医学课件：软镜的设计

1、Contact Lensesa bi-lingual course,School of Optometry & Ophthalmology, The Wenzhou Medical College,Wear Schedules,Daily wear Wear during waking hours only No overnight wear Extended wear Wear overnight up to 7 days in a row Any lens approved for EW Continuous wear Wear continuously up to 30 day in a

2、 row Only for silicone hydrogels,Replacement Modality,Conventional Frequent replacement Disposable,Conventional,Lens is replaced when it needs replacing Typically 12 months for a SCL Patient receives one pair of lenses at a time If a lens is lost or damaged, a replacement must be purchased More lens

3、 care required More deposit related complications,Frequent Replacement,Also called Programmed Replacement Lens is replaced on a regular schedule, 2 weeks to 3 months Lens is worn on a DW or EW basis Lens is reused after removal and disinfection Fewer complications Still requires lens care More costl

4、y Confusion with various replacement schedules,Disposable,One time use Daily wear: 1 day Extended wear: 1 week Continuous wear: 1 month Greatest convenience No lens care Most costly,Contact Lens Terminology and Design,Goals for this lecture,Start to become familiar with contact lens terminology Disc

5、uss various lens parameters Zones, curves, thicknesses, etc. Discuss various lens design categories Start to discuss basic concepts for contact lens fitting,Lens Dimensions,Overall diameter Optic zone diameter Peripheral curves Secondary curve Intermediate (tertiary) curve Peripheral curve,Lens desi

6、gns,Monocurve Bicurve Tricurve Tetracurve Aspheric,Lens curves,Base curve radius Peripheral curve radii Secondary curve radius Intermediate (tertiary) curve radius Peripheral curve radius Junction blend Light, medium, heavy,Lens thickness,Center thickness Edge thickness Junction thickness,Edge desig

7、n,Edge profile Edge lift,Lenticular designs,Minus carrier Anterior optic zone diameter Junction thickness Anterior peripheral curve radius,Anterior peripheral curve,LID,Lenticular designs,Plus carrier Anterior optic zone diameter Edge thickness or anterior peripheral curve radius,Other design featur

8、es,Prism ballast Peri-ballast Thin zone / double slab off Truncation,0.5 mm truncation,Lens power,Back vertex power Front vertex power,Lensometer,Lens Design Aspects,Spherical Aspheric Toric Multifocal Reverse Geometry,Spherical Design,Same spherical refractive power throughout the optic zone Spheri

9、cal base curves,r,Aspheric Design,Gradual change in curvature from center to periphery of the optic zone Power gradient: Multifocal powers possible Better corneal alignment,Eccentricity (e-value),Rate of flattening or steepening of an aspheric curve Greater e means larger power gradient Central corn

10、ea is roughly an ellipse with e 0.5,Toric Design,Different curvatures in the two major meridians Cylindrical power Can be front or back toric or bitoric,+1,-1,Multifocal Design,Multiple optical powers within the optic zone Allows focus of distance and near light Various designs to achieve multifocal

11、 power,D N,-1.00,+1.00,Net add: +2.00,Reverse Geometry Design,Central portion of lens is flatter than periphery For post-surgical “plateau” topographies For myopia reduction,Flat base curve,Steeper secondary curve,Flat peripheral curve,Flat,Steep,Key CL Concepts,Sagittal Depth Flat vs. Steep vs. Ali

12、gnment Radius vs. Diopters,Sagittal Depth,Vault of the back surface of the contact lens Describes how tight or loose the lens will fit Greater sag = tighter Smaller sag = looser Back surface curvatures and diameters affect sag,Steep BC and large LD = greater sag,s,r,C,h,Flat vs. Steep vs. Alignment,

13、Description of lens-cornea relationship Flat = less curved than the cornea Steep = more curved than the cornea Alignment = equally curved to the cornea Relationships will change with various parameter changes Careful observation of these relationships will be critical in accurate fitting,Radius vs.

14、Diopters,Radius = curvature Measured in mm Constant with change in material and thickness Diopters = power Measured in D Variable with change in material and thickness Conversion factor: 337.5 Calibrated to n of tears Used to convert K readings to mm of curvature,Radius vs. Diopters,Example: K-readi

15、ng of 45.00 D Using conversion factor, radius of curvature = 337.5 45.00 D = 7.50 mm If using a higher index material, D increases for same radius of curvature,SCL Design,Base Curve,Also referred to as Sagittal depth (sag) or Vault Same as for RGPs Tend to be much flatter than K due to large diamete

16、r Typical range: 8.00 to 9.20 mm,Power,Back vertex power Determined by BC, front curve, CT, n Effective power not altered by lacrimal lens Assume that LL is plano for most SCLs,Lens Diameter / Optic Zone,Larger than RGPs in general Increases stability and comfort Decreases tear exchange Typically 13

17、.5 to 15.0 mm Creates greater sag, resulting in need for flatter BCs,Center and Edge Thickness,Thinner than RGPs due to decreased fragility of material (greater flexibility) Min CT = 0.03 mm, increases for higher water content materials Affects Dk/L Edge profile may be more important to consider,Len

18、ticulation / Edge Design,Due to large diameter, all SCLs are lenticulated to maintain thin profile Edge designs vary,Water Content,Water is bound within a hydrophilic polymer matrix to provide flexibility and oxygen permeability The amount of water determines material characteristics Range: 25 to 74

19、% Low 50% (FDA),Tints,Handling / Visibility Enhancing Opaque cosmetic Prosthetic masking,Handling / Visibility Tints,Light tints to aid in lens handling Can see more easily in case, sink, or counter Not meant to change eye color Can change eye color in light blue irises Virtually all current lenses

20、have handling tints,Color Enhancing Tints,Change eye colors of light irised patients Blue, green, hazel eyes Will only darken brown eyes Combines with natural eye color to create a new color,Opaque Tints,Tints that change dark irises to other colors: “Brown eyes to blue” Mask underlying iris color M

21、ay see some iris through clear pupil Patient may notice some blur around the edges,FreshLook Colors Demo,Prosthetic Tints,Mask underlying disfiguration of the eye Corneal scars Iris defects Can be clear or occluder pupil lenses Can be painted any color Very expensive and long production time,Prosthe

22、tic Tints,Ciba: Special Eyes Program CooperVision: Prosthetic lenses Adventure in Colors Crystal Reflections,Inversion Markers,Tell a patient if a lens is inside-out Tells you if the lens is inside-out on the eye Many manufacturers now put letters/numbers on their lenses,Manufacturing,Spincasting La

23、the cutting Cast molding Combination lathe / spincasting Lightstream Technology,Spincasting,Oldest SCL manufacturing technique Otto Wichterle, 1960s Put SCL monomer in curved well Spin the well at proper speed to produce lens with specific thickness, diameter, and power Faster spin: larger, thinner,

24、 more minus Slower spin: smaller, thicker, more plus Very inexpensive and reproducible,Spincasting,Wichterle made his first spincasting unit out of a childs erector set,Spincasting,Lathe Cutting,Button in dry state is cut on a lathe, as are RGPs Lens is then polished Lens is then hydrated and sterilized Hydration causes lens parameter expansion: may cause variab