• Document: TORIC AND MULTIFOCAL GP AND SCL PRESCRIBING Edward S. Bennett OD, MSEd, FAAO
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6/9/16 1 TORIC AND MULTIFOCAL GP AND SCL PRESCRIBING Edward S. Bennett OD, MSEd, FAAO 2 l Dr. Bennett is a consultant to the Contact Lens Manufacturers Association 3 SOFT TORICS: Good Candidates l Astigmatic and do not desire GPs l Poor vision with spherical soft lenses l Athletes and any astigmatic patient who desires occasional wear l Refractive astigmatism ≥ 0.75D 4 FITTING PEARLS l Wait 5 – 10 minutes before assessing l Is lens stable on eye? l Evaluate fit first; if variable or excessive rotation it is preferable to then refit l Rotation is judged from fitter’s perspective l Use LARS and add to refractive axis 5 From Bennett ES, Henry VA: Clinical Manual of Contact Lenses (4th edition) 6 Methods of Rotation Evaluation 1 l Conventional: n Trial Frame n SWAG l Today! 7 FITTING PEARLS (cont.) l Know available lens parameters l When in doubt, under-prescribe on cylinder l Vertexing very important with ≥ 4D in either or both meridians l Example: -4.25 – 2.25 x 180 = -4.00 – 2.00 x 180; -6.50 – 2.75 x 180 = -6.00 – 2.25 x 180 8 Cross Cylinder Calculators l AOA E-Z Fit l Eyedock.com 1 l Therightcontact.com l Most contact lens companies 7 FITTING PEARLS (cont.) l Know available lens parameters l When in doubt, under-prescribe on cylinder 6/9/16 l Vertexing very important with ≥ 4D in either or both meridians l Example: -4.25 – 2.25 x 180 = -4.00 – 2.00 x 180; -6.50 – 2.75 x 180 = -6.00 – 2.25 x 180 8 Cross Cylinder Calculators l AOA E-Z Fit l Eyedock.com l Therightcontact.com l Most contact lens companies 9 So What Lens Do I Select? l Replacement Schedule (1 month, 2 weeks, 1 day) l Daily for dry eyes, occasional wear l Daily wear versus extended wear 10 GPS AND HIGH ASTIGMATISM With > 2.00D corneal cylinder the following problems can occur with a spherical GP: • Flexure • Decentration • Corneal Warpage • Corneal Desiccation • Lens Awareness 11 BACK SURFACE VS. BITORIC l Both indicated with ≥ 2.50D corneal cyl l Back surface toric only lenses have a toric back surface (identical in curvature to a bitoric) as verified with a radiuscope l Back surface torics induce a residual cylinder equal to about one-half of the back surface cylinder of the lens due to differences in refractive indices between lens and tear film 12 BACK TORIC l Determination of Base Curve Radii: l (Mandell-Moore) l Corneal Cyl Flat Meridian Steep Meridian 2.0 - 2.25D “On K” 0.50D Flat 2.5 - 2.75D 0.25D Flat 0.50D Flat 3.0 - 3.25D 0.25D Flat 0.75D Flat 3.5 - 3.75D 0.25D Flat 0.75D Flat 4.0 - 4.75D 0.25D Flat 0.75D Flat ≥ 5.0D 0.25D Flat 0.75D Flat 13 BACK SURFACE TORIC: INDUCED CYLINDER 2 l Exp: +1.00 – 4.00 x 180; 41/45: Toric BCR: 40.75/44.25; desired powers: +1.25/-2.25 l (Mandell-Moore) l Corneal Cyl Flat Meridian Steep Meridian 2.0 - 2.25D “On K” 0.50D Flat 6/9/16 2.5 - 2.75D 0.25D Flat 0.50D Flat 3.0 - 3.25D 0.25D Flat 0.75D Flat 3.5 - 3.75D 0.25D Flat 0.75D Flat 4.0 - 4.75D 0.25D Flat 0.75D Flat ≥ 5.0D 0.25D Flat 0.75D Flat 13 BACK SURFACE TORIC: INDUCED CYLINDER l Exp: +1.00 – 4.00 x 180; 41/45: Toric BCR: 40.75/44.25; desired powers: +1.25/-2.25 l BST induces cylinder equal to 40 – 50% of back surface cylinder l If there is 3.5D of back surface cylinder induced is to -1.75D x 180; this will be present via over-refraction l On lensometer there will 3/2 x back surface cylinder or 5.25D; if most plus meridian is unchanged, power in other meridian = -4D 14 BITORICS l When you correct for induced cylinder (ie, in previous example, add +1.75 x 180) on front surface, you have a bitoric design l Provides good centration; should fit like a spherical lens on low astigmatic cornea l Provides good vision l Results in good corneal integrity l When induced cyli

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