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OPT 514 > Refractive Status > Flashcards

Refractive Status Flashcards

1
Q

Emmetropia

A

Normal

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2
Q

Ametropia

A

Abnormal
Influenced by difference in
-location of optical element in regards to the retina
-refractive power of the optical element.

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3
Q

Mypoia

A
  • Light focuses in front of the retina

- correction: concave minus lenses

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4
Q

Axial Myopia

A

Relatively longer axial length

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5
Q

Refractive Myopia

A

Excessive refractive power

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6
Q

Hyperopia

A
  • Light focuses behind the retina
  • Correction: Convex plus lens
  • hereditary factors influence more than environmental factors
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7
Q

Axial Hyperopia

A

Relatively shorter axial length

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8
Q

Refractive Hyperopia

A

Insufficient refractive power

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9
Q

Accomodation

A

the ability to temporarily INCREASE the dioptric power of the crystalline lens

  • under the age of 40(presbyopia)
  • changes shape of the lens
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10
Q

Anisometropia

A

A difference in refractive status between the two eyes

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11
Q

Isoanisometropia

A

Both eyes have the sign, one is just more significant than the other

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12
Q

Antimetropia

A

The eyes are opposite in sign

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13
Q

Problems with anisometropia

A

Induced prism with glasses

  • stimulus to accomodation
  • image magnification
  • too high, brain shuts down (can’t get the object to focus at the same time)
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14
Q

Regular and irregular astigmatism

A

regular- Difference is 90 degrees

irregular- Difference is not

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15
Q

Corneal and Lenticular astigmatism

A

corneal- the shape of the cornea causes difference

lenticular- the shape of the lens causes difference

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16
Q

With the rule and against the rule

A

with the rule- weaker power is in the horizontal

against the rule- weaker power is in the vertical

17
Q

Astigmatism

A

Light focused differently in different meridians

-correction: lenses with different power in different meridians

18
Q

Corneal Power

A
  • focusing strength of the cornea
  • normal is 43.25D
  • reaches adult level early in life
  • determined by curvature
  • increased in myopes, but not proven
19
Q

Crystalline lens power

A
  • focusing strength of crystalline lens
  • normal is 20D
  • changes occur through life (decrease 6-8)(increase the rest of the time)
20
Q

Anterior Chamber Depth

A
  • Distance fro cornea to lens
  • normal is 4mm
  • increases until teenager (to go a long with decrease of crystalline lens power) then decreases (again, because of crystalline lens power)
  • effect on refractive status and dependent on axial length
  • if axial length stays the same and increase ACD, decrease refractive power
21
Q

Axial Length

A
  • length of entire eye
  • normal is 24mm
  • rapid increase in early life, slows and stabilizes by 15(your body pretty much stops growing)
    - not the case with adult onset myopia
  • longer=myopia
  • shorter=hyperopia.
22
Q

Emmetropization

A

The different components work together to compensate and result in more emmetropes than we would expect
-active emmetropization effect is not perfect

23
Q

Keratometry and Corneal Topography

A

Measure anterior corneal curvature via reflected light

  • kerotometry measures curvature
  • corneal topography uses colors. red=steep(anterior chamber depth)
24
Q

Ultrasound and doppler interferometry

A

Measure thickness of cornea and length between ocular structures via sound and light rays respectively

  • ultrasound-pulse to eye and echoes are generated at each change in media density, so time it takes for echoes to come back determines separation of each boundary.
  • interferometry can predict before cat surgery on how to increase vision. (axial length)
25
Q

Theories of myopic development

A

Biological-statistical theory-refractive error ranges from high myopia to high hyperopia so ametropia is just a biological variation

Use and Abuse theory- myopia onset due to abusing the eyes during strained near vision (more prevalent in people who do lots of close work/ reading.

Theory of emmetropization- coordinated growth of the optical elements. more emmetropes due to negative feedback, self-focusing control system.

26
Q

What are the main components of refraction?

A
  • corneal power
  • crystalline lens power
  • anterior chamber depth
  • axial length

OPT 514 (6 decks)

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