correcting ametropia

Question 1

Bring object from infinity to the fat point

Answer 1

myopia correction

Question 2

Minus lens

Answer 2

Virtual image to the left of the lens

Question 3

Positive lens

Answer 3

Converges beam
Image on the right
Real image

Question 4

Bring object from infinity to the far point

Answer 4

Hyperopia correction

Question 5

To function as correcting lens….

Answer 5

The lens secondary focal point F’ coincides with the far point of the eye

Question 6

To correct myopia

Answer 6

-decrease the optical power and thus we use a diverging minus lens

Question 7

To correct hyperopia

Answer 7

-increase optical power, and this we use a converging, positive lens

Question 8

Because the spectacles are not in contact with the eye, what is involved

Answer 8

Vergence

Question 9

The unit of vergence is

Answer 9

Diopters

Question 10

What is the refractive index of the eye?

Answer 10

1.336

Question 11

Are F and F’ the same?

Answer 11

No they are different because of different RI

Question 12

How do you find vergence in a medium other than air

Answer 12

n/l

Question 13

The vergence L of a ray bundle is

Answer 13

• the wavefront curvature
• the reciprocal of the distance L required to converge to a point
• for a collimated ray bundle, vergence is 0
• for propagation to the right, if the bundle converges, vergence is positive, while if the beam diverges, negative

Question 14

The required power of a lens to produce the SAME optical effect at a different location

Answer 14

Effective (downstream) optical power

Question 15

Which needs to have more power, spectacles far away from the eye, or one that is closer?

Answer 15

One that is closer

Question 16

What is the average vergence distance?

Answer 16

10-15mm

Question 17

What is the vergence distance for CL?

Answer 17

0

Question 18

This hyperopia is referred to as

Answer 18

+10.00 vertex distance 15mm

I know this is weird, because you cant see the pic. Just know that you use the power of the spectacles and then state the vergence distance (distance between the specs and the eye itself)

Question 19

When is vertex distance important?

Answer 19

When converting between contact lenses and spec Rx

Question 20

When does vertex distance become significant?

Answer 20

If the spectacle Rx is +/-4.00D or more or vertex greater than 12

Question 21

What vertex distances give a bigger jump in power?

Answer 21

12 and 15

Question 22

When we measure front and back focal lengths what are we supposed to measure and what do we actually measure?

Answer 22

We are supposed to measure from the principal point to the focal point, but we actually measure from the vertex point to the focal point because it is more practical