Making the Most of Your Corneal Topographer

BY WALTER D. WEST, O.D., F.A.A.O.
AUG. 1997

As with any new technology, corneal topography is getting better and the cost is coming down. Many practitioners have already seen the advantage of corneal topography in caring for pre- and postop patients -- both cataract and refractive surgery cases -- and for patients with irregular astigmatism and keratoconus. But the practitioners who are really using the technology to its fullest potential are also using it for pre-fit and post-fit contact lens evaluations as well as to pinpoint the causes of unexplained reduced acuities.

HOW KERATOMETRY CAN FAIL

I recently saw a 10-year old girl with reduced visual acuity in her right eye. She is a hyperopic astigmat who had been in vision therapy with patching for 18 months. She wore spectacles with no prescription for the left eye. Her best corrected visual acuity at the time of the exam was 20/50. The topographer revealed that she had irregular astigmatism in the form of an asymmetric error that the keratometer didn't identify.

To confirm and demonstrate the diagnosis, we placed an RGP lens on her eye and overrefracted to 20/30. After seeing the dramatic improvement and consulting with the child's mother, we prescribed the lens. Within three weeks, the patient's visual acuity was 20/20.

This is not to imply that vision therapy is not a valid treatment, but it does show how keratometry lets us down. First, it assumes that the cornea is a sphere, but we all know the cornea is aspheric. Next, rather than measuring radius of curvature, the keratometer averages four data points compared to topography's thousands. The keratometer is accurate to only plus or minus a half-diopter, and it often presents a somewhat misleading picture by overlooking many of the irregularities and eccentricities of the cornea. The corneal topographer brings all of these nuances to light, giving us more data to evaluate.

JUSTIFYING THE COST

When it comes to justifying a $12,000 instrument that you may use only once a week or once a month, it just doesn't appear to be reasonable. But when you recognize that this technology should be used daily, and when you realize the impact it can have not just for pre-fit and post-fit evaluation of contact lens wearers, but for patients with reduced acuities, justifying the cost becomes easy. It stops being an affordability issue, but becomes a profitability opportunity for your practice.

ENSURING APPROPRIATE REIMBURSEMENT

There is no discrete CPT code for corneal topography. It's billed under the code for unlisted ophthalmologic procedures (92499). When you bill for an unlisted procedure, you must explain and justify the test. I have developed a form that I send along with the claim (Table 1).

LOOKING FORWARD TO EARLY RETIREMENT

Daily, the corneal topographer shows me something that the keratometer would have missed or misled me on. I haven't thrown my keratometers out yet, but I'm using them less often. As soon as someone develops a handheld corneal topographer, or as soon as the prices come down enough so that I can have more than one, you can be sure I'll retire all my keratometers.