wk11: BV - Strabismus 1 and 2 Flashcards
Define phoria (note how this is different from strabismus)
phoria is misalignment of one visual axis from fixation when the opportunity to fuse is removed, but accurate alignment when fusion is allowed)
Define Sensory fusion
ability of the eyes to contribute to the binocular percept.
Classically, what are the 3 proposed levels of fusion?
Simultaneous perception (first degree fusion)
Superimposition (second degree fusion)
Stereopsis (third degree fusion)
Define simultaneous perception
Being aware of an input into each eye that is different such as Maddox rod and torch
Define Superimposition
Being aware of an input into each eye that is similar and in the same position such as howell phoria card
Define Stereopsis
Being aware of depth due to stimulation of disparate receptors
Clinically, what is the most common way to measure sensory fusion?
stereopsis
Define motor fusion
the ability to maintain motor alignment to achieve sensory fusion
How do you measure motor fusion? (2)
prisms in free space (usually) (i.e. prism bar)
Instruments that can change vergence demand, e.g. synopthpore, red-green anaglyphs
Strabismus develops due to an imbalance between which two factors?
Factors which increase the demands on fusion (if this side is heavier, you will get strabismus)
Factors which improve quality of fusion
What factors that increase demand on fusion can lead to strabismus? (3)
High refractive error (esp. high hyperopes causing esotropia)
Abnormal innervation (e.g high AC/A ratio, 3rd nerve palsy)
Eye muscle disturbance (e.g. malinsertion of eom)
What factors which decrease the quality of fusion can lead to strabismus? (4)
Congenital lack of fusion
Reduced acuity in one eye
Peripheral retinal disease
Nystagmus
What does congenital lack of fusion lead to (specifically)?
nearly always causes an infantile esotropia and occasionally infantile exotropia
What are our objectives when assessing strabismus? (3)
To ascertain the patient’s and the family’s experience of the strabismus
To describe the motor aspects of the strabismus
To describe the sensory aspects of the strabismus
What must case history for strabismus include? (10 + 2)
Which way does the eye turn (in, out, up or down?)
◆ Do you think the right eye or the left eye is turned, or does it change?
◆ How long has the strabismus been present?
◆ Has the strabismus ever changed for better or worse?
✦ Are there particular times you think the strabismus is better or worse? ✦ Has the strabismus got better or worse over time?
◆ (Do you have double vision?)
◆ Have you or your family/friends noticed anything else? (recent head trauma,
white pupil, neurological symptoms, head tilt/turn, monocular eye closure) ◆ Is your child well? (headaches, nausea) ◆ Is the child healthy? (?developmental problems, any pregnancy/birth
problems, systemic health?) ◆ Has there been any treatment given for this strabismus? ◆ Is there a family history of strabismus?
When is the prognosis for a cure for strabismus poor? (2)
Early onset (before age two)
Long delay between age of onset and first treatment (6 months)
How does pre-existing neurological problems relate to strabismus?
Higher incidence of strabismus in children with multiple neurological problems
What percentage of esotropia presentations (in infants/toddlers) are “pseudo strabismus”?
50%
What is Pseudo strabismus?
Some young children appear to have esotropia on casual inspection but are straight with cover test.
What causes pseudo strabismus? (1)
epicanthal folds (skin fold of the upper eyelid covering the inner corner of the eye.) that are visible in young infants/toddlers with not fully developed facial features with a wide nose bridge
When does pseudo strabismus go away?
When the infants get older, the bridge of the nose will narrow and the epicanthal folds in the corner of the eyes will go away. This will cause the eyes to appear wider, and thus no longer have the appearance of strabismus
How do epicanthal folds create the illusion of strabismus?
Due to epicanthal folds, nasal sclera is less visible than temporal sclera in each eye (but nasal is sclera is same in each eye and not in strabismus)
How do we assess the motor aspects of strabismus? (6 steps)
- Detection of the strabismus: is misalignment present?
- Direction of the strabismus: in/out/up/down?
- Magnitude of the strabismus: how big is the deviation?
- Laterality: which eye fixates, and which eye has the
strabismus? - Comitancy: does the magnitude of the strabismus change
with gaze direction? - Distance near incomitance
How should you describe strabismus/what characteristics? (4)
By constancy (constant or intermittent?)
By direction (eso, exo, hyper, hypo)
By laterality (which eye?)
By commitancy
Describe a comitant strabismus
has (essentially) the same magnitude (size) in all directions of gaze
Describe an incomitant strabismus
has a different magnitude (size) as direction of gaze changes (or viewing distance changes)
What should you consider when using a hirschberg test for strabismus? (1)
are the corneal reflexes symmetric?
How do you perform a Hirschberg test?
Is a corneal reflex observation. Shine a pen torch between the eyes of the patient from about 50cm. Observe the corneal reflexes from the light:
What will you expect on a hirschberg test when there is NO strabismus? what about when there IS strabismus?
If there is no strabismus, reflexes will be symmetric and about 0.5mm nasal to pupil centre
In esotropia, the reflex on the fixating eye will be normal, but the reflex on the esotropic eye will be temporally displaced
Which test is the most sensitive test for strabismus?
Cover test
Describe the fixation reflex (as the basis for cover tests)
Macula has sensory AND motor superiority and so when a deviated eye is uncovered and the non deviated eye covered the deviated fixates the object of regard with the macula of the deviated
eye.
What does a unilateral cover test tell you? (4)
Tells you if phoria or tropia and direction
If tropia tells you if unilateral or alternating
Tells you the fixating eye.
Forced or True alternation.
What type of V.A can you expect from somebody with forced alternation in cover test?
At least 6/21, usually 6/9 or better
What type of V.A can you expect from somebody with true alternation on cover test?
better than 6/6. And the acuity is equal between eyes
True or False: Cover Test and/or Hirschberg’s test can both give useful
information on the direction of the strabismus
True
In what units do we specify size of strabismus?
prism diopters
Which test is the least precise measure of strabismus magnitude?
hirschberg test
How many cm of deviation is 1 prism diopter equivalent to?
1 pd = 1 cm deviation at 100cm (2pd approximately 1 degree)
How many prism diopters of strabismus is a 1mm displacement of the reflex on hirschberg test equivalent to?
1mm displacement of reflex = 22pd strabismus
Can hirschberg detect small strabismus?
no
Can hirschberg detect intermittent strabismus?
no
Can hirschberg detect phoria?
no
How do we measure the size of strabismus in hirschberg test?
Size of strabismus can be estimated by the mislocation of the corneal reflex relative to major landmarks of the eye
In hirschberg, what is the prism diopter amount for reflex at the following landmarks on the eye?
- pupil margin
- mid iris
- limbus
Pupil margin: 15 p.d
Mid iris: 30 p.d
Limbus: 45 p.d
What is the Krimskey test?
The Krimsky test is essentially the Hirschberg test, but with prisms employed to quantitate deviation of ocular misalignment by determining how much prism is required to centre the reflex
(i.e. prism neutralised hirschberg)
To how many prism diopters of strabismus is the hirschberg test accurate?
10-15 p.d
To how many prism diopters of strabismus is the krimskey test accurate to?
Accurate to 10 p.d in any hands
(most accurate measure for the neophyte)
What is the most accurate objective tool/test for assessing strabismus?
Alternating cover test with prism bar
How should you assess strabismus with alternating cover test with prism bar?
Place prism in the spectacle plane of the fixating or strabismic eye,
repeat the alternating cover test, adjust the prism power until you do not see any movement
The prism power for neutralisation of the movement is the size of the
strabismus
What is the disadvantage of maddox rod for strabismus assessment?
Subjective tools such as the Maddox Rod may be more accurate, but can only be used in a minority of adults with strabismus due to sensory adaptations such as suppression
Where is the corneal reflex on hirschberg if the eye is up?
down
Where is the corneal reflex on hirschberg if the eye is left?
right
Does an alternating cover test diagnose phoria from tropia?
No it does not.
If assessing magnitude of phoria (rather than tropia) is alternating cover test with prism bar still the most accurate?
No. Use Howell prentice card in this case as that’s more accurate
What is the accuracy of assessing strabismus magnitude with alternating cover test with prism bar?
4 p.d (when an experienced optom)
When neutralising strabismus with prism in alternating cover test: How do you neutralise esotropia vs exotropia vs hypertropia?
Base out for Esotropia
Base in for Exotropia
Base down for Hypertropia
Can you infer amblyopia from unilateral movement (not true alternation)?
no you can’t infer anything.
What test should we use to assess the laterality of the strabismus? (i.e. which eye)
Unilateral cover test
Define unilateral strabismus, alernating strabismus, and forced alterating strabismus (in regards to outcomes on cover tests)
unilateral: one eye always used for fixation
alternating: either eye freely fixate
forced alternating: strabismic eye fixate at times on cover test
What is the implication of alternating fixation
Patient who has strabismus but who can
hold fixation with either eye (alternating strabismus) has equal acuity in each eye. ◆ Each macula has equal sensory superiority
What can you infer about about a patient with unilateral strabismus?
will often (but not always) have amblyopia in the strabismic eye
How does the magnitude of the strabismus change with gaze in a patient with comitant strabismus?
same magnitude in all directions of gaze
How does the magnitude of the strabismus change with gaze in a patient with incomitant strabismus?
Incomitant strabismus varies by 10pd or more in different positions of gaze
How should you annotate krimskey results?
Kn for near, Kd for distance
What possible causes could be responsible for an incomitant strabismus? (4 conditions, and each with a respective incomitance)
4th nerve palsy - vertical incomitance in R-L gaze
6th nerve palsy - horizontal incomitance in R-L gaze
muscle mal-innsertion (AV patterns) - horizontal incomitance in up-down gaze
high AC/A ratio (converg excess) - horizontal incomitance in near-far fixation
List 3 common incomitancies
A and V pattern in esotropia and exotropia
4th Nerve (superior oblique) palsy
Duane’s Syndrome (congenital 6th palsy)
What does the incomitancy of A and V pattern in esotropia and exotropia indicate?
Indicate early onset strabismus with poorer prognosis
List 3 uncommon incomitancies
Browns Syndrome
6th Nerve Palsy
3rd Nerve Palsy
What does the incomitancy “brown’s syndrome” suggest?
Problem relaxing superior oblique through trochlea that often
improves with age
is 3rd nerve palsy generally congenital or acquired?
generally congenital
Is a 6th nerve palsy generally congenital or acquired?
generally acquired
How serious is 3rd nerve or 6th nerve palsy?
serious
How can we perform a static assessment of comitancy?
Do a cover test in all 9 positions of gaze, then record this in a 3x3 grid
When should we use Park’s three step test?
When there is a change in vertical deviation during excursions
Outline the three steps in park’s three step test
- Which eye is “higher” (hypertropic) in primary gaze? (draw a H in results with SR, IO, and IR, SO. Then circle the 2 muscles for each eye that could be the problem
- Is the hypertropia worst in left or right gaze? (circle the relevant 2 gaze depressors/elevators for each eye)
- Is the hypertropia worst when the head is tilted to the left or to the right? (circle the relevant diagonal muscles which match the direction off the midline of the face when the hypertropia is worse)
How do you record step 1 of the park’s three step test (I won’t bother asking the other steps)
Step 1:
SR IO IO SR
I_____I I____I
I I I I
IR SO SO IR
What are the three golden rules of Pratt Johnson?
- Superior Oblique Palsy until proven other wise.
- Congenital until proven otherwise.
- Patients usually don’t fixate with the eye that has a palsy
What is “V” pattern
tropia that gets worse if you look up or down (esotropia get worse if you look down, and exotropia getting worse when you look up)
Why is acquired 6th nerve harder to find than congenital 6th nerve palsy? Which one should you worry about more?
Because acquired 6th nerve palsy is partial. Worry about acquired 6th nerve palsy more. It is serious
What is responsible for congenital 6th nerve palsy?
Duane’s syndrome!!
True/False: In esotropia the deviation at near is often the same as distance
True
True/False: In esotropia very occasionally the distance deviation is
worse (greater than 10pd) than the near deviation and this is called divergence insufficiency
True
What is near incomitancy usually caused by?
acquired 6th nerve palsy which innervates the lateral rectus (so there is often a abduction deficit)
Define Strabismus
misalignment of one visual axis from fixation in the presence of a full opportunity to fuse (i.e. one visual axis is not directed at the object of interest)
