Orthoptics | Flashcards
What is orthoptics?
Straight sight
What are 3 reasons that children are referred to orthoptics?
- Presence or suspicion of squint
- Reduced visual acuity
- Family history of squint/reduced VA in childhood
What are 3 reasons that adults are referred to orthoptics?
- Presence of diplopia (double vision)
- Presence of squint (sudden onset or requiring cosmetic surgery)
- Asthenopic symptoms (eye strain)
What is the role of the orthoptist?
Involved in the investigation, diagnosis and management of binocular vision and ocular motility disorders
What is binocular vision?
Brain’s ability to perceive an image with each eye simultaneously as a single image
What is strabismus?
Squint
What are the 2 types of strabismus?
- Manifest strabismus
2. Latent strabismus
What is a manifest strabismus?
An inward, outward, upward, downward deviation of one eye, so that the visual axes are not aligned
-The squint is there all the time
What test detects a manifest strabismus?
Cover-uncover test
What is a latent strabismus?
A tendency for the eyes to deviate inwards, outwards, upwards, downwards. Under normal circumstances, the visual axes are aligned
-The squint only appears when eyes are tired or dissociated?
What test uncovers a latent strabismus?
Alternate cover test
What are the 2 possible clinical outcomes of a manifest squint? Why do they occur?
- Diplopia
- Suppression - no double vision
They occur because the visual axes are not aligned. Binocular vision is therefore not possible, as both eyes are not pointing towards the object of interest
Why does diplopia occur with a manifest squint?
When does it occur?
Each eye perceives the image of what it is looking at so you get double vision
Commonly occurs when the onset of the manifest squint is after visual development i.e. > age 7
Why does suppression occur with a manifest squint?
When does it occur?
There is no double vision as the patient suppresses the image from the squinting eye
Commonly occurs when the onset of the manifest squint is during visual development i.e. =< age 7
What is amblyopia?
Lazy eye - a reduction of vision in one or both eyes with no evidence of structural abnormality, and persists after correction of refractive error and removal of any pathological obstacles to vision
On visual acuity assessment there is a difference of 2 lines or more between the eyes, or the best corrected visual acuity is 20/30 without any identifiable cause
What is the pathophysiology of amblyopia in children?
Lack of visual stimulation reaching the retina during the critical period of visual development (0-7 years) causing the eye and the vision to not grow and develop properly
-there are structural and functional changes to the lateral geniculate nucleus and striate cortex in the occipital lobe
What are the causes of amblyopia in children (3)?
- Squint (strabismic)
- Refractive error
- Obstruction to visual axis (stimulus deprivation) i.e. cataracts, congenital 3rd nerve palsy
What is the visual development period?
Period in which VA can be improved when amblyopia is present, due to plasticity of the visual cortex
Before 7 years old
Why is VA tested or screened in young children?
Check for amblyopia - it can be corrected before the age of 7 years old due to plasticity of the visual cortex
What is the management of amblyopia (2)?
- Occlusion of the good eye, so that the patient is forced to use the amblyopic eye
-Sticky eye patch which sticks to the skin around the good eye
or
-atropine (dilates pupil to stop accommodation, forcing child to use bad eye - Glasses
How long is the adaptation period in the management of amblyopia?
16-24 weeks
What are 2 things that are important to check for in a patient with occlusion treatment?
- Close observation to monitor the improvement in VA of the amblyopic eye
- Check that the good eye isn’t disadvantaged by intensive occlusion - make sure you haven’t induced occlusion amblyopia in the good eye
What distance does the patient stand when reading off the Snellen chart?
6m
How is VA recorded from a snellen chart (2)?
- As a fraction i.e. 6/6 (6m as numerator)
2. Odd letters recorded as + or - e.g. 6/6-2
What is the suffix used for someone with a manifest squint?
Tropia
What is the suffix used for someone with a latent squint?
Phoria
What are the prefixes for someone with the following squints:
- Convergent
- Divergent
- Up
- Down
- Eso
- Exo
- Hyper
- Hypo
What is the term for someone with a divergent manifest squint?
Exotropic
What is the term for someone with a convergent latent squint?
Esophoric
What is a concomitant vs incomitant strabismus?
Concomitant = a squint that remains the same size and direction in all positions of gaze
Incomitant = A squint that changes in different positions of gaze due to extraocular muscle imbalance
What test do you do to differentiate between a concomitant/incomitant squint?
Cover test performed at each of the 9 positions of gaze (star shape)
What are 5 causes of squints in adulthood?
- Cranial nerve palsy
- Mechanical - facial injury/trauma/iatrogenic
- Myasthenia gravis
- Thyroid eye disease
- Childhood squint
What is the effect of a squint in an adult?
Diplopia
What is the effect of a squint in a child?
Suppression i.e. no diplopia
What is vision?
The level of vision that an eye can resolve unaided
-determined by the size of the smallest line of letters or symbols on the test chart that can be read without any for of optical correction in place
What is visual acuity?
Measure of the patient’s ability to resolve fine detail with the optimum optical correction in place
-determined by size of the smallest line of letters or symbols on the test chart that can be read after any defects of focusing, other than aberration have been corrected
What is a refractive error?
An imbalance of the optical components of the eye i.e. the cornea, lens and axial length
What are the 2 main types of refractive error?
- Hypermetropia or hyperopia = long-sightedness
2. Myopia = short-sightedness
What are the 6 extraocular muscles?
- Medial rectus
- Lateral rectus
- Superior rectus
- Inferior rectus
- Superior oblique
- Inferior oblique
- Levator muscle
How do the 4 extraocular rectus muscles attach to the eyeball anteriorly and posteriorly?
- Anteriorly on the sclera
2. Posteriorly, they have a common attachment to a ring of connective tissue which surrounds the optic foramen
What is the memory aid to remember what nerves innervate what extraocular muscles?
LR6 SO4
Lateral rectus - VI abducens
Superior oblique - IV trochlear
All others (including levator) - III oculomotor
Why do extra ocular muscles have primary, secondary and tertiary actions?
Due to the angle that they insert onto the globe
What is the action of the medial rectus muscle?
Adduction of the eye (medially)
What is the action of the lateral rectus muscle?
Abduction of the eye (laterally)
What is the action of the superior rectus muscle?
- Primary action
- Secondary action
- Tertiary action
- Elevation
- Intorsion
- Adduction
What is the action of the inferior rectus muscle?
- Primary action
- Secondary action
- Tertiary action
- Depression
- Extorsion
- Adduction
What is the action of the superior oblique muscle?
- Primary action
- Secondary action
- Tertiary action
- Intorsion
- Depression
- Abduction
What is the action of the interior oblique muscle?
- Primary action
- Secondary action
- Tertiary action
- Extorsion
- Elevation
- Abduction
What is a mneumonic for remembering secondary and tertiary actions?
RADSIN
Recti adduct and superior muscles intort
What extraocular muscles of the eye are supplied by CNIII?
- MR
- IR
- SR
- IO
- Levator palpebral
- Spincherter pupillae and ciliary muscle
What extraocular muscles of the eye are supplied by CNIV?
SO
What extraocular muscles of the eye are supplied by CNVI?
LR
What deviations are experienced in 3rd nerve palsy (3)?
- Exotropia and hypotrophia of the affected eye
- Deviated out and down - Ptosis
- +/-Dilated pupil
What deviations are experienced in 4th nerve palsy (2)?
Hypertropia and excylotorsion
-deviated upwards and patient c/o tilted image so patient may tilt their head to try ti align the tilted 2nd image
What deviations are experienced in 6th nerve palsy?
Esotropia
-eye deviated inwards
(worse in the distance compared to near
Does suppression/diplopia usually occur with nerve palsies in children?
Suppression likely, leading to risk of developing amblyopia
Does suppression/diplopia usually occur with nerve palsies in adults?
Diplopia
What are 7 causes of neurogenic palsies?
*most common
- Trauma*
- head injury - SOL - tumour
- commonly brain stem/cerebellar tumours
- Primary, secondary, metastases (orbital and ocular metastases are common - SOL - vascular abnormality
- aneurysm, carotid cavernous fistula, subdural haematoma, PCCA - Microvascular
- Likely if 3rd nerve palsy with pupil sparing - Inflammatory
- e.g. Tolosa-Hunt syndrome (inflammation in cavernous sinus)
- Post viral i.e. herpes zoster, meningitis - Infection
- Gradenigo’s syndrome (inner ear infection and 6th nerve palsy)
- Herpes zoster ophthalmicus (HZO) involving 1st division of trigeminal nerve, 6th and 3rd nerve palsies most common - Demyelination
- Optic neuritis
- 6th nerve palsy most common
In a cranial nerve palsy in a child, what must you suspect?
A sinister pathology e.g. trauma/tumour
If a 3rd nerve palsy has pupil involvement (sphincter pupillae affected and pupil dilated, what must you suspect?
Posterior communicating artery aneurysm (PCCA)
What is the management of diplopia (3)?
- Prisms
-Join up the 2 diplopic images - Occlusion
-Cover one eye to block off the diplopic image - Surgery
-If ocular motility and strabismus are stable, surgery can be done to realign eyes in primary position
or
-Surgery can be done to reduce muscle incomitance and eliminate diplopia in as many positions as possible
