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Sclera/Cornea
| Question | Answer |
|---|---|
| How much of the globe does the sclera cover? | 5/6 |
| Is the sclera thicker in the anterior or the posterior? | Posterior |
| What is the thickness of the sclera at the macula? | 1 mm |
| What is the thickness of the sclera at the equator? | .4 - .5 mm |
| What is the thickness of the sclera towards the front of the eye? | .3 mm |
| Definition of Tenon's Capsule (also known as Bulbar sheath)? | Thin membrane which envelopes or encases the eyeball from the optic nerve to the corneal-sclera limbus. |
| What is a fascia? | Any band of tissue that separates different tissues. |
| What is the Ligament of Lockwood? | The Tenon Capsule changes shape anteriorly to become like a sling or hammock to support the eye. |
| What are the three layers of the sclera? | Episclera; Scleral Stroma; Lamina Fusca |
| Which is the outer layer of the sclera that can be seen? | Episclera |
| Which layer of the sclera contains the blood supply? | Episclera |
| Which is the middle layer of the sclera? | Scleral Stroma |
| Which layer of the sclera is thickest? | Scleral Stroma |
| Into which layer of the sclera do the eye muscles insert? | Scleral Stroma |
| Definition of Lamina Fusca | Thin layer of pigmented connective tissue on the inner surface of the sclera. Connects the sclera with the choroid. |
| Which layer is the innermost layer of the sclera near the choroid? | Lamina Fusca |
| Which layer of the sclera contains melanocytes? | Lamina Fusca |
| What are mellanocytes? | Cells that produce melanin or pigment. |
| Which layer of the sclera is dark brown in color? | Lamina fusca |
| What is the posterior scleral foraman? | Hole formed and occupied by the optic nerve. |
| What is the anterior scleral foraman? | Hole occupied by the cornea |
| What is the dural sheath? | When the outer 2/3 of the sclera go on to produce the sheath which surrounds the optic nerve. |
| What is the passage for the optic nerve and central retinal vessel (entrance, exit). This is where the sclera is weakest. | Lamina cribosa |
| What is the corneal-sclera limbus? | Border between the sclera and cornea that goes all the way around the iris. Provides the pathways for aqueous humor outflow. Is also the site of surgical incisions for cataract and glaucoma. |
| How much of the globe does the cornea cover? | 1/6 |
| How thick is the cornea at the center? | .52 mm |
| How thick is the cornea towards the posterior? | .70 mm |
| What is the fastest healing tissue in the body? | The cornea |
| How long does it take for a corneal abrasion to heal? | 24-36 hours |
| What is the first refractive surface on the eye? | Tear film |
| What is the second refractive surface on the eye? | The cornea |
| What is astigmatism? | When the cornea is not spherical and there is a different steepness in every meridian. |
| Where is most astigmatism found? | Cornea |
| What are the three layers of the Pre-Corneal Tear Film? | Oily Outer Layer; Middle Watery Layer (aqueous); Inner Mucus Layer |
| What gland produces the aqueous part of the tears? | Lacrimal gland |
| Where is the lacrimal gland located? | Below the eyebrow |
| What produces the outer oily layer of the tear film? | Meibomian Glands |
| What produces the inner mucus layer of the tear film? | Goblet cells of the conjunctiva |
| Where are meibomian cells? | Along the outer edge of the eyelids |
| Functions of the tear film | Provides moist environment for the epithelial cells; Fill in irregularities on the corneal surface; Nutrition, waste removal, and antibacterial action for cornea; Defense against infection; Ensure comfort |
| What is the conjunctiva? | A thin mucus membrane that lines the eyelids and the sclera, but not the cornea. |
| What are the three parts of the conjunctiva? | Bulbar conjunctiva; Palpebral Conjunctiva; Fornix Conjunctiva |
| What is the bulbar conjunctiva? | Thin mucus membrane that covers anterior portion of the sclera. |
| What is the palpebral conjunctiva? | Part of the conjunctiva that lines the inner eyelids. |
| What is the fornix conjunctiva? | The fold between the anterior sclera and the palpebral conjunctiva; between the eyelid and the eyeball. |
| The conjunctiva provides some protections, but what is the primary function? | Lubricate the outer layer of the eye |
| What are the five layers of the cornea? | Epithelium; Bowman's; Stroma; Decemets; Endothelium |
| What type of epithelium is the corneal epithelium? | Stratified-squamous |
| How many layers of cells are in the corneal epithelium? | Five to six |
| What is the thickness of the corneal epithelium? | 50 to 100 microns thick |
| What type of cells are in the corneal epithelium? | Squamous cells; Wing Cells; Columnar Cells |
| What is the basal layer of the corneal epithelium? | Columnar Cells |
| How often do the cells in the corneal epithelium regenerate? | Every seven days |
| In what order do the cells in the epithelium regenerate? | From the basal columnar cells, out to the squamous flat cells, and into the tear film. |
| What percentage of corneal thickness is the epithelium? | 10% |
| How thick is Bowman's membrane? | Approximately 12 microns thick |
| Does the Bowman's membrane heal if damaged? | No, but it leaves no scarring. |
| What is Bowman's membrane? | Non-cellular layer composed of randomly oriented collagen fibers within an extracellular matrix. Very strong and resistant to injury and disease |
| Where is Bowman's membrane located? | Between the epithelial basement membrane (basal columnar cells) and the stroma. |
| Why do babies eyes have a blue tint to the sclera? | Sclera is still thin, and pigment can be seen through it |
| What causes a yellow tint to the sclera in older people? | Yellow, fatty lipid deposits |
| What is the main purpose of the corneal endothelium? | Deturgesence (pump water from the stroma) |
| The sclera is quite smooth except for where? | Where the muscles are inserted |
| Which layer of the sclera is strongly connected to the Tenon's Capsule? | Episclera |
| Where does lacrimal fluid gather before it is drawn into the puncta? | Lacrimal lake |
| The corneal Decscemet's membrane is how thick? | 5-10 microns |
| Does damage to the corneal stroma result in scarring? | Yes |
| Does the normal cornea have blood vessels? | No |
| How big is a micron? | 1/1000 mm |
| What is Fuch's Dystrophy? | Condition of abnormal growth and thickening in the endothelial layer of the cornea, leading to corneal edema. |
| True or False?: The Bowman's membrane contains many polyhedral cells? | False |
| Another name for the corneal stroma layer is? | Substantia propia |
| Which layer of the cornea is approx 500 microns thick? | Stroma |
| What is mucopoly parachloride? | The ground substance between the fibers in the corneal stroma. |
| What is a scleral spur? | A ridge of the sclera from which ciliary muscles fibers take origin. |
| What are the two types of cells found in the corneal stroma? | Wandering cells and keratocytes. |
| What is the corneal stroma made up of? | Many collagen fibers arranged in a very regular pattern. |
| What is the basement membrane of the endothelial layer of the cornea? | Decemets |
| Will the Decemets membrane regenerate if it is damaged? | Yes |
| Does the Descemets membrane contain cells? | No |
| What is the process by which the cornea pumps water out of the stroma? | Deturgesence |
| What percentage of corneal thickness is the stroma? | 90% |
Created by:
griffiskr
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