12_toric by xuxianglp


     Ten Toric Tips
     How to avoid common errors when fitting toric soft contact lenses.
     By Thomas G. Quinn, O.D., M.S

            uccess in fitting toric soft      gels, contributing to a more rapid         the same direction and to the same

     S      contact lenses can be en-
            hanced by avoiding some
            common pitfalls. This article
     will review 10 frequent mistakes
     and how to remedy them.
                                              settling on the eye.

                                              9: Assuming Lens Rotation
                                                 Assess the rotational position and
                                              stability of a lens once it has settled.
                                                                                         degree. A simple adjustment in the
                                                                                         contact lens axis will compensate for
                                                                                         rotation and provide clear vision.
                                                                                         Follow the LARS rule: If the lens
                                                                                         rotates Left, Add to the axis; if it
                                              It’s great when you peer through           rotates Right, Subtract from the axis.
     10: Not Letting a Lens Settle            the slit lamp and find the 6 o’clock          Measuring rotation. Aligning a
        Financial pressures from man-         mark on a toric lens sitting at 6          slit lamp beam with the lens mark-
     aged care and office overhead            o’clock on the eye. The benefit is         ing is an effective measurement tech-
     sometimes have us working so fast        that the axis needed in the contact        nique. However, some fitters simply
     that we rush our way right into          lens matches the spectacle axis.           view the lens markings and estimate
     inefficiency. A perfect, and fre-           In reality, though, the lens often      rotation. A study by Snyder and
     quent, example of this is when we        will rotate on the eye to some             Daum2 found that observers can
     don’t allow adequate time for a          degree. Szczotka1 found that greater       accurately estimate rotation to
     toric lens to settle before assessing    amounts of rotation can be antici-         within 8 degrees 95% of the time. Is
     its performance on the eye.              pated if a topographical map of the        this accurate enough?
        How long should a lens be             corneal surface shows that the                Snyder and Daum also found that
     allowed to settle? This varies with                                                 an observer’s ability to accurately
     design and material. Hydrogel                                                       estimate rotation decreases as the
     lenses dehydrate significantly when
     first placed on the eye, causing the
                                                “rotate as for a lens
                                                   It’s okay
                                                             long as it
                                                                                         amount of lens rotation increases.
                                                                                         This potential error becomes more
     lens to tighten. This affects lens                                                  significant with increasing toric
     movement and oftentimes rotation-          does so consistently in                  power. Linksz3 calculated that when
     al characteristics. For hydrogel                                                    a lens of toric power equal to the
     lenses, at least a 10-minute settling
                                                the same direction and                   astigmatic error of the eye misaligns
     time is recommended. In our office,
     the technician who applies the lens
     notes the time of application on the
                                                to the same degree.
                                                                               ”         by 30˚, the result is residual astig-
                                                                                         matic power equal to the cylinder
                                                                                         power in the contact lens. A 15˚
     fitting sheet and enforces the mini-     astigmatism extends from limbus to         misalignment will result in an error
     mum 10-minute rule.                      limbus. Conversely, a back-surface         of half the toric lens power. In
        Fortunately, new silicone hydro-      toric lens will rotate very little when    essence, incorrect alignment of a
     gel toric lenses appear to settle        topographical analysis indicates           higher astigmatic power will have a
     more quickly than their hydrogel         that the astigmatism is confined to        significantly greater adverse effect
     counterparts. This attribute may be      the central cornea.                        on vision than misalignment of a
     due in some part to design, but the          Some fitters consider any lens         low cylinder power.
     material certainly plays a role. Sili-   rotation a strike against success, but        So, when working with low cylin-
     cone hydrogel materials have been        it’s not. It’s okay for a lens to rotate   der powers that rotate very little, the
     found to dehydrate less than hydro-      as long as it does so consistently in      estimation method is probably

                                                                                                Toric Tips
acceptable. However, when work-             If rotational stability looks good     likelihood that your favorite toric will
ing with higher cylinder powers,         up to this point, proceed to the digi-    be available in the desired power.
especially when observing greater        tal displacement test. While observ-         How low should you go?
amounts of rotation, employ the slit     ing the right lens on the eye, reach      Bergenske and associates4 reduced
lamp beam alignment technique.           around the slit lamp with your            the cylinder power in the phoropter
                                         clean finger (your digit) and manu-       to comply with powers commonly
                                         ally rotate the lens out of position.     available, then adjusted the sphere
                                         Once this is accomplished, swing          power to obtain best subjective acu-
                                         over to the other eye and repeat.         ity. They found this technique to be
                                            Now, come back to the right eye        a reliable indicator of patient
                                         and observe the location of the lens      response to a toric lens incorporat-
                                         marking. If it is back to, or nearly      ing such power adjustments (see
                                         back to, it’s original location, you      step 3 in “Beyond the Best Spectacle
                                         can proceed with a high level of          Refraction,” page 15).
                                         confidence that the fit is stable.           Don’t forget about vertex effects
                                                                                   on contact lens power. A highly
                                         7: Over-Refracting Over                   myopic astigmat will need less toric
                                         An Unstable Lens                          power in a contact lens resting on the
The slit lamp beam alignment technique      Refracting over a toric soft con-      corneal surface than in the spectacle
assesses toric lens orientation.         tact lens offers some distinct advan-     plane. The opposite is true for the
                                         tages. Power changes induced by           high hyperopic astigmat.
                                         lens flexure, vertex changes or the
8: Assessing Lens Stability              presence of a tear lens can all be        5: Fit Change vs. Rx Change
   As mentioned, it’s okay for a         accounted for by this procedure. We          When a patient complains of blur
toric lens to rotate on the eye as       often hesitate to perform an over-        during toric lens wear, ask if the
long as it does so in a stable fash-     refraction for fear of embarking on a     blur is constant or fluctuating. If
ion. Stability is the key to consis-     never-ending quest for an endpoint.       constant, a change in power or axis
tently clear vision. But how is             Recognize that if an endpoint          may solve the problem. If
stability assessed?                      cannot clearly be achieved during         fluctuating, avoid the temptation to
   Most fits begin by observing the      an over-refraction it is because the      “chase the Rx.” Power and axis
toric markings on the lens as the        toric lens is not stable on the eye.      changes will not be fruitful. A
patient looks straight ahead and         Don’t attempt an over-refraction
blinks. If rotational variability is     until you’ve determined that the           Lens Power Tutor
observed under these conditions,         lens fits properly.
                                                                                    Below are sources to find programs that
changes to the fit are required. Does       Once you have a stable fit and a
                                                                                    will assist you in calculating the new lens
stable rotation under these condi-       reliable over-refraction, use the
                                                                                    power following over-refraction.
tions guarantee that the lens will be    many programs now available to
stable as it is worn during day-to-      calculate the new resultant lens           www.eyedock.com
day activity?                            power (see “Lens Power Tutor”).            - Click on Tools/Calculators, then Oblique
   Explore stability further with two    Today’s programs take into                 Crossed Cylinders.
extra steps. As you observe the toric    account any rotation of the lens on        - Calculation based on observed rotation.
marking, ask the patient to look up,     the eye by asking you to input the         - Free.
blink, then look straight ahead. Re-     location of the lens marking or the        www.palmgear.com
assess the position of the lens mark-    patient’s spectacle refraction.            - Enter Contact Lens Calculator Plus into
ing. Repeat, asking the patient to                                                  the search box.
look to the right, left, then down.      6: Over-Correcting Astigmatic              - Calculation based on both observed
The goal is to observe little to no      Refractive Error                           rotation and spectacle Rx.
rotational variability. Lens disloca-       Bias the cylinder power in the          - $12.95.
tion with gaze change may be par-        contact lens low. If the lens should       Manufacturer Web sites
ticularly problematic when it occurs     shift on the eye, the mislocation will     - May require registration.
in down gaze, as this is generally       create less visual disturbance. Biasing    - Free.
the posture taken while reading.         the cylinder down also improves the

                                                                                                     REVIEW OF OPTOMETRY          13
     design change is needed.
        Also, if the blur is fluctuating, ask
     the patient if blinking makes her
                                                  “blur is fluctuating, make aadesign change.
                                                     If blur is constant, make prescription change.
     vision better or worse. If worse, the
     lens is likely too loose, which usu-
     ally demonstrates an unstable orien-
     tation. This can be explored by            change is indicated. Now what?            more sophisticated and sometimes
     observing the lens orientation marks          All you need to know is whether        take a little more time to fit, so it is
     with the slit lamp as described ear-       the lens change you’re making will        a process.”
     lier. If blinking clears the patient’s     satisfy the patient’s visual goals.          Positive Statement 2: “However,
     vision, then the lens surface may be       Rather than scheduling the patient        we often are able to achieve satis-
     dirty, or the lens is too tight.           to return in another week, arrange        factory vision on the first try.”
        If lens orientation appears stable      to contact her via phone, e-mail or          Expectations regarding comfort.
     and the lens is clean but the patient      instant messenger to ask how she is       Due to design features necessary to
     complains of fluctuating vision, the       getting along.                            prevent rotation, toric lenses some-
     cause may be irregular lens flexure,          Generally, the problem will be         times provoke more initial aware-
     which results from incomplete              solved and you will have saved both       ness on the eye. This may especially
     draping of the lens on the anterior        you and the patient some time. If         be the case when fitting some of the
     corneal surface. This is most likely       problems persist, you will often          higher modulus silicone hydrogels. I
     to occur with thicker lenses, such as      already know the next step. You           find it particularly important to
     high-plus or prism-ballasted lenses.       can ask the patient to stop by and        mention this to patients who are
        Irregular flexure induced by a lens     pick up a diagnostic lens with a          being upgraded from a spherical
     that is too steep will result in a         new power adjustment. Simply con-         lenses. Because of their prior wear-
     report of improved vision immedi-          tact her again after one week or so       ing experiences, these patients have
     ately following the blink. This occurs     to confirm success. If problems per-      expectations of how a lens “should”
     because the squeezing force of the         sist, schedule the patient for an         feel. Reassure them that this aware-
     eyelids temporarily aligns the poste-      office visit.                             ness will clear in a few days. To help
     rior lens surface with the anterior                                                  get them “over the hump,” remind
     corneal surface, resulting in a smooth     3: Not Establishing                       them of the improved clarity they
     but transient optical system.              Proper Expectations                       will enjoy with their new lenses.
        Irregular flexure induced by a             Most contact lens candidates
     lens that is too flat will result in a     assume that they need spherical           2: Masking Astigmatism with
     report of worse acuity immediately         disposable soft contact lenses. Any       Spherical/Aspheric Lenses
     following a blink, as the lids effec-      deviation from this can come as quite        Studies have shown that spherical
     tively cause the lens to “wrinkle.”        a surprise—especially if it involves      lenses do not adequately correct
        A suspicion of irregular flexure        unanticipated additional cost!            astigmatism of -0.75D or more.5,6
     can be confirmed by observing irreg-          I begin any discussion I have with     Work by Kollbaum and Bradley7
     ularities in the retinoscopic red reflex   an astigmatic contact lens candidate      has shown that some aspheric soft
     or the keratometry mire pattern over       by demonstrating how astigmatism          lens designs can enhance vision by
     the contact lens-wearing eye.              affects his vision (see item 1 in the     correcting spherical aberration, but
        Changing base curve or going to a       sidebar “Beyond the Best Spectacle        it appears unlikely that they actu-
     thinner lens design can resolve visual     Refraction”). Once the patient under-     ally correct astigmatism.
     blur induced by irregular lens flexure.    stands his eyes are “special,” I employ      Bayer and Young8 fit 150 low
                                                the sandwich approach; I sandwich         astigmats (-0.75D or -1.00D) with
     4: Inefficient Use of Chair Time           the “meat” of what I want to com-         toric lenses. Sixty-two subjects were
        Let’s take the example of a             municate between positive state-          existing spherical wearers. They
     patient you have newly fit with toric      ments. The goal is to be realistic        achieved a 97% fitting success rate
     lenses. She returns for a one-week         without being negative. For example:      with 91% needing only one diag-
     check. The fit and corneal response           Positive Statement 1: “We have         nostic fitting. Prior spherical lens
     are satisfactory, but her visual needs     contact lenses that will provide you      wearers enjoyed an average visual
     are not quite being met. You con-          with clear vision.”                       acuity of nearly one line better with
     clude that a slight power or axis             The Meat: “These designs are           toric lenses. Many others have

                                                                                                                     Toric Tips
demonstrated significantly improved               many factors (e.g., chair time,                  rise to the needs of these patients. The
vision when low astigmats are                     uniqueness of the service, competi-              tools we have at our disposal have
moved from spherical lens correc-                 tion, etc.) may be considered, it                never been better, and our clinical
tion to toric lenses.9,10 The point               comes down to this: Charge what-                 skills are ready for the challenge. ■
here is that torics can be fit with a             ever amount it takes for you to
high degree of success in a relatively            approach the fitting with a willing              1. Szczotka L, Aggarwal T. Utility of conreal topography in
simple fashion, while providing sig-              attitude. If you find that you are               soft toric lens fitting. Am Academy of Optom Scientific
                                                                                                   Poster, December 15, 1997.
nificantly improved visual perfor-                begrudging the returning toric                   2. Snyder C, Daum KM. Rotational position of toric soft con-
mance over what can be achieved                   patient who is back one more time,               tact lenses on the eye-clinical judgements, Int Contact Lens
                                                                                                   Clin 1989 May;16:146-51.
with spherical soft contact lenses.               then you are not charging enough.                3. Linksz A. Determination of axis and amount of astigmatic
                                                     Contact lens manufacturing repre-             error by rotation of trial cylinder. Arch Opththalmol 1942;28:
1: Not Charging Enough                            sentatives can be a helpful resource             4. Bergenske P, Fedor R, Pethe D. Predicting toric soft lens
For Toric Fits                                    in gaining insight as to what other              acuity by attenuated cylinder refraction. Am Academy of
                                                                                                   Optom Scientific Poster, December 9, 2004.
   Although fairly straightforward                successful toric fitters are charging            5. Snyder C, Talley DK. Masking of astigmatism with
for the knowledgeable fitter, toric               for their services. Another helpful              selected spherical soft contact lenses. J Am Optom. Assoc,
lens fitting can, at times, be frustrat-          process is to examine other contact              6. Bernstein PR, Gundel RE,Rosen JS. Masking corneal toric-
ing and time consuming. Complica-                 lens service fees in your office and             ity with hydrogels: does it work?, Int Contact Lens Clin
tions can arise and you need to be                evaluate the relative value of toric             7. Kollbaum P, Bradley A. Aspheric contact lenses: fact and
ready to manage them.                             fitting to these other services.                 fiction, an examination of whether soft aspheric contact
                                                                                                   lenses can correct astigmatism and spherical aberration. CL
   Make sure you are being ade-                                                                    Spectrum 2005;20(3):34-9.
quately compensated for the skills                Take on the Toric Patient                        8. Bayer S, Young G. Fitting low astigmats with toric soft
                                                                                                   contact lenses-what are the benefits and how easily it is
and time you bring to the toric fit-                 Astigmatic contact lens wearers               achieved? Am Academy of Optom Scientific Poster, Decem-
ting process. You should be reward-               have been underserved for years,                 ber 2005.
                                                                                                   9. Kruse A, Lofstrom T. How much visual benefit does an
ed for taking on the challenge of                 either by being fit with spherical soft          astigmat achieve being corrected with a toric correction? Int
meeting the needs of this oftentimes              lenses or by being discouraged from              Contact Lens Clin 1996;23:59-65
                                                                                                   10. Dabkowski JA, Roach MP, Begley CG. Soft toric versus
underserved population. But how                   pursuing contact lens correction alto-           spherical contact lenses in myopes with low astigmatism, Int
much should you charge? Although                  gether. It’s time to change course and           Contact Lens Clin 1992;19(11&12):252-5.

  Beyond the Best Spectacle Refraction
  When examining an astigmatic contact            distance acuity chart as you remove the         to 20˚ before the patient reports blur, it is
  lens candidate, some great information          astigmatic correction. He or she will           likely he will tolerate toric lens rotation
  can be obtained immediately following the       report blur.                                    without visual complaint.
  completion of the best spectacle refrac-           d. Re-enter the astigmatic correction.          e. Repeat for the other eye, if indicated.
  tion. While the patient is still lined up       Vision will be clear again.
                                                                                                     3. Reduce the cylinder component in
  behind the phoropter, perform the follow-          e. Repeat for the other eye, if indicated.
                                                                                                  the phoropter to the next lower power
  ing three steps, which only take two to
                                                     2. Rotate the best cylinder correction       commonly available in toric designs.
  three minutes:
                                                  in the phoropter.                                  Why? To see how low the astigmatic
     1. Demonstrate vision with and with-            Why? To assess the patient’s visual          power in the contact lens can be reduced
  out astigmatism correction.                     sensitivity to astigmatic axis rotation.        to minimize the potential visual distur-
     Why? To communicate the importance           Here’s how:                                     bance with lens rotation on the eye.
  of correcting astigmatism. Here’s how:             a. Occlude one eye.                             a. Occlude one eye.
     a. Occlude one eye.                             b. Ask the patient to observe the dis-          b. Reduce the cylinder component in
     b. Tell the patient, “In addition to being   tance acuity chart and report to you when       the phoropter to a level commonly avail-
  nearsighted (or farsighted), I’m finding        he first notices blur as you rotate the         able in toric lens designs.
  you also need correction for astigmatism.       astigmatic lens in the phoropter.                  c. Adjust the spherical component to
  I’m going to take the astigmatism correc-          c. If the patient reports blur almost        obtain best subjective acuity.
  tion out of this instrument to show you its     immediately, he will likely be intolerant of       d. If good acuity is obtained, it is likely
  effect on your vision.”                         any toric contact lens rotation on the eye.     that the patient will do well with a contact
     c. Ask the patient to observe the               d. If you are able to rotate the lens 15˚    lens of the lower toric power.

                                                                                                                            REVIEW OF OPTOMETRY                     15

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