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Contacts Test 1

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

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.
What are the two types of contact lenses? Corneal or scleral
What is another word for scleral? Haptic
What does PMMA stand for? polymethylmethacrylate
What is the problem with PMMA? Does not allow oxygen to the cornea
What are three types of rigid gas permeable lenses? CAB - cellulose acetate butyrate; SA - silicone acrylate; FSA - fluorosilicone acrylate.
Do GP lenses allow oxygen to pass through? Yes
What are two types of corneal lenses? Rigid Gas Permeable and PMMA
What are the scleral(haptic) softlenses? Hydrogel; HEMA; Hydrophilic; Silicone hydrogel
What does HEMA stand for? hydroxyethylmethacrylate
What are the three types of wear schedules? Daily wear (DW); Extended (continuous) wear (EW or CW); Flexible wear (FW)
What is the wearing schedule for daily wear lenses? Worn only during the waking hours and removed every night.
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.
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.
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.
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.
What are some examples of a disposable lens? Single use; 1 week EW disposable; 30 day (silicone hydrogel)
A spherical lens has the same _________________ for the entire lens. radius of curvature
An aspheric lens ________ towards the periphery. flattens
What is monovision contact lens design? one lens for near vision and one for distance vision
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
What is a front toric lens? Anterior surface of lens is toric; posterior surface is spherical
What is a back toric lens? Posterior surface of lens is toric; anterior surface of lens is sperical
What is a bitoric lens? Both anterior and posterior surfaces are toric
What is a handling (visibility) tint? Lens is tinted to be able to see to handle it.
What is an enhancement tint? enhances light colored eyes only
What is an opaque tint? Changes the color of light and dark eyes.
Who, because of their sketches, is credited for coming up with the idea for contact lenses in 1508. Leonardo Divinci
What is keratoconus? A corneal deformity; the central portion of the cornea thins out and protrudes causing a cone shaped cornea.
PMMA lenses were the first plastic lens available it was referred to as the....? Hard lens
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
What is the healthiest lens available and when were they first available? One day disposable lenses (Acuvue One Day) in 1994
What is the most important part of the eye for contact lens fitting? Cornea
What are some characteristics about the cornea? Transparent; avascular; overlies the iris and the pupil
What is the refractive power of the cornea? 43.00
What is the diameter of the cornea? 11.5 mm
Where does the cornea get its nutrients? From the tears, aqueous humor, and the vascular blood vessels in the limbus.
The epithelium is the outermost layer of the cornea and what percentage of corneal thickness? 10%
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.
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)
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.
How does edema of the cornea effect vision? The cornea loses its transparency and becomes cloudy causing reduced visual acuity.
What is recurrent corneal erosion? Recurrent loss of epithelial cells due to failure of the cells adhering to the bowman's layer.
What is the bowman's layer? Condensed outer layer of the stroma; very thin layer
If the Bowman's layer is injured does it regenerate? No; leaves an opaque scar
What percentage of thickness is the corneal stroma? 90%
What is lamellae? Collagen fibers in the stroma arranged at right angles to each other so that light may pass through
Where does the stroma get its oxygen? From aqueous humor
Does injury to the stroma result in scarring? Yes
Why is the Dua's Layer important? Will improve surgery procedures
What is the Descemet's Layer? A strong elastic layer that will regenerate after injury
What is the innermost layer of the cornea? Endothelium
What is deturgescence? The pumping action to remove excess fluid from the stroma; keeps the cornea transparent
What happens if the endothelium is injured? The hexagonal cells shift and change size and shape to cover the wound
What is polymegathism? term used for the variation in endothelium cell size
What is polymorphism? term used for the variation in endothelium cell shape
What does the tarsal conjunctiva cover? The inner surface of the eyelids
What does the bulbar conjunctiva cover? the anterior surface of the sclera
What is the fornix conjunctiva? joins the tarsal and bulbar conjunctiva; prevents a CL from going behind the eye...
What does the conjuctiva contain? Blood vessels; nerves; goblet cells; leukocytes; mast cells
What is hyperemia or injection? dilation of blood vessels within the conjunctiva
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.
What is pinguecula? a small, round, yellowish/brown elevation on the bulbar conjunctiva; it can appear on either side of the cornea
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.
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.
What is the average palpebral fissure measurement vertically? 10 to 10.5 mm
What is the average palpebral fissure measurement horizontally? 30mm
What are some functions of the eyelids? protects the eye; blocks light; removes foreign matter; helps with tear drainage; distributes the tear layer.
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
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
What reduces the blink rate? reading or performing concentrated work
Where is a chalazion located? underneath the eyelid
What is an ectropian? outward turning of the eye
What is an entropian? inward turning of the eye
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
What is trichiasis? Inward turning of the eyelashes
What is the first refractive surface of the eye? Tear film
What does the lipid layer of the tear film do? Reduces water evaporation of the underlying aqueous layer.
What does the aqueous layer of the tear film do? prevents epithelial drying; keeps the anterior portion of the eye moist
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.
What is the average pH of the tears? 7.4
What is the tonicity of the tears? 0.9% NaCL Sodium chloride (salt)
What are the three tear assessment tests? Break up time (BUT); Schimer Test I, Schimer Test II
What does the break-up time test measure? How quickly the tears evaporate or break-up; recorded in seconds
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
What is used to perform a BUT test? Slit lamp, blue light, diffuse illumination; sodium fluoresein
What is the difference in Schimer Test I and II? Shimer Test II uses an anesthetic which helps with tear reflex.
What does the Schimer Test measure? Tear flow rate and quantity of tears.
What is the normal output for the Schimer test? 15m of the strip is wet
How does flourescein work? Stains the tears
What is Rose Bengal? a red dye that stains the cells; detects dead or degenerated cells of the cornea and conjunctiva
What is lissamine green? stains dead or injured cells on the surface of the eye. (bluish-green stain)
What is the average horizontal visible iris diameter? (HVID)? 11 1/2 mm
What is the average diameter of the pupil? 4.5 - 5 mm
Created by: griffiskr