How to Use the LRI Calculator

It has been said, “Necessity is the mother of invention.” This is true of LRICalc.com.

As the widely used Donnenfeld nomogram was developed specifically for manual incisions, Preeya K. Gupta, MD, and Gary Wörtz, MD, realized the field could benefit from a formula—specifically designed for arcuate incisions made with a femtosecond laser—to obtain precise, individualized measurements and placement for limbal relaxing incisions (LRIs).

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The development of the Wörtz-Gupta Formula

Thus, Arcuate Innovations, with its revolutionary Wörtz-Gupta Formula and associated femtosecond laser LRI Calculator, was born. The formula and findings are highlighted in their paper “Outcomes of Femtosecond Laser Arcuate Incisions in the Treatment of Low Corneal Astigmatism.”

To summarize, the study analyzed the real-world outcomes of 224 patients (124 study eyes, 100 control eyes) in regard to the management of low-level astigmatism of 1D or less with corneal arcuate incisions performed with a femtosecond laser during cataract surgery.¹

It was determined that patients who had femtosecond laser-assisted cataract surgery (FLACS) with arcuate incisions were 1.8 times more likely to achieve 20/20 uncorrected visual acuity (UCVA) or better and 3.54 times more likely to achieve 20/25 UCVA or better.¹

Key principles of the Wörtz-Gupta formula and calculator

This straightforward formula applies four primary principles.

The Wörtz-Gupta LRI calculator is designed:

For arcuate incisions with a femtosecond laser.
To treat low levels of corneal astigmatism; the calculator will lock out at values above 1.25D diopters of astigmatism.
With the intention that incisions be opened and irrigated.
For incisions to be placed at the 9mm optical zone at 80% depth.

Taking into consideration the amount of posterior corneal astigmatism and the low level of surgically-induced astigmatism (SIA) encountered by most surgeons, the creators also baked these factors into the formula. In addition, they accounted for the fact that most surgeons approach cataract surgery temporally.

Note: Through studies and personal practice, both surgeons have discovered that, for levels of astigmatism over 1.25D, toric intraocular lenses (IOLs) can be more effective.

Calculating with convenience

To ensure you can access these calculations straight from the operating room, there is a mobile version of the calculator for both iPhone- and Android-based smartphone operating systems, all available at www.LRIcalc.com.

The formula in action

When utilizing the Wörtz-Gupta Formula, it’s a simple plug-and-play process. Once the requested data has been inputted into the respective fields, the algorithm will supply individualized calculations.

After reading a short disclaimer and checking an acknowledgment, you will input the following information:

ID number—do not provide protected health information
Patient age
Right eye vs. left eye
Level of corneal astigmatism—this value must be 1.25D or below
Steep corneal axis, between 0° and 180°

Then, hit calculate. Along with a summary of the provided information, you will be given the degree of the phaco incision and lengths for Arc Length #1 and Arc Length #2.

Figure 1 below reveals the calculations for a 65-year-old patient with 1D of astigmatism and steep corneal axis of 90° in the right eye.

^{Figure 1: Courtesy of the authors.}

A note on safety and size

Based on clinical experience and research while developing this formula, both surgeons found that incisions larger than 50° have an increased potential for corneal destabilization and related complications; therefore, there is never an option for an arc length larger than 50° in the online calculator.

In closing

Whether you're a new surgeon who is just finding their footing or a more experienced surgeon seeking a simplified solution to LRI calculations, the Wörtz-Gupta Formula can be beneficial.

Demonstrating the core value of an interventional mindset, the developers of LRICalc.com did so to help ophthalmologists of all skill levels potentially achieve better and more predictable results to optimize patient care.

Both surgeons welcome feedback from colleagues who have utilized the tool.

Disclaimer: The Wörtz-Gupta Formula (Patent Pending) femtosecond laser arcuate incision calculator is meant to serve as an adjunct tool to assist physicians in the correction of astigmatism in conjunction with the intraocular lens (IOL) placement.

The information contained herein is derived from the work and nomogram(s) of Gary Wörtz, MD, and Preeya Gupta, MD. The medical opinions and views expressed in the Calculator are those of Drs. Wörtz and Gupta and not those of any manufacturer of femtosecond lasers.