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NAO Course II
Corpuscular theory of light - Answer-light consists of tiny particles of corpuscles, emitted by light source and absorbed by the eye- Newton Electromagnetic wave theory - Answer-light travels in a series of waves moving outward from light source- James Clark Maxwell Frequency - Answer-the number of wavelengths that pass by a point each second Beam - Answer-group of pencils all pointing on light source Pencil - Answer-group of ray emanating from light source Visible Light Spectrum Wavelength range - Answer-400nm-700nm dispersion - Answer-separation of various colored light UV-C - Answer-200-290nm; absorbed by ozone
UV-B - Answer-290-320nm, absorbed by tear film, cornea, conjunctiva, portions of UV-B that reaches lens can be cause of cataracts UV-A - Answer-320-380nm, transmitted by cornea and partly absorbed by lens, ocular hazard HEV - Answer-High Energy Visible Light; blue light 380-460nm, factor to age related macular degeneration Critical Angle - Answer-the angle of incidence that produces an angle of refraction of 90 degrees How to find Critical angle - Answer-Sin(i)= N(2)/N(1) Sine of angle of incidence equals index of refraction of 2nd medium divided by index of refraction of 1st medium Internal Reflection - Answer-when light travels from a medium of greater index to a medium of lesser index, it is refracted away from the normal destructive wavelength - Answer-2 waves moving in same direction but crest are opposite or out of phase; they cancel each other out- no reflection (out of phase) Constructive wavelength - Answer-waves moving in same direction and crest are at the same place and time (in phase)- reflection occurs Index of refraction - Answer-a measure of the amount a ray of light bends when it passes from one medium to another n= (speed of light in air)/(speed of light in medium) where "n" is index of refraction higher index of refraction - Answer-the more it bends light and slower the speed
light traveling from one medium to another, direction of travel is perpendicular or normal to interface - Answer-it will change speed but NOT direction Light travels from a less dense material to a denser material @ and angle to normal - Answer-it will bend toward the normal light travels from denser material to less dense material @ angle to the normal - Answer-it will bend away from the normal absorbtion - Answer-when ray of light enters lens some light will not completely travel through lens specular reflection - Answer-forming of a clear image when light strikes a surface diffuse reflection - Answer-reflection of light from a rough surface, does not produce clear image sides of prism material are NOT parallels to each other - Answer-ray emerges traveling in different direction than original path. it is deviated Sides of prism material are parallels to each other - Answer-ray emerges traveling in same direction as original path. it is displaced but not deviated light strikes a prism and is deviated toward base - Answer-image is displaced toward apex characteristics of Convex/ plus lenses - Answer-2 prisms base to base; rays are converged, real image magnified, power weakens as vortex shortens. Against motion
characteristics of concave/ minus lens - Answer-2 prisms placed apex to apex. diverge light rays, virtual image minified, power strengths as vertex distance shortens. With motion image will move in same direction characteristic of sphero-cylinder/ compound lens - Answer-combine spherical front w/ a toric or cylinder back surface. 90 degrees apart Optical center of lens - Answer-singular point which light may pass through w/o being deviated , point of no prism Greater the angle of apex of a prism - Answer-the thicker the prism and the greater the power stronger the prism - Answer-more it will bend light, shorter the focal length what visible light wave have the longest wavelength, travels the fastest and bends least - Answer-RED focal power - Answer-total power of a lens to bend light focal length - Answer-distance at which the lens brings light to a focus Positive focal length - Answer-in plus lens light brought to focus behind lens, image is real Virtual Focal length - Answer-with minus lens focal point is in front of lens, image is virtual Focal length Equation - Answer-f=1/D, where f is focal length in meters and D is dioptric power of lens Lens power equation - Answer-D=1/f D is dioptric power f is focal length
convert 1 meter to: decimeters cm mm - Answer-10 decimeters 100cm 1000mm higher the index of refraction.. - Answer-the more the material will bend light rays Index of refraction for: Crown Glass CR- Polycarbonate Trivex Hard Resin 1.67 - Answer-glass-1. CR-39-1. Poly-1. Tri-1. Hard Resin 1. Abbe number - Answer-tells us how much chromatic aberration a lens will produce Abbe Value - Answer-the reciprocal of the dispersive power of the lens ranges 20-
higher the Abbe #... - Answer-the less chromatic dispersion occurs Abbe Value for: Crown Glass CR- Polycarbonate Trivex Hard Resin 1.67 - Answer-Crown Glass- CR-39- POly-29- Trivex-43- Hard Resin 1.67- Specific Gravity - Answer-a measurement of physical density not optical characteristic, higher the value the heavier the lens will be High Velocity Impact Test - Answer-1/4 inch round pellet fired @ 150ft/ second, required for some safety glasses, 2.0mm lens thickness-AR coating can reduce impact resistance High Mass Impact Test - Answer-A pointed, conical - tipped projectile weighing 500g is dropped from 50.0 inches through onto glasses. No thickness requirement CR-39 - Answer-pros- light weight, good optical properties, tints well Cons- thickest material and scratches easily Crown Glass - Answer-Pros- optical clarity, resistance to scratches, least susceptible to chemicals Cons-heaviest material, less impact resistance
Polycarbonate Frames - Answer-pros- close to unbreakable, light weight, uv light absorption cons- adj is difficult to achieve, east to scratch Kevlar - Answer-pros-great safety product, unaffected by temp. swings cons- adj is difficult, limited colors, alterations to bridge are difficult Aluminum - Answer-pros- light weight low density, good resistance to corrosion cons-durability of color is poor, fitting is limited Nickel - Answer-pros- works well in nose pads, readily shaped, good strength, resists corrosion Cons-high cost Titanium - Answer-Pros- great strength, flexibility and light weight, resists corrosion, easy adj Cons-higher cost Trilliam - Answer-combo of Nickle copper and tin, flexible and strong but adj is hard Segmented/lined multifocal - Answer-image jump, ledge that may reflect lights into eyes, line is in pts. view Trifocal - Answer-credited by John Isaac Hawkins, first fused straight-top trifocal development by Hancock in 1936 Hard Design - Answer-wider distance and near zones, shorter and narrower progressive corridors, higher levels of astigmatic error
Softer Design - Answer-narrower distance and near zones, longer wider progressive corridors, lower levels of astigmatic error Varilux - Answer-first progressive lens, designed by Bernard Maitrenaz, produced by Essilor in 1959 No surface astigmatism Varilux II - Answer-1972 in both glass and plastic, completely aspheric, soft lens design, Ultravue - Answer-1975 by American Optical, large wide distance zone, high levels of surface astigmatism Ray Tracing - Answer-determine how an object will image on the retina after passing through a lens and eye The boxing system - Answer-standardized method of determining frame and lens measurements Effective Diameter - Answer-(ED) twice the length of the longest radius of the lens C-size - Answer-measurement of circumference of lens Datum Line - Answer-180 line, reference point for measurements Distance PD - Answer-distance between pupillary centers when pt. is fixating @ distance or about 40cm/ 16 inches when using a ruler Near PD - Answer-distance between pupillary centers when pt. is fixating @ a near 12-18 inches
when using a pupilometer the cross hairline is adj. to - Answer-corneal reflex Why is plastic a popular material for spectacle frames? - Answer-It can be easily molded and shaped which plastic frame will shrink if overheated? - Answer-polyamide What material adjustments the most difficult to achieve due to its tendency to relax? - Answer-Kevlar Which material recommends cold snap lens insertions? - Answer-Polyamide what style of frames are not frames at all but rather mountings? - Answer-zyl rims what is the difference between regular and fulvue rimless mountings? - Answer-temporal points of attachment are in a higher horizontal plane with fulvue mountings What style temple would be recommended for a ten year old boy? - Answer-riding bow what is a good general use style of a temple that distributes weight over a large area? - Answer-library If a temple was marked 4 3/4-6, what is its overall length? - Answer-6inches which type of temple curves around the ear following the crotch of the ear where ear and head meet extending to the level of the earlobe? - Answer-riding bow which frame material can be made thin and lightweight with frame colors that are primarily opaque? some problems may be encountered with breakage in cold weather. - Answer-optly
a patients bridge supports 50% of the weight of the frame, true or false? - Answer-false what is the name of the bridge that was originally made popular in the late 1800s and is being brought back in several new retro styles? - Answer-metal saddle bridge whena ray of light travels from a denser medium to a less dense medium, r is greater than i and d is negative. T or F? - Answer-false when a ray of light travels from a less dense medium to a denser medium, r is less than i and d is positive. T or F? - Answer-true a ray of light is deviated by -10 degrees from its path when it passes from one material into another. if it was originally traveling at an angle of 29 degrees to the normal, it is ... - Answer-exiting the denser material what is the name of the instruments used to check to see if a glass lens has been heat treated? - Answer-colmascope and polariscope crown glass, CR-39 with transitions, polycarbonate and clear CR-39. List from most uv protection to least Uv protection - Answer-polycarbonate, CR-39 with transistions, clear CR-39, crown glass what do you look for when you are trying to determine which lens material would be the thinnest? - Answer-highest index of refraction how are glass lenses hardened? - Answer-heat treatment since fabricating laboratory take full responsibility for the accuracy of safety and sports eyewear, verification of lens thickness by the dispenser is unnecessary. T or F? - Answer-False
which glass bifocal lens desogn was the first to use a fusing process? - Answer-The kryptok when was the first trifocal lens developed? - Answer- what is the furthest and closest a person will be able to see if he is looking through a plano distance add multifocal and has a 4.00D of accommodative amplitude? - Answer-40cm to 15.4cm the blended region between the distance and near zones of a progressive addition lens is known as the ... zone. - Answer-intermediate when a lens has its surface astigmatism concentrated into smaller areas of the lens, it is classified as..... design. - Answer-hard which progressive lens design classification do most manufactures use? - Answer-a combination of hard and soft how did the original varilux lens use aspheric power? - Answer-it used all its progressive power in 12mm How did the Varilux II lens use aspheric power? - Answer-The lens was completely progressive from top to bottom what is the advantage of a short corridor progressive design? - Answer-it allows the use of shallow B measurement frames what is the best method for assessing the potential success of a progressive addition lens? - Answer- wearer trials
all early progressive addition lenses were designed for...? - Answer-general use What is the name of the software files used by the direct to surface (free form) generators? - Answer- Point files what is the first step in fitting the progressive addition lenses? - Answer-sit across from pt. at the same eye level Monel Metal - Answer-alloy made cooper, zinc, iron and manganese. Cost effective, good resistance, adj will hold What color would be perceived at 550 millimicron? - Answer-Green. Millimicron=nanometer Digression - Answer-lenses for people with increased need for near and intermediate vision What company introduced CR-39 lenses? - Answer-PPG Company what is a synonym for Nickel Silver? - Answer-German Silver What is birefringence? - Answer-double refraction, is the decomposition of a ray of light into two rays when it passes through certain materials corrected curve theory - Answer-best form lenses by matching certain RX's with Base Curve what is the area between focal points on the retina that assumes conoid shape? - Answer-Sturm positive-of-wear lenses - Answer-contacts
