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Optics to Memorize > Physiological Optics 2 > Flashcards

Physiological Optics 2 Flashcards

1
Q

Gullstrand’s Eye model

-# of surfaces and # of n

A 
6 surfaces (2 cornea, 4 lens)
4 n
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2
Q

Parameters of a Reduced Eye Model

A 
n = 1.33
Total Power = +60.00D
Axial Length (K to post. focal pt) = 22.22mm
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3
Q

The center of curvature of the far point sphere of the eye is the same as…

A

The eye’s center of rotation

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4
Q

Far Point (Punctum Remotum)

A

Point in space that forms a point image on the retina
Emmetropes: infinity
Myopes: negative (in front of retina)
Hyperopes: positive (behind retina)

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5
Q

Near Point (punctum proximum)

A

The point in space that forms a point image on the retina when the eye is using maximum accommodation

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6
Q

Factors contributing to night myopia

A

increased spherical aberration

low light levels hinder relaxation of accommodation

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7
Q

% of people with myopia of at lease -0.50D at age 6 and 20

A

6: 2%
20: 20%

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8
Q

Latent Hyperopia

A

Hyperopia eliminated by accommodation

Shows more hyperopia on objective refraction than subjective refraction

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9
Q

Manifest Hyperopia

A

Amount of hyperopia on a subjective refraction

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10
Q

Absolute Hyperopia

A

Amount of hyperopia unable to be eliminated by accommodation

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11
Q

Facultative Hyperopia

A

Maximum amount of hyperopia that can be eliminated by accommodation

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12
Q

Trends of Hyperopia

A

%6 of kids 6-15
Constant from 20-40 but may increase after age 45
Expected refractive condition at 14 based on hyperopia at age 5
>1.5: hyperope
0.5-1.25: emmetrope
<0.5: myope

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13
Q

PD readings from pupilometer reduce influence of…

A

Parallax

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14
Q

Equally Mixed Astigmatism

A

Mixed astigmatism where the COLC falls on the retina

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15
Q

Major Meridian of the Eye

A

The STEEPEST corneal meridian (one with most plus power)

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16
Q

Recognition Acuity

A

Resolution at high frequencies and high contrast

-not suitable for pt with problems at other frequencies (cataracts)

17
Q

Minimum Detectable Acuity

A

Minimum visible line

  • usually better than recognition and resolution
  • tested via veneer acuity
18
Q

Resolution Acuity

A 
Distinguish pattern (sine wave) from a uniform patch
-Cutoff usually 40-60 cpd (MAR = 0.75)
19
Q

Hyperacuity

A

Sense of directional relationships (are two lines parallel?)

-Higher cortical processing

20
Q

MAR

A

Minimum angle of resolution in arcmin (1/60 degree)

MAR = 1/snellen (so 1 MAR = 20/20 = 0logMAR)

21
Q

Which acuity chart is used in research because of its logMAR scaling?

A

ETDRS

22
Q

Allen Vision Test

A

Good for kids
-Determine longest distance they can resolve the image monocularly
Acuity = distance/30

23
Q

Which Acuity methods require a child to match the test letter to a “key”

A

STYCAR, HOTV, LEA

Sheridan- Gardiner is similar but includes near vision

24
Q

Static Retinoscopy

-motion

A

The good ol’ phoropter kind (no accommodation involved)
-horizontal streak scopes the vertical meridian and a vertical streak scopes the horizontal meridian
Hyperope: with motion
Myope: against motion

25
Q

Dynamic Retinoscopy

-methods

A

Measures accuracy of accommodation (lead/lag)
MEM: uses quick presentation of lenses
Nott: moves the retinoscope (away = lag)

26
Q

JND calculation

A

Snellen denominator/100

-present lenses +/- one half of JND

27
Q

Stenopaic Slit

A

Reduces entrance pupil perpendicular to slit orientation

  • clearer slit orientation = SRx axis
  • good for determining astigmatism
28
Q

Astigmatic Dial

A

Fog, ask which lines are darkest, add minus cyl until all lines are equal, then add minus sphere til best acuity
-Lowest # on clear meridian x 30 gives Cyl axis

29
Q

Duochrome Test Acuity Threshold

A

RAM-GAP pts only if they are 20/30 or better

-deficiencies in color vision do not affect ability to do test

30
Q

Methods for balancing Accommodation

A

Fogging: fog +2.00 then present -0.25 in succession until clarity b/t eyes switches back and forth
Risley Prism: the one you do
Prism Dissociated Bi-Ocular: best if acuities are different

31
Q

Reasons to use Cycloplegic refraction

A

convergent strabismus
significant eso at near
young adult complaining of HA with no hyperopia

32
Q

How much accommodation can a person use comfortably

A

50%

33
Q

Average Accommodation equation

A

A = 18.5 - 0.3 age

34
Q

Half Amp method equation

A

Determine 1/2 amp then subtract from working distance to find add

35
Q

Magnification effects in aphakic pts

A

M = -F1 / F2

36
Q

Symptoms of Aphakia

A 
Pincushion distortion
Ring scotoma
Convergence demands due to large BO effects
Diplopia
Anisekonia
37
Q

Why does over minusing make images appear smaller?

A

Combo of a minus lens and a plus lens (eye) acts like a Galilean telescope

38
Q

Mohindra/Near retinoscopy

A

Dynamic Ret technique used to determine kids refractive status
-monocular, in the dark at 50 cm, and must subtract 1.25 adjustment factor

39
Q

Anisometropia

A

Difference in refractive errors b/t eye usually > 1.00D

Optics to Memorize (9 decks)

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