Lens II Review Flashcards by Madison Adrianna

Vertical Imbalance Steps.

find power @ 90
find optical difference. same signs subtract, opp add.
use formula Dd/10=^

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Segments
Rd 22

Location?

11mm

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Segments
Rd 25

Location?

12.5mm

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Segments
Rd28

Location?

14mm

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Segments
Ft25, Ft28, Ft35

Location?

all 5mm.

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Segments
Ultex

Location

19mm

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Segments
Exec

Location

0mm

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Calculating IJ

ex. 22Rd w/ +2.00ADD

To solve, use Dd/10=^

where D = near oc, d=ADD, and 10 is constant.
(11)(22)/10=22/10=2.2^IJ

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Power at 90

if the axis is 0 away from 90, how much cyl is felt?

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Power at 90

if the axis is 30 away from 90, how much cyl is felt?

25% felt

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Power at 90

if the axis is 45 away from 90, how much cyl is felt?

50% felt

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Power at 90

if the axis is 60 away from 90, how much cyl is felt?

75% felt

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Power at 90

if the axis is 90 away from 90, how much cyl is felt?

100% felt

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Calc. power at 90

ex. +1.00-4.00x060

axis is 30 away from 90, so 25% of cyl felt. (-4.00x25%=-1.00)
take 1.00 and combine with sph. (-1.00 + 1.00 = PL)
PLANO=power at 90

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t/f
A FT BF has its near optical center 5mm below the segment line regardless of the width and regardless whether its a BF or TF.

True,

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The wearer can opt for two pairs of glasses to correct for VI at near.

true

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Fused MF construction methods are only used with glass?

t/f

true

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Reverse Slab Off

reverse is ALWAYS BD

find power at 90
find optical difference, same sub, opp add
calc VI with ^= Dd/10
^ goes in lens with LEAST - or MOST +

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Reverse Slab off goes in the lens with the least minus, most plus.

t/f

true

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Slab off is always ground BU on the lens with the MOST minus, LEAST plus.

t/f

True

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Calc. Slab Off

find power at 90
find optical diff. (same signs sub, diff add)
Calc VI using ^= Dd/10
BU on lens w/ MOST minus & Least plus

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Cosmetic appearance is a factor when using dissimilar segments to correct for VI @ near.

t/f

true

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Prism segments are widely used to correct VI

true/false

false

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Vertical imbalance of more than 2D should always be considered.

t/f

true

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Reverse slab off is available in fused FT-28 BF t/f

false. reverse= front molding

Reverse slab off is placed in the most _____ lens. minus plus

plus

Conventional slab off is available in PAL t/f

true

A client has VI of 2.5D BD OD, what should we do to compensate?

Slab off 2.5 BU OD. If VI is BD, give BU to neutralize. BU= slab off BUMM

Reverse slab off is molded not ground. t/f

true reverse= molded on front lens slab off= ground on back lens

A client has VI 2.00BU OD, what should we do to compensate?

REVERSE slab off 2.00BD OD give BD to neutralize. BD = Reverse slab off. BDMP

VI compensation at near is required when there is a VI of 1.00D or less between two eyes. t/f

false. 1.5VI or more.

Conventional slab off is available in a one-piece FT-28 BF t/f

true

Conventional slab off is placed in the most _____ lens. minus plus

minus

Reverse slab off is base _____ prism. up down

down

Conventional slab off is base ____ prism. up down

up, BUMM

AR coatings help eliminate specular reflections t/f

true, higher the index of refraction, more light reflected.

The pupil of the wearer reduces the effect of spherical abberation. t/f

true, not a problem in lower power lenses because of the small limiting size of the pupil.

In curvature of field, the image is curved. t/f

true

Reverse slab off is available in half diopter steps. t/f

true

Chromatic aberration is a result of the nature of the material of the lens. t/f

true

The higher the index of refraction of the lens, the greater amount of specular reflection will occur. t/f

true

An aspheric front surface of a plus lens steepens towards the periphery t/f.

false, flattens is periphery.

Most ophthalmic lenses have no aberrations. t/f

false

1 surface of percent of intensity 4. 3% 3. 94%

4.3%

2 surfaces for percent of intensity. 4. 3% 3. 94%

3.94%

In coma, the abberation is a result of the rays of light oblique to the lens surface. t/f

true

Spherical aberration results from the lens having different powers in different areas. t/f

true

Conventional slab off is available in quarter diopter steps t/f

true

In coma, the aberration is a result of rays of light parallel to the lens surface. t/f

false, coma is oblique.

In distortion, the object will appear to have a pincushion look when viewed through a minus lens. t/f

false. Pincushion is plus, Barrel is minus

In coma, the pupil of the wearer has no effect on the aberration. t/f

false. The pupil acts as a small aperture which limits the light rays at periphery of lens.

The refracting power of a lens decreases toward the periphery t/f

false, it increases, decreases at near OC

All lenses moved farther away from the eye will gain in plus power, we compensate for this by adding minus power. t/f

true

The law of reflection states that the angle of incidence is always greater than the angle of reflection. t/f

false, its equal to.

A high plus lens will show _____ distortion pin barrel radio wave

pin. PLUS

A convex surface has ____ dioptric power plus minus plano

plus = convex, minus = concave

As a ray of light passes from a more dense to a less dense material at an oblique angle, the refracted ray will be deviated _____ the normal. away toward parallel

away, more to less dense.

Vertex distance compensation should be considered when the total power of the lens, in any meridian, is +/-7.00 or greater. t/f

true

A high minus lens will show ____ distortion. pin barrel radio

Barrel

A surface with a flatter curve will have less dioptric power. t/f

true.

In the surface power formula, we must be sure that "r" (radius) is in meters, not mm, or cm. t/f

true

When light strikes an object, 3 things occur. They include: refraction, absorption, and reflection. t/f

true

As light strikes a lens with a spherical front surface, it refracts more at the periphery than near the center. t/f

true

A surface with a shorter radius will have a flatter curve t/f

false, steeper=shorter, flatter=longer.

As a ray of light passes through from a LESS dense to a MORE dense material at an oblique angle, the ray will be more deviated ___ the normal. toward away

less->more dense, toward the normal.

In coma, the aberration is a result of rays of light parallel to the lens surface. t/f

false, coma=oblique

A plano surface has____ power zero minus plus

zero

A concave surface has ____ power minus plus plano

minus, convex = plus

In curvature of field, the image is curved convex towards the object. t/f

False. Curvature=concave

Convex surfaces: t/f covex surface bulging converges light rays plus power

true

Concave surfaces: t/f minus diverges light concave surface is hollow

true

Radius of Curvature: t/f Curve on a smaller circle is steeper than the curve of a larger circle.

true

Radius of curvature: t/f the steeper the curve, the more power

true

Surface Power Formula D=n-1/r

where D= power nr=index of refractive material ni=index of the incident material r=radius of curves of meters

Vertical Imbalance of less than 2D is never noticeable to the wearer. t/f

false, anything 1.5^ or more is noticeable.

Example of Surface Power Formula. A concave surface with a radius of 50cm and an index of 1.6. What is the surface power? Convert 50cm to meters = .5

D=n-1/r 1.6-1=.6/.5 D=1.2 rounded to the nearest 1/8D, 1.2=1.25

Index of poly? 1. 498 1. 586 1. 523

1.586

Index of cr-39? 1. 498 1. 586 1. 523

1.498

Index of crown glass? 1. 586 1. 523 1. 530

1.523

Index of trivex? 1. 530 1. 523 1. 498

1.530

Angle of incidence is the angle formed between the refracted ray and the normal. t/f

true

The angle of refraction is the angle formed between the refracted ray and the normal. t/f

true

The angle of deviation is the angle formed between the refracted ray and the path the incident ray would have taken had it not been refracted. t/f

true

Compensating for Vertex Power CAP, FAM t/f

True

Compensating Vertex Distance formula power x power x distance moved/1000=amount of compensation

CAP, FAM

Lens II Review Flashcards

(85 cards)