Optics Flashcards
ATR
S - C x 090
in minus form, axis at 090
Steeper meridian at 180
WTR
S - C x180
in minus form, axis at 180
Steeper meridian at 090
Spherical CL fit over WTR astigmatism
Horizontal dumbbell shape fluorescein pattern
Spherical CL fit over ATR astigmatism
Vertical dumbbell shape fluorescein pattern
Amp Equations
Avg: 18.5 - 0.3(age)
Min: 15 - 0.25(age)
Sheard’s Rule
Exo
Demand should be at least 2x reserve
Prism needed: 2/3(phoria) - 1/3(blur/break pt)
Percival’s Rule
Eso
Bigger break/blur should be at least 2x smaller
Prism needed: 1/3(bigger blur) - 2/3(smaller blur)
Frame PD
FPD = A + DBL
Lens Decentration
Dec = (FPD - PD)/2
Minimum Blank Size
MBS = ED + 2(Dec) + 2mm
Seg Inset
SI = (Dist PD - Near PD)/2
Total Inset
TI = Dec + SI
Frame Adjustments
Move temple toward the problem
Decrease seg height by:
Increasing panto tilt
Decreasing vertex distance
Optimal Refractive Index of AR Coating
nₐᵣ = √nₗₙₛ
Polarizing Lenses limit light from what direction
Limit light reflected horizontally
(Allow only vertical)
Lens Clock
Fₜ = F꜀ [(nₜ-1)/n꜀-1)]
n꜀ usually 1.523
Equivalent Power
Fₑ = F₁ + F₂ - (t/n)F₁F₂
Front Vertex Power
Fₙ = F₁ + F₂/(1-(t/n)F₂)
Back Vertex Power
Fᵥ = F₁/(1-(t/n)F₁) + F₂
Lens Thickness
t꜀ - tₑ = (Fₐr²)/[2(n-1)]
Microscope Magnification
Mag = (Lateral Mag)(Fₒ/4)
Hand Held Magnifier
Mag = dF
Spectacle Magnification
What increases Spec Mag
Increased thickness
Increased BC
Increased F
Increased vertex distance on PLUS lens
Decreased vertex distance on MINUS lens
Decreased n
Power of a Mirror
F = -2n/r
Distance lensometer must be turned to focus lines
x = Pₗ (fₛₜ²)
BC/Keratometry Conversion
K = 337.5/BC
Deviation Angle
θ = θₐ (n-1)
1ᵒ is about 1.75PD
Amount of light reflected at a surface
R = [(n₂ - n₁)/(n₂ + n₁)]²
(Light transmitted = 1 - R)
Do myopes accommodate and converge more with CLs or specs
More with CLs than specs
What does keratometer treat the cornea surface as
Convex mirror
Knapp’s Law
Axial ametropes best corrected with specs
Refractive ametropes best corrected with CL
Night myopia occurs due to
Increased pupil size causing:
Decreased depth of focus
Increased aberrations
Induced/Inaccurate accommodation
BIO vs DO
BIO:
- Inverted
- Reduced magnification
- Bigger field of view
- Greater depth of focus
DO:
- Upright
- Increased magnification
- Smaller field of view
- Increased depth of focus
VA
20/SD
(20/Snellen Denominator)
Measure of high spatial frequency cutoff on contrast sensitivity function
VA to Cycles Per Degree
600/SD
20/20 VA = 30 CPD
1M to VA
1M = 20/50
MAR
MAR = 1/VA
Log MAR Estimation
20/20 = 0 LogMAR
0.1 = 1 line
0.02 = 1 letter
Axis of astigmatism by sharpest clock dial line
Minus cylinder axis = clock hour x 30