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Types/Designs Wear/Replacement Schedules; History; A&P...

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Question
Answer
What is a contact lens?   Thin corrective lens that fits directly on the cornea, or on the cornea and extends out onto the sclera; a medical device used to correct a refractive error, as a bandage lens for healing, or to change eye color.  
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What are the two types of contact lenses?   Corneal or scleral  
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What is another word for scleral?   Haptic  
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What does PMMA stand for?   polymethylmethacrylate  
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What is the problem with PMMA?   Does not allow oxygen to the cornea  
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What are three types of rigid gas permeable lenses?   CAB - cellulose acetate butyrate; SA - silicone acrylate; FSA - fluorosilicone acrylate.  
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Do GP lenses allow oxygen to pass through?   Yes  
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What are two types of corneal lenses?   Rigid Gas Permeable and PMMA  
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What are the scleral(haptic) softlenses?   Hydrogel; HEMA; Hydrophilic; Silicone hydrogel  
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What does HEMA stand for?   hydroxyethylmethacrylate  
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What are the three types of wear schedules?   Daily wear (DW); Extended (continuous) wear (EW or CW); Flexible wear (FW)  
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What is the wearing schedule for daily wear lenses?   Worn only during the waking hours and removed every night.  
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What is the wearing schedule for extended wear?   Lenses can be slept in and can be worn for 6 nights/7 days; there are also three lenses that have been approved for 30 days of continuous wear.  
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What is a conventional replacement schedule?   When lenses wear out, become damaged, or the RX changes they are thrown out. There is no specific replacement schedule. Used mostly for GP lenses.  
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What is a planned replacement schedule?   Comes with a specific time to replace it (2 weeks, monthly, etc.) The patient knows exactly when to throw out the lenses.  
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What is the FDA definition of a disposable replacement schedule?   Medical device; one that is used for one time only and comes with no instructions for reuse.  
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What are some examples of a disposable lens?   Single use; 1 week EW disposable; 30 day (silicone hydrogel)  
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A spherical lens has the same _________________ for the entire lens.   radius of curvature  
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An aspheric lens ________ towards the periphery.   flattens  
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What is monovision contact lens design?   one lens for near vision and one for distance vision  
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What are some properties of toric contact lens design?   Different radii of curvature in each meridian; principle meridians are 90 degrees apart; used to correct astigmatism  
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What is a front toric lens?   Anterior surface of lens is toric; posterior surface is spherical  
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What is a back toric lens?   Posterior surface of lens is toric; anterior surface of lens is sperical  
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What is a bitoric lens?   Both anterior and posterior surfaces are toric  
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What is a handling (visibility) tint?   Lens is tinted to be able to see to handle it.  
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What is an enhancement tint?   enhances light colored eyes only  
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What is an opaque tint?   Changes the color of light and dark eyes.  
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Who, because of their sketches, is credited for coming up with the idea for contact lenses in 1508.   Leonardo Divinci  
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What is keratoconus?   A corneal deformity; the central portion of the cornea thins out and protrudes causing a cone shaped cornea.  
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PMMA lenses were the first plastic lens available it was referred to as the....?   Hard lens  
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When did soft contact lens hit the market, and what was the first company to receive FDA approval to market it?   1971; Bausch and Lomb  
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What is the healthiest lens available and when were they first available?   One day disposable lenses (Acuvue One Day) in 1994  
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What is the most important part of the eye for contact lens fitting?   Cornea  
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What are some characteristics about the cornea?   Transparent; avascular; overlies the iris and the pupil  
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What is the refractive power of the cornea?   43.00  
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What is the diameter of the cornea?   11.5 mm  
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Where does the cornea get its nutrients?   From the tears, aqueous humor, and the vascular blood vessels in the limbus.  
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The epithelium is the outermost layer of the cornea and what percentage of corneal thickness?   10%  
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What happens if the epithelium is injuIred?   The squamous cells shift and cover the wound in about 24 hours, and then it takes about a week for the epithelium to regenerate and heal.  
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How is oxygen provided to the epithelium?   It comes from the atmosphere, then it is dissolved in the tear film, and diffuses across the epithelium. (Atmosphere, Tears, Epithelium)  
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What is hypoxia and what does it result in?   A term that refers to lack of oxygen....results in edema (swelling) of the cornea due to retention of fluid.  
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How does edema of the cornea effect vision?   The cornea loses its transparency and becomes cloudy causing reduced visual acuity.  
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What is recurrent corneal erosion?   Recurrent loss of epithelial cells due to failure of the cells adhering to the bowman's layer.  
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What is the bowman's layer?   Condensed outer layer of the stroma; very thin layer  
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If the Bowman's layer is injured does it regenerate?   No; leaves an opaque scar  
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What percentage of thickness is the corneal stroma?   90%  
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What is lamellae?   Collagen fibers in the stroma arranged at right angles to each other so that light may pass through  
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Where does the stroma get its oxygen?   From aqueous humor  
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Does injury to the stroma result in scarring?   Yes  
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Why is the Dua's Layer important?   Will improve surgery procedures  
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What is the Descemet's Layer?   A strong elastic layer that will regenerate after injury  
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What is the innermost layer of the cornea?   Endothelium  
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What is deturgescence?   The pumping action to remove excess fluid from the stroma; keeps the cornea transparent  
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What happens if the endothelium is injured?   The hexagonal cells shift and change size and shape to cover the wound  
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What is polymegathism?   term used for the variation in endothelium cell size  
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What is polymorphism?   term used for the variation in endothelium cell shape  
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What does the tarsal conjunctiva cover?   The inner surface of the eyelids  
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What does the bulbar conjunctiva cover?   the anterior surface of the sclera  
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What is the fornix conjunctiva?   joins the tarsal and bulbar conjunctiva; prevents a CL from going behind the eye...  
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What does the conjuctiva contain?   Blood vessels; nerves; goblet cells; leukocytes; mast cells  
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What is hyperemia or injection?   dilation of blood vessels within the conjunctiva  
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What is giant papillary conjunctivitis?   Conjunctivitis caused by wearing dirty contact lenses; identified by large bumps called papillae that appear over the superior tarsal conjunctiva.  
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What is pinguecula?   a small, round, yellowish/brown elevation on the bulbar conjunctiva; it can appear on either side of the cornea  
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What is a pterygium?   A wedge-shaped, non-cancerous growth, usually on the medial bulbar conjunctiva. It can be on one or both eyes. Doesn't have to be surgically removed until it starts growing on the cornea.  
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What is the palbebral fissure, how is it measured?   The opening between the upper and lower eyelids; measured with a PD stick vertically for CL fitting.  
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What is the average palpebral fissure measurement vertically?   10 to 10.5 mm  
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What is the average palpebral fissure measurement horizontally?   30mm  
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What are some functions of the eyelids?   protects the eye; blocks light; removes foreign matter; helps with tear drainage; distributes the tear layer.  
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As tears are secreted, they collect along the top and bottom lid margins forming a tear reservior, referred to as??   Tear meniscus or lacrimal lake  
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What is the average blink rate, and how often do we blink?   Blink rate 10-17 per minute; normally we blink every 3 to 6 seconds  
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What reduces the blink rate?   reading or performing concentrated work  
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Where is a chalazion located?   underneath the eyelid  
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What is an ectropian?   outward turning of the eye  
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What is an entropian?   inward turning of the eye  
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What is lagophthalmos and why is it important to contact fitting?   incomplete closure of the eyelid; sleeping with eye half-open causes there to be dry spots on the cornea  
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What is trichiasis?   Inward turning of the eyelashes  
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What is the first refractive surface of the eye?   Tear film  
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What does the lipid layer of the tear film do?   Reduces water evaporation of the underlying aqueous layer.  
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What does the aqueous layer of the tear film do?   prevents epithelial drying; keeps the anterior portion of the eye moist  
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What does the mucous layer of the tear film do?   makes the cornea wetable by providing a surface over which aqueous will spread evenly and absorb into the epithelial layer. Keeps the tear film intact to the microvilli which are intact to the cornea.  
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What is the average pH of the tears?   7.4  
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What is the tonicity of the tears?   0.9% NaCL Sodium chloride (salt)  
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What are the three tear assessment tests?   Break up time (BUT); Schimer Test I, Schimer Test II  
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What does the break-up time test measure?   How quickly the tears evaporate or break-up; recorded in seconds  
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What is the average time for the BUT test?   10-12 seconds; less than 10 seconds and the eyes are too dry for contact usage  
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What is used to perform a BUT test?   Slit lamp, blue light, diffuse illumination; sodium fluoresein  
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What is the difference in Schimer Test I and II?   Shimer Test II uses an anesthetic which helps with tear reflex.  
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What does the Schimer Test measure?   Tear flow rate and quantity of tears.  
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What is the normal output for the Schimer test?   15m of the strip is wet  
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How does flourescein work?   Stains the tears  
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What is Rose Bengal?   a red dye that stains the cells; detects dead or degenerated cells of the cornea and conjunctiva  
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What is lissamine green?   stains dead or injured cells on the surface of the eye. (bluish-green stain)  
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What is the average horizontal visible iris diameter? (HVID)?   11 1/2 mm  
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What is the average diameter of the pupil?   4.5 - 5 mm  
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