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Contact Lens III
Test 3
| Question | Answer |
|---|---|
| Bandage lenses are used to...? | relieve pain; promote healing; hold medication and deliver it to the eye to reduce infection; protect the cornea; maintain ocular surface hydration; improve vision |
| What type of lenses are usually used for bandage lenses, plano or Rx? | plano - although Rx lenses can be used depending on the condition |
| What lens materials are used in bandage lenses? | hydrogel; silicone hydrogel, GP sclera (haptic) lenses, and collagen |
| What type of lens is being used more now for bandage lenses? | Silicone Hydrogel, because they are more oxygen permeable |
| Are bandage lenses made from silicone hydrogel usually DW or CW? | CW |
| What soft CLs are available in silicone hydrogel? | Acuvue Oasys; Alcon-Air Optix Night and Day Aqua; B&L Purevision --- also HEMA lens - United States Contact lenses UCL 55 |
| How do collagen shield-lenses dissolve in the eye? | They become gel-like and eventually liquify. |
| What is collagen? | A naturally occurring protein. |
| What is collagen extracted from? | Porcine sclera |
| What is the name of the collagen lens made by B&L? | BioCora collagen shield - available in different shapes and thicknesses. Dissolves in 6, 12, 24, 48, and 72 hours, and even one week. |
| What are scleral GP bandage lenses used for? | severe ocular disease, irregular cornea, corneal thinning, scarring, keratitis, and irregularities due to ocular surgery. |
| How does a scleral GP bandage lens work? | Vaults the cornea and traps fluid (unpreserved saline) behind the lens correcting the irregular astigmatism and distortion and keeps the eye wet. The liquid acts as a bandage |
| Fitting procedures for TCL's? | Must center well, adequate movement for the condition, patient must be comfortable, and vision should not be worse than without the lens. |
| What is recurrent corneal erosion? | Failure of the epithelial cells to adhere to bowmans layer. the epithelial cells will regenerate in 7 days if intact to bowmans, but if dislodged could take months to heal. caused by injury, chemical burns, surgery, infections, etc. |
| A lens fit for recurrent corneal erosion should have ______ movement. | minimal |
| What is bullous keratopathy? | The endothelium breaks down and caused edema that causes bullae (blister like lesions). The bullae proceed to the epithelial layer and causes painful breaks |
| A lens fit for bullous keratopathy should have what type of movement? | minimal |
| What are the two types of corneal ulcers? | Infectious and non infectious |
| What causes infectious corneal ulcers? | bacteria, viruses, parasites |
| What causes non infectious corneal ulcers? | abrasion, injury, chemical burns, thermal burns |
| What kind of movement should a contact lens for corneal ulcers have? | Depends on the severity of the injury |
| How does a TCLs help with a corneal laceration or perforation? | Tissue adhesive glue or sutures are used and the bandage lens serves as a splint to avoid wound leaking. |
| In trichiasis and entropian conditions, a TCLs is used for...? | comfort |
| What is important when fitting TCLs? | oxygen transmission; hydrogel lenses - higher water content and thinner; silicone hydrogel and GP - higher DK |
| A presbyopic eye has.... | reduction and eventual loss of accomodation; reduction of lid tonicity; reduction of tear volume and quality; reduction of corneal sensitivity; reduction in pupil size |
| What should we evaluate mature CL candidates? | physical characteristics; acuity; occupation/hobbies; motivation |
| What is important for our patients to understand about presbyopic CLs? | It will not give them their youthful vision back; may need glasses for fine print or driving; they may need lots of follow ups; must be able to accept compromise |
| What are some methods of fitting presbyopic patients with CLs? | Reading glasses over distance CL's; Distance glasses over near CL's; Monovision; Modified monovision; Multifocal |
| What type of multifocal CLs are available? | Segmented bifocals, annular or concentric, aspheric=progressive type, diffractive |
| When checking monovision always check it with....? | Both eyes, OU |
| For hyperopic patients in monovision, ________ the distance a little to balance both eyes. | over-plus |
| For myopic patients in monovision, _________ both lenses to balance. | under correct |
| Advantages of a monovision fit? | easier to fit that bifocal CLs; more choices of material; replacement; spherical or toric; wider field of view; less expensive; more comfortable |
| Disadvantages of a monovision fit? | Headaches; depth perception may be off; adaption period required; doesn't work well with high adds; may require reading or distance glasses over the top |
| Can pilots have monovision? | NO! |
| What is modified monoviison? | 1 sv lens for distance or near and 1 bifocal or multifocal cls |
| What is modified bivision? | 2 different types of bifocals |
| Good candidates for multifocal cls include | high motivated people, can afford them and return for follow ups; healthy eyes; no allergies or medications; Add powers between +1.00 to +1.75; hyperopes do better than myopes; low Rx's; astigmatism less than -2.00 |
| Patients that are difficult to fit in MF CLs | cranky; don't have time to return for follow ups; unhealthy; flaccid lids, unsuccessful CL wear in the past; opposite of good candidates |
| What are the two basic bifocal contact lens designs? | 1. Alternating Vision/translating bifocal; 2. Simultaneous Vision |
| What is alternating vision bifocals? | lens translates from distance vision to near vision; has 2 zones one for DV and one for near. view distance through the top portion, when you look down lens shifts upward to read through near segment |
| What is simultaneous vision bifocals? | both distance and near are superimposed and the brain selects the image that is in focus; |
| In alternating vision the lens is _____ lid dependent and the _____ lid induces the translation. | lower; upper |
| What is used to stabalize an alternating vision bifocal lens? | Prism ballast or truncation |
| Does alternating vision BF CLs allow for sharp DV and NV? | Yes |
| Are alternating lens available in soft, GP, or both? | GP mostly, sometimes one will be available in soft, and then discontinued. |
| Segmented bifocals have _______ like spectacle lenses. 2 zones one for ____ vision and one for _______ vision. | segments; near; distance |
| How do segmented lenses work? | Segmented reading portion moves up when the patient looks down to read. |
| What makes segmented lenses more difficult to fit? | Proper seg height; adequate transition from DV to NV; stable lens with minimal rotation |
| Fitting GP Alternating Design.... | Examine lid position; Record K's - use MF guide for BC (fit flatter than K); Evaluate fit; Observe segment placement; Over-refract; Record BC, Power (DV/NV), Dia, Seg height, prism ballast 1.25 to 2.5 or truncation .3 to .6 mm |
| When examining the lid position if the lower lid is at or slightly above the limbus? | use alternating design |
| When examining the lid position, if the lower lid is below the limbus? | use simultaneous |
| If a GP alternating lens doesn't translate (move up when reading) refit with a.... | flatter or steeper lens |
| Where should the seg be on a GP alternating design lens? | top of seg should be at lower pupil margin in normal room lighting. Good starting point is to order a lens with seg 1 mm below the geometric center |
| What do we check when verifying a GP Alternating Design lens? | BC; Power DV and add; Measure Seg Height from bottom of lens to the top of the seg using measuring magnifier; measure diameter - if truncated two diameters |
| When fitting a simultaneous lens it should be fit with _______ movement and good centration. | minimal |
| Is prism ballast and truncation needed for simultaneous lenses? | No, rotation is not an issue. |
| Ashperic lenses, also called progressive addition lenses or multifocal lenses, how do they work? | The power of the lens increase in plus toward the periphery |
| Are aspheric lenses available in GP and soft? | Yes |
| Aspheric lenses are defined by __________ values? | eccentricity values (e values) |
| What is an e value? | measurement of how far from a circle the shape varies |
| A spherical lens has an e value of? | zero |
| What is the range of aspheric e values? | .1 to 1.0 mm (cornea e value 0.4 to 0.6mm) |
| The lower the e value the _______ the fit. | tighter |
| The higher the e value the _______ the fit. | looser |
| What are diffractive bifocal CLs? | looks like a Fresnel press on prism - the rings are smaller than a lathe mark; simultaneous; prism like facets that diffract light instead of refract |
| When are GP diffractive lenses used? | When patients want sharper vision |
| When are soft diffractive lenses used? | Pt's that desire comfort. |
| What determines the diopter power of a diffractive lens? | The separation of the rings and the depth of the facets |
| Is truncation or prism ballast required for diffractive bifocal CLs | No, rotation stabilization not required |
| What are concentric (annular) bifocal CLs? | Mostly simultaneous, but the lens with near center and distance in the periphery can be fit alternating. This lens can also have distance center and near periphery. |
| Fitting Simultaneous lenses |
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griffiskr
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