GCSE AQA Biology- The Eye

Sclera

Tough protective, supportive layer around the eye

Cornea

Transparent outer layer found at the front of the eye. Refracts (bends) light into the eye

Iris

Contains muscles that allow it to control the diameter of the Pupil (hole in the middle) and therefore how much light enters the eye

Lens

Focuses light onto the retina

Retina

Contains receptor cells (rods and cones) sensitive to light intensity and colour

Rods

responsible for vision at low light levels, black and white vision

Cones

active at a higher light level; red, blue or green vision

Ciliary Muscles

Controls the shape of the lens

Suspensory Ligaments

Attaches the lens to the ciliary muscle

Optic Nerve

Carries image impulses from the receptors on the Retina to the Brain

Adjusting To Bright Light

Pupil decreases in size as the circular muscles in the Iris contract and radial muscles relax

Adjusting To Dim Light

Pupil enlarges in size as the radial muscles in the Iris contract and the circular muscles relax

Focusing On Near Objects

Ciliary muscles contract, meaning the suspensory ligaments slacken, causing the lens to fatten (curve) increasing the amount by which it refracts light

Focusing On Distant Objects

Ciliary muscles relax, meaning the suspensory ligaments tighten, causing the lens to become thinner (less curved), meaning it refracts light by a smaller amounts

Long-Sighted (Hyperopia)

-Unable to focus on near objects

-Image behind retina instead of in it

-Lens doesn't refract the light enough

-Convex Lenses are used

Short-Sighted (Myopia)

-Unable to focus on distant objects

-Eyeball too elongated

-Lens refracts light too much

-Concave Lenses are used

Contact Lenses

Thin and sit on the surface of the eye and compensate for fault in focusing

Laser Eye Surgery

Can correct vision by changing the shape of the Cornea but has the risk of complication

Replacement Lens Surgery

More effective than Laser Eye Surgery but carries even higher risks

Accommodation

process of changing the shape of the lens to focus on near or distant objects