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Contacts Test 1
Types/Designs Wear/Replacement Schedules; History; A&P...
| 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. |
| 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
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