Physiological Optics 2 Flashcards

1
Q

Gullstrand’s Eye model

-# of surfaces and # of n

A
6 surfaces (2 cornea, 4 lens)
4 n
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Factors contributing to night myopia

A

increased spherical aberration

low light levels hinder relaxation of accommodation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

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

A

6: 2%
20: 20%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Latent Hyperopia

A

Hyperopia eliminated by accommodation

Shows more hyperopia on objective refraction than subjective refraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Manifest Hyperopia

A

Amount of hyperopia on a subjective refraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Absolute Hyperopia

A

Amount of hyperopia unable to be eliminated by accommodation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Facultative Hyperopia

A

Maximum amount of hyperopia that can be eliminated by accommodation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

PD readings from pupilometer reduce influence of…

A

Parallax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Equally Mixed Astigmatism

A

Mixed astigmatism where the COLC falls on the retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Major Meridian of the Eye

A

The STEEPEST corneal meridian (one with most plus power)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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?

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
Dynamic Retinoscopy | -methods
Measures accuracy of accommodation (lead/lag) MEM: uses quick presentation of lenses Nott: moves the retinoscope (away = lag)
26
JND calculation
Snellen denominator/100 | -present lenses +/- one half of JND
27
Stenopaic Slit
Reduces entrance pupil perpendicular to slit orientation - clearer slit orientation = SRx axis - good for determining astigmatism
28
Astigmatic Dial
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
Duochrome Test Acuity Threshold
RAM-GAP pts only if they are 20/30 or better | -deficiencies in color vision do not affect ability to do test
30
Methods for balancing Accommodation
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
Reasons to use Cycloplegic refraction
convergent strabismus significant eso at near young adult complaining of HA with no hyperopia
32
How much accommodation can a person use comfortably
50%
33
Average Accommodation equation
A = 18.5 - 0.3 age
34
Half Amp method equation
Determine 1/2 amp then subtract from working distance to find add
35
Magnification effects in aphakic pts
M = -F1 / F2
36
Symptoms of Aphakia
``` Pincushion distortion Ring scotoma Convergence demands due to large BO effects Diplopia Anisekonia ```
37
Why does over minusing make images appear smaller?
Combo of a minus lens and a plus lens (eye) acts like a Galilean telescope
38
Mohindra/Near retinoscopy
Dynamic Ret technique used to determine kids refractive status -monocular, in the dark at 50 cm, and must subtract 1.25 adjustment factor
39
Anisometropia
Difference in refractive errors b/t eye usually > 1.00D