multifocal lenses

Question 1

what are trifocals thought of ?

Answer 1

. can be thought of as a bifocal with an additive intermediate section

Question 2

what are trifocals described by?

Answer 2

. trifocals are described by segment size

. s= straight top, the depth of the intermediate section and the diameter of the segment
eg s728

Question 3

how does the size of the intermediate section vary?

Answer 3

. the size of the intermediate section varies between lenses
. if px does more intermediate work we are able to extend that
. if px does limited intermediate work , we can make that section smaller

Question 4

how to work out prescription required in the intermediate section of trifocal?

Answer 4

. to work out prescription required in the intermediate section of trifocal
. we use the IP/RP ratio

Question 5

what is the IP/RP ratio?

Answer 5

. IP/RP ratio= (IP add/RP add) x100

Question 6

what is the most suitable IP/RP ratio ?

Answer 6

50-60%

Question 7

what are the advantages of trifocals?

Answer 7

. intermediate section
. full distance portion which is not available in progressive lenses
. no distortion
. wide intermediate and near portion

Question 8

what are the disadvantages of trifocals?

Answer 8

. seg top 3mm above limbus-may interrupt distance vision
. reading portion 2mm lower than bifocals
. 2 areas of jump- if px suffered with jump in bifocals, trifocal isn’t a good option

Question 9

when to set the segment 2-3mm higher than normal ?

Answer 9

• if a px is getting on with bifocals, but just requires the limited extra near or intermediate use
• we can set segment 2-3 mm higher than normal
• make segment easier to assess and give them larger area

Question 10

what are some occupational trifocal lenses?

Answer 10

1. double D segment trifocal is popular for pilots and other occupations where they will be looking at small detail above and below the eye line
2. rodenstock C40 datalit trifocal - gives a large area for intermediate and near
   - intermediate is section is 10mm deep

Question 11

what are varifocal design?

Answer 11

1. hard design

2. soft design

Question 12

what is the difference between close and far lines in varifocal designs?

Answer 12

. know as isocylinder lines

. the closer the lines are together, the steeper that surface astigmatism is , the quicker the px will get to it

. the far apart lines tend to indicate that astigmatism is more gentle

Question 13

what is a hard design?

Answer 13

. has no distortion in distance portion
. good for drivers, golfers

. intermediate is very narrow - - obvious distortion

Question 14

what is a soft design?

Answer 14

. more distortion in distance portion

. wider intermediate section - softer distortion

Question 15

what is firm / ultra soft design?

Answer 15

. combination of hard and soft design

Question 16

what are freeform design lenses ?

Answer 16

. has less surface stigmatism
. available in different fitting heights - suitable for different frames
. they employ computer aided technology in the manufactures , which increases the accuracy of their design

Question 17

what do traditional lenses use to create the progressive surface ?

Answer 17

. traditional lenses use a glass mould to create the progressive surface on the front

. this meant no change can be made to the front surface, distance prescription can be worked on the back

Question 18

where do free form lenses have the progressive surface?

Answer 18

. can have the progressive surface on the back, front or mixture of both surface

Question 19

what is the benefit of freeform lenses being highly individual?

Answer 19

. freeform lenses are highly individual , this helps to compensate for the aberrations and distortions a patient might notice when wearing traditional bifocals

Question 20

what is the benefit of freeform lenses being available in multidesign?

Answer 20

. back surface designs which allows modification of lens parameters such as the inset
. we can alter the corridor length - how quickly the patient gets into NV

Question 21

what is the difference between head and eye movers?

Answer 21

. patients will either be head or eye movers
. eye movers - experience chromatic aberrations
. head movers - get into varifocals better , because they don’t look into that area of surface astigmatism

Question 22

how does freeform lens put distortion in different areas?

Answer 22

. can match astigmatism on right and left eye
. can put distortion in different area
. e.g. if px does a lot of reading , the distortion may be put towards the temporal side instead on nasal side

Question 23

what are the benefits of freeform lenses?

Answer 23

. framization -takes into account frame measurement
e.g. pantoscopic tilt

. multidesign - back surface designs which allow modification of lens parameters
e.g. variable inset, corridor length

. physiological - consider head and eye movement

Question 24

what do the freeform lenses take into account ?

Answer 24

. the design of freeform lenses changes with

• right and left eye
• the level of hyperopia or myopia
• the add
• the body posture
• behaviour
• frame chosen

Question 25

why are freeform lenses difficult to focimeter?

Answer 25

. the focimeter doesn't adopt a natural wearing position . powers you read for the focimeter might not be accurate for the lens . these lenses when dispensed , will often be sent with lens packages which tell you which powers you should be reading on the focimeter

Question 26

what some occupational progressive lenses?

Answer 26

. driving lenses . office lenses . intermediate/near only

Question 27

what are driving lenses ?

Answer 27

. driving lenses concentrate on having wider distance and intermediate section . have limited near vision section - not good for long term NV use

Question 28

what are office lenses?

Answer 28

- give good visual comfort when looking at intermediate and near - not good for DV - wider corridor for the IV and NV section - good for px with indoor use - not suitable for driving - can be tailored for px depending on the intermediate work they do - often coated

Question 29

what are the names of manufactures of office lenses?

Answer 29

. zeiss gradal PD . Varilux digitime room . Norville bureau HD - which correct up to 5m- good for office worker

Question 30

what are enhanced readers?

Answer 30

. good for patients who do large IV and NV use . don't need to look far . low levels of surface astigmatism . ordered differently to varifocal design - order them with reading prescription and how much distance prescription you want

Question 31

what are some occupational considerations?

Answer 31

1. visual task analysis - ask px about task size - ask px about working distance - still/moving task - position of task and patient 2. amount of distance vision required 3. amount of intermediate vision required 4. amount of near vision required

Question 32

what to do when asking question regarding occupation?

Answer 32

. make sure you are specific e.g. ' how many hours a day do you use a computer' - how many hours a day are you driving - what are the main tasks involved in your occupation

Question 33

what to consider when thinking about task px does?

Answer 33

1. important to know task size and if its still or moving . this can affect the amount of distortion the px is aware of . if task is moving px will benefit from free form lens or an occupational lens 2. important to consider the position of task - - if intermediate task is high , the px will look through the distance section and vision will be blurred

Question 34

what to recommend if working distance is mainly distance

Answer 34

. if DV is what they will be using the best - recommend an occupational lens designed for driving . hard, freeform, occupational varifocals are the best option

Question 35

what to recommend if mainly using IV?

Answer 35

. soft , firm or occupational varifocal with a wide corridor for intermediate vision

Question 36

what to recommend if mainly NV ?

Answer 36

. freeform or occupational varifocals are the best option

Question 37

what else to consider for occupational lenses?

Answer 37

1. safety - lens material 2. glare from artificial lighting - multi antireflection coating 3. glare from sunlight - tints with UV400 coating - transitions 4. sun glare from surface - polarised