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116 Cards in this Set
- Front
- Back
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What points should be noted when writing an order for the optical lab? |
1) write legibly (best is ballpoint pen) 2) lens powers should be written in minus cylinder 3) all lens powers should be written with 2 digits after the decimal and MUST include either the + or - sign 4) an order with prism must specify amount in prism diopters and the base direction 5) both distance and near PD's must be included for MF lenses (PALs require only split monocular distance PD) or distance PD and seg inset on some orders (seg inset = distance PD-nearPD) 6) for MF, must include seg type and height and add power 7) material (with tints/coatings) 8) special impact resistance, if needed 9) frame name and manufacturer |
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lensometer/focimeter |
-instrument to measure the power of glasses -measures sphere power, cylinder poewr, and cylinder axis, and amount of prism and its orientation, location of prism reference point, and powers of MF adds |
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trade names used for lensometers |
-lensometer; American Optical Corp. -lensmeter; Marco Ophthalmic Inc., Topcon America Corp -vertometer; Reichert Ophthalmic Instruments -lens analyzer; Humphrey Instruments |
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lensometer focus and calibration check |
1) turn on; pilot light indicates power 2) focus eye piece; don't turn past the point at which sharp focus is first obtained 3) check power calibration |
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sphere lines |
the closely spaced set of target lines |
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cylinder lines |
the widely spaced set of target lines |
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Measuring distance power of single-vision lenses and multifocal lenses |
1) position glasses on lens stop; concave/back side on the stop; move lens table up/down to center lens; lower lens holder gently 2) attempt to focus target; if both sets of lines focus at the same time, it's a spherical lens, if not, it's a spherocylindrical lens 3) when lens is a sphere, the power of the lens is the power wheel reading when both sets of lines are in focus 4) spherocylinder: if lines appear broken, rotate axis until unbroken; sphere power = where reading stands at clear unbroken lines; rotate wheel into the minus until the cylinder lines focus, difference of sphere to reading = cylinder |
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Measuring bifocal add powers |
-a bifocal lense has 2 areas of different power; major/upper for distance, and lower segment for near 1) turn glasses areound so convex/front side is touching the lens stop with the distance portion lined up 2) focus one set of target lines (the more vertical set), mark the reading 3) move lens up so bifocal seg is in front of the stop; turn power wheel toward plus until same, more vertical lines focus, note the power wheel reading 4) the bifocal add power is the difference between the two readings |
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Recomended procedure for verifying lens centration and prism |
-check original order form -mount right lens in lensometer until target lines are positioned on the reticle -use lensometer ink marking system to dot the lenses (center pin will be centered on the lens stop and lens holder), middle dot represents the PRP -repeat for the left lens -measure the center dots, if the lab has made the glasses correctly, the distance should be the patients PD -measure PRP distance per boxing system |
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the boxing system |
-adopted in 1962 -used for specifying the sizes of most spectacle lenses and frames made today -all boxing system measurements are made to the tops of the lens bevel (the bevel apex) or to the tips of the groove on the inside of the frame eyewire -"A dimension" = frame eyesize = largest horizontal distance between the two vertical tangents -"B dimension" = largest vertical dimension between the two horizontal tangents -bridge size = DBL (distance between lenses) |
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verification of spectacle lenses |
-power (both distance and near) -prism and lens centration |
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measuring trifocal add, and intermediate powers |
-a trifocal lens has three areas of different power (diatance, near, and intermediate) -intermediate power is measured the same way the near power is measured, but it is written as a percentage of the near add power (typically 50%) |
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measuring aphakic (cataract lenses) |
-measured the same way you would measure single-vision -all power measurements made through the distance portion should be made with the targets as close to the center of the reticle as possible |
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auxiliary prism |
-because of prismatic effects in aphakic lenses, sometimes it's very difficult, if not, impossible to see the target lines in a lensometer; when this occurs, the target must be moved back into view using auxiliary prism -2 types: loose suxiliary prism and Risley prism |
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power measurement with automatic lensometers |
-measures the power of a lens at the touch of a button, with no need to focus a target -tinted lenses may cause measurement difficulties |
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measuring prism |
-usually only one point on a lens will have no prism (optical center) *patients PD must be taken into account* -measured using the lensometer reticle (back surface against the lens stop) -reticle rings measure the amount deflection in units of prism diopters and the direction of deflection shows the base direction |
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PRP/MRP |
-prism reference point/major reference point -is centered laterally on the patients pupil -optical center is usually the same as the PRP |
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level PRP |
-is the vertical distance from the lowest part of the lens bevel at the bottom of the lens to the PRP position -usually 3-5 mm below the pupil center |
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verifying vertical lens position or vertical prism |
1) determine which lens has the most power in the vertical meridian 2) place that lens on the lens stop 3) center the target on the reticle 4) move other lens in front of the lens stop (don't move the table to center the lens) 5) focus the target lines and eliminate any horizontal prism by moving the lens sideways; any remaining vertical target deflection is the amount of vertical prism -the amount equaled should be the amount ordered -vertical prism in one direction for one lens is equal to vertical prism in the opposite direction for the other |
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power measurement routine |
1) measure power of right lens 2)determine if there is prosm, measure appropriately and use ink-marking system 3) repeat steps 1 & 2 for left lens 4) measure separation of PRP dots 5) measure add power 6) verify measurements match the order form |
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distinguishing glass lenses vs. plastic lenses |
-tapping: glass has a "sharp" sound, plastic has a "dull" sound -touch to cheek: plastic lenses feel warmer than glass -polariscope: plastic may show characteristic stress patterns -dropping gently: glass has a "ringing" sound, plastic is a dull "click" |
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how to distinguish glass multifocal lens vs. plastic multifocal lens |
-plastic "D" or flat-top has a ledge at the top of the sement, glass has no ledge -plastic round 22 forms a small bump on the front of the lens, glass has no bump -both glass and plastic executive-style will have a ledge -neither glass or plastics PALs will have a ledge |
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What design type are most lenses? |
meniscus design |
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meniscus lenses |
-front surface is plus power, back surface is minus power -the sum should be equal to the total power of the lens |
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back surface toric |
minus cylinder lens |
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the base curve of a single-vision lens is: |
the front surface power as measured with a lens clock |
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the base curve of a multifocal lens is: |
the power of the front surface in the upper distance portion as measured with a lens clock |
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lens clock |
-used to measure surface powers and base curve of a lens -pegs are placed gently and perpendicular to the surface -black (plus scale) for front, red (mius scale) for back surface -measurements should be made to the nearest 1/8 (.12) D -must be rotated to determine the powers of a toric surface; in the two principal meridians minimum and maximum values are at the meridians |
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lens clock calibration |
-good calibration surface is a plate glass window -lens clock should read zero with pegs on a window -if lens clock is out of calibration, lens surface power readings must be corrected by the error |
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lens warpage |
-can't be measured with lensmeter -can cause difficulty adapting to new lenses
i.e. front surface has 2 different curves as well as the back surface; probably was placed in too small a frame, and the pressure caused the lenses to warp |
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center thickness |
-the thickness at a lenses optical center/PRP -must be measured at a number of points -industrial eyewear minimum = 3.0 mm -polycarbonate lens minimum = 2.2 mm -minus lens minimum = 3.0 mm -plus lens minimum = 3.0 mm (edge thickness) -high-plus lens minimum = 2.5 mm (edge thickness) |
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thickness caliper |
-must be calibrated first -tops of jaws touching, dial should be at zero -lens places between jaws and GENTLY released, do not drag across the surface |
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dial-thickness gauge |
-calibration must be checked before use -two rounded ends touching; dial should be at zero, if not, error can be corrected by loosening the small knob -read by placing lens gently between the jaws (top jaw is raised and lowered using the arm at the top of the gauge) -measure to the nearest 0.1 mm |
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lens tempering |
all glass lenses are treated/tempered by the optical laboratory |
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heat tempering |
the lens is heated almost to its melting point, then rapidly cooled |
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chemical tempering |
-more commonly used than heat tempering -lens is immersed in a molten potassium salt solution, usually for 16 hours |
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polariscope/colmascope |
-used to verify if a glass lens has been tempered (very difficult) -consists of a light source and 2 polarizing filters with their axes of polarization 90 degrees apart -heat tempered = light/dark pattern surrounded by da dark band -chemically or untempered = uniformly dark -plastic lens under stress - light/dark pattern |
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verifying tint and tint transmittance |
-match color against demonstration lenses -tint transmittance is normally correct when tint is correct |
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verifying antireflective coatings |
light reflected from the lens surface will be colored, most commonly reddish or greenish |
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How is UV radiation associated with cataracts? |
long-term, chronic exposure, especially to UV-B radiation, between 290 & 315 nm is associated with developing cataracts |
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How is UV radiation associated with retinal damage? |
chronic exposure to solar UV-A radiation; 315-380 nm |
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UV protection |
-polycarbonate and high-index plastics absorb all UV radiation below 380 nm -CR-39 treated with a UV-protective dye absorbs all UV radiation below 400 nm -CR-39 plastic lens tints absorb all UV below about 360 nm and most between 360-400 nm |
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Spexan Spectrometer |
-more accurate; more expensive -is an attachment for the Humphrey Lens Analyzer -provides a graph of both the UV and visible transmittance of a lens, along with UV-A, UV-B, and visible light transmittance values |
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verifying segment type of a multifocal lens |
can be verified by either comparison with known samples, or by reference to manufacturers' literature |
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verifying segment height and width of a multifocal lens |
-bifocal segment height is the distance from the bottom of the boxing system box surrounding a lens (lowest part of the lens bevel), to the top of the segment -trifocal height is bottom of box to top of the intermediate segment -bifocal/trifocal width is widest horizontal dimension (impossible to measure width of executive style, or if segment has been removed during the edging process) -trifocal intermediate width is the vertical height of the intermediate portion |
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standard terminology for specifying D-shaped trifocal size: |
-7/25, 7/28, and 8/35 -number on the left is the vertical intermediate width in mm -number on the right is the maximum horizontal segment width |
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verifying segment alignment of a multifocal lens |
-top edges that have flat tops must be level with the horizontal (use a PD rule across both lenses); if segment edges cannot be aligned, one or both lenses is either rotated in the eyewire, or improperly made -turn lens in eyewire using lens-twisting pliers; if rotation creates an error in the sylinder axis or distorts frame shape, the lens will need to be remade |
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near PD |
-for a patient to view through centers of the MF segment at near, the segment optical centers must be separated by the patients near PD -best verified by distance from the temporal edge of one to the nasal edge of the other (should match near PD -the2 segments should also be equidistant from the nasal sides of the eyewire |
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near PD for executive-style bifocal |
1) hold glasses so ledges are viewed from below; mark each lens with felt-tipped pen at the position where the ledge is thinnest, near PD is the distance between marks as measured with a PD rule 2) straight edge/line viewed through the lens; find the point where the line viewed through distance portin and near portion are aligned; mark each point on lens with felt-tipped pen; measurement with the PD rule should match the near PD |
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bevels |
when a lens blank is edged to the proper shape and size to fit into a spectacle frame, the lens edge can be finished in any ont of a number of different shapes; termed bevels |
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standard bevel/V bevel |
-used for most low power lenses to fit into plastic and metal frames -the two surfaces come together at an angle of about 115 degrees |
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safety bevel/pin bevel |
sharp corners of a standard bevel, at about 115 degree angle, are removed with a safety/pin bevel |
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hide-a-bevel |
used with high minus powers to decrease the visibility of reflections from the lens bevel |
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bevel apex |
-distance of bevel apex from the lens may be specified -postitioning bevel apex forward on the bevel edge can hige the thick edge of a high minus lens in a frme so that the edge is more cosmetically appealing |
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rimless bevel |
-used for lenses to be mounted in some rimless and semi-rimless frames -this bevel is normally roughened so it has a whitish appearance, but can be polished to a smooth finish |
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roll-and-polish |
rounds sharp edges of a bevel |
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nylon syspension grooved bevel |
-used for lenses that held in a frame by nylon line -a groove is cut entirely around the edge of a rimless bevel, and the nylon line fits into the groove |
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optical quality |
-condition of the lens surfaces and the optical quality of the lenses should be examines -surface defects are best found by examining the lens under bright lighting with lens in front of a dark background -lens optical quality-high-contract, well-lit grid pattern (venetian blinds/grating over a light fixture) makes a good test target area of localized waviness or distortion which is cause for rejection |
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moderate-power aspheric lens designs |
-used for high plus power aphakic lenses (aspheric front surface; front surface steepens/flttens toward the edge, back surface is spherical or toric) -often fit using split PD and level PRP measurements (optical center heights) -always be sure to verify measurements |
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lenticular lenses (high-power lenses) |
-a lenticular lens has a central area of useful optics, the bowl, where all power measurements should be made; this area is surrounded by a carrier, an area of the lens that has no optical function -a plus lenticular lens looks like a fried egg (yolk is the bowl, egg white is the carrier) sometimes worn by aphakes -minus lenticular lens appears to have its very thick outer edge removed -myodisc lens has a front surface that is plano and lenticular area on lens back surface that is flat |
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verification of blended bifocals |
-are one piece glass or plastic bifocals -junction between the distance and near portions are smoothed and polished/blended to make the segment difficult to see -identified because blended zone is visible as a ring of distortion or poor optics surrounding the segment (when held in front of a patterned surface) -sement height measured to the point at which the distortion of the pattern ends at the top of the bifocal |
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verification of progressive addition lenses |
-holding lens up to bright light, add power is etched into the lens -distance is measured at top circle -near power at the bottom circle -prism - center small dot on lens stop, amount of vertical or horizontal deflection from reticle center=prism -use fitting cross to verify lens position in the frame (in front of patients pupil) -center of frame bridge=split PD; veritcal distance from lower part of bevel to center of cross=fitting height |
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fitting height |
distance from bottom of frame box to the center of the pupil |
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American National Standards Institute (ANSI) |
-standards used for lens manufacturing; ANSI Z80.1-2005 - American National Standard for Ophthalmic Lenses - Recommendations -every component should be correct within the error tolerance determined from the ANSI standards |
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Which 2 standard testing for lenses are required by the goverment? |
-the drop-ball test for dress lenses -industrial eyewear standard |
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frame book |
compilations of manufacturers' literature on spectacle frames that contain information on available sizes, and colors of almost all frames made |
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verification of spectacle frames |
-3 dimensions to verify: eye size, bridge size, and temple length (A + DBL = frame PD) -measuring A dimension - PD rule horizontally with 0 mark at temporal-most extent of the lens bevel, distance to nasal-most extent is A dimension -temple length measured from temple hinge barrels to end of temple in either mm or inches -color should be compared to the order form -verify frame shape against information in the frame book -verify temple type -verify bridge type |
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standard alignment |
-a beginning point for frame adjustments -both lenses will be in the same plane -frame will have small amount of pantascopic tilt -temples will be parallel and will extend back from frame front at a 90 degree angle |
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Tolerance on Direction of Cylinder Axis |
> 0.00 D,≤0.25 D ±14° > 0.25 D,≤0.50 D ±7° > 0.50 D,≤0.75 D ±5° > 0.75 D,≤1.50 D ±3° > 1.50 D ±2° |
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Tolerance on Cylinder Power |
≥0.00 D, ≤ 2.00 D ±0.13 D > 2.00 D,≤4.50 D ±0.15 D > 4.50 D ±4% |
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Tolerance on Unwanted Horizontal Prism |
≥0.00 D, ±2.75 D ±0.67 ▲ Total > ±2.75 D ±2.5 mm Total |
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Tolerance on Unwanted Vertical Prism |
≥ 0.00 D,≤ ±3.37 D ±0.33 ▲ Total > ±3.37 D 1.0 mm Difference |
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Tolerance on Vertical Fitting Point Height |
±1.0 mm Each |
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Tolerance on Horizontal Fitting Point Location |
±2.5 mm Total (OC) |
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Tolerance on Center Thickness |
when specified ±0.3 mm |
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Tolerance on Base Curve |
when specified ±0.75 D |
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Tolerance on Segment Size |
for multifocals ±0.5 mm |
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Tolerance on Warpage |
1.00D |
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On orders that include prism, both the amount of prism and the prism _____ direction should be specified. |
base |
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What instrument is used to measure the power of spectacle lenses? |
Lensometer |
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Which part of the lens measuring device indicates that the instrument has power? |
Pilot Light |
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What is the FIRST procedure in lensometry? |
Focus the eyepiece |
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When measuring a lens, if both sets of lines making up the target sharply focus at the same time, the lens is a _________ power lens. |
spherical |
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How is the power wheel scale graduated for power between -3.00 and +3.00? |
1/8 D steps |
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When measuring a lens, you find that the target sphere lines focus at -2.25D with the cylinder axis wheel at 93 degrees, and the cylinder lines focus at -4.75D without changing the cylinder axis. What would be the prescription of the lens? |
-2.25 -2.50 x 093 |
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The amount of prism in a lens is measured using the lensometer _______. |
reticle |
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In the boxing system, the _______ dimension is the largest vertical dimension measured between the two horizontal tangents to the bevel tips. |
"B" |
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A __________ is used to measure the surface powers base curve of a lens. |
lens clock |
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A colmascope is used to verify that a glass lens has been _____________. |
heat-tempered |
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When verifying lens optical quality, the primary defect to search for is a localized area of ___________? |
poor optics |
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What cylinder powers would be acceptable, according to ANSI standards, for a lens with a prescription of +3.00 -1.75 x 100? |
anywhere from -1.62 to -1.88 |
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What is the cylinder axis tolerance for a lens with a cylinder power of -1.00D? |
±3° |
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There can be no more than ____ prism diopters of unwated horizontal prism in a lens. |
2/3 or ±0.67 Δ Total |
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There can be no more than ____ prism diopters of unwanted vertical prism in a lens. |
1/3 or ±0.33 Δ Total |
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The vertical segment location tolerance for a mounted lens is within ____ mm of specification. |
1.0mm |
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For special purpose prescription lenses, the thickness tolerance is ___ mm. |
±0.3 mm |
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If a base curve is specified whena lens is ordered, it should be supplied within ______D. |
±0.75 |
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If the distance PD is 64 and the near PD is 60, what is the seg inset? |
4mm |
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Describe gradient tint. |
lightens toward the bottom of the lens |
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When focusing the eyepiece of a lensometer, why is it important to stop turning the eyepiece when a sharp focus is first obtained? |
turning the eyepiece past the point of focus could cause accommodation |
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If the lensometer is in proper calibration, and the eyepiece is properly focused, the target will come into a sharp focus without a lens present at ____. |
zero |
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When the lensometer was calibrated, the target focused sharply at +0.25 and was blurred at 0. You are neutralizing a lens and have a reading of +1.00 on the lensometer. How would you record this reading? |
+0.75 |
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If both sets of lines making up the target sharply focus at the same time, the lens being neutralized is a: |
sphere |
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If the two sets of lines in the target will not come into focus at the same time, the lens being neutralized is a: |
spherocylinder |
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The cylinder lines will focus at a more ______ power reading than the sphere lines when neutralizing a lens in minus cylinder. |
minus |
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If the sphere lines are focused and unbroken at -1.00, axis 100, and the cylinder lines focus at -1.50, how would the prescription be recorded? |
-1.00 -0.50 x 100 |
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If the sphere lines are focused and unbroken at +3.00, axis 090, and the cylinder lines focus at +1.00, how would the prescription be recorded? |
+3.00 -2.00 x 090 |
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When measuring a lens in minus cylinder, if the cylinder lines focus at a more plus reading than the sphere lines, you should rotate the axis wheel by ___ degrees. |
90 |
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If the vertical target lines in the distance prescription focus at -2.00 and the same lines focus at +0.50 in the near segment of the lens, the near power should be recorded as: |
+2.50 |
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An important factor in measuring lenses with an automated lensometer is keeping the lens _____ against the lens stop. |
flat |
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What must be accounted for when measuring prism? |
the patient's PD, the oreintation of the prism, and the location of the lateral PRP/MRP |
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When tapping a glass lens with your fingernail, the sound will be __________ than the __________ sound of a plastic lens. |
sharper, dull |
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A lens clock is used to: |
measure the surface powers and base curve of the lens |
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True or false: a polycarbonate lens should be treated with a UV coating to avoid damage to the eye from UV radiation. |
false |
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The lens bevel most commonly used for low power lenses edged to fit into plastic and metal frames is called a: |
standard or V bevel |
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What does the fitting cross represent in the markings of a progressive lens? |
the position of the pupil on the lens |
