Physiological Optics 2 Flashcards
Gullstrand’s Eye model
-# of surfaces and # of n
6 surfaces (2 cornea, 4 lens) 4 n
Parameters of a Reduced Eye Model
n = 1.33 Total Power = +60.00D Axial Length (K to post. focal pt) = 22.22mm
The center of curvature of the far point sphere of the eye is the same as…
The eye’s center of rotation
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)
Near Point (punctum proximum)
The point in space that forms a point image on the retina when the eye is using maximum accommodation
Factors contributing to night myopia
increased spherical aberration
low light levels hinder relaxation of accommodation
% of people with myopia of at lease -0.50D at age 6 and 20
6: 2%
20: 20%
Latent Hyperopia
Hyperopia eliminated by accommodation
Shows more hyperopia on objective refraction than subjective refraction
Manifest Hyperopia
Amount of hyperopia on a subjective refraction
Absolute Hyperopia
Amount of hyperopia unable to be eliminated by accommodation
Facultative Hyperopia
Maximum amount of hyperopia that can be eliminated by accommodation
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
PD readings from pupilometer reduce influence of…
Parallax
Equally Mixed Astigmatism
Mixed astigmatism where the COLC falls on the retina
Major Meridian of the Eye
The STEEPEST corneal meridian (one with most plus power)
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