The Eye Flashcards
Anatomy of the eye: Retina
Packed with receptor cells, which are sensitive to both the brightness (light intensity) and the colour of light
Anatomy of the eye: Optic nerve
Transmits visual information, in the form of electrical impulses, from the retina to the brain
Anatomy of the eye: Sclera
The white of the eye; the opaque protective outer layer
Anatomy of the eye: Cornea
The transparent frontal portion of the eye responsible for refracting light
Anatomy of the eye: Pupil
A hole in the centre of the iris through which light passes to get to the retina
Anatomy of the eye: Iris
Controls pupil diameter and, therefore, the quantity of light reaching the retina
Anatomy of the eye: Ciliary muscles
A ring of smooth muscle that can change the shape of the lens, which the eye uses to focus light
Anatomy of the eye: Suspensory ligaments
A ring of fibres that connect ciliary muscles to the lens
The sclera is
the white of the eye and the opaque protective outer layer of the eye. The cornea is the transparent frontal portion of the eye responsible for refracting light.
Retina Scanning
Your retina is full of receptor cells, which are sensitive to both the brightness (light intensity) and the colour of light.
Scanning the retina
Retina scanning looks at the pattern of blood vessels in your retina to identify you.
The Eye: The iris controls
pupil diameter and the quantity of light reaching the retina. If there isn’t much light then the iris will make our pupils dilate (get bigger).
Accommodation
Accommodation is the process of the lens in your eye changing shape to focus on an object as its distance from the eye changes. This is done by the ciliary muscles and the suspensory ligaments.
Focus
The ciliary muscles and the suspensory ligaments are controlled in different ways. This depends on whether the focus point is close or distant,
Ciliary muscles
A ring of smooth muscle that can change the shape of the lens, which the eye uses to focus light.
Suspensory ligaments
A ring of fibres that connect ciliary muscles to the lens.
Close
Focusing on a close object requires contraction of the ciliary muscles and loosening of the suspensory ligaments. This causes the lens to become thicker and rounder, resulting in significant refraction (bending) of light rays.
Distant
Focusing on a distant object requires the relaxation of the ciliary muscles and tightening of the suspensory ligaments. This causes the lens to become flatter and thinner, resulting in only minor refraction (bending) of light rays.
To focus on a nearby object
, we need our ciliary muscles to contract, loosening our suspensory ligaments. This causes the lens to become thicker and rounder, causing a significant refraction (bending) of light rays.
Adapting to Light Conditions
The iris controls how our eyes adapt to different light levels by controlling the size of the pupil. If there is too much light, the iris decreases the pupil size to reduce the amount of light that reaches the retina.
The control of pupil size
by the iris in response to light changes is an example of a reflex action.
How the iris responds to light intensity:
Iris: dim light (Iris increases pupil size) too much light (Iris decreases pupil size)
Eye Defects
Both short-sightedness and long-sightedness can be treated using different methods.
Treating eye defects
Glasses fitted with lenses that refract light rays to allow the image to form on the retina.
Contact lenses and laser eye surgery can also correct these issues. Synthetic lenses can replace faulty lenses with cataracts. There is no accepted treatment for colour blindness.
Short-sightedness
Short-sightedness happens when rays of light focus in front of the retina.
Long-sightedness
Long-sightedness happens when rays of light focus behind the retina.
Colour blindness
Colour blindness is an inherited condition. It is caused by defects in the cone cells. Cone cells (detect light color) and rod cells (detect light intensity) are photoreceptors (light-sensitive cells in the retina). Red-green colour blindness is the most common type and is more common in men than in women.
Blue-yellow is equally rare in men and women.
Cataracts
Cataracts are caused by a build-up of protein on the lens, that make the pupil cloudy.
Short-sightedness and long-sightedness are
traditionally treated using spectacles fitted with lenses. Modern alternative treatments include contact lenses, laser eye surgery, and replacement eye lenses.
