05 Flashcards
- Premie babies tend to be (hyperopic/myopic), with (round/flat) lenses positioned very far (forward/backward)
- How about full-term babies?
- At 5 yrs (child), what’s the mean Rx?
- when (at what age) does myopia often begin?
Premies: myopic, ROUNDED lenses (zonules not strong enough to pull), FORWARD.
Term: slightly hyperopic, FLATTER lens
5Y/O: ~+0.50D
-14Y/O: onset of myopia
Which type of accommodation is primarily used (esp in infants), explaining how infants are highly hyperopic that eventually move toward emmetropia?
TONIC accommodation - allows massive amts (~3D) of accommodation while infant is highly hyperopic, until it levels out
What mechanism allows almost all children ~3Y/O to have approximately the same refractive error?
VISUAL FEEDBACK mechanism - majority (80%) of 3Y/Os have +0.50 to emmetropia
If visual feedback is disrupted (but LIGHT is still allowed in to the covered eye), myopia develops solely due to WHAT?
AXIAL ELONGATION (anterior seg still nml)
If the optic nerve is cut and the NASAL RETINA ONLY is deprived of visual feedback, what’s the result?
elongation of the TEMPORAL retina only….STILL HAPPENS w/ cut optic nerve
–suggests the process happens LOCALLY w/i the eye, has nothing to do w/ the brain
Changing the thickness of the ____ can allow for a transient Rx change when looking @ a near target
-what three things make this possible?
choroid
1) quick accommodation
2) thinning of the choroid (hrs-days)
3) elongation of the post. pole of the sclera
T/F: the eye will recover after removal of form deprivation, but the process is slow and takes several months
FALSE - it’s fast! Within a week!
So, the DEFAULT condition for a form-deprived eye is what? What controls it, effectively slowing it?
AXIAL ELONGATION
-visual feedback slows it
If an eye is biased and exposed to a minus lens half the time, then a plus lens half the time, it will end up slightly (myopic/hyperopic)
hyperopic
- if lenses removed altogether, it will return to emmetropia.
- w/ minus lenses - axial elongation
- w/ plus lenses - axial growth stops
- dopamine, acetylcholine, atropine, and pirenzepine act at a ____ level
- retinoic acid acts at a ____ level
- ECM acts at the ____ level, along with its growth factors (VEGF, Zenk)
- retinal
- choroidal
- scleral
T/F: A child’s Rx PRIOR to emmetropization (~3-4Y/O) can predict the amount of future myopia as the kid ages
-tends to follow what type of fxn?
True
-Gompertz function: suggests that mechanism causing myopia is similar regardless of age or amt of myopia**
Does the Gompertz fxn state that the onset of myopia is gradual or rapid? When does leveling off occur?
RAPID; levels off around 12-13Y/O (relatively quick finish also)
- Is there a simple genetic pattern explaining myopia, genetically?
- How do the myopia rates b/w children w/ NO or ONE myopic parent compare? How about two myopic parents?
- what about asian population?
NO
0-1: similar rate of myopia
2 parents: higher correlation (60%)
-with TWO myopic parents (regardless of amt of myopia), whildren are 2.5-3X MORE LIKELY to be myopic
-asians: equal rate of myopia w/ either one OR two myopic parents
Which situation is the only case where genetics alone (no environmental factors) can explain myopia?
HIGH myopia (6D or more)
Does environment play a role in myopia progression?
-Study in the amazon found that 16Y/O amazon teens have an identical refraction to __-__Y/Os in america (as if they never went to school)
absolutely
5-6Y/Os - because they never did go to school; they’re emmetropes
only 1.6% HAVE BILATERAL MYOPIA!! ALMOST NONE! 2 teachers, one seamstress, one extensive reader