Flashcards in Orthoptics Deck (31):
What are the three grades/principles of binocular vision?
1) Simultaneous perception (from each eye)
2) Fusion (into a single image)
3) Stereopsis (depth perception)
What is a squint medically known as?
What are the two main subtypes of strabismis?
Describe a tropia.
There will be an obvious visible inward, outward, upward, downward deviation of one eye.
Describe a phoria.
(latent strabismus) The eye will deviate when using an alternate cover test.
What symptoms will patients describe who have a manifest squint.
Adult will have diplopia.
Childrens (≤7) brains are able to suppress the affected eye and thus do not have diplopia.
What is amblyopia?
A reduction in vision in one eye due to a lack of stimulation reaching the retina during the critical period of visual development.
What are the ages of critical visual development?
What are the three reasons for developing amblyopia?
1) Stimulus deprevation
What is anisometropia
A difference in refraction of at least 1 dioptre between eyes. The eye with highest refraction is affected.
How is amblyopia treated? (when must this occur?)
(It must occur before 7y/o) Treatment is occlusion of the good eye.
How are squints usually managed?
With correction of the refractive error. If this fails surgery to alter the length of extraocular muscles can be used.
What is used to treat convergent strabismus?
Convex lenses (long sighted)
What is used to treat divergent strabismus?
Concave lenses (short sighted)
Explain what a cover test is used for and what you would find?
It checks for manifest squints
It involves covering one eye and then removing the cover. When the normal eye is covered the bad eye will correct itself (and under the card the good eye will deviate). When the card is removed the good eye will return to its normal place and the bad eye will deviate again.
Explain what an alternative cover test is used for and what you would find?
It is to check for latent squint and involves covering one eye and then the other in quick succession. The covered eye will deviate under the card and will return to the normal position when uncovered.
What is a concomitant strabismus?
A squint that remains in all positions of gaze
What is an incomitant strabismus and what causes it?
A squint that changes in different positions of gaze and is due to extraocular muscle imbalance
What are the actions of the superior oblique?
1ry --> intorsion
2ry --> depression
3ry --> aBduction
Remember the SO is the "reading muscle" so you look down towards your nose.
What are the actions of the inferior oblique?
1ry --> extortion
2ry --> elevation
3ry --> aBduction
What are the actions of the superior rectus?
1ry --> Elevation
2ry --> Intorsion
3ry --> aDduction
What are the actions of the inferior rectus?
1ry --> depression
2ry --> extortion
3ry --> aDduciton
What are the actions of the lateral rectus?
What are the actions of the medial rectus?
It is a mnemonic to help with 2ry + 3ry actions of the extraocular muscles. Recti ADuct Superior INtort.
What are the cranial nerve innervations of the eye?
CN 3 Oculomotor n --> IO, MR, IR, SR and levator palpebrae superioris and along it runs parasympathetic fibres that innervate the pupil.
CN 4 Trochlear n --> SO
CN 6 Abducens n --> LR
How is diplopia managed?
Prisms, occlusion of working eye, surgery.
What are the signs of a 3rd nerve palsy?
1) exotropia and hypotropia of affected eye (out and down)
3) dilated pupil
What are the signs of a 4th nerve palsy?
1) hypertropia and excylotorsion of affected eye (deviated downwards & patient complains of tilted image)
2) Patient may tilt head to try to align the tilted 2nd image
What are the signs of a 6th nerve palsy?
1) Esotropia (deviated inwards)
2) Esotropia worse at distance compared to near