Optics Flashcards
Prentice position
back surface perpendicular to the visual axis; max bending
image jump
image displacement
image displacement more bothersome
Round top only good for hyperopia for displacement
Flat top good for jump and myopia for displacement
energy for different color of light
ROYGBIV (lower to higher)
SAM
FAP
Steep add Minus (if RGP steep than cornea then tear lens is plus lens, then power of RGP need to add more minus)
Flat add Plus
Transverse mag of lens
M=U/V=i/o
MUV in and out
ultrasound move faster in lens or aqueous
lens
? prescribe glasses hyperopia of low level hyperopia and eso myopia astigmatism amblyopia
hyperopia of lower level: no need
the rest: yes
laser
stimulated emission
lens material most common
CR-39
Trevix good optic also shatter-resistant
OCT
base on Michelson interferometer
positive angle kappa
visual axis slight temporal to pupillary axis (fovea slightly temporal)
far point of eye
1/sphere of lens + vertex distance
cold mirror
reflect all visible light but infrared
index of reflection is defined
at 589nm line of sodium light
reduced schematic eye
cornea to nodal point 5.6 mm nodal point to retina 17 mm total length of eye 22.5 mm index of refraction 1.33 total power is 60D
fit soft CL
3 touch method: limbus on each side and cornea apex
lensmaker’s equation
p=(n1-n2)/r
normal AC/A ratio
3:1 to 5:1
excimer laser length
Femtosecond laser
Yag
Rhodopsin
Excimer laser: 193nm; argon-fluoride laser; UV laser; 6.4 eV per photon. (laser need 4 eV to breaker C-C or C-N bond); low tissue penetration; photoablation Femtosecond laser (eg. intralase): 1053nm infrared range; photodisruption Yag: 1064nm; photodisruption Rhodopsin most sensitive to green light 510nm
minimize meridonal mag
- lower the cylinder
- grind cylinder to the back surface
- change axis more closer to 90 or 180 degree
- decrease vertex distance
with-the-rule astigmatism
against-the-rule
WTR: steep at 90 degree/vertical meridian; correcting plus lens placed at 90 degree
ATR: steep 180/horizontal; correcting with plus lens placed at 180/horizontal
correct vertical prism effect of glasses
- slab-off: grind more minus or less plus to create base-up prism over reading area
- reverse slab-off: add base-down to more plus lens
Adjusting to new vertex
D2=D1+S(D1)^2
s=difference in vertex (in meter)
Toric soft CL
adjusting for soft toric CL rotation
LARS (left add, right substract)
error in post-refractive myopia surgery
hyperopic surprise
- radius error
- keratometer index error
- formula error ( 3rd gen Holladay 1, Hoffer Q, SRK/T using A and K to estimate ELP; 4th gen Haigis, Haigis-L do not use K)
index of refraction
cornea 1.376
aqueous 1.336
duochrome test
+0.50D between red and green
RAM-GAP
good for color blind patients
fitting hard CL
0.5D steeper than lower K-reading
Photometer
Radiometer
P measure eye response to light, unit is lumen
R measures energy or power, unit is power
eye more sensitive to yellow light
To make a CL tighter
decrease radius/base curve
increase diameter
20/20 E is ~9 mm
so how much 20/60
9x(60/20)=9x3=~27mm
60 arcmin is 1 degree
20/20 is 5 arc at 20feet
newborn
3D hyperopia, then 1 year old , 1D
then 1st decade eye longer/myopic change, cornea power decrease/hyperopic change, lens power increase/myopic change
