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Ophthalmic Optics Block 9 > Lensometry Multifocal > Flashcards

Lensometry Multifocal Flashcards

1
Q

What is the green and orange light on the lensometer for

A

Green for light lenses

Orange for sunglasses

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2
Q

Lenses that contain two or more loess power to let you see at different distances

A

Multifocal

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3
Q

Who wears multifocal

A

Over 40, children

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4
Q

Types of multifocal

A

Progressive
Bifocal
Trifocals

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5
Q

Must you set the axis on 180 before doing lensometry>

A

No

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6
Q

Line multifocal design

A

Front surface design

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7
Q

What is the distance between the optical center and the top of a bifocal

A

3-5mm

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8
Q

What is the distance between the optical power and the trifocal add power

A

1-3mm

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9
Q

How to read the add power on lensometer

A

Go from single to single or from cyl to cyl. Don’t fluctuate between the two

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10
Q

What side of the lens is thicker on multifocal

A

Front

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11
Q

How do you read the add power on a multifocal in lensometry

A

Flip the glasses around and find it that way. Also check the distance power again flipped and subtract the difference between the two, to make sure you are using a uniform side to do this.

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12
Q

When should you do the proper front/back vertex reading for add power

A

When the Rx is: +/-5 with an add of +2.50 or greater

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13
Q

Corrective lenses used in eyewear to correct presbyopia or other accommodation issues

A

Progressive lenses

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14
Q

Types of progressives

A

Multifocal, no lines, PAL

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15
Q

Downside of progressive lenses

A

Distortion on the side

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16
Q

Designates the point on a lens that should be placed at the center of the pupil

A

Fitting point

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17
Q

Areas used to verify prescribed distance power

A

Distance reference circle

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18
Q

Optical center of a PAL, used to check prism

A

Prism reference point

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19
Q

Located on nasal side, under micro-circles/references lenses type/material

A

Alignment markings and manufacturing logo

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20
Q

Used to verify total near point

A

Near reference point

21
Q

Located on temporal side/ used to verify add power

A

Add power

22
Q

What side is is the add power always on

A

Temporal side

23
Q

When reading progressives, it is important to mark these points on each lense before proceeding

A

Dot it up

24
Q

Where is the reference point usually

A

4mm up from the 180 line

25
Q

Where is the prism in a progressive lens

A

Right int he middle of the 180 line

26
Q

Reading distance on progressive lenses

A

Distance reference point

27
Q

Where do you read the add power on a progressive lens

A

Read add power from the near reference point (down to the nasal)

Some manufacturers tell you not to do this. Short frames will read inaccurate. Digitally surfaced lenses will not be in quarter increments. Can be a +1.56 or something to that effect

28
Q

How do you read the prism on a progressive

A

Right in the middle of the 180 line

29
Q

Triangulated pieces of glass that pass through it and change the direction of light

A

Prism

30
Q

Thinner in the middle, thicker on the side

A

Minus

31
Q

Thicker inthe middle

A

Plus

32
Q

A unit that describes the power of a prism to produce a cone centimeter deviation in a ray of light at a distance of one meter from the lens

A

Prism diopter

33
Q

Involves the grinding of the surface of a lens during a manufacturing

A

Ground in prism

34
Q

Involves decentering the optical center to utilize the pristmatic effects of sphere-cylindrical lens. Prentice’s rule

A

Induced prism

35
Q

How do you know you have ground in prism

A

It will never lien up with the mires

36
Q

How do you know you have induced prism

A

The mires can only be centered when the lens is decentered

37
Q

What kind of lenses can you induce prisms into

A

Single vision lenses

38
Q

What kind of prism has to be in progressives

A

Ground in

39
Q

Minor powers and prism

A

Cannot induce prism

40
Q

Unwanted prism

A

Calculate prentice rules

Can be vertical and horizontal imbalance

41
Q

Too much BD prism

A

Vertical objects appear taller than they are. Looks like you are walking up a hill

42
Q

Too much BU prism

A

Vertical objects will appear smaller

43
Q

Too much BI or BO prism

A

Horizontal lines will have a curve to them

44
Q

PAL and prism thinner

A

In PAL, surface power power increases as you go down, but it also increases thickness on the opposite side. Manufacturers want their lenses to look as good as possible, use prism thinning which induces prism, whether Rxed or not.

Most thinning is BD

45
Q

Prism that is up in both eyes, or down in both eyes

A

Cancel each other out

46
Q

Prism that is in in one eye, and out in the other eye will

A

Cancel each other out

47
Q

How do you read prism on a progressive lens

A

Read from the prism reference point

48
Q

3 ways you can get prism from a single vision

A

Exam history
Lab ticket
Getting optical center while patient wears them

Ophthalmic Optics Block 9 (3 decks)

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