Lecture 45: Vision 1

Question 1

What is the visible spectrum?

Answer 1

Wavelengths of ~400-750 nm

Question 2

What are the 2 basic components of the eye?

Answer 2

1. Optical component: collecting and focusing light into the plane of the retina
2. Neural component: converts energy of light into patterned changes of membrane potential

Question 2

What is the job of the visual system?

Answer 2

Detect visible radiation and to use it for formation of visual perceptions of the world and guide behaviour

Question 2

Give 2 examples of electromagnetic waves that are present but invisible to the human eye:

Answer 2

Radio and wifi

Question 2

What is the eye?

Answer 2

Organ that detects light and processes visual information to create visual perceptions

Question 3

What is the cornea of the eye?

Answer 3

Transparent avascular capsule in front of iris

Question 4

What is the sclera of the eye?

Answer 4

Fibrous connective tissue forming outer layer of eyeball - whites of the eye

Question 5

What is the iris of the eye?

Answer 5

• Pigmented contractile disc
• Regulates pupil diameter

Question 6

What is the pupil of the eye?

Answer 6

• Black centre aperture
• Appears black due to light absorption into the eye

Question 7

What is the lens of the eye?

Answer 7

Transparent, fibrous and elastic structure, held in place by zonule fibres (ligaments)

Question 8

What is the ciliary body of the eye?

Answer 8

Smooth circular muscle surrounding the lens

Question 9

What is the retina of the eye?

Answer 9

• Inner posterior wall
• Contains light sensitive neural component

Question 10

What is the optic disc of the eye?

Answer 10

• Head of the optic nerve where the axons exit the eye
• Contains no light sensitive neural components

Question 11

What is the choroid of the eye?

Answer 11

• Black pigmented layer behind the eye
• Absorbs stray light and prevents reflection

Question 11

What is the fovea of the eye?

Answer 11

Part of retina where we have highest visual acuity - 2 point discrimination

Question 12

What is the aqueous humor of the eye?

Answer 12

• Fluid between cornea and the lens

Question 13

What side is the optic nerve on?

Answer 13

Neural retina

Question 13

What are the roles of the aqueous and vitreous humor?

Answer 13

• Keeps eye inflated at a constant pressure
• Allows diffusion of nutrients and waste

Question 13

What is the vitreous humor of the eye?

Answer 13

• Gelatinous fluid behind the lens - squishy eyes

Question 13

What is refraction?

Answer 13

• Occurs when light travels from a medium of one refractive index to a medium of a different index e.g. air to water
• Results in change in direction of light

Question 14

What 2 factors is refraction dependent on?

Answer 14

1. Refractive indices of the two media
2. Curvature of the refractive surface

Question 14

What is the refractive index of water?

Answer 14

1.333 - higher than air (1)

Question 14

What is refractive power and what is it measured in?

Answer 14

Ability of a lens to “bend” light
* Measured in diopters

Question 14

What part of the eye is responsible for the greatest amount of refraction?

Answer 14

Cornea

Question 14

What part of the eye is responsible for the fine tuning of refraction?

Answer 14

Lens

Question 15

What does each diopter mean?

Answer 15

* 1 Diopter: lens that converges light to focal point 1 metre away * 2 Diopter: lens that converges light to focal point 0.5 metre away * 10 Diopter: lens that converges light to focal point 0.1 metre away

Question 15

Name 3 processes occur when gaze shifts from distant to near objects:

Answer 15

1. Accommodation 2.Constriction of pupil 3. Convergence of eyes

Question 15

What is the refractive power and focal point of the human eye?

Answer 15

Refractive power: 60 diopters at rest. Focal point: ~1.7cm beyond the lens

Question 15

What occurs during accomodation of the eyes in the near response?

Answer 15

* Contraction of ciliary muscle to alter lens shape and change refractive power (60 → 75 diopters) * Distance vision: ciliary muscles relaxed, lens is flatter, more tension in zonule fibres * Near vision: ciliary muscles contracted, lens is rounder, no tension in zonule fibres

Question 15

What occurs during constriction of pupil in the near response?

Answer 15

* Improved depth of focus, fewer optical aberrations by excluding edges of lens * Sphincter pupillae contracts which only allows central rays through

Question 16

What occurs during convergence of eyes in the near response?

Answer 16

* Objective remain in register on corresponding parts of the two retinae * As object gets closer eyes converge

Question 17

What is myopia?

Answer 17

Nearsightedness * Parallel light rays from distant objects focus in front of retina * Eyeball too long * No mechanism to decrease refractive power of lens further from rest * Distant objects remain out of focus * Image can be focused as object moves closer

Question 18

What is emmetropia?

Answer 18

Normal vision * Parallel and diverging light rays are in focus on the retina * All distant objects are clearly visible with ciliary muscles relaxed * Near objects are clearly visible with ciliary muscles contracted

Question 19

What is the correction of myopia?

Answer 19

Concave/diverging lens to decrease refractive power