Exam 1 pruned for exam 2 Flashcards
What is the visible spectrum?
380-760 nm
What is the UV spectrum
200-380 nm
Describe ophthalmic crown glass transmission characteristics
10% reflection, not a good UV blocker
Describe CR-39 transmission characteristics
10% reflection, improved UV blocker
Describe polycarbonate transmission characteristics
10% reflection, great UV blocker
What is the reflection equation?
Note that it’s like n2-n1front surface: (1.5-1)back surface (1-1.5)
n for crown glass
1.523
n for Cr-39
1.499
n for polycarbonate
1.586
n for trivex
1.53
n forCrown glassCR-39PolycarbonateTrivex
Crown glass N=1.523CR-39 N=1.499Polycarbonate N=1.586Trivex N=1.53
What is essential for calculating Lambert’s law of absorption?
the trasmittance factor (q)
What is ultimate transmission?
multiplying the seperate transmition of each lens to find ultimate transmission
Opacity equation:
O= 1/Transmission
Ultimate opacity equation:
OOO or (1/T)(1/T)
What is the Abbey for crown glass?
59
What is the Abbey for CR-39?
58
What is the Abbey for polycarbonate?
30
What is the Abbey for Trivex?
43-46
What are the abbey numbers?
Crown glass Abbey 59CR-39 Abbey 58Polycarbonate Abbey 30Trivex Abbey 43-46
What are the specific gravities?
Crown glass specific gravity 2.54CR-39 SG 1.32Polycarbonate SG 1.20Trivex SG 1.11
Crown glass specific gravity
2.54
CR-39 specific gravity:
1.32
Polycarbonate specific gravity:
1.20
Trivex specific gravity
1.11
Optical density equation:
OD = -log(Transmission)
Distracting glare is…
caused by annoying lens reflections. AR can help
Discomfort glare is….
in field of view but does not interfere with resolution
Disability glare is….
causeslower contrast,does interfere with resolution. Central 10 degrees of visual field. Prevent with deeper tints or photochromics
Reflected glare is…
caused by reflected light. AKA blinding glare
polarized lenses removes…. How is the transmission axis ortiented?
specularly reflected horizontally polarized light. the transmissiona axis is at 90 degrees
Brewster’s angle equation
Tan i = n.i is the angle between ray and the normal
What is Malus’ law of polarization?
I0= Icos2θI = initial light intensityI0 = new light intensitytheta = angle between transmission axis of the 2 polarizers
What is “In-mass” photochromics?
spiropyranphotochromics throughout the lens
What is imbibed photocrhomic technology?
spiropyrans are in a surface coating for consistant darkening
What are the steps to get frames into standard alignment?
- Horizontal alignment,2 Vertical alignmnet (4 point touch test)3: Open Temple Alignment (90-95 deg)4: Temple Parallelism (flat surface touch test upsidedown)5: Alignment of the bent-down portion of the temple (rightside up)6: Temple-fold angle
What is invovled in Vertical alighment of frames (step 2)
4 point touch test (lenses and nose are all in same plane), make sure there is no X-ing
___% of lenses are AR coated in the US
30
Neutralization in AR happens when the path difference is an ___ number of half wavelengths
odd
Reinformcementin AR happens when the path difference is an ___ number of half wavelengths
even
The ___ the index of refraction, the greater the glare and reflections
The higher the index of refraction, the greater the glare and reflections
Index of coating equation:
nc= sqrt (nL)nc = index of coating needednL = index of lens
The best AR should have a thickness ___% of the desired wavelength
The best AR should have a thickness 25% of the desired wavelength
What wavelength is generally selected for AR?
want to block 555 nm
How is AR applied to glass?
cleaning, heated in vaccum, AR heated even higher
How is AR applied to plastic?
clean, bake to remove water, 100 deg C heating in vaccum, quartz for outer layer.
how long does AR take to apply?
4 to 10 hours
What is the outermost layer of AR?
hydrophobic coating that also increases hardness to prevent scratching
Most AR coatings are ___ layers
Most AR coatings are 5-6 or as many as 11 layers
How are mirrored coatings accomplished?
constructive interference on front of lens
what are the two types of mirror coatings?
metalic (scratches easily) anddielectric (durable)
What is a mounting? What are the 3 brands?
The “frame” for rimless or semirimless glassesBalgrip/IlfordNumontWils-Edge
Keyhole
A bridge type (the nose is the “key”)
Saddle
bridge type that is curvy on top and bottom, does not protrude
comfort bridge
has ugly nose piece
Semisaddle
Bridge protrudes a little in front and has plastic nose pads
What is a modified saddle?
the semisaddle (has plastic nose piece).
What is the W bridge?
it’s the metal saddle (has no nose pieces)
What are the different endpiece types? 6
American, English, French, butt-type, mitre-type, turn-back
Which hinge type has the “shield” visible from the font?
Riveted hinge
Which hinge has apperatus anchored directly into plastic?
Hidden hinge
What are the different temple styles?
skulllibraryconvertible (either of 1st two depending on how bent)riding bow (curve in plastic)comfort cable (curve in metal)
Which temple is curved in plastic?
riding bow
Which temple is curved in metal?
comfort cable
What are some problems you can have by correcting refractive error of anisometropia?
Magnification differences, vertical imbalance when reading, and horizontal vergence problems
Anisometropia is….
when the Seq of both eyes differ by 1.00 D or more
Anisometropia vs aniseikonia?
Anisometropia :unequal refractive erroraniseikonia: differing retinal image sizes
If a patient’s reading position is 10 mm below optical centers, how much anisometropia can they have before they will have symptomatic vertical imballance?
1.00D of aniso. This means that the person experiences 1 prism D of vertical imballance.
If there is too much vertical imbalance for reading because of anisometropia, what lens technique can fix the vertical imballance?
Slab off removes base down from the most minus lens
What is aniseikonia?
unequal image retinal sizeor unequal shape differences between retinal images
symmetrical vs asymmetrical aniseikonia:
Symmetrical: size change is equal in all directionsAsymmetrical: meridonialimage size is changed in one dimention (not both)or there is disortion (progressive changes in dimmensions)
What is asthenopia?
eyestrain from dissimilar images. eyes feel “funny”, HA, photophobia, nerviousness.occluding an eye relieves these symptoms
1.10 would be ___% magnification, 0.92 would be ___% minification
10% and 8%
What is the total spectical magnification equation?
Shape factor * power factor(1 / (1-[t/n]F1) ) * (1 / (1-hFv)
What is the shape factor equation?
1 / (1- [t/n] F1)
What is the power factor equation?
( 1 / (1-hFv)
What is the equation for changing spec RX into CL RX?
Fs / (1 - dFs)
How does astigmatism affect spec mag? What about in CLs?
each diopter of cyl makes a difference in mag by 1.5% 0.3% for CLs
uncorrected axial myope or hyperope has larger image size?
myope has larger image size
uncorrected refractivemyope or hyperope has larger image size?
neither! it’s about the same
What is Knapp’s Law?
axial ametropic eyes corrected with specswill have similar retinal sizes as an emetropic eye.
According to Knapp’s law, how are axial myopes best treated? Refractive myopes? what does correcting in these ways help avoid?
axial best treated with spectacles (but CLs are ok too, clinically)refractive with CLsthese help avoid Aniseikonia
A high Rx greater than ___D is usually from abnormal axial legnth
+/- 4.00 D
low refractive error (probably less than +/-4.00D) is refractive or axial?
low refractive error is a combination of both refractive and axial!
Image size differences greater than ____% will usually result in loss of binocularity
Image size differences greater than 5% will usually result in loss of binocularity
What is the “rule of thumb” for aniseikonia?
1.00D difference between eyes has 1% image size difference
What is the most popular plastic frames material?
Zyl, or cellulose acetate
Zyl characterisics: hypoallergenic, lightweight, strong, flexible…
hypoallergenic yeslightweight yesstrong noflexible no
What are Zyl advantages/disadvantages?
colors, easily worked, can grow/shrink for sizing errorsBrittle with age, lose luster, heavier than other plastic frames
Propianate characteristics:
hypoallergenic yes very hypoallergeniclightweight yes very hypoallergenicstrong noflexible yes
What are some advantage/disadvantages of Propionate?
less “dulling” food flex, verylightweight and hypoallergenicnot as common a zyl,heat and solventsensitive.lens size has to be exact
Optyl characteristics
Thermoelastichypoallergenic yeslightweight yesstrong yesflexible yes
Optyl advantages/disadvantages
very light, excellent shape retetion, hypo-allergenic, very heat and solvent resistantDifficult adjustments that require heat, will not shrink
Aluminum characteristics
hypoallergenic nolightweight yesstrong yesflexible nocorrosion resistantyes
Aluminum advantages/disadvantages
good to very good resistance, high luster, lightlens often have “gapping”, complicated manufacturing with rivets
Monel characteristics
most widely used, has nickel (and copper, etc)hypoallergenic nolightweight nostrong noflexible highly flexiblecorrosion resistantyes (when plated)
Monel advanteges
Cost-effective and efficient, malleablemedium corrosion resistance unless plated, heavier
Titanium characteristics
hypoallergenic yeslightweight yesstrong yesflexible nocorrosion resistantyes
Titanium pros/cons
very light and hard, hypoallergenicvery expensive, not very flexible
Flexon characteristics, pros/cons
Titanium alloy (Marchon), AKA memory metalhypoallergenic yeslightweight yesstrong yesflexible highly flexible can bend to original shapecorrosion resistantyeshard to adjust, patterns not as available
Beryllium,characteristics, pros/cons
low-cost alternative to titaniumhypoallergenic nolightweight yesstrong yesflexible yes, but springycorrosion resistantyesgood for salty/acidic patients
Stainless steel characteristics, pros/cons
steel chromium alloyhypoallergenic yeslightweight yesstrong yesflexible no, springycorrosion-resistant yes
Which nosepad is hard and nonflexible?
Acetate
Which nosepad is flexible, slippery?
Vinyl
Which nosepad is grippy and sticky?
Silicone
