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Contacts II Test 2
Soft Contact Fitting
| Question | Answer |
|---|---|
| What was the first method of manufacturing soft lenses? | Soft cast |
| Who invented the spin cast method? | Otto Wichterle in 1951 |
| What was the first company to gain FDA approval and market spin cast lenses? | B&L |
| What is the spin cast method? | mold that spins on a spindle. liquid polymer is added while it spins. material is treated w/ UV and heat to cure. |
| What curve is on the front of the lens? | Base Curve |
| What curve is on the back of the lens? | Power Curve |
| What is the problem with the spin cast design? | Fit depends on the power of the lens, because each power has a different back curve. |
| For every __D change in power the back curve is different. | .25 D |
| What lenses are made from the lathe cut manufacturing? | Soft, GP, PMMA, and spectacle lenses |
| How are lathe cut lenses manufactured? | Begins with a hard blank or button of a contact lens material. A diamond edged blade is used to shave the material. Material is polished to remove lathe marks, improve optics, and smooth the edge. |
| What has to be done to soft CL's after polishing in the lathe manufacturing process? | immersed in saline to transfer to a flexible material |
| How are cast-molded lenses made? | Uses a plus/minus mold. Liquid polymer is placed in minus section - molds are clamped together and cured with UV light |
| What patients are best when fitting soft contacts. | aged 13-30, women do better than men, Rx of greater than 1 D, cylinder less than -2.75, average K's, BUT of 10-12 seconds, patients with healthy corneas and good health, good upper and lower lid position |
| Who are the least successful patients when fitting soft CL's? | pt's that need them for a trip, party, or right away; smokers, pt's that can't afford them, poorly motivated, jobs such as hair dressers and truck drivers, work in dusty environments, myopic becoming presbyopic |
| Why do we fit soft lenses more? | initial comfort is better, less chair time, easier to fit, occasional wear time, better for sports, single use, planned replacement, enhance/change eye color |
| What do we consider when fitting a soft contact lens? | Oxygen Permeability, Thickness, Deposit Resistance, Edge Design, Tint/UV, Wear Schedule, Replacement Schedule, and Parameters. |
| What do we look at when determining the oxygen permeability of a soft hydrogel lens? | The water content. Higher water content means more oxygen. |
| What do we look at when determining the oxygen permeability of a silicone hydrogel lens? | Dk value. Higher Dk value is more oxygen |
| What is group one of the CL materials? | low water content/ non-ionic |
| What is group two of the CL materials? | high water/ non-ionic |
| What is group three of the CL materials? | low water, ionic |
| What is group four of the CL materials? | high water, ionic |
| What is group 5? | |
| What is the water content of a lens? | The amount of water that soft lenses retain. A lens is only fully hydrated when soaking in solution, when lens is on the eye, the front surface of the CL's starts to dry out. |
| What is the water content range for hydrogel lenses? | 33 to 79% |
| What is the water content range for silicone hydrogel lenses? | 24 to 48% |
| What is the water content for Dailies Total 1 lenses? | 80% water surface, 33% water core |
| What is true about hydrogel lenses with high water content? | Higher water so more oxygen. More comfortable because they are softer and more flexible. They attract more deposits which reduce oxygen. Need more tears to stay hydrated. |
| What disinfection methods can be used with hydrogel lenses with high water content? | Chemical, oxidative, and UV. |
| What disinfection method can not be used with hydrogel lenses with high water content? | Heat |
| Hydrogel lenses with low water content | needs fewer tears to stay hydrated. Easier to handle b/c they are a stiffer lens. Can be disinfected using all methods. |
| What is the Dk of a lens? | Oxygen transmission through a given material. |
| What is the Dk/l or Dk/i of a lens? | oxygen transmission in relation to its thickness. |
| What can effect a soft CL in size, shape, and power? | water content, salt content, and PH change |
| What happens to a CL size when it looses moisture? | Lens gets dryer and shrinks, becomes steeper in base curve, fits tighter on the eye, and becomes brittle |
| What is a hypertonic solution and what happens when a lens is stored in one? | Hypertonic solution is saltier than human tears. The lens will shrink, become steeper, and fits tighter |
| What is a hypotonic solution and what happens if a lens is stored in one? | Becomes larger, flatter, and will adhere to the cornea |
| What could cause a lens to become stuck, and what should we advise the patient to do if this happens. | Lens is stuck because it's not wet enough, salty enough, or is too acidic. Patient should irrigate the eye with a sterile isotonic solution to loosen lens. |
| What is an isotonic solution? | Same salt content and pH of tears. |
| What does the electronic charge indicate? | The attraction of the CLs to deposits. |
| What does ionic mean? | carries the same charge and attracts dirt, protein, and deposits |
| What does non-ionic mean? | fewer particles adhere to the CL (CL has a less reactive surface) |
| Why are surface deposits important? | they can reduce oxygen flow, cause discomfort, increase dryness, reduce VA, cause infections, GPC or other problems. Good deposit resistance is a MUST for lenses the will be worn a long time. |
| What are the two main factors when selecting a soft hydrogel lens? | Water content and thickness |
| What are the two main factors when selecting a silicone hydrogel lens? | DK and thickness |
| What are advantages of a thicker lens? | Easier to handle, durable, visual stability, less apt to dry out |
| What are disadvantages of a thicker lens? | Less comfortable and less oxygen. |
| What are advantages of a thinner lens? | allows more oxygen and comfort |
| What are disadvantages of a thinner lens? | harder to handle |
| Why is edge design important? | Important for patient comfort. Thinner lenses have thinner edges, which make them more comfortable. Some materials and manufacturers will have better edge design than others. |
| How much light does a handling/visibility tint absorb? | 10% |
| How much light does an enhancement tint absorb? | 10-20% |
| What should we consider when choosing a wear schedule and replacement schedule for the patient? | What the patient expects from their lenses and how they expect to use them. |
| What allow us more flexibility in fitting soft contact lenses, so we don't need as many sizes? | The draping effect |
| If the lens is fit correctly we will have....? | Three point touch, the lens will touch at the apex and at two opposite edges in the periphery. |
| The diameter of a lens must be large enough...? | to cover the cornea, vault the limbus, and extend over the limbus 1mm all the way around. |
| What is the rule of the thumb when selecting a diatmer? | At least 2 mm larger than the HVID |
| Can a lens diameter be too big and still fit? | Yes, but it can NEVER be too small and still fit |
| People with steep corneas have a smaller or larger HVID? | smaller |
| What should we check for if there is a problem with the fit? | GPC...could have missed in pre-fitting exam |
| What should the bottom of a soft CL come in contact with in order to stay moist? | The tear meniscus |
| How long does a lens need to equilibrate for before evaluating the fit? | 20 minutes. Lens becomes hydrated w/ pt's tears and reaches temp of 98.6 |
| What are the 5 fitting criteria in order? | Complete Corneal Coverage; Adequate Movement; Three Point Touch; Good Visual Acuity; Good Comfort |
| How do we check for complete corneal coverage? | Slit lamp - low illumination, low mag, check edge of lens in relation to the limbus, while the patient is looking in the primary position. Note whether the lens is well centered or decentered |
| What do air bubbles that persist indicate? | That there is something wrong with the fit of the lens |
| Air bubbles in the center of a lens mean? | BC is too steep or diameter is too large |
| Bubbles under the periphery that extent to the edge? | base curve is too flat or diameter is too small, or the peripheral curves of the lens are too flat |
| Why is adequate movement important in the CL's? | lens must move on the eye to flush out the old tears and debris, and to bring new tears and oxygen in. |
| If the lens allows more oxygen is it okay for there to be less movement? | Yes |
| Manufacturers of newer lenses suggest that they move how much? | .5 to 1.0 mm |
| Older lenses had to have how much movement? | 1 to 2 mm |
| How do we check movement? | Slit lamp - indirect illumination, 2-3 mm wide beam, 45 degree angle, check the lens at 5 and 7 o'clock having the patient blink. |
| What is lens LAG? | Pt looks side to side and if lens has good LAG it should move with pt. |
| How do we check for lens LAG? | keep light low and wide beam. have pt look up and blink with light at 6 o'clock. if lens doesn't move it's too lose. A contact lens with proper movement will follow the cornea w/ little lag and not hit the limbus |
| What is the push up test? | If you can't observe movement, push the edge of the lens w/ lower lid margin using your finger or thumb. NCLE advises to use with thin hydrogel lenses. |
| What will movement be like if the lens is too lose? | Slides away easily and has trouble finding its way back on center. Do not want so much movement that hits the limbus. |
| How do we correct a lens that's too loose? | make sure lens is not inside out. needs a larger diameter or steeper base curve |
| How do we correct a lens that is too tight? | smaller diameter and flatter base curve |
| What three ways can we verify three point touch? | Keratometer; Retinoscope; Snellan Chart |
| How do we check three point touch with keratometer? | Focus the mires so everything is clear. Tell patient to blink. |
| What is a loose fit checking three point touch? | Clear mires, blurry mires, clear mires |
| What is a tight lens checking three point touch? | Blurry mires, clear mires, blurry mires |
| If VA is is blurry throughout the blink cycle then problem is probably with the...? | Power |
| How do we FOG the patient? | refraction refinement technique a lens is placed in front of the eye to blur VA and relax accomodation. Overplus the patient so vision is blurry, start with a +1.50 to FOG. Immediately hold the correct power in front of pt's eye and check VA. |
| Myopes are under or over corrected w/ fogging? | under |
| Hyperopes are under or over corrected w/ fogging? | over |
| If patient is having discomfort with only one lens, what may be the problem? | Lint or something else on lens. Have pt take lens out and rinse to see if corrects |
| If discomfort is in both eyes, what may be the problem? | Lens too thick, poor edge design, or poor fit. |
| What does a well fitted soft contact lens have (5 fitting)? | complete corneal coverage; good movement and lens lag; three point touch, visual acuity 20/20, good comfort |
| What does a tight fitting lens have (5 fitting)? | Good centration/coverage; Little or no movement and no LAG; may have central bubbles that persists, no 3 point touch; VA's will be BCB; comfort is good (may take hours or days to become uncomfortable) |
| What is the exception to a tight lens and movement? | May have excessive movement due to lack of 3 point touch. |
| What is circumcorneal injection or limbal conjunctival hyperemia? | blood vessels are dilated, the area around the limbus will be red and swollen |
| What is a circumcorneal indentation? | compressed ditch all the way around the limbal area because the lens is too tight. |
| A lens may behave like a tight lens even if the fit is good because...? | Blinking is infrequent and the lens dries and shrinks. Also if the lens is overworn and not replaced. |
| Wat are the corrections for a tight lens that is lathe cut or molded? | smaller diameter, flatter BC |
| What are the corrections for a tight lens that is spin cast? | smaller diameter and thinner lens, changing the BC would change the power of the lens. |
| What are the indications of a loose fitting SCL? | Decentering (poor centration); Excessive movement and lens LAG; lens edge standoff and bucking (bottom edge will flip out or lens may buckle and fold); Three point touch will be CBC; Vision will be unstable; lens may fall out; comfort will be reduced |
| What are the corrections for a loose lens? | steeper base curve, larger diameter |
Created by:
griffiskr
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