Lecture 1- Eyes Flashcards
What are the special senses?
Vision, smell, taste, hearing and equilibrium
Special sensory receptors
Distinct receptor cells located in the head region
Which sense is most dominat?
Vision
70% of sensory receptors are found in the eye
Accessory structures of eye
eyebrows
eyelids
conjunctiva
lacrimal apparatus
extrinsic eye muscles
What does the eye consist of?
Accessory structures and the eyeball
Palpebrae (eyelids) and eyelashes
protect eye from physical danger as well as drying out
Conjunctiva
Transparent membrane that produces lubricating mucus to prevent eye from drying out
What does Lacrimal apparatus consist of?
lacrimal gland, that secretes a dilute saline solution (tears) and small ducts that drain excess fluid into the nasolacrimal duct.
What does lacrimal fluid contain?
mucus, antibodies, and lysozyme to cleanse, moisten, and protect the eyes.
What is the movement of each eyeball controlled by?
six extrinsic eye muscles that are innervated by the abducens and trochlear nerves.
What are the Three layers the wall of the eye is composed of?
Fibrous
Vascular
Inner layers (retina,neural)
Fibrous layer
Two regions
Sclera (white part of eye) and cornea (clear, allows light in)
Sclera
White part of eye
Cornea
Clear and allows light to enter the eye
Anterior cavity
Before lens
filled with aqueous humour, that supplies nutrients and oxygen to lens and cornea while carrying away wastes.
This fluid is continuously produced and drains away.
Posterior cavity
After lens
filled with clear gel called vitreous humour that transmits light, supports posterior surface of lens, holds retina firmly against pigmented layer, and helps maintain intraocular pressure.
Choroid
vascular middle layer of tissue that nourishes eye layers.
Ciliary body
consists of smooth muscle that encircles the lens, determining its shape and controlling the amount of light that enters the eye.
Iris
surrounds the pupil, controls pupil size and the amount of light that enters the eye.
Has only one colour - brown
What does the Inner layer of eye contain?
the photoreceptors, rods and cones, as well as bipolar cells, ganglion cells, and glia.
What does Neural layer of retina include?
an optic disc (blind spot), where the optic nerve exits the eye; there is no room for photoreceptors here.
Macula lutea
has a pit in its centre called the fovea centralis.
Fovea centralis
has the highest density of cones, producing the most detailed colour vision.
only contains cones, so that is the region with the best visual acuity. We move our
eyes to focus the image of an object on the fovea.
Rods
highly sensitive to light
best suited to night vision but cannot resolve colour or sharp images.
found in your peripheral vision and are more numerous than cones.
Cones
less sensitive to light
best adapted to bright light and provide high-resolution colour vision.
Humans have three kinds of cones.
Glaucoma
condition in which drainage of aqueous humor is blocked, causing fluid to back up and increase pressure within the eye.
Pressures may increase to dangerous levels and compress the retina and optic nerve, leading to blindness.
Cataracts
clouding of the lens that can cause dim vision, blurry vision, faded colours, trouble with bright lights and trouble seeing at night.
Lens
avascular, biconvex, transparent, flexible structure that can change shape to allow precise focusing of light on the retina.
Distant vision
ciliary muscles are completely relaxed causing maximum flattening of the lens.
Far point of vision
The distance beyond which no change in lens shape is required.
In a normal eye, this is a distance of about 6 meters, or 20 feet.
Close vision
Lens thickens to increase light refraction
Pupils constrict to better direct light into lens
Convergence of eyeball to allow object to remain focused on foveae
Near point of vision
occurs at the point of maximal thickening of the lens, and is 10 cm, or 4 inches, from the eye.
Myopia (nearsightedness)
Occurs when objects focus in front of retina
Can see close objects without a problem but distant objects are blurred
Hyperopia (farsightedness)
Occurs when objects focus behind retina
Can see distant objects clearly but close objects are blurred
Astigmatism
results from an uneven curvature of the cornea or lens, which produces blurred images.
What must light pass through in order to be detected?
cornea, aqueous humour, lens, vitreous humour, the entire neural layer of retina, and finally arrive at the photoreceptors.
Most refraction occurs at cornea but it cannot change focus
