Spectacle Magnification

Question 1

What is anisometropia?

Answer 1

two eyes with unequal refractive power

Question 2

What is antimetropia?

Answer 2

subclass of anisometropia - one eye is myopic, one eye is hyperopic

Question 3

What could occur from anisometropia and antimetropia?

Answer 3

aniseikonia

Question 4

spectacle magnification compares what?

Answer 4

size of image seen by person when wearing glasses with the size of the image seen when that same person is not wearing glasses

Question 5

SM=

Answer 5

retinal image size in corrected eye/retinal image in same eye uncorrected

Question 6

normal image size is taken as image size for the standard emmetropic eye with _ refractive power

Answer 6

+60.00 (magnification of 1.00)

Question 7

What 2 factors contribute to magnification or minification of an image?

Answer 7

power of lens

shape of lens

Question 8

Power factor includes? (2)

Answer 8

vertex distance, back vertex power

Question 9

Shape factor includes? (3)

Answer 9

thickness, index of refraction, FBC

Question 10

SM=

Answer 10

(shape factor)(power factor)

Question 11

shape factor=

Answer 11

1/[1-(t/n)f)]

Question 12

power factor=

Answer 12

1/[1-(dP)]

Question 13

relative spectacle magnification compares what?

Answer 13

standard emmetropic eye with magnification of an ametropic eye

Question 14

RSM=

Answer 14

image size for CORRECTED ametropic eye/standard image size for standard emmetropic eye

Question 15

What is Knapp’s Law? His untrue assumption?

Answer 15

When a refractive error is caused by excessively long or short eyeball length (axial), vertex distance of 15mm will create retinal images of same size, no matter what
–assuming spectacle lenses are flat and thin

Question 16

percent gain in magnification =

Answer 16

(Mspec-1)*100%

Question 17

The aperture of the eye is the entrance pupil is the _, located _mm behind cornea

Answer 17

pupil, 3

Question 18

in power factor equation, d =

Answer 18

vertex distance + 3mm to entrance pupil (in METERS)

Question 19

when considering CLs, d=

Answer 19

3mm

Question 20

Even ~6% is a noticeable difference and is and advantage of contact lenses for myopes

Answer 20

–

Question 21

only using power factor with - lenses is very similar to shape factor and power factor because:

Answer 21

minus lenses CT doesn’t usually vary much

flatter FBC

Question 22

Difference with aniseikonic symptoms vs uncorrected refractive error symptoms is:

Answer 22

symptoms are not helped by rx

problems appear after other problems are corrected

Question 23

indications for clinicially significant aniseikonia:

Answer 23

high anisometropia, high astigmatism
IOL, optic atrophy
spatial distortion
better comfort when only one eye is used

Question 24

physiologic (natural) aniseikonia is useful in small amounts created how?
gives clues to?

Answer 24

different locations of two eyes

depth, object location

Question 25

symmetrical aniseikonia is

Answer 25

equally smaller/larger in every meridian

Question 26

meridional aneiseikonia is is it symmetrical? caused by?

Answer 26

meridional size difference in a meridian of one eye compared with that of the other eye - yes, symmetrical - significant astigmatism

Question 27

asymmetrical aniseikonia:

Answer 27

progressive increase/decrease across the visual field

Question 28

with accommodation relaxed, parallel rays of light do not focus on the retina when _ is present

Answer 28

ametropia

Question 29

2 types of ametropia?

Answer 29

axial - unequal eye lengths | refractive - unequal curvature of refractive components of the eye

Question 30

if K readings are equal, rxs are significantly different; _ ametropia is present

Answer 30

axial

Question 31

K readings are different proportionally to rxs; _ ametropia is present

Answer 31

refractive

Question 32

is spectacle lenses are used for high astigmatism, each meridian will cause different amounts of magnification -correction of choice would be _

Answer 32

contact lenses

Question 33

When using eyewear to correct aniseikonia: | use frame with _ vertex distance

Answer 33

short

Question 34

When using eyewear to correct aniseikonia: | use frame with _ eyesize

Answer 34

small, reduces vertex distance

Question 35

When using eyewear to correct aniseikonia: | use _ lens design, which _ base curve

Answer 35

aspheric, flattens

Question 36

When using eyewear to correct aniseikonia: | use _ lens material

Answer 36

high index, thins plus lens CT

Question 37

when correcting aniseikonia for presbyopes, it may be necessary to correct _ at the same time

Answer 37

vertical imbalance

Question 38

_ is a lens to assist in the matching of retinal sizes

Answer 38

size lens or iseikonic lens

Question 39

when correcting aniseikonia with specs, keep decentration _

Answer 39

to a minimum (frame pd=pt pd as much as possible)

Question 40

base curves range from _ to _

Answer 40

.50 to 8.00

Question 41

if you choose to use aspheric lenses, you must _

Answer 41

use it in both lenses!

Question 42

for poly or trivex: finished= _ mm min CT semi-finished= _mm min CT

Answer 42

1. 0 | 1. 5

Question 43

normal vertex distance is _ mm | _ mm is too close, lash crash

Answer 43

13 | 11

Question 44

thickness: _ mm is industry standard min poly or trivex, surfaced to _mm or thick stock lens as _ mm

Answer 44

2.0 1.5 mm 1mm

Question 45

if you bring retinal image size between eyes to be just less than _%, patients can fuse 95% of the time

Answer 45

4%

Question 46

4 lens components:

Answer 46

FBC index of refraction vertex distance center thickness

Question 47

we cannot add _

Answer 47

minification

Question 48

``` to add magnification: steepening FBC = _ CT increasing CT = _ magnification flattening FBC = _ CT decreasing CT = _ magnification ```

Answer 48

adds increases reduces decreases

Question 49

increasing vertex distance for any lens, makes it more _ power, and _ magnification

Answer 49

plus | increases