Psychology of sight

Question 1

Describe the cornea

Answer 1

• Dome-shaped window which provides the majority of the focusing power of the eye
• It’s clear + avascular and continuous with the sclera

Question 2

Describe the iris

Answer 2

• Thin, elastic, circular structure responsible for controlling the diameter and size of the pupil and this the amount of light reaching the retina
• The iris determines eye colour

Question 3

Describe the lens

Answer 3

• Crystalline structure which aids focusing of light onto the retina
• It’s curvature is altered and controlled by the ciliary muscles and the zonule fibres.
• Clouding of the lens causes cataracts

Question 4

Describe the aqueous humor

Answer 4

• Transparent gel like fluid which fills the anterior part of the eye between the lens and the cornea.
• Formed by the ciliary body and drains via the trabecular meshwork
• It maintains intraocular pressure (IOP), nourishes and removes debris from the avascular anterior segments of the eye

Question 5

What is glaucoma caused by

Answer 5

• An increase in IOP commonly caused by degeneration of the trabecular meshwork reducing drainage of the aqueous humor

Question 6

Describe the sclera

Answer 6

• Fibrous white opaque connective tissue layer covering 5/6 of the eye ball
• Continuous with the transparent cornea.
• Both the sclera and cornea are made of Type 1 collagen

Question 7

Describe the choroid

Answer 7

• Vascular connective tissue layer
• Contains melanin pigment and nourishes outer1/3 of the retina
• Continuous with the ciliary body

Question 8

Describe the retina

Answer 8

• Light sensing layer composed of the retinal pigment epithelium and the neural retina

Question 9

Describe the vitreous humor/body

Answer 9

Transparent gel which provides structure to the eyeball

Question 10

Describe how light enters the retina

Answer 10

Light is focused by the cornea and the lens and then passes through the vitreous humor to the retina

Question 11

What are the 2 types of photoreceptors

Answer 11

• Cones - colour system - daylight
• Rods - no colour - low light levels

Question 12

Where does the process of absorption occur

Answer 12

In the outer segments of the photoreceptors

Question 13

What does the outer segment of a photoreceptor contain

Answer 13

Stack of membranous discs which contain the light sensitive photopigments

Question 14

Describe the appearance of rod cells and cone cells

Answer 14

• Rods have long, cylindrical outer segment containing many disks
• Cones have a short, tapering outer segment with few membranous disks

Question 15

Describe retinal cells

Answer 15

• Horizontal, bipolar, amacrine and ganglion cells do the ‘pre-processing’ before sending the visual information through the optic nerve
• Each photoreceptor is in synaptic contact with two types of retinal neurons: bipolar cells and horizontal cells
• Bipolar cells create the direct pathway from photoreceptors to ganglion cells
• Horizontal cells feed information laterally in the outer plexiform layer to influence neighbouring cells
• Amacrine cells control and modulate the majority of the inputs to the retinal ganglion cells and the ganglion cell responses

Question 16

Describe the spectral sensitivity of photoreceptor pigments

Answer 16

• The pigment in all rods is called rhodopsin
• In each cone there is one of three types of opsins; red, green and blue
• Each cone opsin has a different spectral sensitivity