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The Business of Contact Lenses
Becoming a Contact Lens Expert: Soft Toric Prescribing
By Clarke D. Newman, OD, FAAO
Yes, this column is about the business of contact lenses. However, the best tip that I can give you to make money in the contact lens business is to become a contact lens expert. That does not mean setting up a “contact lens center” the way we are setting up “dry eye centers.” This is not about getting equipment and making brochures, even though you should do that, too.
No, what I mean is: cultivate real expertise in all facets of contact lenses. A few months ago in this column, I talked about spline curves. Understanding spline curves and how they affect lens designs is the mark of a contact lens expert. However, splines are an advanced technique.
The foundation of expertise is a solid understanding of the basics. We “ooh” and “ahh” when Tiger Woods hits a crazy fade shot around a tree, but he can't do that without a firm understanding of proper stroke mechanics and what changes must be made to create the fade. So, too, contact lenses. For my next few columns, I will focus on some of these basic elements.
Toric Lens Basics
So, let's talk about toric alignment. Almost all of the hydrogel toric contact lenses that we prescribe today are back-surface torics. So, one of the things you should look for is whether or not the refractive and corneal cylinders are the same. If they are not, you may have alignment problems. Anticipating problems is the mark of an expert.
One technique that is really useful is looking at centration, movement, and rotation when the patient's head is not in the slit lamp head rest. Having a patient lean forward with his chin on the chin rest and his forehead against the forehead rest is a very unnatural position that causes misperceptions of these dynamics. Use a Burton lamp or a +20D lens with a transilluminator. It is quick, easy, and much more accurate.
For hydrogel torics, changes to the cylinder affect the back of the lens and changes to the sphere affect the front of the lens. Whenever possible, change the sphere power to improve visual acuity. Because the cylinder is on the back of almost all soft toric lenses prescribed today, every time you change the cylinder power or axis, you change the alignment and the way that the lens drapes on the eye.
When observing lens rotation, lenses that rotate are either too tight or the patient has dry eyes until proven otherwise. Run those traps first before applying LARS (left add, right subtract). I am not a big fan of axis compensation. There are too many good lenses that will probably provide proper alignment. In my practice, any lens that rotates more than 10 degrees is out on that patient, and we are on to the next design.
Another rule of thumb is that patients will put up with constant defocus before they will put up with variable acuity. However, the hallmark of a well-prescribed toric lens is good, stable acuity. If you cannot achieve excellent acuity with a sphero-cylindrical overrefraction, then there is usually something wrong with the alignment of the lens. Change to a different lens before wasting your time and the patient's time trying to make the same design work.
Something that I have noted in my career is that fuzzy vision can make lenses uncomfortable because patients are trying to squint. Minor comfort complaints are often solved with an over-refraction.
Finally, use a good optics program to resolve crossed cylinders. A crossed cylinder over-refraction often points to lens rotation—even when you cannot see the rotation. CLS
|Dr. Newman has been in private practice in Dallas, Texas since 1986 specializing in vision rehabilitation through contact lenses as well as corneal disease management, optometric medicine and refractive surgery. He is a Diplomate in the AAO and a consultant to B+L and AMO. Contact him at email@example.com.|
Contact Lens Spectrum, Volume: 27 , Issue: August 2012, page(s): 46