05 Flashcards

1
Q
  • 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?
A

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

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2
Q

Which type of accommodation is primarily used (esp in infants), explaining how infants are highly hyperopic that eventually move toward emmetropia?

A

TONIC accommodation - allows massive amts (~3D) of accommodation while infant is highly hyperopic, until it levels out

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3
Q

What mechanism allows almost all children ~3Y/O to have approximately the same refractive error?

A

VISUAL FEEDBACK mechanism - majority (80%) of 3Y/Os have +0.50 to emmetropia

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4
Q

If visual feedback is disrupted (but LIGHT is still allowed in to the covered eye), myopia develops solely due to WHAT?

A

AXIAL ELONGATION (anterior seg still nml)

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5
Q

If the optic nerve is cut and the NASAL RETINA ONLY is deprived of visual feedback, what’s the result?

A

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

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6
Q

Changing the thickness of the ____ can allow for a transient Rx change when looking @ a near target

-what three things make this possible?

A

choroid

1) quick accommodation
2) thinning of the choroid (hrs-days)
3) elongation of the post. pole of the sclera

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7
Q

T/F: the eye will recover after removal of form deprivation, but the process is slow and takes several months

A

FALSE - it’s fast! Within a week!

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8
Q

So, the DEFAULT condition for a form-deprived eye is what? What controls it, effectively slowing it?

A

AXIAL ELONGATION

-visual feedback slows it

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9
Q

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)

A

hyperopic

  • if lenses removed altogether, it will return to emmetropia.
  • w/ minus lenses - axial elongation
  • w/ plus lenses - axial growth stops
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10
Q
  • 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)
A
  • retinal
  • choroidal
  • scleral
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11
Q

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?

A

True

-Gompertz function: suggests that mechanism causing myopia is similar regardless of age or amt of myopia**

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12
Q

Does the Gompertz fxn state that the onset of myopia is gradual or rapid? When does leveling off occur?

A

RAPID; levels off around 12-13Y/O (relatively quick finish also)

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13
Q
  • 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?
A

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

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14
Q

Which situation is the only case where genetics alone (no environmental factors) can explain myopia?

A

HIGH myopia (6D or more)

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15
Q

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)

A

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

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16
Q

T/F: more than 1% of illiterate people living in the amazon become myopic in both eyes

A

FALSE - LESS THAN 1% of the ILLITERATE people (don’t include the literate ones)

17
Q

How do aberrations induce myopia?

A

degrade retinal image timilar to partial pattern deprivation –>breaks fdbk loop, changes the point spread fxn–> increases the eye’s depth of focus–>makes it less sensitive to blur—>reduces fdbk signal even more–>allows MORE axial elongation

18
Q

T/F: astigmatism rarely causes myopia.

A

FALSE - HIGHLY correlated to development of myopia!

->1D ATR astig kids 9-12mos develop myopia sooner and in larger amounts, AND their astigmatism increases

19
Q

During myopia progression, does changing the object distance change the accommodative demand? If not, WHAT DOES?

A

NO!!

  • it’s the STIMULUS itself (lenses, etc.) that cause the eye to accommodate –> NOT the distance of the stimulus
  • result: myopes have trouble INTERPRETING blur/responding appropriately
  • response to defocus RETURNS TO NORMAL when myopia progression stops
20
Q

T/F: adult myopes are insensitive to defocus, but have normal accommodation.

If true, HOW is this possible?

A

TRUE

-neural up-regulation: blur signals are used more effectively than perception

21
Q

Is accommodative variability greater in adult myopes? Do they have the same accommodative lag as emmetropes?

A

YES, YES

-myopic accomm fdbk system has REDUCED sensitivity and ELEVATED gain - leads to increased variability

22
Q

T/F: when given an increasing near demand, myopes have a higher percent of look-aways compared to emmetropes

A

FALSE - they look away LESS frequently

23
Q

**T/F: if myopes remain steadily fixated when viewing near text, their feedback control is MORE susceptible to hyperopic defocus

A

TRUE –important concept

-excessive hyperopic defocus, intense fixation, nearer reading distances, and insensitivity to blur are all explanations as to why some children become myopic (and others don’t)

24
Q

T/F: the near peripheral retina can guide refractive development

A

true - can have fovea missing entirely and still get emmetropic eye (monkey)

25
Q

Emmetropic eye: more ____ (shape); fovea slightly (myopic/hyperopic) and periphery slightly (myopic/hyperopic)

-Myopic eye: more ____ (shape) - what’s the relationship here? Implications of a FULLY corrected myope?

A

emmetropic: OBLATE (flat in back) - fovea slightly hyperopic, periphery slightly myopic (protective against myopia)
myopic: PROLATE (longer @ PP)- fovea more myopic, periphery more hyperopic - induces further myopia
- fully corrected myopia: peripheral defocus even MORE hyperopic; myopia even more likely to be induced

26
Q

Ortho-K lenses aim to provide ____ correction, shifting peripheral ____ defocus to ____ defocus, theoretically stopping myopia progression

-what type of aberration do these lenses cause? (INTENTIONALLY?)

A

optimal

hyperopic peripheral defocus shift to MYOPIC defocus (like in emmetrope) –> halts myopia

-cause POSITIVE SPHERICAL aberration

27
Q

T/F: daytime illumination has no effect on myopia progression

A

FALSE: the brighter the light, the SLOWER the progression of myopia - unknown mechanism

28
Q

Is myopia caused by genetics, or the environment?

A

trick question –> BOTH

-INTERACTION of genes/env causes myopia

29
Q

name three drugs used/being tested in treating myopia

A

atropine, pirenzepine, dopamine agonists

-Note: pirenzepine: DOESN’T affect accomm or pupil size –> mech of action must be related to the CIRCUITRY of the retina, not changes in accomm or pupil size

30
Q

Which form of atropine therapy is MOST successful? 1%, 0.5%, 0.05%, or 0.01%?

A
  1. 01% - ULTRA-WEAK - MOST SUCCESSFUL
    - virtually NO effect @ 8 months, but then myopia progression suddenly STOPS, even after DC’ing. And there’s NO REBOUND (works for at least one year)
    - generally, strongest percentages have the strongest effect/biggest reversal of myopia, but they all cause some type of rebound, EXCEPT 0.01%