Topic 5- Homeostasis- The Eye Flashcards
Description of the eye
The eye is a sense organ that contains receptors sensitive to light intensity and colour.
The Cornea
Transparent lens
Refracts (bends) light as it enters the eye
Iris
Controls how much light enters pupil
Pupil
Hole that allows light to enter the eye
Lens
Transparent disc
Changes shape to focus light onto the retina
Retina
Contains receptor cells rods and cones
Rods
Rods in retina detect light intensity
Cones
Cones in retina detect colour
Optic nerve
Seneeiy neurone that carries electrical empulses between the eye and the brain
Ciliary muscle
Muscle in shape of a ring around the eye.
It changes shape of the lens to when eyes focus on a near object.
Process is called accomodation
Accomodation
When the ciliary muscles around eye contract to when eyes focus on an object’s that near
The Pupil Reflex
It’s a reflex action to protect the eye from any damage caused by bright light and protect us from not seeing objects in dim lights
As it’s a reflex, it happens automatically
Dim light:
Pupil dilates (widens) so more light enters the eye
Radial muscles contract
Circular muscles dilate
Bright light:
Pupil constricts (becomes smaller/narrows) so less light enters the eye
Radial muscles relax
Circular muscles contract
Close up objects:
Ciliary muscles contracts
Suspensory ligaments relax
Lens become thicker
Result: light is refracted more by lens to focus in near object
Distant objects:
Ciliary muscles relax
Suspensory ligaments are pulled tight
Lens become thinner
Result: light is refracted less allowing the eye to focus on distant objects
What are the two common defects if the eye
Myopia
Hyperopia
What is Myopia and how is it treated?
Myopia is shirt sightedness:
The eyeball is too elongated
The lens are too thick and curved
The image is in focus in front if the retina
Treatment:
Concave lens corrects rays so that they can focus on the retina
What is hyperopia amd how is it treated?
Hyperopia is long-sightedness:
The eyeball is too short
Therefore the image is brought into focus behind the retina
Treatment:
Convex lens refracts light rays so that they can focus on the retina
Appart from slectacke lenses, what other treatments are available for both myopia and hyperopia?
Hard + Soft contact lenses
( Soft lenses have a higher risk of eye infections)
Laser surgery
(For myopia: the conrea isslimmed down, reducing refractive power)
(For hyperopia:the cornea shape is changed so that the refractive power increases)