1
Q
List and describe the grades of the binocular single vision?
A
1) simultaneous perception: the ability to perceive two SEPARATE image one on each retina at the same time
2) fusion
i) sensory fusion: the ability to perceive two SIMILAR image from each retina And interpret them as one
ii) motor fusion: the ability to maintain sensory fusion trough a range of vergence movements. it allows us to maintain single vision as we converge or diverge to fix an objects at different distances.
3) stereopsis:perception of depth that can be achieved by the sensory fusion of the two SLIGHTLY DIFFERENT images we perceive from each eye.
2
Q
4 obtacles to BSV?
A
Opah Suka Makan Cacing
- orbit
- sensory
- motor
- corticol
3
Q
How can fusional obstacles occur?
A
fusional obstacles can arise from refractive errors.
eg. hyperopia results in excessive accommodation associated with excessive convergence.
fusional reserve might not be adequate to cope with this large deviation.
if we remove the obstacles, the fusion might be possible
4
Q
How can cortical be as an obstacle to binocular single vision?
A
these arise when there is failure of binocularly driven cells in the visual cortex developing.
If there is disruption to the visual cortex due to trauma, tumours, or infections.
5
Q
what do we need for normal development of BSV?
A
1) globe
2) orbit
3) visual pathway
4) decussation of retinal fibrs
5) visual field
6) normal retinal correspondence (NRC)
6
Q
What happens following failure of fusion and development of squint?
A
1) pathological diplopia
2) confusion
7
Q
what is pathological diplopia?
A
1) presence of a manifest ocular deviation
2) simultaneous appreciation of two separate images caused by stimulation of non-corresponding points by one object
3) Divided into two:
- homonymous diplopia (esotropic)
- heteronymous diplopia (exotropic)
8
Q
what is homonymous diplopia?
A
- when the eye is ESOTROPIC
- the image of the fixation object is received on the nasal area of the retina of the deviating eye and is projected temporally.
- resulting in uncrossed diplopia
9
Q
what is heteronymous diplopia?
A
- when the eye is EXOTROPIC
- when the image of the fixation object is received on the temporal area of the retina of the deviating eye and is projected nasally
- resulting in crossed diplopia
10
Q
what is confusion?
A
- when an object is viewed by the peripheral retina of the squinting eye, it stimulates the fovea of the other eye
- at the same time another object might also stimulates the fovea of the squinting eye
- the image of this object maybe superimposed onto the image of fixation object.
- this develops confusion
11
Q
what is suppression?
A
- mental inhibition of one eye in favour of the other when both eyes are open.
- this is a corticol phenomenon although it is often described in relation to the retina
- suppression of the fovea avoids confusion and suppression of the peripheral retina avoids pathological diplopia.
- these 2 points extend to become measurable area called the suppression scotoma
12
Q
what is esotropia?
A
- manifest deviation
- misalignment of the visual axis
- resulting in an inward turning of one eye
esotropia is a manifest deviation where there is misalignment of the visual axis resulting in an inward turning of one eye.
13
Q
What are the four types of esotropia?
A
1) primary (constant or intermittent)
2) secondary/sensory: deviation results in poor vision in one eye
3) consecutive
4) residual
14
Q
what is the classification of intermittent esotropia (primary esotropia)?
A
Aku Dah Tak Nak Non-specific
1) Relating to ACCOMMODATION
- fully accommodative
- convergence excess
2) Relating to DISTANCE
- near eso
- distance eso
3) Relating to TIME
- cyclic eso
4) Non-specific
15
Q
what is intermittent esotropia?
A
intermittent esotropia only present under certain conditions.
when the eyes are staright normal binocular single vision is present.
16
Q
what is fully accommodative esotropia?
A
- fully accommodative esotropia is constant esotropia with onset usually between 1.5yo to 2.5yo.
- refraction shows hyperopia usually between +3.00 to +6.00DS
- constant esotropia when the hyperopia is not corrected
- binocular single vision was retained for all distances when hypermetropia is corrected
- when doing CT a manifest deviation is seen without the spectacle correction but is controlled to a latent deviation with the full hypermetropic correction.
- management is to treat pre-existing amblyopia and fully correct hyperopia
- do not require surgery
17
Q
what is convergence excess esotropia?
A
- there is binocular single vision for distant fixation, but esotropia on accommodation for near fixation
- esotropia at near but straight with BSV at distance
- onset usually 2-5yrs
- may be hyperopic, emmetropic, or even myopic.
- with their refractive error CORRECTED they will STILL BE ESOTROPIC at near fixation.
- aetiology: high AC/A ratio (higher than 5:1)
- management is bifocals to eliminate need to accommodate or bi-medial recessions
- the aim is to restore binocular single vision, as soon as possible by reducing the bifocal segment strength over the follow-up period.
18
Q
what is near esotropia?
A
- esotropia present at near fixation
- straight with BSV at distance
- unrelated to refractive error or accommodation ( test with +3.00DS, if the divertion remains then its near esotropia, if resolve; convergence excess)
- management usually surgical if cosmesis is poor
19
Q
what is distance esotropia?
A
- esotropia at distance fixation
- straight with normal BSV. at near
- must be differentiated from 6th nerve palsy
- management usually surgical if poor cosmesis
20
Q
what is cyclic esotropia?
A
- an esotropia that is present at regular interval
- eg: esotropia present on alternate days with BSV on staright days
- prevalance of esotropia may increase
- usually require surgery ( with good results even operated in a traight days)
21
Q
what is non-specific intermittent esotropia?
A
- often a large esophoria that is intermittently decompensating
- management is to fully correct hyperopia but surgical intervention is often required
- exercise involving improvement of fusional reserves
22
Q
What are the components of constant esotropia?
A
1) with accommodative element: the deviation increases when accommodation is exerted
2) without accommodative element: the deviation is unaffected by accommodation.
eg: infantile esotropia, nystagmus block syndrome.
23
Q
what are the characteristics of constant esotropia with an accommodative element?
A
- presentation usually between 18months to 3years
- commonly large angle esotropia present at all distances but bigger for near fixation
- hyperopic usually +3.00DS to +6.00DS
- when hyperopia corrected angle reduces
- often demonstrate inferior oblique overaction
- usually amblyopic if unilateral squint
24
Q
what are the management of constant esotropia with accommodative element?
A
1) order full prescription
2) treat any amblyopia
3) surgical if cosmetically poor with glasses
25
what are the characteristics of constant esotropia without accommodative element (infantile esotropia)?
- large angle esotropia usually greater than 30^ not associated with Rx
- onset before 4 months in most cases
- usually alternates with cross fixation
- poor prognosis for BSV even if treated early
- abnormal OKN
26
what are the association of the infantile esotropia?
1) manifest latent nystagmus
2) dissociated vertical deviation
3) overacting inferior obliques
4) sometimes exhibit limitation of abduction but in view of cross gixation ductions can be greater than versions
27
what are the characteristics of nystagmus block syndrome (constant esotropia without accommodative element)?
- nystagmus compensation syndrome
- develop in patients with congenital nystagmus by constantly trying to adduct the fixing eye to dampen the nystagmus
- variable often large angle esotropia though both eyes may appear convergent
- often an abnormal head position to maintain fixing eye in adducted position (face turn towards fixing eye)
- amblyopia common
- nystagmus often increases on lateral gaze
28
what is secondary esotropia?
- an esotropia that develops as a result of loss or severe impairment of vision which maybe unilateral or bilateral
- a secondary esotropia indicates the loss of vision probably occured between 6 months and 7 years whenn accommodative convergence is most active.
29
what is consecutive esotropia?
- an esotropia in a px who initially had an exotropia or exophoria
- usually as a result of surgical overcorrection
- often be intentional
- spontaneous consecutive esotropia is rare
- may complain of diplopia immediately postoperatively but this often resolves
- may be limitation of abduction especially if overcorrection was not planned
30
what are the management of the consecutive esotropia?
- relieves symptoms of diplopia with prism if troublesome
- treat any amblyopia
- prescribe any convex lens if appropriate
- may require further surgery to restore BSV if any potential exists or to improve cosmesis
31
what are the characteristics of primary constant exotropia?
Primary constant exotropia can be either
1) early onset exotropia
- poor prognosis of binocular f(x)
2) decompensated exophoria or intermittent exotropia that has become constant
- better prognosis for binocular f(x)
32
what are the management of the primary constant exotropia?
- treat any amblyopia
- most require surgery (consider lateral incommitance)
- depending on post op diplopia test, some may require botolinum toxin prior to surgery
- some cases of decompensating exophoria may respond to orthoptic exercises to improve fusional reserves.
33
the primary intermittent exotropia consists of distance exotropia and near exotropia, compare and contrast between these two:
distance exotropia consists of exotropia in the distance and orthophoria (or exophoria) for near fixation. Due to the XT at the distance, when it manifest, it will produce a suppression. meanwhile, BSV is present at near when it is well controlled.
Near exotropia is XT at near fixation and orthophoria (or exophoria) at distance fixation. one may complain of diplopia at near if associated with poor convergence.
34
what are the classification of exotropia?
primary: constant and intermittent (near, distant ; true or stimulant, non specific)
secondary
consecutive
35
what are the clinical characteristics of microtropia?
1) unilateral reduction of VA
2) anisometropia
3) small angle of strabismus; less than 10 dioptees
4) usually esodeviation, may be exo, rarely vertical
5) foveal suppression of the deviating eye
6) Eccentric fixation
7) Abnormal Retinal Correspondence
8) reduce fusion and stereopsis
36
what are the classification of the microtropia?
1) primary: microtropia is the initial defect, no history of previous large angle starbismus, microtropia stable and deterrioration into large angle uncommon.
2) secondary: previously large angle strabismus that has been REDUCED IN SIZE to a microtropia by surgery, correction of refractive error (fully accommodative intermittent esotropia controlled), and orthoptic exercise
3) decompensated esotropia:
- onset 1-3 years old
- originally a microtropia that has increased in size.
37
what is abnormal retinal correspondence?
a binocular condition in which there is a change in visual projection such that the fovea of the fixing eye has a common visual direction with an area other than the fovea of the deviating eye.
38
explain the differences between a microtropia with identity and without identity.
1) with identity:
- no movement seen in CT
- harmonious ARC
- angle of 'pseudo-foveal' or squinting equal to angle of eccentricity
- absolute eccentric fixation
- when the fixing eye is covered,no movement seen in the deviating eye because it has been fixating with the eccentric fixation (the squinting eye doesnt need to move as the eye already fixing with its eccentric point)
2) without identiy
- movement seen in CT
- may have central or non-absolute eccentric fixation.
- retinal correspondence may be ARC or NRC with central suppression and peripheral fusion.
39
Explain the differences between a true and a simulated distance exotropia. how would you differentiate between the two?
- a true distance exotropia will habe a distance angle > near angle
- a simulated distance exotropia will show a smaller near angle because the patient uses FUSION TO CONTROL NEAR ANGLE (fusional reserves or accommodation excess)
-to differentiate between true and simulated (by disrupt fusion and eliminate accommodation):
=occlude one eye for one hour to disrupt fusion and then remeasure near angle
=do a prism cover test using +3.00D at near fixation to eliminate accommodation
=if the angle has increased in either case then the distance exotropia is simulated because the fusional reserves and excess accommodation have been knocked out.
40
is amblyopia is a common finding in distance exotropia?
Yes. Due to the XT at the distance, when it manifest, it will produce a suppression. The suppression means one eye is better then the other, consequently develops amblyopia.
meanwhile, BSV is present at near when it is well controlled.
41
what influences decision regarding patients that need further management with distance exotropia?
- observation: V pattern would be normal, wont rush into surgery
- only decide for surgery if it is cosmetically poor or decompensating for near
- treat amblyopia, should be less for well controlled for near.
- use MINUS LENS THERAPY to induce ACCOMMODATION AND THEREFORE CONVERGENCE. repeat until their control of overcorrection and reduces deviation.
42
investigations on duanes syndrome and brown syndrome?
1) history
2) observation on AHP
3) CT
4) Prism Cover Test in 9 directions
5) access binocular functions
6) Occular movements (motility)
7) hess chart
8) field of binocular single vision
Duane has additional test,
9) convergence
43
infantile esotropia vs nystagmus block syndrome
infantile esotropia:
- large angle
- latent nystagmus
- limited ocular movements
- Rare amblyopia
- DVD is common
- surgery is predicted
nystagmus block syndrome:
- manifest nystagmus
- amblyopia may present
- full ocular movement
- variable angle.
- compensation of nystagmus
- DVD is rare
- surgery is unpredictable
44
Duane vs Congenital 6th nerve palsy?
1. In Duane, the primary position esotropia is relatively small compared to the lateral rectus underaction.
2. Narrowing of the fissure of the involved eye occurs only in Duane (may be hard to see in a child).
3. The small head turn in Duane results in alignment, but not so likely in sixth nerve palsy.
4. Congenital sixth nerve palsy can be transient; Duane is permanent.
In a congenital setting with abduction deficit, an esotropic Duane is far more common than a congenital sixth nerve palsy.
5. As a last resort in the differential diagnosis, watch the infant. The answer will become clear with time.
6. In duane's syndrome , there is usually no diplpopia present-px maintain good bv and stereo in the area of BSV.
7. A and V pattern may documented in Duane's syndrome
45
aetiology of duane's retraction syndrome?
1) mechanical
- thin elastic muscle
- muscles bound to orbital wall
- posterior insertion of the medial rectus
- inelestiv, fibrotic LR with abnormal attachments
2) innervational
- absent 6th nerve nucleus
- partially formed 6th nerve
- co-contraction theory whereby the lateral rectus is partially innervated by the 3rd nerve, producing contraction of the lateral and medial rectus on adduction with globe retraction ------------->affected eye going to experience retraction, mild adduction paresis, and narrowing pf palpebral fissure.
46
What is the most likely cause of diplopia complaint in consecutive exotropia?
consecutive exotropia exists in a px that previously had an esotropia
- can occur spontaneously (eyes diverge with time) or post operatively
- patient may complain of diplopia if out of suppression scotoma:
- -- surgery with overcorrection may be deliberate, particularly for esotropia with an expected functional result
- --spontaneous cases occur in weak or absent fusion
47
What does post-operative diplopia test measure and what is its clinical use when investigating patients with strabismus?
-post operative diplopia test was done to investigates the area of suppression and therefore the possible occurance of post-operative diplopia if the surgery were to result in ocular alignment in which images fall outside the suppression area.
(bila ada surgery yg sebbkn ocular alignment outside suppression area, dia kena measure the suppression area untuk investigate kemungkinan dapat diplopia)
-the patients appreciates diplopia, it is important to assess whether this may be ignored. if the patient capable of ignoring or resuppressing the second image then this would alwrt the surgeon not to correct the deviation.
48
what is the advantage of using botulinum toxin in patients who have a positive post operative diplopia test?
a reliable test for diplopia can be done by injection of botolinum toxin into an eye muscle. thus a predominantly transient paresis is produced during which there is parellelism for a sufficient period of time, so that the patient has time enough to experience disturbing double vision or its absence.
49
a patient is being investigated for hyperthroidism. what signs and symptoms would she present if she was being treated for TED?
- insidious onset of diplopia
- upper lid retraction
- lid lag
- reduced frequency of blinking
- weak convergence
- inability of hold fixation on extreme lateral gaze
- staring appearance
- chemosis
- odema
- low VA
- AHP
50
list the extra ocular muscle involved in TED in order of most common involvement?
```
IR (most common)
MR
SR
LR
Oblique muscles are involved but to a lesser extent.
```
limited elevation is most common, followed by limited ABduction, depression and ADduction.
51
what symptoms would you expects from a 22 years old woman with convergence insufficiency?
```
headaches
difficulty in changing focus
blurring of print
intermittent diplopia
asthenopia
ocular fatigue from prolonged close work
near vision may be reduce if accommodation involved
```
52
What is convergence insufficiency?
inability to obtain and maintain adequate binocular convergence without undue effort.
- NPC greater than 10cm
1) primary convergence insufficiency
- wide IPD
- occupations/hobbies involving a lot of uni ocular work
- little or no close work
- precipitating causes including: illness, fatigue, prolonged close work, poor lighthing, toxins, age, pregnancy.
2) when convergence insufficiency is a secondsry condition;
- squint (latent or manifest)
- refractive error
- systemic disorders
- accommodative anomalies
53
what are the aims of orthoptic exercises in convergence insufficiency?
- (appreciate diplopia)
- improve convergence
- improve fusional reserves
- achieve voluntary convergence
54
explain on procedures of orthoptic exercises:
- instruct patient to fixate on approaching target
- encourage patient to maintain fusion by keeping the target single.
- when diplopia is noticed (convergence is broken), patient must move the target back until single vision is restored.
- repeat for a few times for 10-15 times in 3-4 times per day.
- encourage the patient to relax eyes following each period of exercise.
- when NPC has improved with exercises jump convergence can be introduced.
- the px is instructed to fix on each point individually and encouraged to maintain single vision.
- exercise continue until convergence improves to normal or no further improvement is possible.
- in extreme cases, surgery or BASE IN prism incorporated into readers can be used to alleviate symptoms.
OPTOM
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