Bifocal, trifocal and progressive additional lenses

Question 1

how are bifocals arranged

Answer 1

top = distance , bottom = near

periphery is important for motion

smaller segments are to help people to to stop falling them over

Question 2

what type of bifocal is used for convergence excess

Answer 2

executive - used for convergence excess

Question 3

what age does accomodation deteriate

Answer 3

by 55 no accomodation left

need to replace accomodation that is left

add goes on to your normal refractive prescription

Question 4

how would an add of +1.00 and +1.00 be added to an prescription of -2.00/-1.00 x 180

Answer 4

add goes on to your normal refractive prescription
because it is a - you would add the - in the form of a segment

so it would be -3.00 -1.00 x 180

and it would be -2.00 / -1.00 x 180

Question 5

what are trifocals and progressive additional lenses for

Answer 5

they are for really reduced accomodation
in late presbyopia you only have depth perception left

trifocals have 3 powers and 3 foci

Question 6

what is a consequence of varifocals

Answer 6

varifocals have no lines and don’t offer clear vision across the whole of the Lens - they work by having a change In curvture to the lens surface as you go from the top down to the bottom

a consequence of this is the production of areas of distortion in a typical design

going straight to trifocals are easier to adapt to the areas of distortion instead of going from bifocals to trifocals