schematic eye

Question 1

outline basic principle of image formation (3)

Answer 1

1. light enters eye through cornea and is refracted by cornea and lens
2. lens shape can be altered to change power when the eye focuses at different distances (accomodation)
3. beam diameter of pencil is controlled by iris (aperture stop) and light pencil passes through pupil (iris opening)

Question 2

real eye vs schematic eye (2v4)

Answer 2

real eye:

• aspheric surface
• crystalline lens with a gradient refractive index

schematic eye:

• spheric surface
• lens with constant refractive index
• complexities ignored -> only optical components considered
• prioritize cardinal points (principal, nodal and focal points)

Question 3

outline the 2 schematic eye models (4v3)

Answer 3

1. six surface schematic eye (gullstrand-emsley)
   - 2 for cornea, 4 for lens
   - equivalent core lens
   - hyperope (+1D)
   - accomodated and unaccomodated versions
2. three surface schematic eye
   - 1 for cornea, 2 for lens
   - emmetropic
   - refractive index of lens increased to 1.416 to make up for loss of gradient

Question 4

at what interfaces does refraction by eye occur (3)

Answer 4

1. air-cornea interface (majority)
2. aqueous humour-lens interface
3. lens-vitreous humour interface

80% refraction -> in cornea
20% refraction -> in lens

Question 5

outline reduced eye model (3)

Answer 5

• single refracting surface
• average equivalent power (+60D)
• emsley + bennet-rabbetts eye model

Question 6

what effect would occur when replacing the cornea with a single refracting system

Answer 6

• replacing cornea with a single refracting system would NOT affect the size of the retinal image
• > but would make the design unsuitable for the study of purkinje images