of a long standing incomitant deviation
-duane's retraction syndrome
-developmental issues with anatomy of orbit, ocular muscles or their nerve supply
129
give 5 examples of diseases that cause
non long standing incomitant deviations
-diabetes
-hyperthyroidism
-multiple sclerosis
-tumour
-trauma of the eye or head
130
give an example of a comitant deviation
congenital strabismus
131
give symptoms that are related to eye movements and whether they are long standing vs recent
check screenshots
132
how should you check for eye movements if your patient has a head tilt?
-check it in both the habitual head position and the corrected head position
133
when doing the motility test, how far away should you hold the pen torch?
hold it 50cm away
134
when doing a motility test, why could you move the torch diagonally, right and left?
because it allows you to identify individual muscles that are not working
135
when doing motility test, why move the pen up and down?
-to check for V patterns (when angle of deviation is biggest at downgaze)
-to check for A patterns (when angle of deviation is biggest at upgaze)
136
when testing motility. when is the angle of deviation largest?
when the eyes are turned in the direction of maximum angle of the affected muscle
137
when testing motility what should you ask patients who are reporting diplopia?
ask them how the images are separated - whether its horizontal or diagonal
138
in motility testing, if less underaction is occuring during version (both eyes) what is more likley?
paresis is more likely in less underaction
139
in motility testing, if similar underaction (both) and duction (one eye occurs, what could this mean?
-that mechanical restriction is the most likely cause
140
for the Hirschberg test,
-what is it
-what is it used for
-what are its advantages
-what are its disadvantaged
-a test to compare the corneal reflexes of the two eyes
-used for detecting the presence of strabismus rather than measuring it
-adv: quick and easy to perform, needs little cooperation from the patient
-disadv: can only be performed at near and intermediate distances
141
in measuring motility, how does the brucker test work and why is it unreliable?
-it relies on a comparison of the brightness of the retinal reflex of the two eyes as in presence of strabismus, the reflex can be seen to be brighter and whiter in the deviating eye compared with the normal fixating eye
-prone to false positive findings where strabismus is thought to be present when its not
142
give three tests other than the cover test that allow you to detect and measure strabismus. who would you mainly use them on?
-hirschberg test
-krimsky test
-bruckner test
-mainly used in young children who may be unable to maintain fixation for long enough to allow the cover test to be performed
143
in the hirschberg and krimsy test in eye motility, how far from the pupil centre is the reflex decentred and why is this?
usually decentred about 0.5mm nasally with respect to the centre of the pupil because angle kappa is normally positive
144
what is the angle kappa?
the angle between the visual axis and the pupillary axis
145
what is the visual axis?
the line connecting the fixation point with the fovea
146
what is the pupillary axis?
the line that perpendicularly passes through the entrance pupil and the center of curvature of the cornea
147
in hirschberg and krimsky tests, how do you know if a strabismus is present?
if the corneal reflex of the other eye will have shifted in a direction opposite to the strabismus e.g. in esotropia, corneal reflex will be displaced temporally on the patient's cornea relative to the position of the reflex in the fellow eye
148
in hirschberg test how do you correct present strabismus
by estimating the magnitude of deviation from the displacement of the reflex in mm relative to the reference position using the approximation of 1mm = ∼22Δ
149
in krimsky test, how do you correct a present strabismus
use a prism bar in front of the fixating eye and vary the prism power to achieve symmetrical positioning of the reflexes in the two eyes
150
for the hirschberg and krimsky tests, what indicates
-exotropia?
-esotropia?
-hypotropia?
-hypertropia?
-nasally displaced reflex
-temporally displaced reflex
-superior displacement
-inferior displacement
151
give the four most common errors using Hirschberg, krimsky and bruckner tests to measure motility
1. basing the decision on the absolute position of a single reflex relative to the pupil centre rather than on a comparison of the relative locations of the corneal reflexes in the two pupils in hirschberg and krimsky
2. not viewing the patient's eyes from a position that is directly behind the penlight for the hirschberg and bruckner tests of from directly in front of the deviating eye as in krimsky
3. trusting the sensitivity and accuracy of these tests too much
4. not realising the interocular differences in reflex brightness may be caused by factors other than strabismus in bruckner test like cataract or retinoblastoma
152
what is the difference between paralysis and paresis?
paralysis is where the action of one muscle or a group of extraocular muscles in completely abolished whereas in paresis, the action of a muscle is impaired but not abolished
153
in motility testing, how can you distinguish paresis from mechanical contriction?
because an incomitancy caused by mechanical constriction continues to exibit the same restricted movement when assessed monocularly whereas the movements of a paretic eye are normal when assessed monocularly
154
when doing the motility test when will it be most obvious that there is a problem with an elevating eye muscle?
when the patient is asked to look upwards
155
in motility testing, when is the primary angle of deviation observed? when is the second angle of deviation observed?
when the non-fixating eye fixates, when the affected eye fixates
156
in motility testing, what distinguishes a paralytic from a non-paralytic strabismus?
the difference between the primary and secondary angles of deviation
157
why should a patient remove their spectacles when doing the motility test?
-frame may hide the fixation target
-in peripheral gaze, diplopia can be induced by the prismatic effect produced by anismetropic spectacles
-in peripheral gaze, diplopia can be induced by the jack in the box effect of myopic spectacles
158
when recording motility, what does SAFE stand for?
-Smooth
-Accurate
-Full
-Extensive `
159
what does 'no incomitancy detected' mean?
when normal motility was found in a patient with strabismus where the size of the strabismus did not change objectively in different directions of gaze
160
in motility testing, what is the A pattern? what is the v pattern?
-a movement that is observed during the motility test where the deviation is significantly more convergent in upgaze than in down gaze
-a movement that is observed during the motility test where the deviation is significantly more divergent in upgaze than in down gaze
161
what are the 6 most common errors in motility testing?
-allowing the patient to turn their head towards the target when it needs to stay still
-not using a penlight
-relying too much on the patient to report doubling and not paying attention to symmetry of corneal reflexes and appearance of the relative positioning of the eyes
-moving the target too quick or slow
-moving the target in a straight line rather than an arc so that increasing unequal angular demands are made of the two eyes as the target is moved into a peripheral position of gaze
-not elevating the top eyelid when viewing the eye movements in downgaze
162
in motility testing, why use a penlight as the target?
allows you to see the corneal reflexes so you can determine when the target is entering the monocular field
163
what muscles do eye movements on the right along the horizontal meridian assess? what about the left?
-the right lateral rectus and left medial rectus
-the left lateral rectus and right medial rectus
164
what is a tropia compared to a phoria?
tropia is the misalignment of the visual axis under conditions where binocular vision could be present where as phoria becomes present in monocular conditions
165
what symptoms may a patient with decompensated phorias experiece?
blur, headaches and eye strain even though fusion is single
166
what is unique about the cover uncover test?
it is the only currently available test that can differentiate between a strabismus and a heterophoria
167
when would you use maddox rod and wing?
if you cannot see any strabismus and then cannot see any phoria in the cover uncover test
168
why does the deviation that gets observed in the alternating cover test look larger than that seen in the cover-uncover tests?
this is because during the alternating cover test, binocular vision is suspended altogether whereas in the cover uncover test, binocular vision is only interrupted and then restored
169
when doing the alternating cover test, what does it mean when cover is switched but the patient reports a shift in apparent target position?
there is a phoria present (target moves with occluder movement = exophoria and target moving against occluder movement = esophoria
170
why might the cover test be run subjectively?
because by asking the patient to say if the target being viewed appears to move when the cover is transferred from one eye to the other, it allows you to identify small vertical deviations which can otherwise be missed
171
in the cover uncover test, what does it mean if the right eye moves when the left eye is open?
a strabismus is present in the right eye
172
in cover test, if you find strabismus what should you do next?
move on because it is not necessary to search for phoria
173
why is the alternating cover test only used on patients without strabismus?
because it cannot differentiate between a phoria and strabismus
174
in the cover uncover test, how will poor fusion reflexes look?
-slow
-hesitant
-jerky movements
175
in cover testing, what are phi movements?
subjectively reported movements of the target
176
what is a unilateral constant deviation?
where one eye deviates all of the time and it is always the same eye
177
what is a unilateral intermittent deviation?
where the deviation is only present some of the time and when it is present, it is always the same eye that deviates
178
what is an alternating constant deviation?
there is always a deviation present but the deviating eye can be the right eye or the left eye
179
what is an alternating intermittent deviation?
the deviation is not always present and when it is, the deviating eye can be the right eye or the left eye
180
how can you adapt cover test for childeren
-use pictures but make sure they are not too large as they still need to induce accommodation
181
how can you adapt cover test at near for older patients?
-in presbyopes, needs to be done with multi/varifocal lenses/ appropriate correction in trail frame
-in near cover testing, may need to gently hold up eyelids to get better visibility of their eyes
-may need to perform the test in primary gaze instead of preferred downward gaze if eyelids are too droopy
182
what is an alternating strabismus?
where the right eye will exhibit the strabismus when the left eye fixates during the cover test and vice versa
183
explain why diagnosing alternating strabismus is difficult
-strabismus movement only occurs during the first run of the cover uncover test
-this is because the eye that was deviating has now become the one that is fixating so doing the cover test for the second time, the eye will stay still
184
what does herring's law state?
innervation to synergist muscles of the two eyes is equal
185
why should you be careful not to confuse hering's law with a heterotropic movement?
because hering's law predicts that when one eye is uncovered,
1. both eyes would make a version movement equal to half the movement equal to half the deviation
2. then both eyes make an equal fusional (vergence) movement to restore deviation
186
whats the difference between hering's law movements and heterotrpic movements?
-heretotropic cover test movements are in one direction and take place when the cover is introduced to the other eye whereas hering's law movements have the appearance of a 'wobble' and take place when the cover is removed
187
give 6 of the most common errors when doing cover test
-not getting a clear view of the patients eyes
-blocking the patient's view of the distance target
-covering and uncovering the eyes too quickly so the eyes don't have time to readjust from the present deviation
-using a fixation target that is too large so accommodation and fixation are not controlled
-not moving the cover quickly enough in the alternating cover test causing binocular vision to not be fully suspended
-mistaking a hering's law movement for a strabismus
188
what if you need to use too much fusional convergence?
can cause double vision, eye strain and double vision
189
what causes a tropia to occur?
not enough fusional vergence in reserve and so the eyes cannot align
190
when doing the cover test, what component of the visual system are we measuring?
the fusional component, how much its putting in to make the vision clear and single, how much fusional convergence we need
191
what is the difference between a compensated and decompensated phoria?
a compensated phoria is usually normal and vision is clear and single whereas a decompensated phoria causes eye strain and headaches
192
what are the 5 advantages of the cover test?
-quick
-gives you a lot of info
-doesnt need any special equipment
-objective
-its the only test you do that can differentiate between a phoria and a tropia
193
what is the disadvantage of the cover test?
it takes a lot of practise to get good at as the movements can be very small
194
what is an excyclo deviation?
outward rotation of the upper limbus
195
what is an incyclo deviation?
an inward rotation of the upper limbus
196
what is the definition of a prism dioptre?
the distance in cm that a prism displaces an image over a distance of 1m
197
what are the two types of tropias and what are the symptoms
-with double vision: double but clear
-with compensatory single vision: single but suppression
198
what is the age of onset for tropias?
they are usually congenital so acquired tropias in adults are serious
199
how is accommodative esotropia different to partially accommodative esotropia?
in accommodative esotropia, the deviation disappears when the full refractive correction is worn whereas in partially accommodative esotropia, the deviation partially disappears when the full refractive correction is worn
200
what the relevance of cosmesis in patients with tropias?
rating it on good average and poor to determine if the deviation is obvious to other people and so help decide if referral for surgery is necessary
201
what abbreviations are used of exo deviations and eso deviations?
exo = XO
eso = SO
202
why would you want to use maddox rod and wing if you have cover test?
because it allows the deviation to be assessed with the new refractive correction (in trial frame)
203
what is a drawback of the maddox rod test?
-spotlight used is a poor stimulus for accommodation
204
what are the drawbacks of maddox wing?
-figures used on the scale are big, accommodation is not stabilised and so exo overestimation and eso underestimation
-eyes may not be fully dissociated because the septum may allow peripheral fusion to occur
-uses standard fixed centration distance between the lenses and a fixed testing distance of 25cm hard to see w a phoropter
205
in adults how much vertical phoria could be normal?
up to 0.5 prism D
206
in older adults, how much exophoria is normal?
up to 6D of prism
207
what are the most common errors in maddox wing?
-not allowing the patient sufficient time for the arrow to stop moving with horizontal phoria measurement
-not encouraging the patient to keep the arrowhead in sharp focus to help reduce its apparent movement on the scale
208
what can cause lens induced deviations?
a head tilt behind the phoropter or a trial frame not being level
209
in maddox rod, what does it mean if the rod looks to the right of the spot? how do you correct it?
esophoria, base out prism
210
in maddox rod, what does it mean if the rod is seen to the left of the spot, what do you use to correct it?
exophoria so base in prism
211
is crossed diplopia eso or exo?
exo
212
is uncrossed diplopia eso or exo?
eso
213
in maddox wing, why may some patients seem more exophoric?
-the testing distance is short (only 33cm)
-large print reduces accommodative demand and so accommodation/ convergence is reduced
-if you hold the maddox wing for the patient instead of the patient holding it
