Amblyopia Flashcards
1
Q
What is Amblyopia?
A
- A reduction in vision in one or both eyes, persistent after correction of refractive error
- Absence of retinal pathology or any disease of the afferent visual pathway
- Most common cause of vision loss in children, interruption of normal visual development
2
Q
Mechanism of Amblyopia
A
- Deprivation of form vision
- Can be partial or complete
- Complete - No image/stimulus reaches fovea
- Partial - Degraded imaging reaching fovea
- Abnormal binocular interaction
- Incomplete images fall on the retina
- Images are incompatible
- Eyes compete for control over cortical connections during development period - better eye gains control
3
Q
Signs of Amblyopia
A
- Reduced Snellen and grating acuity
- Loss of contrast sensitivity
- Shape distortion
- Motion deficits
- Crowding effect
4
Q
Visual Function in Amblyopia
A
- Light sense - ability to distinguish light and dark (rods)
- Form sense - ability to distinguish between spatially separate visual stimulii, ability to discern size and shape of objects - positon/orientation (rods and cones)
- Colour sense - distinguish between light of different wavelengths (cones)
- Motion sense - ability to detect movement of images across retina (visual cortex)
5
Q
Periods of Visual Development _ Critical Period
A
- A few months old, deprivation causes damage
- Period with active neural plasticity (ability of the neural system to undergo change)
- Period where deprivation impacts visual development and amblyopia can develop
- Amblyopia can only develop within this time
- Earlier the onset of deficit and the longer the period of deprivation - worse the outcome
6
Q
Periods of Visual Development - Sensitive Period
A
- Deprivation in teenage yrs, amblyopia less likely to occur but improvement possible
- Improvement is possible during this time
- The younger the px the quicker the response to treatment
- Less common after 8 yrs of age
7
Q
Effect of Strabismus
A
- Abnormal visual cortex may be responsible for loss of binocular stereoscopic vision
- Alternating strabismus results in equal number of cells for right and left and virtually no binocularly driven cells
8
Q
Investigations for Amblyopia
A
- H&S - FH of childhood eye problems!
- Ocular examination - assess media and fundus
- Full cycloplegic refraction
- VA Assessment - age and ability, appropriate test selection
- Cover test - is there a manifest deviation? What is the fixation preference/pattern
- Contrast sensitivity - very useful, amblyopes can have reduced contrast sensitivity at higher spatial frequencies in comparison to non-amblyopes
- Uniocular fixation
- 4^ test
9
Q
Assessment of Uniocular Fixation
A
- Assess the point of the retina that the px is using for fixation when the other eye is occluded
- Using visuscope or ophthalmoscope
10
Q
Assessment of Uniocular Fixation - Method
A
- Dim room lights
- Ask px to fixate at distance
- Occlude “fellow normal eye”
- Line up instrument
- Get px to fix on centre of light
- Assess where the “bright” reflex is positioned
11
Q
Uniocular Fixation - Findings
A
- Central fixation - object on fovea
- Eccentric fixation
- Uniocular condition
- Fixation is by a point which isn’t the fovea
- This point is the principle visual direction
- The degree of eccentric fixation is defined by the distance between the fovea in degrees
- The further from the fovea - worse the level of VA
- Estimated line reduces by 1 line per 0.5 degrees of eccentricity
- Wandering fixation - uniocular condition, fovea has lost its fixation superiority and no single area of the retina is used for fixation
12
Q
Strabismic Amblyopia
A
- Result of constant or near-constant childhood strabismus in one eye
- Mostly esotropias as many exotropia’s are intermittent in childhood
13
Q
Strabismic Amblyopia - Clinical Characteristics
A
- Reduced vision in one eye
- Strabismus found on CT - usually not freely alternating
- No pathology detected on ocular examination
- Risk is 4x greater if one parent has strabismus
14
Q
Anisometropic Amblyopia
A
- Significant anisometropia present (At least 1D difference)
- Clearer vision in one eye for all distances
- Can be mostly spherical or mostly astigmatic
- Hypermetropia - most common
- Meridional (astigmatism) - Oblique astigmatism: more likely myopic
- Myopia - Can be avoided if one eye clear for distance and one eye clear for near
15
Q
Stimulus Deprivation Amblyopia
A
- Stimulus form vision deprivation amblyopia
- One or both eyes
- Little or no light enters the eye
