09

Question 1

EXOs almost always have _____ fixation.

• there is no ____ eye, so NO ____ develops.
• what IS there a loss of?
• results?

Answer 1

exo = intermittent

• no dominant eye = no amblyopia
• loss of BINOCULARITY - cells will respond to either contra eye only, or ipsi eye only
• result: poor convergence, asymmetric OKN

Question 2

ESOs almost always have ____ fixation, leading to partial takeover of cortical cells and subsequent ___ loss in the LGN

-what’s different about strab amblyopes as opposed to form-deprived ones?

Answer 2

constant, unilateral, CSF loss in LGN of non-dom eye.

strab amblyos - NO ANATOMICAL CHANGES as seen in form-dep. no shift in oc dom column sizes, LGN cell lack of growth, etc

functional effects are the same - d/t the CORTICAL FDBK LOOP shutting down certain fxns of the LGN

Question 3

Can the unsteadiness of the ET change the severity of amblyopia? If so, what type of induced ET is most likely to show this?

Answer 3

Yes - surgical ET = big effect - reduced cortical response to LGN high-freq CSF in parvo cells (seen in amblyo)

-SIZE of ET poorly correlated to the loss of VA in the amblyo eye

Question 4

What term defines the maintenance of binocularity regardless of small changes in receptive field position?
-Give the amt of realignment possible based on the prismatic correction/amt of deviation:
30PD:

Answer 4

Microstrabismus - can maintain binocularity even w/ slight misalignment

Question 5

Cyclotropia - may cause amblyo as well b/c the eyes rotate when we accommodate

• small amount - effect similar to ___
• large amount - will it cause amblyopia? If so, what severity?

Answer 5

small amount - effect similar to microstrab - projections are aligned if possible: 8 deg: binocularity, 16-24deg: partial breakdown, >30deg: total breakdown of binoc

large amount - YES, a mild amblyopia will develop (intensity based on how much pattern/images align)

Question 6

If a cat has one eye completely immobilized (EOMs cut on one eye only), will changes occur even without ANY visual experience?

Answer 6

YES!!! - issue isn’t imbalance of signals to the eyes, it’s an imbalance of input to the MOTOR system - happens at ANY point in development (independent of critical period)

-therefore: normal EYE MOVEMENTS are important in proper recovery of amblyopia

Question 7

Rearing the right eye with horizontal lines only and the left eye with vertical lines only will result in what two major things?

Answer 7

1) loss of binocularity - obviously. Two diff images.

2) meridional amblyopia - in the OPPOSITE directions in both eyes (i.e. vertical amblyo OD, horiz amblyo OS)

Question 8

If I would stick a +10D lens in front of your right eye (imitating experimental anisometropia), what would be the changes seen in the CSF?
-would there be any anatomical changes?

Answer 8

CSF changes: amblyopic findings! Reduction in the HIGH SFs

-anatomically, it’s just like strabismic amblyo - NO anatomical changes!