The Human Eye Flashcards
Learn about the basic structures of the eye, how they respond to light, and treatments to common defects of the eye (Myopia and Hyperopia).
What is an eye?
The eye is a sense organ, containing receptors to Light Intensity and Colour.
What is the Function of the Cornea?
The conrea Refracts Light (bends it) as it enters the eye.
What is the Iris?
The Iris controls how much light enters the pupil.
What is the Function of the Lens?
The Lens further Refracts Light to focus it on the Retina.
What is the Function of the Retina?
The Retina contains Light Receptors. These Recept light.
What is the Function of the Optic Nerve?
The Optic Nerve carries Impulses between the Eye and Brain.
What is the Function of the Sclera?
The Sclera is a tough, white outlayer of the eye – this helps to protect the eye from injury.
What are the TWO Main Types of Light Receptors, and What are They Sensitive to?
The TWO main types of Light Receptors are Rods and Cones.
Rods are more sensitive to Light than cones, so they are useful for seeing in Dim Light.
Cones are more sensitive to Colour than Rods.
What is Accomodation?
Accomodation is the process of Changing the Shape of the Lens to Focus on a Distant or Near Object.
When Does the Lens Become Thinner, and Why?
To focus on Distant Objects, the Lens becomes thinner; this allows the Light Rays to Refract (Bend) only slightly.
When Does the Lens Become Thicker, and why?
To Focus on Near Objects, the Lens becomes thicker; this allows light to Refract Strongly.
How do Eye Structures respond to the Positioning of Objects?
When the positioning of an Object is Near….
The CIliary Muscles Contract The Suspensory Ligaments Slacken/Loosen The Muscle Tension on the Lens is Low The Lens Shape becomes Thicker/Fatter Light is Refracted Strongly
When the Positioning of an Object is Distant
The Ciliary Muscles relax The Suspensory Ligaments Tighten/Are Stretched The Muscle Tension on the Eye is High The Lens Shape becomes Thin/Thinner Light is Refracted only Slightly
What are Two Common Defects of the Eye, and What do They do?
Two common eye defects would be Myopia and Hyperopia.
Myopia is short-Sightedness, whilst Hyperopia is Long-Sightedness.
How Does Myopia Affect People, and What is it Caused by?
People with Myopia can see Near Objects, but struggle to see Distant Objects.
Myopia is caused by one of two things.
- The Eyeball is Elongated. This makes it so the distance between the Lens and Retina is too great.
- The Lens is too Thick and Curved, so the Light is Focused in-front of the Retina.
How does Hyperopia Affect People, and What is it Caused by?
People with Hyperopia can see Distant objects clearly, but struggle to see Near Objects.
Hyperopia can be caused by one of two things:
- A short eye; when the eye is too short, the distance between the eye and retina is too small;
- Loss of Elasticity in the eye; the eye can’t become thick enough to focus (this is often age-related).
As a result, the Lens focuses light Behind the Retina, instead of onto it.
