optics definition

Question 1

Astigmatism

Answer 1

Difference in power between two perpendicular meridians.

Question 2

Disc of least confusion

Answer 2

Circular blur patch located Dioptrically midway between the astigmatic foci

Question 3

Best Vision Sphere

Answer 3

Correction in the spectacle plane that places the disc of least confusion on the retina for distance vision

Question 4

Simple myopic astigmatism (SMA)

Answer 4

The focus of the least powerful principal meridian lies on the retina with the other principal meridian focus anterior to the retina. (One meridian is emmetropic and the other is myopic)

Question 4

Compound Myopic Astigmatism (CMA)

Answer 4

Both astigmatic foci lie anterior to the retina. (Both principal meridians are myopic)

Question 5

Mixed Astigmatism (MA)

Answer 5

The astigmatic foci lie either side of the retina. (One meridian is myopic and the other is hypermetropic)

Question 6

Simple hypermetropic astigmatism (SHA)

Answer 6

The focus of the most powerful meridian lies on the retina with the other meridian focus posterior to the retina. (One meridian is emmetropic and the other is hypermetropic)

Question 6

Compound Hypermetropic Astigmatism (CHA)

Answer 6

Both astigmatic foci lie posterior to the retina. (Both principal meridians are hypermetropic)

Question 7

Accommodation

Answer 7

Increase in the Dioptric power of the eye with an effort to focus at near

Question 8

Near Point (MP)

Answer 8

Point conjugate with the retina when the eye is in its fully accommodated state

Question 8

Amplitude of Accommodation (Amp)

Answer 8

Maximum increase in the positive Dioptric power of the eye with an effort to focus at near.

Question 8

Accommodation

Answer 8

Increase in power of the eye with an effort to focus at near

Question 9

Emmetropia

Answer 9

Second focal point falls on the retina for the unaccommodated eye.

Question 10

Far Point (MR)

Answer 10

Object point conjugate with the retina in the unaccommodated eye.

Question 10

Hypermetropia

Answer 10

Second focal point falls behind the retina in the unaccommodated eye.

Question 11

Myopia

Answer 11

Second focal point falls in front of the retina in the unaccommodated eye.

Question 12

Minimum Angle of Resolution (MAR):

Answer 12

angular separation, usually in minutes of arc, between two points or lines at the resolution acuity limit.

Question 13

Standard Observer:

Answer 13

an observer with a visual acuity that just allows px to distinguish letters with a limb width of 1’ arc.

Question 14

(Unaided) Vision (V):

Answer 14

acuity, determined by the smallest line of letters or symbols identified on a test
chart, with the unaided eye.

Question 15

Visual Acuity (VA):

Answer 15

acuity, determined by the smallest line of letters or symbols identified on a test
chart, after any defects of focusing have been corrected.

Question 16

Facultative Hypermetropia

Answer 16

Hypermetropia that can be compensated by accommodation to produce distinct vision.

Question 17

2nd focal point F’

Answer 17

The point on the optical axis , if object rays are parallel to each other and to the optical axis their corresponding image rays will intersect at F’