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Transcript of The Eye
Anatomy of the Eye
In Living Color
Using photons that it emits, light whether it's natural or synthetic, it stimulates the Rods and Cones that are embedded within the Pigment Epithelium of our eyes.
When all three of our cones are stimulated, or when our rods are just stimulated you see a white light. This is the reason why its so bright outside when you go outside after being inside all day.
Photons that refract off of objects
will aslo appear white, however
if they're absorbed by our retinas
the objects will appear black.
Visual pigments are created by a compound known as Rhodopsin. This consists of the protein Opsin. Opsin makes up the pigment in our eyes called retinene (Retinal). Vitamin A is the primary component that makes up our Retina. This is why carrots are known to improve vision
Opsin is color, because opsin has varing degrees of light sensitivity because different forms of opsin react to wavelengths of light and color.
There are three types of cones; Red, Green and Blue cones. The different type of stimulation of these cones is the basis for our color vision.
The average person has a cone population of 16% blue cones, 10% green cones, and 74% red cones.
The Red, Green and Blue cones create the color spectrums of our visual worlds.
People who are unable to distingush colors have a form of color blindness.
The most common form of color blindness is
cones are missing, or weak and cannot determine or distingush
Color blindness is inherited, and usually involves one to two pigments.
The sensitivity of the rods
overlap the cones.
These overlaps are
sensitive points of color.
Chambers of the eye
1. Anterior chamber
2. Posterior chamber
There are 3 layers of the eye wall:
The fibrous layer is the outermost layer of the eye.
supports and protects
serves as an attachment site
contains structures that assist in the focusing process
"white of the eye"
Consists dense fibrous connective tissue containing collagen and elastic fibers
The six eye muscles insert on sclera
The surface contains small blood vessels that reach internal structures...can sometimes be visible as red lines
Corneal limbus is the border between the sclera and the cornea
Consists of a dense matrix containing multiple layers of collagen fibers
No blood vessels, superficial epithelial cells obtain oxygen and nutrients from tears
Corneal damage can cause blindness
Corneal replacement is the most common form of transplant surgery
The Fibrous Layer Contains the Sclera and the Cornea
The vascular layer is a pigmented region that include the iris, ciliary body, and choroid.
Providing a route for blood vessels and lymphatics that supply tissues of the eye
Regulating the amount of light that enters the eye
Secreting and reabsorbing the aqueous humor that circulates within the chambers of the eye
Control the shape of the lens
Contains blood vessels, pigment cells, and two layers of smooth muscle fibers...pupillary muscles
The pupil is the central opening of the iris
Eye color is determined by genes that influence the density and distribution of melanocytes on the anterior and interior surface of the iris
Blue eyes happen when there isn't a lot of melanocytes to block the light bouncing of the pigmented epithelium
Vitreous body (posterior): it is a gelatinous mass that helps to stabolize the shape of the eye, which might otherwise distort as the extrinsic muscles change its position within the orbit.
It lies posterior to the cornea and is held in place by ligaments that orginate on the cillary body of the choroid. The lens us used to focus on an image by changing its shape. Concentric layers of cells makes up the lens. A dense fibrous capsule covers it and many of the capsular fibers are elastic. Lens fibers are cells inferior to the lens. They have lost their nuclei and other organelles. Lens fibers are also slender and are filled with transparent proteins called crytallins, whicg allows clarity and focusing power to occur. They are very stable proteins that sta intact forver.
Cataract: when a lens loses its transparency. It can result from injuries, radiation, or reaction to drugs. Senile cataract is natural from aging & is the most common.
Light will be refrated when it passes from one medium to another medium with a different density. The greatest amount of refraction occurs when light passes from the air into the corneal tissues. The lens will create extra refraction as needed to focus the light rays from an object toward focal point whist is a specific point of intersection on the retina. Focal distance is the distance between the center of the lens and its focal point. It is determined by (1) the distance of the object from the lens, and (2) the shape of the lens.
Accomodation is the automatic adjustment of the eye to give it clear vision. The lens will become rounder to focus the image of a nearby object on the retina.
Visual acuity is how the eye is rated. For example, 20/20 is considered "normal." Scotomas are blind spots that appear in the field of vision at postions other than at the optic disc.
Rods and cones of the retina are called phtoreceptors because they detect photons which are the basic units of light. We see the spectrum of visible light. This means that are eyes see specific amounts of color which are photons. Visual pigments are composed of the discs of the outer segement in rods and cones.
Rhodopsin: visual pigment found in rods. It has the protein opsin which is bound to the pigment retinal and that is synthesized from vitamin A.
Retinitis pigmentosa (RP) is is many inherited retinopathies. It is a common visual abnormality which affects 1 of every 3000 people. Visual receptors will deteriorate and a person will become blind.
The intake or release of NA+ ions from a photoreceptor.
NA+ enters the plasma membrane of the photoreceptors, through chemically gated channels.
Chemically gated channels are OPEN in darkness, because of the presence of cyclic-GMP (cyclic guanosine monophosphate), which is made from guanosine triphosphate(GTP).
Membrane potential is -40mV because the photoreceptor is constantly releasing neurotransmitters at its inner segment. It is constantly pumping ions from this location.
As light is introduced to Dark Current, Opsin which is bound to a visual pigment like molecule called Rhodopsin starts to activate.
Opsin has two forms (11-cis or 11-trans)
11-cis is resting form of opsin, but when light absorbtion takes place, it activates the opsin molecule. This activation changes it to 11-trans.
Opsin activates the G-protein transducin
Once the transducin is activated phosphodiesterase (PDE) is activated.
Transducin and PDE binds to the membrane.
PDE breaks down c-GMP.
Because the c-GMP levels declines the Na+ channels close. This happens because during resting state the gates remain open because of the c-GMP.
The rate of Na+ in the cytoplasm decreases causeing hyperpolarization of the membrane to begin.
Na+ reduction equals a reduction in dark current.
Hyperpolarization of the membrane is reach at -70mV.
Neurotransmitter release decrease, this decrease is a form of communication between receptors. It allows receptors to know that photons have been absorbed.
Once signal is transmitted Bleaching takes place.
Bleaching is the breakdown of the Rhodopsin .
Types of Pupillary Muscles
Parasympathetic activation in response to bright light causes the pupils to constrict
Sympathetic activation in response to dim light causes the pupils to dilate
The Ciliary Body
A thickened region that begins deep to the junction between the cornea and the sclera
Ora serrata is the serrated anterior edge of the thick, inner portion of the inner layer
Ciliary muscle is a smooth musclar ring that projects into the interior of the eye
Suspensory ligaments hold the ls posterior to the iris and centered on the pupil so that any light that passes through the pupil will also pass through the lens
The choroid is the vascular layer that separates the fibrous layer and the inner layer posterior to the ora serrata
Contains an extensive capillary network that delivers oxygen and nutrients to the retina
The Inner Layer
The inner layer contains the retina and optic nerve.
The thin outer layer is the pigmented part
The thick inner layer is called the neural part
The pigmented part of the retina absorbs light that passes through the neural part
The pigmented part continues over the ciliary body and iris
The neural part extends as far as the ora serrata
Aqueous Humor is a fluid that circulates within the anterior cavity passing through the pupil. This is formed through active secretion by epithelial cells. This is an important route for nutrient and waste transport. Fluid pressure inside of the aqueous humor helps retain the shape of the eye.
The eye's intraocular pressure is measured in the anterior chamber, where fluid pushes against the inner surface of the cornea. The aqueous humor is secreted into the posterior chamber and then enters the scleral venous sinus, which is a passageway that extends completely around the eye.
The lens lies posterior to the cornea with its primary function being to focus the visual image on the photoreceptors.
The cells in the interior of the lens are known as lens fibers. They are filled with transparent proteins called crystallins which can last for a lifetime. The condition cataracts comes from the lens losing its transparency.
The retina contains many layers of cells
The outermost layer contains photoreceptors
Highly sensitive to light
Enable us to see in a dimly lit room
Sherper, clearer images
Requires intense light
The macula region has no rods
The area of highest concentration of cones is called the fovea centralis...sharpest vision
The Optic Disc
The optic disc is a circular region just medial to the fovea
The origin of the optic nerve
The central retinal artery and vein pass through the center of the optic nerve
Commonly called the blind spot
If light is not refracted properly, the image will be distorted resulting in astigmatism which is a degree curvature in the cornea and lens.
Accomodation- the automatic adjustment the eye makes for clear vision
The lens provides extra refraction needed to focus the light rays from an object toward a focal point ( specific point of intersection on the retina. You can find the focal distance by the distance between the center of the lens, and the focal point. Focal distance has two factors:
1. distance of the object from the lens-
2. shape of the lens.
The retina has about 130 million photoreceptors. To provide useful information, the eye must focus. Focusing usually occurs in two steps, light passes through the cornea, then the lens. The light is refracted or bent when it passes from one medium to another medium with different density.