Fresnel Lenses, Aspheric Lenses, Jump In Bifocals

Front 1

Give 10 facts about fresnel lenses and prisms.

Back 1

1. They are 1mm.

2. They go in one same direction.

3. They are usually made of polyvinyl chloride.

4. They stick on with water.

5. They are light weight.

6. They are flexible.

7. They range from 0-30 prism diopters.

8. They correct high prism without surfacing lenses.

9. They are cosmetically unattractive.

10. They reduce VA's by 2 lines.

Front 2

Give 10 facts about aspheric lenses.

Back 2

1. They are flatter than the spherical equivalent.

2. They are thinner.

3. Lighter.

4. They reduce magnification and minification.

5. They are made by rotating an eclipse about its conic sections.

6. They require vertical heights.

7. They require a BVD measurement.

8. Parabola and hyperbola are most commonly used.

9. In the sag formula for aspheric lenses r and y are divided by p. P = asphericity of surface.

10. For each 2 degrees of tilt you should reduce heights by 1mm.

Front 3

Give 10 facts on jump in bifocals.

Back 3

1. Jump is the sudden introduction of prism base down.

2. There is more jump in a round self as base is lower down.

3. There is more prism in a larger seg.

4. You can use different size R segs to reduce or illuminate vertical differential prismatic effect between eyes.

5. For a round seg jump is measured by timing the seg radius by the add.

6. For a d seg measure seg top to o.s times the add.

7. Jump causes an image to suddenly appear.

8. You can get just in a trifocal at both dividing lines.

9. Executive or e line bifocals have no jump as optical centre is on the line.

10. There is no jump in a PPL.