Orthoptics

Question 1

How is binocular vision formed ?

Answer 1

The brains ability to perceive an image with each eye as a single image- the three principles of this are
Simultaneous perception
Fusion
Stereopsis- depth perception

Question 2

What are the 2 main subtypes of strabismus (squint)?

Answer 2

Manifest squint (tropia)-  which is an obviously visible inward, outward, upward or downward deviation of one eye. (diplopia, looking at 2 different things 
Latent squint (phoria)- the tendency of one eye to deviate under certain circumstances
Concomitant strabismus- a strabismus that remains the same in all positions of gaze
Incomitant strabismus- a strabismus that changes in different positions of gaze and is due to an extraocular muscle imbalance

Question 3

What is amblyopia?

Answer 3

reduction of vision in one eye due to a lack of stimulation during the critical period of visual development:
Stimulus deprivation
Strabismic (squint)
Anisometropic: large different in refractive errors of over 1 dioptre – eye with highest refractive error is affected

Question 4

How is visual acuity screened in young children?

Answer 4

Preferential looks- card is held up with a pattern on one side and a blank space on the other. Useful for a very young child and shows they have some form of sight -the user can look though the centre dot to see where the child looks. The stripes get thinner to give a form of grading
Cardiff cards- cards with the same picture on at the top or bottom of the card, the child will then look up or down. The picture will get smaller and less defined on a grading system
Kays pictures- picture form of the Snellen chart, used when a child can verbalise what the picture are off. These get smaller graded by width of lines
LogMAR crowded and uncrowded, useful when a child can read letters the crowded test is usually done as uncrowded tests can be easier, in the crowded test the letters are together in a line, surrounded by a box

Question 5

What is a Bailey lovie chart? =

Answer 5

Proper LogMAR chart, this varies from Snellen as there is the same number of letters per line to make it a fairer test With Snellen’s it is an easier test if you have poor vision and a harder test if you have good vision
Visual acuity is recorded as a decimal with 0 being normal and 1 being 6/60 so higher is worse vision, a negative number is better than normal

Question 6

What movements due to ocular muscles control?

Answer 6

SR inserts at an angle of 23o to medial wall of orbit and does elevation, intorsion and adduction
IR inserts at angle of 23o to medial wall of orbit and does depression, extorsion and adduction
SO inserts at an angle of 51o to medial wall of orbit and does intorsion, depression and abduction
IO inserts at an angle of 51o to medial wall of orbit and does extorsion, elevation and abduction

Question 7

Which nerves innervate the eye muscles?

Answer 7

Occulomotor (III)
SR,MR,IR,IO, levator pepebrae 
Abducent (VI)
LR
Trochlear (IV)
SO