The Eye Flashcards
Photoreceptors
The receptors that detect light stimuli
Outer fibrous layer of eye:
SCLERA
- white inelastic layer of connective tissue
- protects internal parts of eye
- helps to maintain spherical shape of eye
- serves for muscle attatchment
Outer fibrous layer of eye:
CORNEA
- transparent front part of sclera
- more convex than rest of eyeball
- allows light though to inner layers of eye
- NB curvature causes the refraction of incoming light rays
Middle Vascular Layer:
CHOROID
- darkly pigmented vascular layer
- Pigment absorbs light to prevent internal reflection which may cause blurred images
Middle Vascular Layer:
CILIARY BODY
Thickened front part of the choroid with involuntary muscles. These attach to the lens and can contract to change the curvature of the lens
Suspensory ligaments
A series of fibres that connect the CILIARY BODY of the eye with the lens, keeps it in place.
Middle Vascular Layer:
IRIS
- Round
- Coloured
- Has both radial and circular involuntary muscles that pull the iris open or closed
- NB THIS ALLOWS REGULATION OF LIGHT INTO THE EYE
Lens
- rubbery, elastic transparent, biconvex structure (held in place by suspensory ligaments attached to the ciliary body)
- changes shape to refract light of near and far objects onto the retina
Aqueous humours
Watery fluid in front of the lens, to maintain shape of the eye and holds the retina against the choroid
Vitreous humours
watery fluid behind the lens, similarly to the function of the aqueous humours
RETINA
pigmented layer and nerve tissue with photoreceptors that detect light stimuli and convert the stimuli into nerve impulses.
There are 2 types of photoreceptors: Rods and Cones
Rods
light sensitive and give rise to black and white vision
Cones
allow for bright light and color vision
How your eye works (FRIP)
F - focused onto retina
R - refracted light on retina is upside down
I - info sent along optic nerve
P - processed by brain so you see it normally
ACCOMMODATION
Distant Objects
concave and/or flatter
contracting ciliary muscles
suspensory ligaments relax
ACCOMMODATION
Nearby objects
convex and/or rounder
ciliary muscles relax
suspensory ligaments contract
PUPILLARY MECHANISM
-DIM LIGHT
radial muscles contract
circular muscles relax
pupil widens (dilates)
PUPILLARY MECHANISM
BRIGHT LIGHT
radial muscles relax
circular muscles contract
pupil shrinks (constricts)
Binocular vision
The left and right eyes each form their own image of am object. This provides a wider field of vision and is known as binocular vision.
Stereoscopic Vision
The ability of the brain to combine the two images in the left and right eyes to form one, 3D combined image with depth perception.
SHORT-SIGHTEDNESS
myopia
Caused by:
- elongated eyeball
- the cornea being too curved for the length of the eyeball
- the inability of the lens to become -less convex
When looking at distant objects, the light rays focus in front of the retina, causing blurred vision
LONG-SIGHTEDNESS
hypermetropia
caused by:
- an eyeball that is too short (rounded)
- the cornea not being curved enough for the length of the eyeball
- the inability of the lens to become more convex
Astigmatism
With an astigmatic cornea, light entering the eye is not focused evenly on the retina. This leads to blurred vision, headaches and squinting of the eyes.
Treatment:
- glasses with prescription lenses
- contact lenses
- laser therapy
Cataracts
Cataracts occur when the clear transparent lens becomes cloudy. This prevents light from entering the eye and results in blurred vision. The cataract develops slowly and increases in size over time.
The causes could be due to congenital factors, age-related hardening of the lens, diabetes, strong sunlight, and heavy smoking.
