Optics Flashcards
Convex lens
Wraps around material with the higher n value. Positive (i.e. converging)
Concave lens
Wraps around material with a lower n value. Negative (i.e. diverging)
When do you get internal reflection
When n2
What happens to power of lens as you move them from the eye
Become more plus
What happens to the power of lenses as you move them closer to the eye
Become more minus
Aperture Stop
Limits the amount of light entering the system
Field stop
Limits the size of an object that can be imaging
Entrance Pupil
Image of the aperture stop formed by lens in front of aperture stop
Exit pupil
Image of the aperture stop formed by lenses behind aperture stop.
Depth of focus
Area on the retina where an image can be clear
Depth of field
Area of an object that can be clear without accommodaiton
What increases DOF
Decreased aperture and decreased focal length.
Field of view
The extend of an object that can be imaged
Lenses and FOV
Minus increase FOV. Plus decrease FOV.
Panto tilt of a minus lens
minus cylinder at 180
Face form tilt of a minus lens
Minus cylinder at 90
Cl always require more…
Plus power
Spectacles always require
More minus power
Properties of indirect
Larger FOV, less magnification, inverted, larger Depth of focus.
Prism with lensometer
Base is wherever the lines are. I.e. line above bullseye means BU
What is the cornea in keratometry
A convex mirror (negative). Measure the size of the reflected image.
How do you get BC from radioscope
The distance between the two clear images.
What do keratometers assume
N=1.3375
Magnification of funds lens
M=-Feye/Flens
High mass impact ANSI
Pointed projectile, 500 g from 50 inches.
High velocity impact
Steel ball, 0.25 inches in diameter, fired at 150 feet per second.
Spherical lenses base curve
Front sphere curve
Minus cylinder lens base curve
Front sphere curve. Back flatter curve is topic base curve. other back curve is cross curve
Base curves for contact lens
typically on back surface
What to do if seg is too low
decrease panto tilt, shrink the bridge, increase vertex distance, move pads down, narrow the pads.
Spherical abberation
Marginal rays bend more than axial rays. Don’t have to consider too much as pupil blocks out. On and off axis.
Coma
On axis only. Magnification is varied by height of incident rays above the axis is varied. Results in a comet shaped patch.
When do we need to worry about spherical aberations
Very high powered lenses. use aspheric lenses.
Radial Astigmatism
Due to rays hitting the lens surface obliquely. A flat object plane gives a warped image plane.
Tschnering Ellicple
How to get rid of radial astimagism. Wollaston is bigger bc so typically use Ostwalt.
Curvature of Field
Warpage of the plane. Due a plane image be formed as a curve.
Point Focal Lens
A lens corrected completely for radial astigmatism.
Perceived form lens
A lens corrected completely for curvature of field.
Pincushion
Plus lens
Barrel
Minus lens
How does power affect CA
Greater power mean more CA.
Slab off
Correct vertical imbalance. Slab off on the more minus lens (BUMM). Makes the lower half have more BU.
Fo every 1D difference in power there will be ____ percent difference in size
1
How much aniseikonic can a person handel
3%
How much residual astigmatism can a patient handel
1.00 D WTR 0.75 D ATR
Ideal edge thickness
Thickness of -3 for promoting lid attachment
How to change edge lift
Change the peripheral cruve
Excessive edge lift
Movement, awareness of edge. 3 and 9 staining
Inadequate edge lift
No movement, no complains, no tear exchange
Pros/cons of center thickness thin
Increased O2 transport, more comfort, more contraption. Con: flexure
The more _____ the center of gravity the better the centration
Posterior
Spherical fit over WTR
Fluorescent will pool in vertical meridian and touch in horizontal.
Spherical fit over ATR
Flurzscene will pool in horizontal and touch in vertical.
Bitoric Ridge Lens
Use when corneal astigmatism is <2.50. Need back to fit and then front to compensate for greater induced astigmatism.
How are most bitorics fit
0.25D flatter than K
The 2 biotic fitting guides
- Saddle fit: Both principle meridians fit by 0.25D flatter 2. Low topic stimulation: On K to 0.25D flatter in the flat corneal meridian and 0.75D-1D flatter than K for the steep meridian. Creates 0.75D WTR for a better fit.
Back Toric CL
Can only use if corneal astigmatism >2.5 and lenticular astigmatism is 1.5Xcorneal
Front surface CL
Use if corneal astigmatism <2.50 but great lenticular.
What do you often have to do with front surface CL
Use periballisting to stop rotation (BD prism in the bottom)
When do you use front surface aspheric CL
When lots of residual or hyperacidity demands
When do you use back surface CL
Use with ATR astigmatism, irregular astigmatism, or borderline corneal astigmatism
Flexure vs. warpage
Flexure on eye. Warpage anytime.
When do you get more flexure
Thinner lenses, more astimagism, thicker, high dk, increase in OZD
Silicone Acrylate vs. floor-silicone acrylate
Fluor is the boss. Silicon has flexure, warpage, and deposits.
Hype ropes Dk material
High Dk for daily and hyper high for extended. (thicker center)
Myopes DK material
low dk for daily and high for extended
When can you fit a patient in a spherical CL
<100 WTR or <0.75 ATR
Prism balasting
BD prism in the bottom of the lens.
Peribalasting
BD prism but only outside of OZ
Dynamic stabilization
Both the superior and inferior are thinned.
Eccentric lenticulation
Inferior and superior front portions of the contact lens outside the OS are removed. Periballasting and dynamic.
Truncation
Lower low contact lens is removed
Rotation left
clockwise
Rotation RIght
Counterclockwise
How are soft contact lenses typically fit with bc
4 D flatter than K
Diameter with soft contact lenses
HVID + 3 mm
High water content in traditntal hydrogel
More permeability
High water content in silicon hydrogel
less silicon so less oxygen permability
Peli robison
Letters the same size with decreasing contrast
Balie Lovie
Same contrast with letter increasing or decreasing in size.
Do neutral density filters affect contrast?
NO. all wavelengths are still transmitted equally. Just less of them.
Blue blockers
have increased contrast and less glare.
