Vision – Space – Flashcards
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What are the accessory structures of the eye?
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- eyelids - eyelashes - eyebrows - lacrimal (tearing) apparatus - extrinsic eye muscles
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What do the upper and lower eyelids do?
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- termed palpebrae - shade the eyes during sleep - protect eyes from: excessive light foreign objects - spread lubrication secretions over the eye
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What muscle moves the upper eyelid?
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Levitator palpebrae superioris muscle.
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What is the space between the upper and lower eyelids?
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Palpebral fissure
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What are the angles of the palebral fissure called?
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Commissures
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Where is the medial commissure?
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Nearer the nasal bone.
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Where is the lateral commissure?
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Closer to the temporal bone.
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What is in the medial commissure?
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Lacrimal caruncle.
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What does the lacrimal caruncle contain?
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Sebaceous oil glands Sudoriferous sweat glands
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What are the structures of the eyelid from superficial to deep?
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- epidermis - dermis - subcutaneous tissue - fibers of orbicular is oculi muscle - tarsal plate - tarsal glands - conjuctiva
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What is the tarsal plate?
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Thick fold of connective tissue that gives form and support to the eyelids.
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What are the tarsal glands?
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Modified sebaceous glands that secrete a fluid that helps keep the eyelids from adhering to each other.
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What is the conjuctiva?
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- Thin, protective mucous membrane.
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What is conjuctiva composed of?
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- Stratified columnar epithelial with many goblet cells
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What does the palpebral conjuctiva line?
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Lines the inner aspect of the eyelids
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What surface is the bulbar conjuctiva on?
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On the anterior surface of the eyeball.
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What does the bulbar condjuctiva cover?
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The bulbar conductive covers the sclera, not the cornea.
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What is the lacrimal apparatus?
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A group of structures that produces and drains lacrimal fluid, or tears.
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What is lacrimal fluid?
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A watery solution containing salts, some mucus, and lysozyme.
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What does the lacrimal gland secrete?
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Lacrimal fluid
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Where does the lacrimal fluid drain into?
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Drains into the excretory lacrimal duct and then onto the surface of the conjuctiva of the upper eyelid.
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Which direction do tears pass?
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Pass medially over the eyeball.
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After passing medially over the eyeball, where do tears go?
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They enter two small opening called lacrimal puncta.
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After entering the lacrimal puncta, what do tears pass into?
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Tears pass into tow ducts called the lacrimal canals (superior and inferior).
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Where do the lacrimal canals lead to?
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They lead to the sacrimal canal. Then to the nasolacrimal duct.
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What does the nasolacrimal duct carry and to where?
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Carries the lacrimal fluid into the nasal cavity.
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What is lacrimation?
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Lacrimation is a protective mechanism: the tears dilute and wash away irritating substances.
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What are the extrinsic eye muscles?
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- Superior rectus - Inferior rectus - Lateral rectus - Medial rectus - Superior oblique - Inferior oblique
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Which cranial nerves innervate the muscles of the eye?
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Cranial nerves III, IV, or VI.
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Which direction does the extrinsic eye muscles move the eyeball?
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Laterally, medially, superiorly, and inferiorly.
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Which direction do the rectus muscles move the eye?
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Moves the eye in a plane.
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What do the oblique muscles do?
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They preserve rotational stability of the eyeball.
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What are the 3 layers of the eyes?
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- Fibrous tunic - Vascular tunic - Retina
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What is the fibrous tunic?
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- Is the superficial coat of the eyeball - Is avascular - Consists of: Cornea Sclera
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What is the cornea?
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- Transparent coat that covers the iris - Is curved, so it focuses light - Has 3 layers
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What are the 3 layers of the cornea?
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- Outer nonkeratinized stratified squamous epithelium - Middle coat of collagen fibers and fibroblasts - Inner surface is simple squamous epitheloium
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What is the sclera?
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- "White" of the eye - Dense connective tissue, mostly collagen and fibroblasts - Covers the entire eyeball except the cornea - Gives shape to the eyeball, makes it more rigid, and protects inner parts of the eye
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What is the vascular tunic?
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- the middle layer of the eye - has 3 parts: choroid ciliary body iris
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What is the choroid?
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- Highly vascular - Lines most of the internal surface of the sclera - Provides nutrients to the posterior surface of the sclera
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What does the ciliary body consist of?
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- Ciliary processes - Ciliary muscle
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What are ciliary processes?
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- Protrusions or folds on the internal surface - Contains blood capillaries that secrete aqueous humor
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What is ciliary muscle?
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- A circular band of smooth muscle that alters the shape of the lens - When it contracts it reduces tension on suspensory ligaments that hold the lens, thereby allowing it to assume a more spherical shape (for closer vision)
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What is the iris?
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- The iris is the colored portion of the eyeball - It is attached at its outer margin to the ciliary processes - It regulates the amount of light entering the eye through the pupil, via autonomic reflexes
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What do parasympathetic neurons do to the iris?
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Parasympathetic neurons stimulate the sphincter pupillae (circular muscles) contract to cause a decrease in the size of the pupil (constriction)
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What do sympathetic neurons do to the iris?
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Sympathetic neurons stimulate the dilator pupillae (radial muscles) of the iris to contract, causing an increase in the size of the pupil (dilation)
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What is the retina?
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- The third, and inner coat of the eyeball - The retina lines the posterior ¾ of the eyeball - It is the beginning of the visual pathway
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What is specific about the retina with regards to an opthalmoscope?
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- The surface of the retina is the only place in the body where blood vessels can be viewed directly (ophthalmoscope) and examined for pathological changes
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What is the optic disc?
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- The optic disc is the site where the optic nerve exits the eyeball
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What is adjacent to the optic disc?
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- The central retinal artery and central retinal vein are adjacent to the optic disc
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What is the pigmented layer?
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- The pigmented layer of the retina is a sheet of melanin-coated epithelial cells
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What does the pigmented layer absorb?
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- It absorbs stray light, thereby preventing reflection and scattering
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What is the neural layer?
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- The neural layer of the retina is an outgrowth of the brain - It has three distinct layers of retinal neurons - It also has two zones—a zone between each layer
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What are the 3 distinct layers of the neural layer?
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- Photoreceptor layer - Bipolar layer - Ganglion layer
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What are the layers between each zone in the neural layer?
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- Outer synaptic layer - Inner synaptic layer
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What are the 2 types of photoreceptors that transduce light rays into receptor potentials?
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- Rods, which have a low light threshold and enable seeing only shades of gray - Cones, which have a higher light threshold and provide color vision
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What is the fovea centralis?
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The central fovea is a small depression in the center of the macula lutea.
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What is the macula lutea and where is it?
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The macula lutea (macula = small flat spot; lute = yellowish) is in the exact center of the visual axis of the eye of the posterior portion of the retina.
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What does the central fovea contain?
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- The central fovea contains only cones - Also, layers of bipolar and ganglion cells do not cover the cones in the central fovea (those cells scatter light to some extent)
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What is specific about the central fovea?
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- The central fovea is the area of highest visual acuity (visual resolution)
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What is a blind spot?
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- The optic disc contains no rods or cones -An image that strikes the optic disc can not be seen
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What is Age-Related Macular Disease?
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Also called macular degeneration AMD is a degenerative disorder of the retina and pigmented layer that may begin to show effects in persons 50 years of age and older Abnormalities occur in the region of the macula lutea Victims of advanced AMD retain peripheral vision but lose the ability to see straight ahead
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What are the 2 forms of AMD?
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- "Dry" in which central vision gradually diminishes because the pigmented layer atrophies and degenerates. There is no effective treatment for this form. - "Wet" form in which new blood vessels form in the choroid and leak plasma or blood under the retina. Treatment for this form is laser surgery to destroy leaking blood vessels.
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Where is the lens and what does it consist of?
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The lens is behind the pupil and iris It consists of proteins called crystallins, which are arranged like the layers of an onion, and enclosed in a capsule It is transparent (normally), and lacks blood vessels It is the variably refractive medium of the eye
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What are cataracts?
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- Loss of transparency of the lens is termed a cataract - The lens becomes cloudy due to changes in the structure of lens proteins
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The lens divides the eye into what two cavities?
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- Anterior cavity - Vitreous chamber
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What is the anterior cavity?
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The anterior cavity consists of two chambers: - Anterior chamber between the cornea and iris - Posterior chamber behind the iris, and in front of the lens Both chambers are filled with aqueous humor
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What is aqueous humor?
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Major contributor of intraocular pressure Manufactured by filtration of blood by capillaries of the ciliary processes Flows between the iris and the lens, through the pupil, into the anterior chamber From the anterior chamber it drains into the scleral venous sinus (canal of Schlemm), which is at the junction of the sclera and cornea Then returns to the blood Normally replaced about every 90 minutes
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What is glaucoma?
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Glaucoma is a high intraocular pressure When unchecked, glaucoma damages the optic nerve and retina, resulting in blindness Glaucoma is usually caused by impaired drainage of aqueous humor The canal of Schlemm is at the vertex of the angle formed by the intersection of the cornea and the iris, called the ocular angle
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What causes primary closed angle glaucoma?
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In primary closed angle glaucoma, pressure from the posterior chamber pushes the iris forward, closing the ocular angle and preventing drainage of aqueous humor.
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What causes primary open angle glaucoma?
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In primary open angle glaucoma the ocular angle remains open, but abnormalities in the trabecular meshwork associated with Schlemm's canal impede the outflow of aqueous humor.
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What is glaucoma treated with?
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Glaucoma is treated with cholinergic agonists (cholinomimetics), which constrict the pupil, contract the ciliary muscles, and decrease intraocular pressure.
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What is the vitreous chamber?
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The larger of the two cavities Contains the vitreous body: Hyaloid canal is the remnant of the hyaloid artery
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What is the vitreous body made of and what does it do?
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- Jellylike substance (about 4ml) - Contributes to intraocular pressure - Holds retina flush against the choroid - Formed during embryonic development, and not replaced thereafter - Contains phagocytic cells that remove debris, thereby providing for unobstructed vision
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What is the jellylike substance composed of?
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- Water - Hyaluronic acid - Collagen
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What are the attachments to the retina?
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- Just behind the ora serrata - At the optic disk
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What is the ora serrata?
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The ora serrata is the serrated junction between the retina and the ciliary body.
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What does the serrata junction mark?
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Marks the transition from the simple nonphotosensitive area of the retina to the complex, multi-layered photosensitive region.
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Where does the vitreous body attach?
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The vitreous body attaches anteriorly just behind the ora serrata.
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Define cataract?
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A common cause of blindness that is caused by the loss of transparency of the lens.
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Define glaucoma?
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It is the most common cause of blindness in the U.S.. It is abnormally high intraocular pressure due to a buildup of aqueous humor w/in the anterior cavity.
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Define blepharitis?
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An inflammation of the eyelid.
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Define conjunctivitis (pink eye)?
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An inflammation of the conjuctivita.
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Define corneal abrasion?
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A scratch on the surface of the cornea.
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Define corneal transplant?
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A procedure in which a defective cornea is removed and a donor cornea of similar diameter is sewn in. Most common and most successful transplant operation.
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Define diabetic retinopathy?
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Degenerative disease of the retina due to diabetes mellitus, in which blood vessels in the retina are damaged or new ones grow and interfere with vision.
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Define exotropia?
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Turning outward of the eyes.
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Define ketatiits?
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An infection or inflammation of the cornea.
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Define miosis?
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Constriction of the pupil.
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Define mydriasis?
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Dilation of the pupil.
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Define photophobia?
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Abnormal visual intolerance to light.
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Define ptosis?
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Falling or drooping of the eyelid (or slippage of any organ below its normal position).
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Define retinoblastoma?
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A tumor arising from immature retinal cells; it accounts for 2% of childhood cancers.
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Define scotoma?
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An area of reduced or lost vision in the visual field.
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Define trachoma?
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A serious form of conjunctivitis and the greatest single cause of blindness in the world. It is caused by the bacterium Chlamydia trachomatis. The disease produces an excessive growth of subconjunctival tissue and invasion of blood vessels into the cornea, which progresses until the entire cornea is opaque.
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Define tonometer?
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An instrument for measuring pressure, especially intraocular pressure.
