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Dispensing Test 3
|Who invented the Snellen Chart?
|What year was the Snellen Chart created, and during what war?
|1862, Civil War
|Who did Snellen use to determine what was normal vision?
|Sharp shooter could discern a feature that subtended an angle of ___ to their eye?
|How many minutes are in one angle?
|How tall are the letters on the 20/20 line of the Snellen chart?
|A whole letter subtends an angle ___ from the eye, but able to discern features at ___?
|5' ; 1'
|The first number in the phrase "20/20" symbolizes what?
|distance at which the test is done
|The second number in the phrase "20/20" symbolizes what?
|distance at which a person with normal vision could read the letters
|What is a person's visual acuity if they see the big E on the Snellen chart?
|How can you determine the size of the letters of any line on the chart?
|divide the denominator by the numerator, and multiply by 8.87
|What are some things that effect visual acuity?
|Contrast; lighting (illumination); pupil size
|If a pinhole doesn't correct or help vision problem is not refractive, it is...?
|Which would help visual acuity a larger pupil size or smaller?
|What is presbyopia?
|Loss of sufficient accommodation at near; crystalline lens can't get as plus anymore
|How much of total accommodation can be used comfortable for a long amount of time?
|What are symptoms of presbyopia?
|blur, headaches, double vision
|How is presbyopia corrected?
|More plus power, convex lens
|What are some options for prebyopes?
|Bifocals, trifocals, single vision readers; two pairs of glasses; monocle; contacts monovision; slide glasses down nose; half-eyes
|What is used to check near VA?
|Reduced Snellen Chart; Jaeger system
|What are the differences in the Snellen chart and Jaeger?
|The distance at which the charts are read, and the Jaeger system is slightly larger. Snellen chart is more accurate
|What distance is the reduced Snellen read at?
|What distance is the Jaegar system read at?
|What is early presbyopia?
|When the near point of the distance prescription is closer than the far point of the add; there is an area that can be seen through distance and add
|What is middle presbyopia?
|When the near point of the distance and the far point of the add are at the same place.
|What is advanced presbyopia?
|When a gap exists between the near point of the distance and the far point of the add; use trifocal to fill in gap. Used when add power gets to +2.00
|What are some fitting problems with first time bifocal wearers?
|restricted field of view; upsets depth perception (things look bigger and closer); nuisance to wear; cylinder changes shapes of objects; reflections; changes in reading habits; bifocal lines bisect field of view; curbs and stairs
|How well a patient adapts to wearing bifocals depends on....
|how the glasses fit into lifestyle; your measurements; your adjustments; and how well you prepare them
|Where do we measure for a lined bifocal?
|lower lash line
|Where do we measure for a trifocal?
|bottom of pupil
|Where do we measure for a child's bifocal?
|center of pupil
|Where do we measure for a progressive lens?
|center of pupil
|What type of frames are good for first time bifocal wearers?
|frames with adjustable nosepads; gives some leeway to adjust segment
|If you have a previous bifocal wearer is it good to set their bifocal where they've always had it?
|Yes, it may bother them if you change it. But ask, the patient may want you to change it.
|How do you want to set a child's bifocal?
|High and wide so they don't look around it; bisect the pupil
|What is accommodation?
|when your eye accommodates for different distances.
|The near point _______ as you age.
|What is the formula for accommodation power?
|What is the difference in myopes and hyperopes when fitting for bifocals?
|Myopes can get along without glasses when needing to read up close; can get away with smaller/lower segments
|When specifying center thickness, what is the minimum for dress eyewear?
|When specifying center thickness, what is the minimum for safety eyewear?
|When is it important to pay attention to center thickness on a bifocal?
|When using a fused segment
|Most bifocals are set too ___? Why?
|low; opticians are afraid to set bifocal correctly, afraid the patient will see the line
|If a patient has a stooped posture, their bifocal needs to be set...?
|If a patient has a very erect posture, we need to set their bifocal...?
|If a patient is really short their bifocal should be set...?
|If a patient is really tall their bifocal should be set ...?
|What methods are used to measure seg height?
|mm ruler (PD stick); seg measures (not used anymore); transparent tape; marker; white marker; electronic
|Should seg heights be set equally?
|Yes, it's best for optics, but not good cosmetically; progressive is best
|Closer VD = _____ field of view
|Farther VD = _______ field of view
|Segs are less noticeable when what is used?
|If a patient does alot of near work, we want their segment to be...?
|wider and set higher than normal
|If patient doesn't use their near vision as much their seg can be...?
|narrower and can be set lower
|With a high power distance Rx how do we want the seg set?
|Get bifocal as close as possible; set bifocal higher
|How does panto affect seg height?
|Increase the panto, it lowers the apparent seg height