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