Term
| What are the y and x axes on a Tcherning ellipse graph? |
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Definition
y-base curve or front surface power needed to correct for oblique astigmatism
x-the back vertex power |
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Term
| For what power prescriptions would we consider an aspheric lense now? |
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Definition
| +/- 4 D, before it was only for lenses above +7.5 D |
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Term
| Which surface of a plus aspheric lense is flattened toward the edge when compared to a spherical lens? |
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Definition
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Term
| What surface of a minus powered aspheric lens flattens toward the edge? |
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Definition
| back surface flattens toward the edge, front surface steepens for a minus powered aspheric lens |
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Term
| What are three advantages of an aspheric lense? |
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Definition
1) Reduce oblique astigmatism
2) Improve cosmetic appearance
3) Flatten the base curve to improve lens appearance or cosmetic design
4) Produce a thinner lighter lens |
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Term
| PALS have always used an aspheric base curve in what portion of the lense? |
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Definition
| The lower front surface of the lens. |
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Term
| Can you decenter an aspheric lense to get a prsmatic effect? |
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Definition
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Term
| Which lenses offer the largest field of view, aspheric or atoric? |
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Definition
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Term
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Definition
| An atoric lense has both an aspheric front and back surface. An aspheric lense only has an aspheric back surface. |
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Term
| Which lense has better acuity, aspheric or atoric? |
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Definition
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Term
| What are three types of lenses used to correct aphakia? |
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Definition
1) Spectacle lenses
2) Contact lenses
3) Intraocular lenses |
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Term
| Of the three types of lenses used to correct aphakia, which type of lenses produce the most disturbing visual problems for the wearer? |
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Definition
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Term
| How much is retinal image size magnified in aphakia? |
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Definition
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Term
| Can most patients adapt to bilateral aphakia and its 28% size magnification? |
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Definition
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Term
| Can a unilateral aphakic patient have binocular vision? |
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Definition
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Term
| What is the field of view for the steadily fixating eye, subtended at the entrance pupil? |
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Definition
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Term
| What is the field of view for the moving eye, subtended at the center of rotation of the eye? |
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Definition
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Term
| What is the amount of peripheral field of view lost in aphakia? |
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Definition
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Term
| What is the macular field of view lost? |
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Definition
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Term
| What is an angular gap in object space caused by the base toward the center effect of a strong plus lense? |
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Definition
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Term
| In what direction does the scotoma move when the eye rotates left? What is this called? |
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Definition
| The scotoma moves in the opposite direction of the eye movement. It's called the "jack in the box" effect. |
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Term
| At what object distances is a ring scotoma most problematic? |
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Definition
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Term
| What is the ring scotoma at normal reading distance of 16"? Is it problematic? |
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Definition
| 15 degrees, It is not problematic. |
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Term
| How large must an object distance be for a ring scotoma to stop being problematic? |
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Definition
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Term
| What do you call a lense that has a central area with the prescribed lense power surrounded by an outside area with little or no power? |
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Definition
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Term
| What do you call the central area of a lenticular lens? |
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Definition
| The Aperture, the, nonprescription part surrounding it is called the carrier |
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Term
| In what portion of the lenticular lense are the optics good? |
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Definition
| the central 30 to 40 degrees |
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Term
| Are lenticular lenses cosmetically appealing? |
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Definition
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Term
| What is the equation for predicting the power of an aphakic lense? |
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Definition
| F(aphakic)=+11.00 + (1/2)F(pre-aphakic) |
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Term
| Which has a larger field of view with correction, hyperope, myope, or emmetrope? |
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Definition
1)myope has the largest
2)emmetrope
3)hyperope |
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Term
| Whose eyes appear bigger when wearing correction, myope, emmetrope or hyperope? |
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Definition
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Term
| What two factors influence the power of a myodisc lense? |
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Definition
| edge thickness and bowl size |
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Term
| What type of lense has a small concave disc ground on the back surface of a plano carrier? |
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Definition
| myodisc lense for high myopia |
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