Lec 10: Visual systems

Question 1

Outer layer

Answer 1

cornea and sclera: protects inner components of the eye and helps to maintain its shape

Question 2

Vascular (middle) layer

Answer 2

choroid, iris, ciliary body. choroid: contains vascular supply and minimises light reflection within the eye. Iris and ciliary body: control amount of light entering eye and focusing of that light on the retina

Question 3

Nervous (inner) layer

Answer 3

sensory layer containing retina. space behind lens contains vitreous humour: watery acellular substance. space between cornea and iris contains aqueous humour: transparent fluid

Question 4

Iris. what is does and muscles around

Answer 4

controls the diametre of the pupil and thus amount of light reaching the retina. contraction of the pupillary sphincter muscle closes the pupil in a circular motion and a set of pupillary dilator muscles pull the iris radially to enlarge the pupil

Question 5

Accommodation (adjusting the lens)

Answer 5

the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. this is done by ciliary muscles of with a change of shape of the lens

Question 6

Ciliary muscle

Answer 6

ring of smooth muscle surrounding the lens, it is attached to the lens through ligaments (zonular fibres)

Question 7

Emmetropia

Answer 7

normal vision

Question 8

hyperopia

Answer 8

(farsightedness) occurs when the focal point falls beyond the retina. It can be corrected by a biconvex lens. (things up close = blurry)

Question 9

myopia

Answer 9

(shortsightedness) occurs when the focal point falls in front of the retina. it can be corrected by a concave lens. (things far away = blurry)

Question 10

Astigmatism

Answer 10

causes blurred vision due either to the irregular shape of the cornea or sometimes the curvature of the lens inside the eye.

Question 11

Vestibulo-ocular reflex

Answer 11

nerve reflex that co-ordinates activation of the vestibular system and eye movement. function is to maintain the orientation of the eyes in space during head movements. achieved by co-ordinatelt relaxing and contracting the lateral and medial rectus muscles so the eyes move in the opposite direction to head movement.

Question 12

Retina

Answer 12

Photosensitive, organised into 2 layers - pigmented epithelial layer containing melanin, neural layer is multi-layered containing photoreceptors and lots of neurons

Question 13

fovea (in retina)

Answer 13

area of greated visual activity due to very high density of cones and the arrangement of their connections with neural cells and absense of blood vessels and other overlying cells

Question 14

optic nerve

Answer 14

leave the eye at the optic disk. there are no visual receptors over the disk it is called the blind spot

Question 15

Photoreceptors: rods

Answer 15

responsible for vision at low light levels (scotopic vision). they do not mediate colour viion and have low spatial acuity (ability to discriminate 2 stimuli close in space)

Question 16

photoreceptors: cones

Answer 16

active at higher light levels (photopic vision), are capable of colour vision and are responsible for high spatial acuity (the central fovea is populated exclusively by cones). 3 types: short-wavelength (S) sensitive cones, middle-wavelength (M), long-wavelength (L)