Spherical Soft Contact Lens Fitting. J. Perrigin OPTO 6374 Spring 2017

Transcription

1 Spherical Soft Contact Lens Fitting J. Perrigin OPTO 6374 Spring 2017

2 Reading Assignment Bennett & Henry: Chapter 11 pages Tables 11.1 &11.2

3 Some Advantages of SCLs versus GPs Initial comfort, little adaptation Variable wearing schedule Availability of daily disposables Dusty environment not a problem High oxygen transmission in most newer designs Ability to fit, dispense, & replace from inventory

4 Cons of SCLs versus GPs Greater risk of microbial contamination & infection Greater risks with non-compliance Some parameter limitations but customized available Possible vision fluctuations with high astigmatic rxes but most do well with contemporary designs

5 How to start Determine if any special features such as tints, UV block, overnight use, etc are desired or indicated Decide on most appropriate replacement schedule Decide on spherical versus toric For the lenses with the desired replacement schedule find the ones that come in the powers & characteristics you need Use Tyler s Quarterly or other reference

6 Soft lens replacement schedule 1 day Biweekly Some (AV) may rec weekly if sleep in CLs Monthly Quarterly: more for custom lenses Yearly/conventional: we almost never Rx for soft now

7 replacement schedule determined by Dr.-not regulated by FDA, but manufacturer usually recommends specific schedule Typically best to use manufacturer recommendation More frequent replacement usually less $$ per box

8 Proven that more frequent replacement decreases the number of adverse events Today s soft lens care products are not designed to make lenses last a year

9 Lens selection Try to stay with state of the art healthiest designs/materials when possible Consider: Pt goals: desired wt, activities during wear, replacement schedule, tints, etc. Ocular health, RX, previous CL wear Always ask if desire anything special such as tint, overnight wear, etc

10 DW/EW/CW/FW lens type or wear schedule DW: remove and clean & disinfect nightly CW: continuous wear for up to 30 consecutive nights EW: no more than 6 consecutive nights without removal. Clean & disinfect each removal unless discarding Counsel pt re increased risk of serious ocular complications with overnight wear espec if std hydrogel FW: occasional overnight wear: not assoc with increase in incidence of infection

11 Wear schedules DW Lens: only FDA approved for DW (no overnight) use Can be low water and/or thick ct Durable, low evaporation rate Proclear, etc EW or CW Lens: Use for DW, FW, or EW Use when require or desire greater O2 transmission (DK values) Will either have thin ct or high water content or silicone component. Most effective is silicone.

12 Why are some high Dks approved only for DW? Some CLs may have O2 permeability (Dk) high enough for EW use but manufacturer chose to only seek DW in FDA testing. So can only market for DW unless do more testing Some do this in order to get lens out into market sooner & later do EW trials

13 After selection of the specific lens Select BC Select power Place on eye product for your patient Evaluate movement, centration, corneal coverage, vision, patient comfort Over refract with spheres If all OK, ready to teach I/R, dispense

14 Sag The BC/OAD combination produces the sagittal depth which in turn controls the fit 8.6 BC/15.0 OAD would most likely fit tighter than 8.6/14.0 in same material & design Doesn t always hold true between brands and different (thinner) materials

15 Contact Lens Fitting by Vishakh Nair

16 In theory, which will be the A. 8.4 BC/14.0 OAD B. 8.7 BC/14.0 OAD C. 8.3 BC/13.8 OAD D. 8.4 BC/14.5 OAD steepest fit? 25% 25% 25% 25% 8.4 BC/14.0 OAD 8.7 BC/14.0 OAD 8.3 BC/13.8 OAD 8.4 BC/14.5 OAD 20

17 BC selection Corneal curvature measurements required by TX law but not always helpful with SCLs SCLs fitted significantly flatter (approx 4D) than patient s flat K 43.00K = 7.85 but if fit with 8.6BC (39.25) Follow manufacturer s recommendations Typically only 1 to 2 choices within a particular lens series Most SCL BCs fall within 8.4mm to 9.2mm range

18 Reality Most current scls offer one BC and one OAD Fits most patients regardless of Ks Manufacturer did many trials to find parameter combination / sag that would fit the majority of patients

19 If you have a BC choice In general but not always: Flat K 41-45D: start with median BC Flattest K > 45.00: start with steepest BC available for that lens Flattest K < 41: start with flattest BC available for that lens Follow manufacturer recommendations

20 SCL BC More significant in thicker, less flexible SCLs like Ciba Night & Day & custom designs Almost irrelevant in thin, very flexible SCLs Many designs can fit approx 80% of population with a single BC Steepens with on-eye dehydration so PM f/u good A particular BC in 1 brand may not fit the same as in another brand or material

21 OAD Most brands only offer 1 choice Need OAD that provides at least 0.5mm extension onto sclera in all directions Typical OADs range from 13.8mm mm with most around 14.0mm. Larger OADs with torics or high RXs to improve centration & stability & for large corneas Custom lenses with larger or smaller OAD available for difficult fits

22 Choosing lens power Vertex BOTH meridians of best spectacle RX to corneal plane For low amounts of cyl, Rx vertexed spherical equivalent Power needed varies slightly between brands/designs CONSIDER toric if cyl or > after vertexing both meridians

23 For trial fits May not have exact power needed in dx set DXs usually in only 0.50D steps Go with closest and may be good enough to wear home temporarily At f/u recheck OR and order best power for year supply

24 Perform OR Don t do OR if poor fit: waste of time OR = refracting while patient wearing CL Only do spherical if good VA obtained Can begin OR with plussing out or scope over CLs Note regularity/quality of retinoscopic reflex & power found Question patient re stability & clarity of vision D & N, particularly following blink

25 Lens power needed OR= over refraction. Perform spherical refraction over the trial CLs using either Loose lenses outside phoropter Phoropter Add OR results to lens power of lens on the eye This is ideally the power needed. If refracting in a very short exam room may need to add -0.25DS to results or reck at > distance. Don t overplus! If OR LIP or loose lens > 4 need to vertex

26 Residual astigmatism with a soft spherical lens All of the manifest cyl in the best spectacle refraction after vertexing Front surface aspherics may provide better acuity but don t actually mask cyl Minimize spherical abberation Only helps if low illumination or large pupils

27 Good comfort (>8/10) Crisp, clear, stable vision D & N Full corneal coverage in all gaze positions Minimum acceptable overlap onto sclera = 0.5mm 360 degrees. 1mm ideal Edge shouldn t cross limbus with blink Desirable fit

28 Due to large OZWs of SCLs, if overlap is adeq, pupil coverage not usually a prob except with opaques or very high Rxs, or torics Centration

29 What is not acceptable re centration Corneal exposure or edge continually passing over limbus Limbal blood flow restriction Limbal or peri-limbal irritation Inflammation

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31 Desirable lens movement Post-blink movement approx 0.5mm N & T Slightly less ok for some SHs Text says.5 to 1.0 but 1mm usually too much unless in upward gaze No resistance & smooth recovery from push-up Lag on change of gaze

32 Slit lamp eval of movement Allow lenses to settle approx 5 min if sph min or more for torics & bifocals Look again before pt leaves Lens movement: Primary function is removal of debris during tear exchange Traditional meth: observe vertical mvt with NORMAL blinking in primary & upward gaze. Expect approx 0.5mm N & T in primary & 0.75mm to 1.5mm in upward gaze. least 2 of 3 be in range Slightly less movement may be acceptable with higher DK/l (high O2 transmission) lenses if good push-up

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35 Inside out CLs Edge stand off (fluting) &/or decentration Excessive movement, lens awareness, may fall out If high modulus such as Night & Day may cause corneal molding especially if inside-out Look for inversion markers to help patient

36 For thin lenses and for patients with tight lids not showing adeq movement wi traditional meth eval by: Lens lag on gaze change Observe degree of lag & speed of recentering mm is desired (just estimate) Resistance to push meth (push - up test) Observe ease of moving lens from its static position & speed of recovery

37 Push-up test

38 Change of gaze

39 Tight lids May pull lens superiorly Traditional movemt may not be seen or possible. For these pts, if lens moves easily with the lids, BC to cornea relationship is usually acceptable.

40 Precautions in Eval of Movement Edge indentation may be > with loose conj Flexure of loose conj may give false impression of movement Loose conj may decrease movement by enveloping lens edge Incomplete blinks: SCL won t move adequately giving false impression of tight fit

41 EMR Recording of Fit Click on yellow box marked observation for choices: Movement/centration good Movement good, minimal, or none Centration good, superior, inferior, nasal, or temporal For pushup record as no resistance to push or as resistance to push if CL is tight or could use scale 0-5 For change of gaze can record in mm change with gaze change or just as good lag with change of gaze

42 Factors Governing Fit Sag of lens versus corneal-scleral sag & asphericity Anterior ocular topography Lid position & tightness Blinking characteristics Tear film quantity & quality Wear environment

43 More factors influencing fit Physical properties of lens Material: stiffer (higher modulus) moves more RX Thickness: overall, ct & midperipheral t Design

44 Unacceptable fits Corneal exposure Limbal impingement Complete lack of movement Blink-related visual disturbances Conjunctival lens edge

45 In General To loosen a SCL fit, while keeping other parameters constant: Decrease OAD Flatten BC Select CL with greater ct or midperiph thickness or higher modulus (stiffer)

46 To improve centration: tighten fit if movemt still adequate Increase OAD or steepen BC Try different brand To tighten a SCL fit while keeping other parameters constant: Increase OAD Steepen BC Decrease ct or overall thickness

47 Blinking/Tear Quality May have more effect on lens positioning & movement than BC or OAD Instead of changing lens fit, try artificial tears, punctal plugs, lid hygiene etc.

48 Blinking & quality of vision If too steep: Vision is clearest immediately after a blink Not always seen if very thin CL If too flat: Vision is blurred immediately after a blink

49 Effect of lens thickness on fit Thicker lenses show > movemt than thin Interact more with lids >post-lens tear volume Except for silicone/hydrogels oxygen transmission decreases as thickness increases

50 Excessively Tight SCLs May: Be comfortable initially Cause hypoxia, edema, neo, injection, conjunctival indentation after several hrs wear Trap debris or bubbles behind the CL Be difficult to remove- ask patient Possibly show conjunctival drag Increase tendency for myopic creep Controversial

51 Excessively Loose SCLs May: Cause discomfort/lens awareness Cause blurring, fluctuating vision, & injection Cause lens loss, decentration, edge standoff Verify not inside out or defective especially if only 1 eye appears loose

52 Remember SCL performance in response to parameter changes not as predictable as with RGPs Different brands with same parameters may not fit the same & F needed may vary

53 Marginal Fits Optimize fit as much as possible by choices of BC, OAD, material, thickness, O2, etc. If best fit still not optimal but you feel the pt should be wearing SCLs: Consider past SCL Hx, presence of neo, edema Limit wt to appropriate level Rx ATs on regular basis Monitor more frequently Advise pt & note in record