W6_02 Optics

Question 1

the snellen fraction refers to what?

Answer 1

e.g. 20/20 vision is a snellen fraction.

Question 2

how far away do you test vision with the snellen fraction?

Answer 2

6 metres

Question 3

vision to be able to drive?

Answer 3

20/50

Question 4

legally blind vision?

Answer 4

20/200

Question 5

OD refers to what?
OS refers to what?
OU refers to what?

Answer 5

OD = right eye
OS = left eye
OU = both eyes

Question 6

what is emmetropia?

Answer 6

normal refractive error

Question 7

what is presbyopia?

Answer 7

near objects out of focus;
insufficient accommodation;
focus is behind retina

Question 8

what is myopia?

Answer 8

far objects out of focus;
power too high;
focus in front of retina

Question 9

what is hyperopia?

Answer 9

near objects out of focus;
eye is too short;
focus is behind retina

Question 10

what is astigmatism?

Answer 10

focusing is ellipsoidal (so never sharp)