Biology- the eyeball

Receptor

A specialised cell that receives stimuli from the external & internal environment

Protective structures in place externally

Bony socket + adipose tissue

Eyebrows

Eyelids + eyelashes - reflex closure when exposed to bright light or moving object

• spreads tears+ oily secretion over cornea

• Stops objects touching conjunctiva

Lachrymal glands- tears wash away dust, moisten conjunctive, lysosome enzymes prevent microbial infections

Glands of Meiboom- oil secretion mixes with tears = hydrates the eye

Define a sense organ

a concentration of a certain receptors, together with other tissues for support and effective function.

Three outer most layers of the eye

• outer sclera - continues into the cornea, opaque, tough

• Middle choroid - vascular and nutritive: it contains pigments and blood vessels provide retina with nutrients and oxygen. - it also continues into the ciliary body, suspensory ligaments and iris

• Retina - contains photoreceptors ( rods and cones)

Another name for 3D vision

binocular vision

Define pupillary mechanism

the physcological response that varies the size of the pupillary

Define accommodation

the adjustment of the curvature of the lens for vision at distances closer than 6m

What shape is this lens? what does it do to light

biconvex, refracts light

What does biconcave mean?

the light is refracted at an angle, this is not the shape of our Len’s

State two functions of the vitreous humour in the posterior chamber.

Helps maintain the shape of the eye

Plays a role in refraction of light

Prevents desiccation of structures in the eye

Describe the visual defect when the curvature of the cornea is uneven

Astigmatism

Explain how someone’s eyesight is effected if they develop cataracts

• the lens will become opaque

• No/ less light will enter the eye

• Causing no sight

Describe the process of accommodation that takes place when an object is less than 6m away

• the ciliary muscles contract

• The suspensory muscles slacken

• The tension on the lens decreases

• Causing lens to become more convex

• Light rays are refracted more

• Therefore light focuses on the retina

answer

B

Name the type of lens for people with Myopia

biconcave lenses will help to diverge the light

To ensure it focuses on the retina

Explain one way that the lens is structurally suited for accomodation

• it is elastic

• It can change its shape to focus on light rays on the retina

Describe astigmatism

Light is refracted unevenly due to uneven cornea

Forms a blurred image

Two pathways of light at two different focal points in the retina