Lec 11: Spherical Ametropia and Astigmatism

Question 1

An unaccommodated eye which brings parallel pencils of rays from a
distant object to a sharp focus on the retina is said to be emmetropic.

Answer 1

Emmetropia

Question 2

An eye which is not emmetropic is termed _________.

Answer 2

ametropic

Question 3

Spherical ametropia

Answer 3

• ‘Axial ametropia’

* ‘Refractive ametropia’

Question 4

Astigmatism

Answer 4

• On-axis astigmatism

* Off-axis (oblique) astigmatism

Question 5

K’

Answer 5

dioptric length of the eye (needs)

Question 6

Fe

Answer 6

dioptric power of the eye (has)

Question 7

K

Answer 7

Refractive error= K’-Fe

Question 8

far point relates to

Answer 8

refractive error

Question 9

near point relates to

Answer 9

accommodation

Question 10

When keep Fe fixed, assume 60D, refractive error changes caused by axial length called?

Answer 10

axial ametropia

Question 11

When keep k’ fixed, assume 22.22mm, refractive error changes caused by refractive power called what?

Answer 11

refractive ametropia

Question 12

1 mm change in axial length produce a change in ametropia of what?

Answer 12

2.6 D

Question 13

0.37 mm changes in axial length alters the refractive

state by what?

Answer 13

by one diopter.
The relationship is always expressed as ‘a variation of three- eighths of a millimeter in axial length alters the refractive state by one diopter’.

Question 14

1 mm change in radius of curvature produce what change in ametropia?

Answer 14

13 D change

Question 15

0.09 mm change in surface curvature alters the refractive state by what?

Answer 15

1 D