Refractive Practices EXCEL with Nomograms
Using specialized software to create yours has advantages, but a standard spreadsheet also works.
GUY M. KEZIRIAN, M.D., F.A.C.S.

Nomograms greatly improve the predictability of refractive surgery outcomes and can reduce enhancement rates to 1% or less. Low enhancement rates significantly increase profitability, and practices that don't employ valid nomograms simply can't compete in today's refractive marketplace. In this article, I explain how to create a nomogram using a spreadsheet or nomogram software.

Why Do We Need Nomograms?

With all the advances in excimer laser technologies over the past few years, it would seem reasonable to expect lasers to work accurately without nomograms. After all, aren't they just "fudge factors" to improve laser accuracy? Shouldn't manufacturers be able to make lasers that take off the right amount of tissue? Don't aberrometers measure refractions to superhuman accuracy? The answer to all these questions is "No." Individual lasers, surgeons, laser rooms, and patients vary, so nomograms are more important than ever to the successful practice of refractive surgery.

Modern nomograms improve laser accuracy and adjust for many variables that affect surgical outcomes, such as variations in room environment, surgical technique, and patient physiology. Manufacturers can provide lasers that ablate with extreme accuracy in plastic, but their performance in the human eye varies significantly. Nomograms can "anticipate" needed adjustments. Aberrometers add new dimensions to the measurement of optical errors, but they are highly user-dependent, and readings can vary from measurement to measurement. Nomograms compensate for some of these variations and can even improve the accuracy of wavefront-guided procedures.

What Is a Nomogram?

The term "nomogram" is derived from the Greek nomos, meaning law or custom, and gram, meaning measure or weight. Throughout science, nomograms or tabular listings of numbers have been used to plot results and to predict the outcome of those results using two known points. In refractive surgery, nomograms were first used to guide radial keratotomy procedures. They were usually in the form of number tables that listed the desired correction on the left and age of the patient across the top and indicated the number and length of incisions to make. Today's nomograms for laser-correction surgery are far more sophisticated and take the form of mathematical equations. Variables about the laser, surgical techniques, the patient, laser room environment, and other factors are taken into account to determine the correct numbers to program into the laser. Because lasers, surgeons, and climates vary, nomograms are used to determine which factors are most important for each procedure and to provide specific adjustments for each eye.

Creating a Spreadsheet Nomogram

Nomograms can be quite complex, but the question they answer is straightforward: What amount should be programmed into the laser to achieve the desired correction? Surgeons can create basic nomograms using spreadsheets such as Microsoft Excel. The first step in creating a nomogram is to create a list of eyes that were operated on under similar conditions and put it in a spreadsheet with the programmed amount in the first column and the achieved amounts for sphere and cylinder in the second and third columns. Additional variables can be added to evaluate other factors such as temperature and humidity.

The results are shown in the sample output (see p. 78). Here the equation is: Sphere Programmed Amount = 0.933 x Desired Sphere Treatment + 0.274 x Concurrent Cylinder Treatment. This shows that to obtain the desired result for the sphere portion of the refraction, it is necessary to decrease the sphere-programmed amount by approximately 7% for each diopter of sphere being treated and to increase the sphere-programmed amount by 0.27 diopters for every diopter of cylinder being treated. In other words, the sphere-programmed amount is not a simple adjustment; it's affected by both the sphere and cylinder components of the refraction, a phenomenon known as "coupling." Nomograms must be developed for both the sphere- and cylinder-programmed amounts. Nomograms based on spheroequivalent cannot factor for coupling, and coupling is present in most lasers. Using Excel to create a basic nomogram can provide good insight into the factors that affect your outcomes. Because nomograms must be developed for each surgeon, laser, optical zone, and treatment range and have to be constantly updated, this approach can be very labor intensive.

Nomogram Software

Using nomogram software has several advantages. The software contains many features for data validation and constantly searches for relationships and variables that affect outcomes. In a single practice with one surgeon, the software can develop 12 or more different nomograms for different procedures. Importantly, the software constantly updates the nomograms with new data to keep them current with changing conditions such as laser services, decay of laser optics, and environmental changes due to seasonal variations.

For the past 5 years, Jack Holladay, M.D., M.S.E.E., F.A.C.S., and I have developed software to create nomograms and evaluate outcomes in refractive surgery. The software, Refractive Surgery Consultant Elite, provides state-of-the-art tools for nomogram development and surgical planning. (See www.RefractiveConsultant.com.)

Implementing Nomograms

Specific nomograms must be developed for each surgeon, laser, and surgical technique, so nomograms that are "borrowed" from other surgeons will not lower your enhancement rate. You have to make your own, and fortunately the process is simple with the software available.

Successful integration of nomograms depends on a motivated surgeon and an effective practice administrator. Nomogram software costs about $8,000 and requires staff time and training to successfully integrate it into a practice. But these costs are more than offset by reduced enhancement rates. Data entry is easy, and not much data are needed: one preoperative examination, information about the procedure, and one postoperative examination. Data for both eyes can be collected on one page at the 1- or 3-month examination (depending on surgeon preference) and entered into the program. The surgeon calls up the information before surgery, often right in the operating room, and determines the correct amount to program into the laser. The total time required per patient is approximately 10 minutes.

Impact of Nomograms on Your Practice

With nomogram software it's not uncommon for practices to lower their enhancement rates to 1% or less, which can significantly impact their profitability and success. Enhancements are anxious events for patients and extremely expensive for a practice. Most practices do not charge patients an enhancement fee, so all the extra examination time and operating room expenses directly detract from profits. Moreover, enhancements divert your personnel, clinic time, and other resources that could be generating new income. Some laser manufacturers also charge an extra fee for enhancements. The hard cost of enhancements ranges from $500 to $750 each.

Added to the dollar cost are the lost opportunity costs and increased potential liability that comes when the initial outcome falls short of a patient's expectations. Enhancements reduce the number of patient referrals because patients who achieve their final result the first time are more likely to recommend your practice to others. Happy patients also allow surgeons and staff to be more productive, which leads to a successful practice.

Guy M. Kezirian, M.D., F.A.C.S., is president of SurgiVisionConsultants, Inc., an ophthalmic consulting firm in Scottsdale, Ariz., and Refractive Consulting Group, Inc., a software company that makes the Refractive Surgery Consultant Elite software. Dr. Kezirian is a board-certified ophthalmologist and works extensively to research and validate ophthalmic lasers. E-mail: Guy1000@SurgiVision.net.