O3A 2 Deviations
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What is a deviation?
when two eyes do not point at the same object of regard- image doesnt fall on both fovea
Whats is a manifest deviation?
- It is there all the time
- heterotropia, strabismus, squint
What is a latent deviation?
- only there when you cover the eye
- brought about by eliminating all stimuli to fusion
What is the stimulus for motor fusion?
What is the stimulus for accomodation?
What is tonic vergence?
- anatomical position of rest
- eyes tend to diverge after death
- whilst alive tend to turn inwards- due to surrounding tissue and tone of muscle
- physical position of rest
what is fusional/disparity vergence?
convergence compensating for any excess or deficit in tonic convergence stimulated by retinal disparity
What is proximal vergence?
voluntary convergence- due to knowlede that the object is nearby
What is accommodative vergence?
What is the physiological position of rest?
position the axes take when stimuli to fusion is absent
What happens if you do not have enough tonic vergence?
fusional divergence has to bring it back to ortho= amount of phoria
What happens if you have too much tonic vergence?
fusional convergence has to make up for it
what is the relationship between accommodation and convergence?
phoria depends on the amount of convergence that accompanies each dioptre of accommodation
does not cause symptoms
thought to generate suppression
tonic aetiology of phoria?
- tonic position gives deviation
- muscle weak/inserted incorrectly- rare
neural aetiology of a phoria?
interaction between vergence and accommodation is abnormal
rx and aetiology of phoria?
uncorrected hyp- overconverge
What are some symptoms of high phoria?
- transient blur/diplopia
- avoidance of near work
- loss of place while reading
- words running together while reading
How to manage high phoria?
aetiology of tropia?
- possible muscle weakness
- same as phoria
sensory anomalies associated with tropias?
- diplopia: superimposition causing confusion
- suppression: adult-> diplopia, in macular to avoid confusion
- ambyopia: strab- occur in deviating eye as a result of continued suppression
- rx- uncorrected aniso or astig
- anomalous correspondence- one fovea of the eye doesnt correspond with the other
- can fix diplopia and confusion
What is the management of tropias?
specs, occlusion, vision training, surgery, botox
What is a nystagmus
A regularly repetitive, rapid involuntary movement of the eye
What is aniseikonia?
unequal image size and shapes
angle of tropia is same in all directions of gaze
angle differs in different directions of gaze
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