Optical Performance of Multifocal Lenses

Question 1

where is downgaze compared to distance OC

Answer 1

10 mm

Question 2

the distance between the GC (or FPD) and the DOC in each eye is called the

Answer 2

inset

Question 3

formula for inset

Answer 3

(FPD - DPD) /2

Question 4

the distance between the DOC and the NOC in each eye

Answer 4

segment inset

Question 5

formula for segment inset

Answer 5

(DPD - NPD) /2

Question 6

the lateral displacement of the segment optical center (NOC) from the geometric center of the lens

Answer 6

total inset

Question 7

formula for total inset

Answer 7

(FDP - NPD) /2

Question 8

total inset=

Answer 8

inset + seg inset

Question 9

what inset is most common?

Answer 9

+ inset, because usually eyes nasal to GC

Question 10

segment inset is always ___

Answer 10

IN (because we converge)

Question 11

2 purposes of segment inset

Answer 11

1. to ensure the fields of view through the 2 segments coincide
2. to prevent the segment from producing horizontal prismatic effects

Question 12

linear field of fixation formula

Answer 12

FOF = [ (d +2.7) x (2h)] / 2.7

Question 13

in linear FOV calculation, what does d and h stand for

Answer 13

d= viewing distance (in cm)
h = 1/2 seg size (in cm)

Question 14

the linear field of fixation through a segment ____ as the segment diameter and viewing distance increases

Answer 14

increases

Question 15

the linear field of fixation through a segment _____ as the vertex distance decreases

Answer 15

increases

Question 16

why do we use 2.7 cm in FOF?

Answer 16

average distance between the spectacle plane and the eye’s center of rotation

Question 17

why does image jump occur?

Answer 17

vertical prismatic effect at the line between the carrier lens and the segment

Question 18

how can the image jump increases?

Answer 18

increases the farther the segment OC is away from the top of the segment line

Question 19

image jump calculation

Answer 19

image jump = F(a) x dcm
F(a) = add power
dcm = distance the seg line is from the seg OC

Question 20

define apparent scotoma

Answer 20

the differential displacement of light at the top of a seg results in an apparent scooter (blind spot)

Question 21

apparent scotoma size formula

Answer 21

size (cm) = (vd/100) x image jump (prism diopter)

Question 22

when does image displacement at the reading level occur?

Answer 22

if the reading level is NOT coincident with the seg OC

Question 23

if reading level is below the optical center, _____ is induced

Answer 23

BU

Question 24

if reading level is above the optical center, ____ is induced

Answer 24

BD

Question 25

formula for image displacement at reading level

Answer 25

= Fa x ds
Fa= add power
ds= distance from the reading level to the seg OC

Question 26

total image displacement is the sum of:

Answer 26

the prismatic effects from both the carrier (distance) and reading seg

Question 27

total image displacement =

Answer 27

(dc x Fc) + (ds x Fa)