Physiological Optics 2 Flashcards by Mary Beth Jones

Gullstrand’s Eye model

-# of surfaces and # of n

6 surfaces (2 cornea, 4 lens)
4 n

How well did you know this?

Not at all

Perfectly

Parameters of a Reduced Eye Model

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

How well did you know this?

Not at all

Perfectly

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

The eye’s center of rotation

How well did you know this?

Not at all

Perfectly

Far Point (Punctum Remotum)

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?

Not at all

Perfectly

Near Point (punctum proximum)

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?

Not at all

Perfectly

Factors contributing to night myopia

increased spherical aberration

low light levels hinder relaxation of accommodation

How well did you know this?

Not at all

Perfectly

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

6: 2%
20: 20%

How well did you know this?

Not at all

Perfectly

Latent Hyperopia

Hyperopia eliminated by accommodation

Shows more hyperopia on objective refraction than subjective refraction

How well did you know this?

Not at all

Perfectly

Manifest Hyperopia

Amount of hyperopia on a subjective refraction

How well did you know this?

Not at all

Perfectly

Absolute Hyperopia

Amount of hyperopia unable to be eliminated by accommodation

How well did you know this?

Not at all

Perfectly

Facultative Hyperopia

Maximum amount of hyperopia that can be eliminated by accommodation

How well did you know this?

Not at all

Perfectly

Trends of Hyperopia

%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?

Not at all

Perfectly

PD readings from pupilometer reduce influence of…

Parallax

How well did you know this?

Not at all

Perfectly

Equally Mixed Astigmatism

Mixed astigmatism where the COLC falls on the retina

How well did you know this?

Not at all

Perfectly

Major Meridian of the Eye

The STEEPEST corneal meridian (one with most plus power)

How well did you know this?

Not at all

Perfectly

Recognition Acuity

Resolution at high frequencies and high contrast

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

Minimum Detectable Acuity

Minimum visible line

usually better than recognition and resolution
tested via veneer acuity

Resolution Acuity

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

Hyperacuity

Sense of directional relationships (are two lines parallel?)

-Higher cortical processing

MAR

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

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

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

ETDRS

Allen Vision Test

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

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

STYCAR, HOTV, LEA

Sheridan- Gardiner is similar but includes near vision

Static Retinoscopy

-motion

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

Dynamic Retinoscopy | -methods

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

JND calculation

Snellen denominator/100 | -present lenses +/- one half of JND

Stenopaic Slit

Reduces entrance pupil perpendicular to slit orientation - clearer slit orientation = SRx axis - good for determining astigmatism

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

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

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

Reasons to use Cycloplegic refraction

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

How much accommodation can a person use comfortably

50%

Average Accommodation equation

A = 18.5 - 0.3 age

Half Amp method equation

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

Magnification effects in aphakic pts

M = -F1 / F2

Symptoms of Aphakia

``` Pincushion distortion Ring scotoma Convergence demands due to large BO effects Diplopia Anisekonia ```

Why does over minusing make images appear smaller?

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

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

Anisometropia

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