Lecture 6

Question 1

what does the law of parsimony recommend for using a model eye?

Answer 1

using the simplest model that is adequate for an application

Question 2

what is the name of the #1 schematic eye and how many surfaces does it have?

Answer 2

Gullstrand/”Exact eye”

6 surfaces

Question 3

what is the name of the #2 schematic eye and how many surfaces does it have?

Answer 3

Le Grand full theoretical schematic eye

4 surfaces

Question 4

what is the name of the #3 schematic eye and how many surfaces does it have?

Answer 4

Gullstrand number 2 schematic eye/Gullstrand-Emsley schematic eye/”Simplified eye”
3 surfaces

Question 5

what is the name of the #4 schematic eye and how many surfaces does it have?

Answer 5

Reduced schematic eye
1 surface (combined cornea and lens)

Question 6

what happens to the cardinal points when you reduce the number of surfaces in a schematic eye?

Answer 6

the cardinal points are unchanged - all have the same function

Question 7

if you wanted to study the back vertex power, which schematic eye would you choose?

Answer 7

Le Grand = needs to have 2 surfaces for the cornea and be the simplest option (so not #1)

Question 8

if you wanted to study accommodation, which schematic eye would you choose?

Answer 8

Gullstrand #2 or Simplified eye = need to have surface for lens and be the simplest (so not 1 or 2)

Question 9

what is the anterior focal length for the schematic eyes? what is the posterior focal length?

Answer 9

anterior = -16.67mm
posterior = 22.22 mm
(eq. power = 60D)

Question 10

what is the 1st focus for the focal points?

Answer 10

axial object position for which the image will be formed at infinity

Question 11

what is the 2nd focus for the focal points?

Answer 11

axial image point of an infinitely distance object

Question 12

what are the nodal points?

Answer 12

any incident ray which passes through the 1st nodal point leaves the system as though from the 2nd nodal point and parallel to the incident ray (unchanged direction but maybe displaced)

Question 13

what do the principal points do?

Answer 13

locate the front and back surfaces of an equivalent thin lens

Question 14

where is the 1st principal point?

Answer 14

located where the exiting rays parallel to the optical axis intersected the refracted rays coming from the 1st nodal point

Question 15

where is the 2nd principal point?

Answer 15

located where the incident rays parallel to the optical axis intersect the refracted rays converging to the 2nd focal point

Question 16

what are cardinal points?

Answer 16

3 paris of points that define an equivalent thin lens whose paraxial performance is identical to the original thick lens or combination of lenses (eye) = F,F’,P,P’,N,N’

Question 17

what is the depth of the first nodal point relative to the anterior corneal surface?

Answer 17

7.05mm (N’ is 0.3mm away from N)

Question 18

what is the reduced surface representing?

Answer 18

the “balance of power” between the cornea and crystalline lens

Question 19

where does the reduced surface sit in the reduced eye?

Answer 19

about 1.67mm behind the (anterior) corneal plane

Question 20

where is the pupil in the reduced eye?

Answer 20

considered to coincide with the reduced surface (in reality it is about 2mm behind the reduced surface)

Question 21

what is the spherical refracting surface in the reduced eye?

Answer 21

5.55mm

Question 22

what index of refraction do you use for the interior of the reduced eye?

Answer 22

n’ = 1.333