Test 1 Flashcards
Tinted solid glass absorptive lenses
- introduces _ or _ during manufacturing.
- How are spectral transmission characteristics controlled?
Problems
- Metals or metallic oxides during manufacturing.
- Controlled by the quantities of the metals used.
Transmission is greatly reduced with tint.
Different areas of lens (thick/thin areas) will have varying shades.
Photochromic lenses contain
Darkening rate is dependent onn
Silver halide crystals that darken when exposed to long wavelength UV radiation.
Temperature- cold works better to activate, warmth returns them to clear.
ideal activation: cold temp and high UV. on top of a mountain
Do photochromic glass lenses wear out?
No, but may need to be broken in
Corning photochromic filter (CPF) lenses - glass
RELIEVE GLARE for patients with severe light sensitivity. Filter rout the shorter (blue) wavelengths. Selective! Ex: block all wavelengths under 511 nm
Ex: retinitis pigmentosa. Bad glare issue, albinism, aniridia.
Photochromic compounds used in plastic lenses
Spiropyrans. UV breaks the bond between the spiro carbon and oxygen. The new open compound strongly absorbs light in the visible region. Reverse when the UV source is removed.
Disadvantage to plastic photochromic lenses
May wear out/fatigue over time. Ex; Couple years
Imbibed photochromic plastic lenses
Darkens consistently across the lens, regardless of rx. Available in wide range of material/design.
4 types of glare
Relatively bright light which interferes with optimal vision or produces discomfort
Distracting, discomfort, disability, reflected
Distracting: Annoying. Caused by lens reflections- when you look at someone and you see yourself reflecting off their glasses. Fix with AR.
Discomfort: Sensation of irritation or pain from sources of light in the field of view. Stray light that causes visual discomfort but DOES NOT interfere with resolution.
Fix by changing environment aka get out of sun
Disability: Causes objects to have a lower contrast than they would if there was no glare. INTERFERES with resolution. Background brightness is increased and object brightness decreases.
Ex: turning on lights while watching a movie.
Light sources within the central 10 degree of the visual field contribute to this glare
Reflected: Caused by reflected light sources.
Ex: Glare off a shiny page in a book when holding it at the wrong angle.
Fix with polarized lenses.
methods to reduce surface reflections
Base curve tilt Pantoscopic tilt Smaller frame Change vertex distance AR coating
Low minus Rx has most reflection
What determines the index of refraction for the coating?
ideal index of refraction for coating = square root of index of ref of lens material
Why should coating be made with an optical thickness of 1/4 wavelength
So the wave will be 1/2 wavelength out of phase
The thickness of the AR coating is going to be 0.25 wavelength of whatever wavelength you are processing. If the wavelength of interesting is 500, the thickness of the coating would be a quarter thickens of that, so 125nm thick
For an AR coating to work properly, we have to satisfy two conditions
Amplitude condition and path control
What is typically used as an AR for glass lenses
magnesium fluoride
3 properties of AR that would be important to the patient
Hydrophobic
Olephobic
Anti-particulate
Production sequence of glass lenses
Clean lens
Heat in vacuum
Add magnesium fluoride
Production sequence of plastic lenses
Clean Baked to remove H20 Heat in vacuum Add AR Sodium dioxide used on outer layer
How many layers is a typical AR coating
5-6 layers
Brewsters angle formula
Tan(angle of incidence) = index of medium to which the light is incident
Tan(i) = n’
Malus’ law
Light passing through 2 polarizer series= light leaving first polarizer (cos)^2 theta axis between the polarizers
Endpiece examples
Two outer areas of the frame from to the extreme left an right where temples attach.
American English French Butt type Mitre-type Turn back
Two types of hinges
Part of the frame that holds the temple to the front and allows the temple to be closed.
Riverted- rivets (apparatus anchored into plastic) attaching to shield plate that is visible from the frame front.
Hidden- Apparatus anchored directly into plastic
Shield NOT visible from frame front.
Types of temples
Skull- most common Library- straight. do not bend Covertible- can be skull or library Riding bow- plastic shank. Curve around ear lobe. Children, athletic, industry safe Cable temples- metal
The frame shape should ___ with the face shape
Contrast. Rounder faces look best with angles
Angular faces look best with curvey frames
Low line temples for a ____ face
High line temples for a ___ face
Low line for long face
High line for short face
The goal/ideal face shape
To make peoples face look oval
How to fit for a long face
Deep frame with low temple attachment
Low riding bridge to shorten nose
Broad frame
What does low riding bridge do?
Shortens nose
How to fit round wide face
Angular frame
Narrow frames, wider than they are deep.
Temples attach high on face
How to fit a square face
Round frame
Narrow, wider than they are deep to lengthen face.
Temples attach high on frame to add length.
What does these do to the length of faces
Dark frame
Light frame
Gradient color
Dark- shorten
Light and gradient length
Primary and secondary elements when determining coloring
Prime: Skin color
Secondary: Eyes and hair
Triangular base up face
Wider frame at bottom to eve out
Triangle base down face
Wider frame at top
Diamond shape frame style
Rimless or oval
When to recommend a low bridge design? Such as a saddle bridge
Someone with a long nose to shorten
When to recommend a high bridge design such as a key hold
For shorter noses to lengthen.
Dark bridge
Draws attention to center. Recommend with wide eye
Clear bridge
Recommended with narrow eyes.
considerations for high minus frame selection
Small frame Small eye wire Minimal decentration Rounded corners High index lenses Polished/rolled edges Flatter or hidden bevels
Considerations for high plus frame selection
Rounded corners AR high index Make sure frame fits pt well- sturdy Cable or securely fitting temples, with adjustable nose pads
Malus= (100%)(Cos^2 alpha)
brewster tan angle= index
PALs benefit from
Minimal vertex distance
Adequate pantoscopic tilt
Sufficient vertical depth especially nasally
Lateral pressure
Pressure of the temples against the sides of the head just above the ears
Fitting triangle
Spectacles should only contact 3 pressure points on the head
Crest above nose
Above top of left and right ear
Steps in frame adjustment
This is after the 6 steps of standard alignment
- Temple spread
- Equality of the lens vertex distance
- Pantoscoptic tilt
- Frame straightness
- Nose pad adjustments
- Temple position and bend
- lateral pressure
- Earpiece curl
Some very pretentious sluts need to learn empathy
Usual pantoscopic tilt
4-18 degrees from vertical
Rims should not touch eyebrows or cheeks
Do this before adjusting nosepads
as the temple wraps down behind ear, should their be friction or pressure?
Friction only
Pressure at tip of ear
No pressure from butt end of temple to ear
