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Cornea

clear/transparent, anterior part of the eyeball covering the iris, pupil, and anterior chamber that functions to refract (bend) light to focus a visual image(admits light into the eye)

Sclera

White of the eye; connective tissue that maintains the shape of the eyeball, provides a site for muscle attachment

Limbus

The area where the sclera and cornea meet.(border)

Iris

diaphragm consisting of thin overlapping plates that can be adjusted to change the diameter of a central opening(pupil)
(The pigmented part of the eye when we look through the cornea.)

Pupil

black adjustable circular opening in the center of the iris through which light passes as it enters the eye

Lens

a biconvex, transparent, flexible, avascular structure that allows precise focusing of light onto the retina, composed of epithelium and lens fibers( lens epithelium, lens fibers)(Cloudy-Cataract;changes shape to help focus images on the retina)

"Eye shine" in nocturnal mammals is different from the "red eye" seen in some flash photographs. Eye shine is the reflection of light off the tapetum lucidum. What visual mechanism might explain red eye?

Due to the bright light reflecting off the back of the retina

What is the consensual reflex of the pupil?

Increase or decrease of one pupil when the other pupil is exposed to a respective decrease or increase in light.

How does vitreous humor differ from aqueous humor in terms of location and viscosity?

Vitreous humor is located in the posterior cavity and is more viscous (thicker) than aqueous humor. Aqueous humor is located in the anterior cavity and is more watery.

What layer of the eye converts visible light into nerve impulses?

Retina

What nerve takes the impulse of sight to the brain?

Optic nerve

What is another name for the sclera?

White of the eye

How would you define an extrinsic muscle of the eye?

Attaches to the sclera and moves the eyeball

What gland produces tears?

Lacrimal gland

What is the name of the transparent layer of the eye in front of the anterior chamber?

Cornea

The iris of the eye has what function?

The iris controls the size of the pupil.
Which in turn, controls the amount of light entering the eye

What is the middle layer of the eye called?

Vascular tunic(Choroid,ciliary body lens)

Is the lens anterior or posterior to the iris?

posterior

Which retinal cells are responsible for vision in dim light?

Rods

How would you define the near point of the eye?

Minimum focusing distance of eye

What do the numbers 20/100 mean for visual acuity?

A person with this vision can see at 20 feet what an average sighted person can see at 100 feet.

What is astigmatism?

Defect in cornea or lens that causes an uneven bending of the light rays in that area of the eye

In what area of the eye is the blind spot located?

Optic Disk.

Fibrous tunic

Outer most layer, sclera & cornea
I.) Mechanical support & some physical protection
II.) Attachment site for muscles
III.) Assist in focusing

Lacrimal gland

Superior and lateral to eyeball in frontal bone
-secretes tears

Nasolacrimal duct

Delivers tears to nasal cavity

Conjunctiva

mucous membrane Covering of inner eyelids & outer eye

Vascular tunic (uvea)

Middle layer(the part of the eye that contains the iris and ciliary body and choroid-uvea)
I.) Route for blood vessels & lymphatics
II.) Regulate amount of light
III.) Secrete & reabsorb aqueous humor within eye chamber
IV.) Control shape of lens

Choroid

a vascular network, many melanin containing pigment cells, appears black in color, prevents the reflection of light inside the eye(in vascular tunic)
-between the retina and the sclera.provides nourishment to the outer portion of the retina

Ciliary body

Ciliary ring: a thickened ring of tissue surrounding the lens, composed of smooth muscle bundles (ciliary muscles), anchors the suspensory ligament that holds the lens in place, changes shape of the lens

-Ciliary process: produces aqueous humor ring of muscle behind the peripheral iris that controls the power of the lens,

Suspensory ligaments

ring of fibers that radiate from the edge of the lens & attach it to the ciliary body. Help change the shape of the lens.

Nervous tunic (retina)

Innermost layer
I.) Pigmented part
II.) Neural part
lines the posterior two-thirds of the eye. Since a significant portion of the retina is made up of nerve fibers that carry light impulses to the optic nerve it has been described as an extension of the brain

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information(Innermost layer of eye;back wall of the eyeball)has over 126 million photoreceptor cells which respond to light,

Macula lutea

-Where visual image arrives, no rods,
-a yellowish central area of the retina that is rich in cones and that mediates clear detailed vision,
- a yellow spot on the retina that mediates the clearest, most detailed vision(responsible for central vision)

Fovea

Highest concentration of cones, center of macula lutea, an area of the retina where vision is the clearest and there are no rods at all(the central focus area of the retina )

Optic disc

location through which nerves exit and blood vessels enter the eye, no photoreceptor cells, the "blind spot" of the eye

Optic nerve

the cranial nerve that serves the retina;
-carries neural impulses from the eye to the brain
-CN II

Eyebrows

prevent perspiration from entering the eyes and help shade the eyes, function: keeps sweat from entering eye, and shade from sun

Eyelids

consist of five tissue layers, protect the eyes from foreign objects (eyelashes help), help lubricate the eyes by spreading tears over their surface, lubricating glands associated with the eyelids; meibomian glands and sebaceous glands, ciliary glands lie btw the hair follicles

Eyelashes

project from the free margin of each eyelid, initiate reflex blinking

The internal cavity is filled with fluids called.....

Humors

Nervous layer

composed of retina, macula (fovea centralis), optic disc

Sphincter pupillae

close vision and bright light: pupils constrict

Dilator pupillae

distant vision and dim light: pupils dilate

Color

is determined by the amount of melanin present, large amounts of melanin (Brown or black eyes) less melanin (light brown, green, or grey eyes) even less melanin (blue eyes)

The eye is composed of 3 chambers

Anterior chamber, posterior chamber, vitreous chamber

Anterior chamber

located between the cornea and the iris

Posterior chamber

located between the iris and lens

Vitreous chamber

much larger then the other two chambers, located posterior to the lens

Aqeous humor

fills the anterior and posterior chambers of the eye, supports, nourishes, and removes wastes for the cornea, which has no blood vessels, produced by the ciliary processes as a blood filtrate, returned to the circulation through the sclera venous sinus(watery)

Vitreous humor

fills the vitreous chamber, contributes to intraocular pressure, helps maintain the shape of the eyeball, holds the lens and retina in place, functions in the refraction of light in the eye(gel)

With age, the lens becomes more compact and dense and loses its

elasticity

Refraction

bending of light, light striking a concave surface refracts outward (divergence), light striking a convex surface refracts inward (convergence), converging light rays meet at the focal point and are said to be focused

What Responsible for the most of the gross refraction of light

Cornea

fine adjustments to refraction are accomplished by changing the shape of the

Lens

Normal resting condition of the lens

relaxation of the ciliary muscles causes the lens to flatten, producing the emmetropic eye

1. Accommodation by the lens*

contraction of the ciliary muscles causes the lens to become more spherical, change in the lens shape enables the eye to focus on objects that are less than 20 ft. away

2. Constriction of the pupil*

increases the depth of the focus

3. Convergence of the eyes*

Medial rotation of the eyes

Structure and function of Retina

Pigmented layer of the retina provides a black backdrop for increasing visual acuity, Rods and cones synapse with bipolar cells, bipolar cells synapse with ganglion cells, which form optic nerve

Rods

responsible for non vision, vision in low illumination (night vision), rod shaped photoreceptive part of the rods contains about 700 double layered membranous discs- discs contain rhodopsin a purple pigment consisting of the protein opsin covalently bound to a yellow photosensitive pigment called retinal (derived from vitamin A)

Rhodopsin

Exposure to light activates rhodopsin, rhodopsin is split by light into retinal and opsin, eventually resulting in an action potential

Light adaption is caused by........

reduction of rhodopsin

Dark adaptation is caused by....

rhodopsin production

Cones

Responsible for; color vision, visual acuity
three types: each type has a different type of iodopsin photopigment, pigments are most sensitive to blue, red, and green light, perception of many colors results from mixing the ratio of the different types of cones that are active at a given moment

Remaining macula

more cones than rods

periphery of the retina

most of the rods contained here

Bipolar and ganglion cells

located in the retina, can modify information sent to the brain

Ganglion cell axons

form the optic nerve, optic chiasm, and optic tracts, extend to the thalamus and synapse, then to the neurons from the optic radiations that project to the visual cortex

Depth perception

the ability to judge relative distances of an object from the eyes and is a property of binocular vision, binocular vision results because a slightly different images is seen by each eye

Lateral Rectus Muscle

Moves eye laterally and the controlling cranial nerve is the abducens

Medial Rectus Muscle

Moves the eye medially and the controlling cranial nerve is the oculomotor.

Superior Rectus Muscle

Elevates eye and turns it medially and is controlled by the oculomotor nerve

Inferior Rectus Muscle

Depresses the eye and turns it medially and is controlled by the oculomotor nerve.

Inferior Oblique Muscle

Elevates eye and turns it laterally and is controlled by the oculomotor nerve

Superior Oblique Muscle

Depresses eye and turns it laterally and is controlled by the trochlear nerve.

Tapetum

is a layer of tissue in the eye of many vertebrate animals, that lies immediately behind or sometimes within the retina. It reflects visible light back through the retina, increasing the light available to the photo receptors. This improves vision in low-light conditions

The ________ transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula. When examining the back of the eye, a portion of the ________ called the optic disc can be seen.

Optic Nerve

The colored part of the eye is called the _____. It controls light levels inside the eye similar to the aperture on a camera.

Iris

The _______ is the opening in the center of the iris. The size of the _____ determines the amount of light that enters the eye. The _____ size is controlled by the dilator and sphincter muscles of the iris. Doctors often evaluate the reaction of ______ to light to determine a person's neurological function.

Pupil

The ________ is the thin, watery fluid that fills the space between the cornea and the iris (anterior chamber). It is continually produced by the ciliary body, the part of the eye that lies just behind the iris. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape.

Aqueous Humor

The ________ is a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye's volume, giving it form and shape. The properties of the ________ allow the eye to return to its normal shape if compressed.

Vitreous Humor

The crystalline ______ is located just behind the iris. Its purpose is to focus light onto the retina. The nucleus, the innermost part of the ________, is surrounded by softer material called the cortex. The ______ is encased in a capsular-like bag and suspended within the eye by tiny "guy wires" called zonules.

Lens

The ______ is a multi-layered sensory tissue that lines the back of the eye. It contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images

Retina

The ______ lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.

Choroid

One function of the _______ is the production of aqueous humor, the clear fluid that fills the front of the eye. It also controls accommodation by changing the shape of the crystalline lens.

Ciliary Body

Extrinsic Eyeball Muscles consists of:

4 rectus muscles; superior, inferione, lateral, and medial. 2 oblique muscles; superior and inferior

3 layers of the eyeball

Fibrous layer (no blood, dense CT), vascular layer (pigmented), inner layer (retina)

Emmetropia

normal vision

Myopia

Near-sightedness---concave lens

Hyperopia

Far-sightedness----convex lens

Outer segment (photoreceptors)

light is absorbed

Visual Signaling Pathway

1. AP from ganglion cells (optic nerve) 2. partial crossing at optic chiasma 3. projection as optic tract 4. most synapse on LGH in thalamus 5. project to primary visual cortex of occipital lobe

Action potential is sent from:
1._______and_______ -->_________-->__________whose axons converge and leave the retina at the________-->_______-->________-->_________-->________-->______________

1. rods and cones, bipolar layer, ganglion cells, optic disk, optic nerve, optic chaisma, optic tract, thalamus, visual cortex of occipital lobe

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