Eye Notes

Parts of sight sense• Eyes• Accessory organs

– Eyelids (palpebrae)-thinnest skin• Protect eye

– Canthus-corners of the eye– Eyelashes-hairs that prevent particles from getting into the eye– Conjuctiva-membrane inside eyelids (prevent eyelids from

sticking together)• Conjunctivitis-pink eye

– Lacrimal apparatus-has a gland that produces tears/pink tissue in corner of eye

• Tears have lysozymes-antibacterial enzyme– 6 muscles

Parts of outer eye

• Cornea-transparent window of the the eye– Focus entering light– Covers colored portion of the eye– Limited repair

• Sclera-white portion of eye– Made of collagen and elastin– Protect eye and attaches muscles

• Optic nerve

Blindness-loss of transparency of corneaCan receive a donor cornea/no blood involved

Parts of fibrous tunic-Mechanical support and physical protection-Important for focus

Vascular Tunic (middle eye)

• Regulate amount of light entering the eye• Control shape of lens (an essential part of the focusing process• Choroid coat

– Vascular and nutritive– Joined to sclera– Melanocytes (pigments)-absorb excess light and keep inside

eye dark (tons of pigments)

• Ciliary body-forms a ring around the eye• Composed of muscles and ligaments• Holds lens in position

Middle Eye (cont)

• Lens-behind the iris and pupil– Held in place by suspensory ligaments– Ciliary muscles and ligaments help to change its

shape in order to focus• Accomodation

– Relaxation creates flat shape to see distance

– Contraction creates convex shape to see close

• Cataracts-lens become cloudy and opaque– Can cause blindness

Iris-part of middle eye

• Thin diaphragm of connective tissue and smooth muscle

• Colored portion of eye– Thickness and # pigments determines eye color– More is black, brown colors; less is blue and gray

• Adjusts the amount of light that enters the pupil – The pupil is the opening at the center of the iris.– Dark part of eye

• Aqueous humor-fluid between cornea and lens– Provides nourishment and maintains shape

Smooth Muscle Role

• Regulates light by regulating pupil size– Contract-small size so

less light• During bright light

– Relax-big size so more light

• During dim light

• http://www.youtube.com/watch?v=0HzWmldLDHI&feature=related

Glaucoma

• Rate of aqueous humor formation is more than its rate of removal

• Builds pressure on the eye– Blood vessels shut-rob cells of nutrients

• Cells die and may cause blindness

Inner Eye Parts• Retina

– Photoreceptors– Thin and delicate

– Contains a depression called fovea centralis– This produces the sharpest vision

• Optic Disc– Where nerve fibers leave the eye and join the optic

nerve– Lacks receptor cells-known as blind spot– Vitreous humor-liquid that fills the posterior cavity

• Floaters-when clumps form in this liquid

Light Refraction

• Refraction-bending of light waves

• Convex surface of cornea and the lens refracts light and converges the rays onto the retina– Image is upside down and reverse

• Visual cortex interprets this image correctly

Visual Receptors

• Rods– Long and thin

– Provide black and white vision

– More sensitive to light

– Provide vision in dim light

• Cones– Short and blunt

– Color vision

– Sharp image– To see something in detail,

a person moves the eyes so the image falls on the fovea centralis (has tons of cones)

– Cone numbers decrease as you move away from fovea centralis

Visual pigments

Rhodopsin-light sensitive pigment Turns into opsin (protein) and retinal in the presence of light

This break down triggers an enzyme to change the cell membrane of the rod cell Change causes a nerve impulse to be sent

Nerve impulses travel away from the retina and are interpreted as vision.

The light-sensitive pigments in cones are also proteins; there are three types, each containing a different visual pigment.

Visual Pigments (cont)

The wavelength of light determines the color perceived from it; each of the three pigments is sensitive to different wavelengths of light.

The color perceived depends upon which sets of cones the light stimulates: if all three sets are stimulated, the color is white; if none are stimulated, the color is black.

Colorblindness-lack of cone pigments

• Nearsightedness-myopia– Concave lens

• Farsightedness-hyperopia– Convex lens

• Ophthalmoscope-used to examine the interior of the eye