Strabismus Flashcards
What is strabismus also known as?
Squint
What is strabismus?
Misalignment of the eyes
What happens as a result of the misalignment of the eyes in strabismus?
The retinal image is not in the corresponding area of both eyes which may cause diplopia in adults or amblyopia in children
What is amblyopia?
Lazy eye
How is strabismus most commonly described?
By the direction of the eye misalignment
What is the suffix for manifest squints?
-tropia
What prefix is used for an inward ocular deviation in strabismus?
eso-
What prefix is used for an outward ocular deviation in strabismus?
exo-
When can the severity of a horizontal squint (eso/exo) vary?
With up/down gaze
If deviation is greater in an upward gaze what pattern does the squint follow?
V pattern
If the deviation is greater in a downward gaze, what pattern does the squint follow ?
A pattern
What prefix is used for an upward ocular deviation in strabismus?
hyper-
What prefix is used for a downward ocular deviation in strabismus?
hypo-
Are vertical or horizontal squints more common?
Horizontal
What is a manifest squint?
A squint present when the eyes are open and being used
What is another term for a manifest squint?
Heterotropia
What is it called when eyes are perfectly aligned?
Orthophoria
What is a latent squint?
When the eye deviates when it is covered or closed
What suffix is used for a latent squint?
-phoria
Do most people have orthophoria?
No, most people have a mild latent squint
What is the mild latent squint that most people have called?
Heterophoria
What are the different ways of classifying a squint?
- Congenital or Acquired
- Right, Left or Alternating
- Permanent or Intermittent
- Manifest or Latent
- Concomitant or Incomitant
- Primary, Secondary or Consecutive
When is a squint congenital?
If onset is before 6 months of age
What is an alternating squint?
The patient can alternate fixation between right and left eye - usually spontaneous but can be voluntary
What is another term for a concomitant squint?
Non-paralytic
What is another term for an incomitant squint?
Paralytic
What happens in a concomitant squint?
The size of the deviation does not vary with direction of gaze
When do concomitant squints normally begin?
Typically between 2-4 years
What type of squint is mostly concomitant?
Esotropias
What happens in an incomitant squint?
The direction of gaze affects the size or presence of the squint
When can incomitant squints arise?
Childhood or adulthood
What causes incomitant squints?
Problems with the muscles controlling eye movement
What sort of problems with they extra-ocular muscles can lead to incomitant squint?
- Neurological problems
- Mechanical problems
- Myogenic problems
Are most squints primary, secondary or consecutive?
Primary
What is a secondary squint?
Arises due to loss or impairment of vision
What is a consecutive squint?
Arises following overcorrection
How do most concomitant squints arise?
Congenital
How are children with concomitant squints eye movements affected?
Should be unaffected when tested separately
Do children with concomitant squints have problems with their extra-ocular muscles or cranial nerves?
No
Do children with concomitant squints have diplopia?
No
What happens to the longitudinal axes of the eyes in people with concomitant squints when eye movements are tested?
Remain the same
What usually causes a paralytic squint?
Damage to the extra-ocular muscles or their nerves
What is a common symptom in paralytic squint?
Diplopia
When is diplopia often at its worst in paralytic squint?
In the direction of gaze produced by the weak muscle
What nerves can be involved in producing a paralytic squint?
- CN III
- CN IV
- CN VI
How many nerves can be affected in paralytic squint?
One or more
What disorders of childhood can squint be more common in?
- CP
- Down’s syndrome
- Hydrocephalus
- SOL
What is the leading cause of strabismus in adults?
Stroke
What are some less common causes of strabismus in adults?
- Neurological problems
- Grave’s disease
- Trauma
- Infection
What can the cause of paralytic squint often vary depending upon?
The nerve that is affected
What are some causes of paralytic squint caused by CN III damage?
- Ischaemic microvascular disease
- Aneurysm
- Tumour
- Herpes zoster
What are some causes of paralytic squint caused by CN IV damage?
- Trauma
- Vasculopathy
- Demyelinating disease
What can vasculopathy causing squint often be associated with?
- Diabetes
- Hypertension
What are some causes of paralytic squint caused by CN VI damage?
- Vasculopathy
- Trauma
- Idiopathic
What are the risk factors for squint?
- Family history
- Prematurity
- Refractive error
How do most non-paralytic squints present in children?
With parental concern due to manifest squint
How else can non-paralytic squints present in children?
- Intermittent closing of one eye especially in sunlight
- Reduced motor skills
- Pre-school screening
- Compensatory head tilt or chin lift
Why may children with non-paralytic squint have a compensatory head tilt or shin lift?
To minimise diplopia
What is the most common symptom of non-paralytic squint in adults?
Diplopia
What are some other symptoms of non-paralytic squint in adults?
- Asthenopia
- Eye strain
- Headaches
- Pulling sensation
- Noticing misaligned eyes
What is asthenopia?
Ocular discomfort
What does the presentation of a paralytic squint largely depends on?
The nerve that is affected
What are some features of a squint caused by CN III palsy?
- External ophthalmoplegia (partial or complete)
- Internal ophthalmoplegia
- Ptosis
What are some features of a squint caused by CN IV palsy?
- Binocular vertical diplopia
- Difficulty in reading
- Sense things appear to be tilted
What are some features of a squint caused by CN VI palsy?
- Horizontal diplopia worse for distance vision and on lateral gaze of affected side
What does the presentation of a multiple nerve plays causing squint depend on?
The combination of nerves involved
What is common feature of squint caused by multiple nerve palsies?
Limitation of a range of eye movements and diplopia
What are some additional features of squint caused by multiple nerve palsies?
- Facial pain
- Ptosis
- Small pupil
What screening methods are used in assessing squint?
- Gross inspection
- Light reflex tests
- Cover tests
- Visual acuity
- Ophthalmoscopy
How is a cover test conducted?
- Object held in front of patient
- Patient focuses on object
- Occlude one eye for several seconds and observe other eye for movement
- As the covered eye is uncovered, observe it for movement
What does the cover test show if the covered eye moves outwards as it is uncovered?
Esotropia in the covered eye (was initially turned inwards)
What does the cover test show if the covered eye moves inwards as it is uncovered?
Exotropia in the covered eye (was initially turned outward)
What additional test can be tried if the cover test is normal?
Alternative cover test
What happens in the alternative cover test?
Occluder is rapidly moved from one eye to the other and observe for movement
What are the differentials for squint?
- Pseudostrabismus
- Blurred vision
- Monocular diplopia
- Convergence insufficiency
What is the treatment of a non-paralytic squint guided by?
The nature for the squint and age of the patient
What is the first step in the management of non-paralytic squints?
Management of refractive errors
What will need treating in patients <8 with non-paralytic squint?
Concurrent amblyopia
How is amblyopia treated?
Eye patching +/- cycloplegic drops
What can patients have to correct non-paralytic squint if it is big enough or resists conservative management?
Surgical alignment
How can surgical alignment of squints be performed?
A combination of muscle resection and antagonistic resection to restore binocular function
Where should patients with paralytic squints be referred?
Ophthalmology for investigation
What further investigations may be performed for paralytic squint?
- Orthoptic assessment
- Blood tests
- Imaging
What can patients be given whilst the underlying cause of a paralytic squint is managed?
Prisms (fixed onto glasses) to alleviate diplopia
What can uncorrected squint lead to?
Amblyopia lazy eye
What can be a complication of corrective surgery for squint?
Under- or over-correction requiring further surgery
What are some other complications of squint?
Psychosocial consequences
Why can squint cause psychosocial consequences?
Because people may find it disturbing to look at or worry that is the case
