Physiological Optics 1.1 Flashcards
Indirect vs Direct Ophthalmoscope
- FOV
- Image Type
- Magnification
- Depth of focus
Indirect has larger DEPTH OF FOCUS and FOV
Direct has larger MAGNIFICATION
BIO/Indirect image is real and inverted; Direct image is virtual and upright
How to solve for power in a DO
Pt RX + Doc Rx
How does a lensometer work?
Move a target so that light from a standard lens converges at the primary focal point of the test lens so parallel light leaves the device
- measures back vertex power
- target moving away = MINUS lens; towards = PLUS lens
Lensometry Equation
Back Vertex Power = distance target moves / standard lens focal length ^2
-both in meters
Motion seen in hand neutralizaton
Minus Lens: with motion
Plus Lens: against motion
How does a radiuscope work
Forms two clear images- one at the surface of the lens and one at the CENTER of curvature. The distance b/t these two is the base curve/RADIUS of curvature
How does a keratometer work
Provides the radius of curvature of the cornea by measuring the size of the reflected image (K acts as a mirror)
What does a lens clock measure and how can you adjust it’s measurement for different n
Sag
Power = [(goal - 1) / (calibrated - 1)] x False Power
Power in a Hruby lens and image formed
-55D, magnified, upright
Components of a slit lamp
Keplerian telescope eye piece
Inverting prism and objective lens (add) for Keplerian telescope
Galilean telescope for magnification
Equation for magnification through a fundus lens
Creates a telescope so M = - F (eye) / F (lens)
- more power in lens gives less mag and bigger FOV
- Equation indicates minification but overall magnification is seen due to the slit lamp optics
ANSI: Sphere tolerance
- 13D
- if its more than +/- 6.50D then 2% of sph. power
ANSI: Cylinder tolerance
0.13 for < 2.00
0.15 for 2.00 - 4.50
4% of cyl for > 4.50
ANSI: Axis tolerance
14 for 0.25 7 for 0.50 5 for 0.75 3 for 1.50 2 for more than 1.50 (all are for the range below value until next threshold)
ANSI: Prism tolerance
VERTICAL: 0.33 PD for sphere power < 3.375
HORIZONTAL: 0.67 PD for sphere power < 2.75
ANSI: Thickness
0.3mm
ANSI: warpage
1.00D
ANSI: Base Curve
0.75D
ANSI: Impact Resistance
Resists 5/8 in. steel ball dropped from 50 in.
ANSI: Safety Standards for Impact
High Mass: 500g dropped from 50 in.
High Velocity: steel ball 0.25 in. fired at 150 ft/sec.
ANSI: requirements for safety eyewear
Organized by HAZARD type
Minimum coverage: ellipse of 40mm by 33mm on geometric center (34 x 28 for small head with “H” marking)
Markings: manufacturer logo, + (impact rating), Z87-2
Toric lens form
one toric surface and one sphere surface
Equiconcave/Equiconvex
Both sides are equally convex/concave thus providing 1/2 total power of the lens
Label the curves on a typical minus cylinder lens
-What is different in plus cyl
Front is Base curve, on the back is the flatter Toric BC and steeper cross curve
-In a plus cyl lens base curve is the flatter curve on the front with cross curve being the steeper, the curve on the back called the sphere curve
