introduction to lenses ( lecture 1 )

Question 1

what is a corrective lens?

Answer 1

. it is worn in front of the eye to correct vision
. in spectacles it is mounted in a frame
. in contact lenses it fits directly on the surface of the cornea

Question 2

what is a spherical lens?

Answer 2

same power in any direction

Question 3

what are the types of lenses ?

Answer 3

. convex - positive , light converges
thicker in the middle , thinner edge
. concave - negative , light diverges
thinner middle , thicker edge

Question 4

what is a toric lens?

Answer 4

different power in meridian

max and min power are 90 deg to one another

Question 5

when is toric lens used ?

Answer 5

used when a patient is astigmatic

Question 6

what is astigmatism ?

Answer 6

prescription varies at different points in the eye

Question 7

what is a prism?

Answer 7

transparent block of material plastic or glass that refracts light

Question 8

what happens in prisms?

Answer 8

light enters prism from air and slows down , this is because material in prism is denser than air , slowing of light causes light to bend which results in refraction

Question 9

what is refraction ?

Answer 9

change in direction of light

Question 10

describe the structure of prism?

Answer 10

prism is thickest in base ,so light bends towards base of prism

Question 11

where is image displaced in prisms?

Answer 11

image is displaced in the apex of prisms which is the thinnest point in prism

Question 12

how are prisms in negative lenses ?

Answer 12

prisms pointing away from one another and apex is touching in middle

Question 13

how are prisms in positive lenses?

Answer 13

base pointing towards one another and apex is away from one another

Question 14

what are lenses composed off ?

Answer 14

lenses are composed of two surfaces
front surface = furthest from eye
back surface = closest to the eye

Question 15

what happens if a curve in a lens is flat ?

Answer 15

it is described as plano

Question 16

what is a plano lens ?

Answer 16

no power

Question 17

what are the types of plano lens ?

Answer 17

plano concave - It has one surface plane and the other surface concave.
plano convex - It has one surface plane and the other surface convex

Question 18

what is a bi-concave or bi-convex lens?

Answer 18

It has both the surfaces concave or convex but different powers

Question 19

what is equi convex or equi concave lens ?

Answer 19

both surface concave or convex and same power

Question 20

what is a minscus lens ?

Answer 20

one concave and one convex surface , most used and give best vision when looking away

Question 21

what are the types of lens forms ?

Answer 21

. equi concave/convex
. bi concave / convex
. minscus lens
. plano concave/convex

Question 22

what is a thin lens ?

Answer 22

. a thin lens is when two surfaces are in close contact ,

so refractive index between two materials is ignored

Question 23

what is the power of a thin lens (F v ‘)?

Answer 23

sum of power of 2 surfaces

F1+F2

Question 24

How to use prisms by themselves?

Answer 24

to deviate light when patients eyes don’t work together