医学课件：环曲面软镜的验配

1、Contact Lenses,School of Optometry vertical = 090 Axis never 180,Nasal side,Temporal side,Temporal side,Spherical soft contact lens for astigmatism Spherical equivalent Least blur circle, relative Acceptable correction,Spherical equivalent Half amount of astig. + spherical part Scientific calculatio

2、n Least blur circle in retina Relative best visual acuity,Astigmatism,轴子午线,水平焦线,垂直焦线,最小弥散环,度数子午线,物体,A,B,D,C,Sturm间隙,Example 1: -3.00D/-1.00 x90 =-3.50D Example 2: +5.00D/-1.50 x180 =+4.25D,Indications for spherical SCL for astig. Astig.1.50D Amount of astig part 25% amount of spherical part Material

3、: relative hard (mild tear lens) SCL : thicker lens (mild tear lens),Consideration of toric contact lens,“K” 42.00 180 / 42.50 90,Rx-3.00 -2.50 x 180,Over-refraction-0.25 -1.75 x 175,Residual astigmatism,Incidence of SIGNIFICANT Astigmatism: Approx 35% of contact lens wearing population,TORIC SOFT C

4、ONTACT LENSESReasons for using toric SCLs,Refractive astigmatism Spherical SCLs failed to mask corneal astigmatism Induced residual astigmatism from RGP lenses RGP lenses causing too much discomfort,When soft toric lenses,Corneal astig. Crystal lens astig. Mixed astig. Not indications for toric SCL

5、Irregular corneal astig. Abnormal lids others,When soft toric lenses,1.50 D (0.75D) cyl 5.00 D vision decreased due to uncorrected astigmatism vision compromised with best sphere S：C 4:1 Can not tolerate RGP,TORIC SOFT CONTACT LENSES,Supply a full compensation for each of the eyes principal meridian

6、s Neutralize meridional refractive errors bring light from all meridians to a common focus on the retina For optimum vision toric SCLs must maintain their correct meridional orientation on the eye Different methods and designs for stabilization To maintain normal eye physiology the toric lens still

7、has to move on the eye,TORIC SOFT CONTACT LENSESSurface Designs,Front Surface Toric Spherical back surface Toric front surface Back Surface Toric Spherical front surface Toric back surface Bitoric (uncommon),TORIC SOFT CONTACT LENSES,Good vision with any kind of toric lens needs stable cylinder axis

8、 location!,TORIC SOFT CONTACT LENSESStabilization Methods,Prism ballast Truncation Double slab-off Peri-ballast Reverse prism,TORIC LENS DESIGNAims,Maximize predictability of axis location Make axis location independent of Rx Maximize physiological performance,TORIC STABILIZATION,TORIC SCL STABILIZA

9、TIONPrism Ballast,1 to 1.5 prism dioptres, base down Lens stabilized by lid forces acting on the prism-induced thickness differences Reduced O2 transmissibility in areas of greater thickness Discomfort along lower lid margin increased thickness of prism base,TORIC SCL STABILIZATIONTruncation,Prism b

10、allasted toric lens truncated along a chord 0.5 to 1.5 mm from the 6 oclock position Truncation shaped to align with the lower lid margin increased lens-lid interaction, theoretically better lens orientation Not always successful in practice truncation alters the thickness profiles and differentials

11、 Usually a last resort technique,TORIC SCL STABILIZATIONDisadvantages of Truncation,Truncated edge(s) often a source of discomfort May be expensive, frustrating and ultimately unsuccessful to fit More patient visits may be required More difficult to manufacture and finish,TORIC SCL STABILIZATIONDoub

12、le Slab-Off,Better comfort because of reduced lens thickness Thin zones superiorly and inferiorly Lens is prismless and symmetrical Thinner than alternative designs available Dynamic stabilization thin zones (upper and lower) interact with the lids (especially the upper lid) to position and stabiliz

13、e the lens on the eye,TORIC SCL STABILIZATIONDouble Slab-Off,Disadvantages: May not be as reliable in patients with loose lids Great reliance on lid interaction may need to use larger total lens diameters,TORIC SCL STABILIZATIONPeri-Ballast,Minus carrier converted into a prism base down effect Uses

14、thickness differences as stabilizing component Discomfort with lens-lid interaction at the thicker inferior half Reduced O2 transmissibility in thicker regions,TORIC SCL STABILIZATIONPeri-Ballast,Thinner superiorly, thicker inferiorly Orientation principle similar to prism ballast Similar overall th

15、ickness to spherical lens Prism-free optic,TORIC SCL STABILIZATIONReverse Prism Designs,Incorporating both prism (base down) and the inferior chamfer (base up) integrated design Should be thinner and more comfortable Base-to-base line is located below the geometric centre of the lens upper lid plays

16、 a greater role in lens orientation Cylindrical component is usually limited to the prismless optical zone,FITTING TORIC SOFT LENSESThe Challenge,Need stable cylinder axis location for good vision Predictable interaction between lid forces and toric lens shape,TORIC SOFT CONTACT LENSES,Reference mar

17、ks are used to assess lens orientation in situ,-3.00D/-1.50 x180,镜片在眼内会旋转,TORIC SOFT CONTACT LENSES,Lens deviation is measured as: Deviation from the vertical (markings at 6 oclock) OR Deviations from the horizontal (markings at 3 and 9 oclock),TORIC SOFT CONTACT LENSES,The magnitude and direction o

18、f any mislocation must be determined Use this to compensate the ocular astigmatic axis for any regular mislocation,Toric Soft Lens The first lenss fitting success is relative low Need trial lens to determine the astig. axis The rotation of lens and stability of lens determine the final acuity.,TORIC

19、 SOFT CONTACT LENSESCriteria for Use,Degree of astigmatism usually correct 1.00 D or more Ocular dominance uncorrected astigmatism more likely to be accepted on the non-dominant eye Viability of the alternatives toric SCLs better than spectacles or RGPS? Assessment of patients visual needs the less

20、critical the visual task, the greater the amount of astigmatism that can be left uncorrected (and vice versa),TORIC SOFT CONTACT LENSESFitting Methods,Special spherical trial lens: Manufactured in a toric design Without the incorporation of a cylinder in the lens,TORIC SOFT CONTACT LENSESFitting Met

21、hods,Special spherical trial lens method: Choice of trial lens is based on BOZR Perform sphero-cylindrical over refraction Assess lens fit Determine and compensate for orientation of trial lens,TORIC SOFT CONTACT LENSESFitting Methods,Toric trial lens: Use a trial lens which incorporates cylinder St

22、abilization features of the trial lens should be representative of any lens ordered from the same series Most reliable technique for toric SCL fitting,TORIC SOFT CONTACT LENSES Fitting Methods,Toric trial lens method: Measure refractive error; correct for vertex distance if necessary Choose a toric

23、trial lens as close as possible to this Rx Assess the lens fit Determine orientation behaviour of the lens Consider any angular mislocation in the final prescription,TORIC SOFT CONTACT LENSESFitting Methods,Empirical Prescribing: No lens fitting OR Spherical soft lens fitting,TORIC SOFT CONTACT LENS

24、ESFitting Methods,Empirical Prescribing: No lens fitting Toric SCL order is based on: refractive error measurement of other ocular parameters BOZR based on keratometer readings Lens diameter usually established by lens design Some manufacturers routinely allow for axis mislocation,TORIC SOFT CONTACT

25、 LENSESFitting Methods,Empirical Prescribing: Spherical soft trial lens Perform sphero-cylindrical over-refraction May need to allow for rotation in final Rx Other lens parameters determined from trial lens design,TORIC SCL FITTING,Full corneal coverage 0.2 0.5mm (1-2mm in book) movement Err on larg

26、e side with respect to TD Good fit quick return to axis if mislocated Tight fit slow return to axis if mislocated Loose fit lens orientation unstable and inconsistent,TORIC SOFT CONTACT LENSESMeasurement of Lens Rotation,Reference mark(s) on lens at 3 and 9 oclock or 6 oclock Lens markings are for r

27、eference only! Measure rotation: narrow slit-lamp beam spectacle cylinder in trial frame protractor scale eyepiece graticule Estimation of degree of lens rotation,TORIC SOFT CONTACT LENSESPredicting Lens Rotation,Average lens rotation is 5 - 10 nasal anticlockwise for RE clockwise for LE Large indiv

28、idual variations Lens affected by lens/eye relationship and lid anatomy Lens allocation affected by lens thickness profile,left,anti-clockwise,clockwise,right,12,6,9,3,Terminology: practitioner view,TORIC SOFT CONTACT LENSESPredicting Lens Rotation,Based on lens thickness profile: Interaction with l

29、ids moves thinnest meridian towards vertical Upper lid is the dominant stabilizing component With respect to rotational influence: oblique is WTR ATR,CYLINDER AXIS ORIENTATION,Look for the lens markings Determine amount of mislocation Note consistency of lens marking position Push lens around to det

30、ermine settling position,TORIC SOFT CONTACT LENSESCompensation for lens rotation,Patient requires axis 90 Lens marking mislocates 15 to the right Right Subtract order (90 - 15) = 75,EXAMPLE:,order 75,105,15 mislocation,TORIC SCL FITTING PROCEDURE,Measure refractive error & vertex distance Select tor

31、ic lens design Select trial lens power to match corneal-plane refraction Select BOZR and/or TD Measure meridional orientation (axis mislocation) Compute final prescription, including axis compensation,Measure of lens rotation,Lens marks for orientation Not for axis indication,Compensation for lens r

32、otation,LARS Compensation added to ocular Rx not trial lens,Trial fitting method,30,Order axis 150,order axis 150,Case :,Spectacle Rx OS 3.00 1.75X140, trial lens OS 3.00 1.50 x 145 Clockwise rotation 20 degrees The order will be -3.00 1.50 x160,Case :,OD:Rx +2.75 1.50 x 15, trial lens +2.50 1.00 x

33、10 Anticlockwise rotation 10 degrees +2.75 1.50 x 5,amount of rotation to the axis of the contact lens Rx,Axis Orientation (LARS),Left Add Right Subtract,LEFT OR RIGHT ROTATION: MESUREMENT METHODS,Trial lens Slit lamp microscope Axial lensmeter estimate,Visual acuity outcome Depends on the lens axis or lens steability More consideration More depends on doc