Optics Flashcards
Prentice rule
PD=h*D
h (cm)
D diopter of lens power
Vergence
U+V=D
Focal length
1/D=f
D= dist to object in m
Spherical equiv
Sphere+1/2cyl
Transverse mag
Image dist/obj dist
Axial mag
M transvrse^2
Simple magnifier
D/4
D= dioptic pwr of lens
Spectacle lens magnification
Mag=2% per diopter of pwr
Magnification of a telescope
Deyepiece/Dobjective
Refracting power of a spherical surface
D= n’-n/r
Power of a thin lens immersed in fluid
Dair = nIOL-nAIR
——- ————
D aqu. nIOL-nAQU
REFLECTING power of a spherical mirror
Dreflecting= 2/r
r= radius of curvture
SRK formula
A-2.5(axl)-0.9K
In lens prob if image is + and is on other side of lens it is….
Real and inverted
In lens prob if image is - and forms on left side it is…
Virtual and upright
In schematic eye how far is K from nodal point?
5.5mm
In schematic eye how far is nodal point to the fovea?
17mm
In schematic eye, what is the axial length of the eye?
22.5 mm
In schematic eye, whats the diameter of the ON?
1.7 mm
Whats the refractive index of the cornea?
1.37
Whats the refractive index of air
1
Whats the refractive index of aqueous?
n=1.33
How much arc does the 20/20 E subtend?
5 min of arc
What’s the radius of the corneal curvature in meters?
r=0.07m
How many min of arc does a 20/200 letter subtend?
50 min
How tall is a 20/20 letter?
9mm
What does laser stand for?
Light amplification by stimulated emission of radiation
what do you worry about w hyperopic shift?
orbital tumor
focal length?
f=1/D
What kind of mirror is a shaving mirror?
concave
reflecting power of a mirror
Drefl=1/f=2/r
when you use u+d=v and the answer is -, what does that mean in terms of real vs virtual etc
if its negative then its VIRTUAL AND UPRIGHT.
In a lens problem it to the left and in a mirror problem its to the right
how do you fix diplopia in anisometropic glasses?
put a “slab-off” prism on the more minus lens
whats placido disc keratometry?
looks like an ophthalmoscope projects rings onto the K gives a sense of irregular astigmatism
if you see scissoring on retinoscopy whats the dx?
kcn
what are the 5 steps in calculating rigid lens power?
1) chose a BC +0.50 steeper than low K value
2) convert rx to minus cyl form
3) drop the cyl
4) convert to zero vertex distance
5) subtract +0.50 from final value
how do you solve vertex distance questions?
1) understand that the glasses rx is not the refactive error of the eye!
2) find FP from the glasses and add the vertex dist- that’s the true fp of the eye
3) find reciprocal of that dist to find real D error of eye
what’s constructive interference?
two light waves from SAME LIGHT SOURCE are added together (laser?)
whats destructive interference?
two light waves from SAME LIGHT SOURCE cancel each other out
whats coherence?
the ability for two light waves or two parts of the same beam to produce interference (ie to interact w each other)
whats diffraction?
a light wave bends when it encounters an obstruction or apperture
what types of wavelengths diffract most?
long wavelengths
how does violet light behave in terms of refraction and diffraction
short wavelengths are refracted more and diffracted less
what phenomenon causes the sky to be blue?
scattering (blue is scattered, the rest of the wavelengths are diffracted)
whats the refractive index of the cornea?
1.376
a pt will feel comfortable using how much of their accommodative amplitude?
1/2
whats compound myopic astigmatism?
both images fall in vit
whats simple myopic astigmatism?
1 image falls on retina 1 falls on vitreous
whats mixed astigmatism?
one image in vit, one image behind retina
how do you make a CL fit tighter (2 options)
1) decr BC
2) incr diameter
what does angular magnification refer to?
magnification of SIMPLE MAGNIFIERS ie just divide by 4
how do you know what size aciol to put in?
take horizontal white to white and add 1
how can you help anisometropia in glasses without cl? hint: reduce everything
a) reduce central thickness of the lenses
b) reduce vertex distance- bring glasses closer to face
c) reduce the front surface power of the lens
what type of telescope is the operating microscope? kepler or galileo?
kepler (then theres a built in prism that flips the image)
whats the critical angle for total internal reflection of the K?
46 degrees
geometric optics deals w light as a…
ray
quantum opics deals w light as a…
photon
physical optics deals w light as a…
wave
whats the visble light spectrum (what nm to what nm?)
400-700nm
whats infrared spectrum what wavelength?
> 700 (longer than red)
what wavelength is ultraviolet?
<160 (much shorter than violet)
whats interference?
when 2 rays of light are brought togther
whats destructive interference?
when 2 waves brought together and the intensity is minimized
what does coherence mean?
the ability of 2 light rays to make interfernce
in what direction are sunglasses polarized?
vertival slats, so any horizontal waves are blocked (light reflected off water is mostly horizontal)
what type of wavelength diffracts (ability to bend around edges) more?
longer wavelengths (like red) think long stretch Armstrong bending around corner
whats brewsters angle?
the angle at which only 1 part of light that is polarized can be completely transmitted
when/how does scattering occur?
when light hits an irregularity in its path, it scatters
what are K edema, tindall effect and halos real life examples of?
scattering of light
whats the unit of photometry (light in units based on the response of the eye?)
candela
whats luminence?
amount of light emited by a surface measured in APOSTILLBS. real world example is GVF
whats the wavelength of yag and what spectrum is it in?
1064- infrared
whats the wavelength of argon green
514
do convex mirror act like + or - lenses?
minus
do concave mirrors act like + or - lenses?
+
whats the circle of least confusion
it represents the best overall focus of a spherocylindrical lens
what the conoid of sturm?
the complicated geometric envelope of light rays emanating from a spherocylindrical lens. The middle of it is the circle of least confusion
if a Maddox rod is held horizontally in front of you, how do you see the line?
vertical red line
why does nighttime exacerbate myopia?
bc pupil is big, light comes through all parts of cornea and causes spherical aberration (light from the steeply curved part of K gets focused anteriorly in the vitreous)
what test uses chromatic aberration?
duochrome (blue falls in vit, red falls behind retina)
whats the optical axis of the eye?
the line that best approximates light passing thru K, puil, lens and fovea
whats the pupillary axis?
imaginary line passing through K and exact center of pupil
whats the visual axis?
line between target and fovea
how does pupil size affect depth of focus?
smaller pupil gives better depth of focus
what is the diameter of the pinhole?
1.2mm
using a PH sc is only good for what refractive errors?
-5 to +5
how tall is a 20/20 E?
8mm
how is amplitude of accommodation expressed?
in D
how is range of accommodation expressed?
in mm
whats “emmitropization” of the eye?
the phenomenon that as a kid’s eye grows, it doesn’t become hugely myopic! the K actually sheds power so that the eye remains emmetropic
during retinoscopy for astigmatism, how do you know if you found the axis?
the reflex appears narrowest
whats the ideal add segment for hyperopes?
round top- decr image displacement but incr jump
whats the ideal bifocal seg for myopes?
flat top- decr jump and displace
how do you use press-on prisms
in one direction in 1 eye or you can out it the opposite direction in the other eye
whats the best way to correct for prismatic effect of anisometropia?
slab-off prism (aka bicentric grinding)
how do scl change the ability to accomodate
myopes have less ability to accommodate
hyperopes have more ability to accomodate
what type of cornea gets high BC?
flat K
How do you create a looser fit with a scl?
1) make BC flatter (incr BC #)
2) Decr the diameter (less of a suction cup)
3) decr the saggital depth
where do you measure white to white?
across horizontal cornea
how close to accurate does an iol with power <25D have to be?
within 0.4D
whats 2 example of a diffractive multifocal iol and how does it work?
reSTOR and technis multifocal IOL
back surface is like Fresnel prisms
IOL 25-30 diopters how close to accurate does it have to be?
0.5D
IOL >30D how close to accurate does it have to be?
within 1 diopter!!
so if you have a supershort eye youre screwed
whats the Q factor of the human cornea (the difference between central and peripheral K)
-0.26
whats the definition of angle kappa in optics terms?
the difference between the visual axis and the pupillary axis
whats the mag of the eye when using a direct?
15x (60/4)
what part of the slit lamp is made of an astronomical telescope?
the eyepiece (theres a prism that flips the image to upright)
what part of the slitlamp is a Galilean telescope?
the mag fxn (knob or flip thingy)
how does the image of the retina appear with a contact lens (tucker style)
minified upright
whats the diameter of the tonometer?
3.06mm
how does specular microscopy work?
its a reflection of the interface of the endothelium and the aqueous
how does a keratometer work? what does it measure?
it measures REFLECTING power (and infers refracting power)
what does placido disc measure
K topography (steepness only)
whats the A scan measure
TIME it takes for the sound wave to bounce back (looks like series of spikes) can be used to measure EOM thickness in TED
How does the laser inferometer work?
projects 2 light beam through dense cataract to macula, pt tries to discern 2 light beams
whats a brightness acuity tester?
looks like a small GVF dome, tests pt with cataract by glaring them w a dome of light
whats the WHO definition of legally blind
1) BCVA better eye of 20/200
or
2) field in better eye 20 degrees or less
how do blind pple deal w scotomas?
perceptual completion- the brain fills in missing parts of image
a pt with a scotoma is able to utilize an eccentric point of the retina for fixation, whats that called in optics terms?
preferred retinal locus
at what dist and w what chart is Va tested in low vision pple?
10 ft ETDRS chart (has more low vision lines)
how do you determine add for a blind person? (kestenbaum rule)
take the inverse of the Va (ex 400/20 = 20)
what should you incorporate into glasses for super blind pple?
BI prism to bring eyes in
whos not a good candidate for handheld magnifier?
parkinsons, RA,
whats a stand magnifier?
a bulky thing you plop down on top of your newspaper
how should pple w low vision set up lamps in their house?
most illumination with least glare possible
How will a thick lens change the dioptric pwr of a lens?
will reduce the power
how much angular mag will be created if the image is virtual?
none
how do you calculate the K for a post-lasik pt if no historical data- do hard pmma lens refraction?
K= BC + Rcl - Rbare
K= K power
B= BC of hard PMMA ie the K
Rcl- refraction w cl on
Rbare= refraction with CL off
how do you calculate the K for a post-lasik pt if no historical data- do hard pmma lens refraction?
K= BC + power cl+ Rcl - Rbare
K= K power
B= BC of hard PMMA ie the K
Rcl- refraction w cl on
Rbare= refraction with CL off
who inserted the first IOL (in 1949)
Ridley
how can hard CL damage the K?
causes central epithelial edema
what can SCL cause on the k?
micropannus
diffraction sets a limit on visual acuity when the pupil is less than what size?
2.5mm
whats the wetting angle of a cl?
the degree to which water beads on the surface
0.13 meters = how many mm?
130mm
given lens +2, how do you find focal length?
d=1/f therefore f= 1/d
1/2
0.5m
how many decimal points do you move over for meter to centimeter?
2!!!!
how many decimal points do you move over for conversion from meter to millimeter?
3!!!!
if u+v+d if the answer is - then what does the image formed look like, and where does it fall in a lens problem vs a mirror problem?
if the answer is (-) then its virtual and upright!
in a lens question it goes to the left of the lens
in a mirror problem it goes to the right of the mirror
an angle of 20 dgrees corresponds to how many PD?
40
Double the angle (unless its >20)
an angle of 45 degrees corresponds to how many PD?
100
in a pt with 20/100 vision can you use a +/- 0.25 D Jackson cross?
no! too weak
must use a 0.75 or 1D Jackson cross
how do you make a Jackson cross cylinder?
the sph equiv of the rx = 0
if given BC in RGP problem, for every 0.05mm difference between the K reading and the BC you should do what?
0.25D/0.05mm
if flatter add plus
if steeper add minus
each clock hour is how many degrees in astigmatism?
30 degrees
how do you calculate post-op lasik K given pre-op refraction and Ks?
0.8 * starting refraction
then take that number and subtract from the avg starting K
indirect ophthalmoscop works like what type of telescope?
kepler (+20 lens of held lens and +60 lens of eye)
using a direct ophthalmoscope on a +10 hyperope, whats the mag?
acts like +50 mag (less condensing bc hyperopic) is 12.5
what type of telescope is the fundus camera?
kepler (the camera is plus lens and the eye works as the other plus lens)
if pt has a small pupil what things you can change on the indirect?
1) move your eyepieces further apart (decreases the EFFECTIVE pupillary distance)
2) bring triangular mirror closer to YOU
3) increase the distance between you and the pt
when prescribing high + add, what else do you have to give pt in his glasses?
give BI prism if add is >+4
give 2 PD greater than the reading add
ex: giving +8D add you should also give 10PD BI prism in each eye
how can you improve low vision in a pt w homonomous hemianopsia
give them prisms with the base toward the hemianopsia
whats 1/1.5? (multiply top and bottom by 2 = 2/3)
0.66
whats 0.5/1.5 (multiply top and bottom by 2= 1/3)
0.33
how do you calculate the power of piggyback lens?
hyperopia- 1.5*refractive error
myopia- 1*refractive error
whats the most vertical phoria that can be tolerated by anyone?
2 PD
What type of scan is best for measuring choroidal melanoma height?
a scan
whats the term that means the most amount of hyperopia and eye can take wo blurring the image?
manifest hyperopia
whats the term for the minimum hyperopic correction needed to see clearly?
absolute hyperopia
whats the term for cycloplegic hyperopia-manifest hyperopia?
latent hyperopia
whats spatial coherence?
when 2 parts of the same wave can produce interference
whats temporal coherence?
when 1 beam of light produces interference with itself
whats the definition of power in phaco?
the length that the phaco tip can travel relative to overall length
whats cavitation in phaco
when the phaco tip forms bubbles which breaks down lens
whats load in phaco?
the amount of lens in contact w the phaco tip
what 2/3?
0.66
whats 1/5
0.2
whats 1/6
0.16
whats 1/7
0.14
whats 1/8
0.12
whats 1/9
0.11
whats 1/15
0.066
how could you see polarized light?
wear polarized glasses and look at blue background (ie sky)
you give a pt more cyl than hes used to, what can you do to help him adjust?
1) turn axis more toward 90/180
2) decrease vertex distance
3) grid cyl onto back of lenses
4) decrease power of the cyl
how does giving a child w XT myopic glasses help?
makes the eye more hyperopic (image falls behind retina) they have to accommodate/converge/bring eye in
how many D of accommodation do you lose every 4 years?
1D
in HCL questions if given radius of K how to adjust?
for every 0.05mm adjust by 0.25D
which is the best iol formula for long eyes?
srk/t
which is the best iol formula for short eyes?
hofferQ
SPK at 3 and 9 o clock indicates tight fitting XXX cl
RGP
how will a spherical lens focus incoming light rays?
blur circle
amplitude of accommodation is what?
near point (D) - far point (D) IT IS NOT THE NEAR POINT
If you mess up axial length, which types of eyes are more effected?
short eyes
lensmeter works based on what principle?
badal principle
when a lens is submerged in water what happens to power?
becomes less powerful. careful if its half in air vs totally in water
what should be the power of the trifocal portion of glasses?
1/2 the add
