Amblyopia pt.1 Flashcards
what is amblyopia
When we are born the visual pathway not complete, causing abnormal visual development
what is the amblyopia caused by
Abnormal visual development caused by:
refractive error - blur
pathology
strabismus
when does amblyopia occur
During critical period (birth to 7-8 years old)
what is the critical period
the period where the visual pathway is still forming
if give an abnormal picture during critical period then the visual pathway grows to be used to that
what is the outcome of amblyopia
permenantly reduced Vision/Visual-Acuity
what is the prevalence on amblyopia
approximately 3% of the population
list the 3 periods of visual acuity
- developmental period
- critical period
- sensitive period
what does the developmental period of visual acuity relate to
The period from birth where vision is developing
what does the critical period of visual acuity relate to
The period where vision is susceptible to abnormal visual input
what does the sensitive period of visual acuity relate to
The period where treatment for amblyopia is effective
usually up to the age of 8, but recently found that on older age groups/teenagers it can work
when does the sensitive period of visual acuity occur
- From time of deprivation to teenage/adult years
- 0-18 years old
when does the critical period of visual acuity occur
After birth to 7/8 years
when dos the developmental period of visual acuity occur
Birth to 3/5 years
at which period of visual acuity is the prognosis for improvement better
the critical period, 7/8 years old
when is the first eye test for a child and how is it done
- at the hospital after birth or within the first 6 weeks of life
- doctor checks a rough rx and checks for a red reflex
what is the red reflex appearance of unequal refraction and what will you do if this is found
- non symmetrical
- one red reflex is brighter than the other
- do a cyclo refraction and check the fundus
what is the red reflex appearance of a patient with cataracts
- there is no red reflex in the eye with the cataract or is very dim
- as the presence of the opacity block the fundus
what is the red reflex appearance of a patient with a foreign body abrasion on the cornea
- the red reflection from the pupil will back light the corneal defects or foreign body
- movements of the examiner’s head in one direction will appear to move the corneal defects in the opposite direction
what is the red reflex appearance of a patient with a strabismus
the red reflection is more intense from the deviated eye
what did research on the critical period suggest about, Induced unilateral strabismus (Hubel and Wiesel)
- Eye with strabismus amblyopic
- Few binocular driven cell - no potential for BSV or stereo (due to squint)
- this is the worst to have
what did research on the critical period suggest about, Induced alternating strabismus (Hubel and Wiesel)
- Neither eye has strabismus
- Few binocular driven cells
- The alternation prevents amblyopia
what type of pathology is worst to have during the critical period and why, and what is done when treating this pathology to avoid amblyopia
- unilateral cataract
- as severe amblyopia may happen and binocular cells may go
- patch the good eye in-between cataract surgery if doing cataract one eye at a time
- for bilateral cataract - simultaneous occlusion should be used, where you patch the good eye when waiting to remove the cataract from the other eye to preserve the binocular cells
where is the damage that causes amblyopia found
- Cortical deficit in V1 measured via (fMRI)
- Higher order areas are now also thought to be affected
for what 2 reasons is amblyopia difficult to assess
- Patient cannot determine what it is like NOT to have amblyopia
- Difficult to separate what is due to e.g:
- Cosmetic aspect of the strabismus
- Treatment (bullying)
- Amblyopia:
Reduced V-A
Reduced S-A (stereo-acuity) and binocularity
list 4 examples of effects of reduced stereo-acuity
- Driving e.g. Breaking distances No. of accidents - Navigating around obstacle course - Threading beads on a string - Reaching and grasping
what does amblyopia double the risk of
binocular visual impairment
list the 5 types of functional amblyopia
- strabismic amblyopia
- stimulus deprivation amblyopia
- anisometropic amblyopia
- meridional amblyopia
- ametropic amblyopia
strabismic amblyopia occurs….
monocularly only
what form of strabismus prevents bilateral amblyopia
alternating strabismus
what type of deviation/tropia does strabismic amblyopia occur in and which type is it more likely to occur in
- a constant manifest deviation
- more likely in an esotropia (as its more likely to be constant)
- XOT often remains intermittent during childhood = sometimes the child gets normal vision which prevents amblyopia from developing
what is stimulus deprivation and list 4 possible causes of this
some sort of pathology which causes obstruction to the clear passage of light, preventing clear formation of an image for example:
- ptosis
- cataract
- retinal problems
- corneal scar
what is important to note with stimulus deprivation
note how much pathology prevents clear image
at the macula and is causing the amblyopia e.g. with ptosis, how much of it is covering the pupil etc
anisometropic amblyopia occurs…
monocularly always
what is anisometropic amblyopia
- Difference in refractive error - one eye receives better visual input at all distances (the one with the higher ref error = amblyopia)
- The refractive error may be spherical and/or astigmatic difference
when does meridional (astigmatic) amblyopia occur monocularly and binocularly
- monocularly with anisometropic amblyopia (if big difference)
- binocularly with ametropic amblyopia (if big asthmatic error in both eyes)
ametropic amblyopia occurs…
bilaterally
what causes ametropic amblyopia
High degree of uncorrected bilateral refractive error
how can high hyperopia cause ametropic amblyopia
cannot be compensated for with accommodation
list 4 things you will ask in history when investigating amblyopia
- What is the problem
- What age did the problem start
- How long has it been there
- Strabismus, is it:
constant/intermittent
or
alternating
why will you carry out ophthalmoscopy when investigating amblyopia
to see if its down to pathology, causing the stimulus deprivation type of amblyopia
what does the RCO, state that the risk values for developing amblyopia isometropic (both eyes) in hyperopia and myopia are
and what age are these values appropriate for and why
- Hypermetropia: +4.50D
- Myopia: -3.00D
- values are appropriate for 3 years old and upwards
- as the younger you are, you will accept higher refractive errors as normal
what does the RCO, state that the risk values for developing amblyopia anisometropic (one eye) in hyperopia , astigmatism and myopia are
and what age are these values appropriate for and why
- Hyperopia: +1.50D
- Astigmatism: 2.00D
- Myopia: -2.00D
- values are appropriate for 3 years old and upwards
- as the younger you are, you will accept higher refractive errors as normal
when do you need more refractive error before considering a child is at risk of developing amblyopia, and what do you do if your not sure
- the younger the patient is, the more refractive error you need before considering
- if never sure, always bring the child back after a few months to check their vision, if there are changes then give glasses
- monitoring is good in a borderline case
when will you only consider giving treatment for a hyperopic px with an esotropia and what will you always give
- if their refractive power is +2.00D or more
- but always give plus at any power as its good for an esotropia
- it can only make an esotropia better
what is the normal range of visual acuity in logmar crowded and uncrowded for 4-5 year old children
- 087 (approx 6/7.5) +/- 0.10 log units for crowded
- 0.010 (approx 6/6) +/- 0.10 log units for uncrowded
LogMAR tests
Always write the type of test chart singles or logMAR
list the 5 things you must do whilst carrying out visual acuity when investigating amblyopia
- Near and Distance
- Use Log MAR - Due to crowding phenomenon
- Name test type
- With and without compensatory head posture (CHP)
- If manifest latent nystagmus may want to use spielman occluder
what test is a more sensitive measure than visual acuity
constrast sensitivity
what are the effects of someones contrast sensitivity dependent on
the type of amblyopia they have
what test will you do on a child if a visual acuity test is not possible and why
- cover test
- it can tell you what the vision will be like
e. g. if the child doesn’t use their fovea to begin with, then the vision will be significantly reduced. the child will use an extra foveal point (eccentric fixation) whereby the visual acuity will not be as good
list the 4 things you must note/observe when doing a cover test on a child
- Note whether alternating unilateral deviation
- Will the amblyopic eye hold fixation to blink
- Central fixation versus eccentric fixation via corneal reflections (gross only)
- Is the deviation constant or intermittent
why is it important to note whilst doing a cover test, if the amblyopic eye will hold fixation to blink
if the child can hold their fixation with their squinting eye straight after the cover is removed from the fixing eye until they blink, then that means they have stronger vision, compared to if the eye moves straight back to their squinting position straight after the cover has been removed from the fixing eye
what can an ocular motility test show you when carried out on a patient with incomitancy (child has slight muscle weakness)
may be more likely to decompensate when you start occlusion
what 3 tests can you do to check binocular status when investigating amblyopia
- Prism Fusion Range
- Stereopsis
- Cover test (recovery)
how will you confirm that your strabismic amblyopic patient does not have binocular functions
by seeing whether they got suppression
a strabismic amblyopic patient will not have binocular functions, but name a type of amblyopic patient that should have some binocular functions and what can you use to measure this
- anisometropic amblyopes - will have some binocular functions
- measured using: prism fusion range, stereopsis, recovery in cover test
how will you measure the deviation when investigating amblyopia, and what must you ensure does not happen and why
- Prism cover test (if possible)
- Ensure that occlusion is not increasing the size of the deviation
- because of risk of decompensation
- so if the deviation increases = sign they will decompensate
e.g. if you find that when you started to patch and their fusional reserves thwarted to reduce as well as stereo acuity and recovery from cover test became poor, you will have to stop the patching treatment. this is because you are more likely to decompensate them. so don’t do this on anisometropic amblyopes as you don’t want to decompensate them
which type of patients is the sbisa bar used on
- Patients with suppression
- In all strabismic amblyopes over the age of 5 years old
- To prevent intractable diplopia
which type and age group of patients will you use a sbisa bar on to measure suppression and why
- In all strabismic amblyopes over the age of 5 years old
- To prevent intractable diplopia
why is there a risk of patching a patient with strabismic amblyopia
although you may increase their visual acuity, but you can reduce their suppression and cause diplopia, which is the most risky on 5 years old and under
what does the sbisa bar measure
the density of suppression
list the steps of how the sbisa bar is used to measure the density of suppression
- Graded bar of varying density of red filters
- Placed in front of the fixing eye
- Patient requested to view light and asked what colour
- Filters slowly increased in strength
- Patient informs examiner:
When light changes from red to white
or
Diplopia appreciated
or
Fixation swaps - Record density
- Density less than 10 consider not patching
which density value on the sbisa bar will you consider NOT to patch and why
- density value less than 10
- as don’t want to risk contractable diplopia
which group of amblyopes should ophthalmoscopes or visuscopes be carried out on and what for
- On all strabismic amblyopes
- Determine whether eccentric fixation present or not
- Determine the location of the eccentric point
- Further away from the fovea the worse the V-A
- To monitor progress with time
If treating via occlusion may find the eccentric point changes with time on a px with a strabismic amblyope
what may you find will change as well as va, on treating a patient with occlusion on a patient with strabismic amblyopia
the eccentric point changes with time
list the steps of how you will use an ophthalmoscope or visuscope to detect subtle eccentric fixation and what can this tell you about a person’s visual acuity
- Occlude untested eye.
- Examiner projects the fixation target onto the fundus close to the fovea.
- Patient is instructed to look directly at the centre of the circle
- The position of the fixation target on the fundus is then noted. e.g. fovea, parafovea, further away etc
- There is a decrease in visual acuity with increasing distance from the fovea
what 3 things in an eye exam can misinterpret a child from having amblyopia and therefore what 4 things must you do to rule amblyopia out and avoid mis-diagnosing
- incorrect v-a (no co-operation on that day)
- incorrect refraction
- mild pathology
Therefore, reduced visual acuity does not equal amblyopia
- Repeat V-A assessment
- Repeat BV assessment (cover test)
- Repeat refraction
- Repeat fundus and media examination
if you find no problems then refer them to hospital
only start patching is there is a amblyogenic risk factor i.e. px has to be anisometropia, ametropia, pathology or a constant strabismus
In which type of amblyopic patient would you measure the density of suppression (3 marks)? Name the piece of equipment that you would use to measure it (2 marks).
- strabismic amblyope over 5 years old
- using a sbisa bar
