5: Models of Ocular Optics

Question 1

the two main classes of schematic eyes are

Answer 1

• paraxial

- finite (wide angle)

Question 2

2 criteria of paraxial schematic eyes

Answer 2

1. spherical refracting surfaces

2. surfaces centered on a common optical axis

Question 3

paraxial eyes are only accurate for paraxial ray tracing, which means:

Answer 3

that the rays must pass within the paraxial zone (to trace outside the paraxial zone with greater accuracy requires finite eyes)

Question 4

list the 3 types of paraxial schematic eyes

Answer 4

1. reduced eye
2. simplified eye
3. exact eye

Question 5

a reduced eye has

Answer 5

only one refracting surface and its single refractive medium has a uniform refractive index

Question 6

a simplified eye has

Answer 6

a single corneal surface and a crystalline lens with two surfaces and uniform refractive index

Question 7

an exact eye has

Answer 7

at least two corneal surfaces and at least two crystalline lens surfaces

Question 8

for Emsley’s reduced eye:

because the eye is emmetropic and contains but one refracting surface, its axial length corresponds to its ____

Answer 8

second principal focal length (f’)

Question 9

for Emsley’s reduced eye:

what values are smaller than normal

Answer 9

the radius of curvature (r) and the axial length

Question 10

for Emsley’s reduced eye:

the single refracting surface must contain power of

Answer 10

both corneal and crystalline lens

Question 11

for Emsley’s reduced eye:

because the retina is artistic (drawn curved), this eye is not suitable for modeling what imaging properties?

Answer 11

not suitable for modeling peripheral imaging properties of the eye

Question 12

the first principal focal point (F) of the eye is the point on axis at which:

Answer 12

an object must be placed to provide an image at optical infinity

Question 13

the second principal focal point (F’) of the eye is the point on axis at which:

Answer 13

an image is formed from an object at optical infinity

Question 14

in schematic eyes, why are the principle point conjugate?

Answer 14

they allow complicated schematic eye to be treated as if it were a thin lens

Question 15

the aperture stop of the eye is the:

Answer 15

anatomical iris

Question 16

the entrance pupil (E) is the:

Answer 16

image of the iris aperture when viewed from object space

Question 17

the entrance pupil is _____(closer, farther) to the cornea than the aperture stop

Answer 17

closer

Question 18

the entrance pupil is ______ (smaller, larger) than the aperture stop

Answer 18

larger

Question 19

the exit pupil (E’) is the:

Answer 19

image of the iris aperture when viewed from image space

Question 20

the exit pupil is _____(closer, farther) to the cornea than the aperture stop

Answer 20

farther

Question 21

the exit pupil is ______ (smaller, larger) than the aperture stop

Answer 21

larger

Question 22

a ray directed towards the center of the entrance pupil appears to emerge from the center of the exit pupil, this ray is called the

Answer 22

chief ray, or paraxial pupil ray

Question 23

the center of rotation of the eye is approximately ____ mm behind the corneal vertex

Answer 23

15 mm behind the corneal vertex

Question 24

the OSA line of sight (z-axis) is the path of the:

Answer 24

chief ray from the fixation point point to the center of the entrance pupil

Question 25

the OSA x-axis and y-axis are located:

Answer 25

both are lying in a frontal plane through E

• the x-axis is horizontal
• the y-axis is vertical

Question 26

the optical axis is defined as:

Answer 26

the line of ‘best fit’ through the centers of curvatures of all the surfaces

Question 27

what is the significance of the line of sight?

Answer 27

is that it describes the center of the actual pencil of rays that enters the eye

Question 28

the fovea is ____ to the optical axis on the retina

Answer 28

temporal

Question 29

the visual axis is composed of ___ line segments

Answer 29

two

Question 30

what are the two line segments of the visual axis?

Answer 30

1. connects the fixation point to the first nodal point (N)

2. connects the second nodal point (N’) to the fovea

Question 31

polychromatic rays incident on the eye are subject to the phenomenon of

Answer 31

dispersion

Question 32

what can dispersion cause

Answer 32

rays entering the eye are usually refracted differently depending on their wavelength

Question 33

what is the foveal achromatic axis?

Answer 33

where light rays of all wavelengths pass undisposed from fixation point to fovea

Question 34

the pupillary axis is the line that is

Answer 34

normal to the anterior corneal surface (containing the center of curvature of the anterior corneal surface, Cc) that passes through the center of the entrance pupil (E)

Question 35

the fixation axis is the line

Answer 35

connecting the fixation point to the presumed center of rotation of the eye

Question 36

angle alpha is defined as the angle between the

Answer 36

optical axis and visual axis

Question 37

angle lambda is defined as the angle between the

Answer 37

pupillary axis and line of sight

Question 38

the significance of angle alpha is that

Answer 38

the fovea does not lie on the optical axis of the eye

Question 39

the significance of angle lambda is that

Answer 39

the fixed relationship between pupillary axis and line of sight is useful in detection of strabismus

Question 40

the clinical form of the Hirschberg test is useful as an:

Answer 40

objective, gross assessment of eye alignment, particularly in infants

Question 41

in the Hirschberg test, the subject fixates a small source such as a penlight. light is reflected from the anterior corneal surface and is visible to the examiner as a small image, known as the

Answer 41

Purkinje-Sanson (PS) image