Getting with the program

In its use of vector analysis, the Alpins method built on the work of others(5,6,7). Alpins finalized the method in 1991 and, seeing its commercial applications, began development of a computer program that incorporated the mathematics. He called the program ASSORT, which stands for Alpins Statistical System for Ophthalmic Refractive surgery Techniques, and in 1992 founded the company ASSORT Pty. Ltd. to market the program. That same year, he filed for a U.S. patent on the method. The patent was granted in May 1996 (patent number 5,514,124). Expansion of the method's applications earned two other U.S. patents, granted in April (5,740,815) and May (5,749,867) 1998. You can find and read these patents using the IBM Patent Server.

The ASSORT program is built on the Paradox database, a product of the Borland company. ASSORT allows the compilation of patient data and the statistical outcomes analysis not only of refractive surgical procedures, but also the treatment of cataract and glaucoma, two common ophthalmic conditions. ASSORT won Borland's 1993 Paradox Challenge, an international competition meant to recognize that year's most innovative application of Paradox.

The ASSORT program is designed to apply the Alpins astigmatism-analysis method to patient data entered by the surgeon or the surgeon's staff. For refractive surgery patients, the data consists of measurements that are routinely taken in association with refractive surgery by instruments and techniques commonly found in the offices of refractive surgeons; that is, standard refraction, keratometry and corneal topography. The Alpins method can be seen as an additional level of the software. In fact, the method is employed within a number of specific components of the program, which the ASSORT company describes as modules. In short, the program applies conventional statistical analyses to the entered data, but can also subject the data to the Alpins method of analysis. Notably, while the Alpins method will forever retain the purity of the mathematical construct it is, the accuracy of its results are invariably tied to the accuracy of the measurements fed into it (topography, keratometry and refraction) and the tools used to perform the surgery. Gauging the accuracy of these devices provides a means to improve their performance.

Commercialization has been a long and expensive process for ASSORT. It was not until early 1998 that the company launched an intensive market development effort in the United States. A primary goal of that effort is to license the Alpins method to manufacturers of refractive lasers and corneal topography systems. ASSORT believes that the Alpins method is a natural fit for incorporation into the programming of such instruments. Currently, it is used mainly by surgeons outside the United States as a stand-alone program installed on laptops or office computers. The discussions with instrument manufacturers are ongoing. Highlights of the ASSORT program are shown here. The remainder of this article will concentrate on the Alpins method of astigmatism analysis.

Refractive errors in the population

Astigmatism can be divided into three main types: 1) Naturally occurring regular astigmatism; 2) naturally occurring irregular astigmatism; and 3) irregular astigmatism associated with disease, trauma or prior ocular procedures. This article deals mainly with the first two.

The amount of myopia, hyperopia and astigmatism is expressed using a unit of measurement called a diopter (D), which describes the ability of a lens to bend (refract) light. By convention, myopia is reported in negative diopters, hyperopia in positive diopters. Corneal refractive surgical procedures exist that can effectively treat myopia from approximately -1 D to -16 D, according to a survey of 30 leading surgeons reported in the September 1997 issue of EyeWorld (upper limit of -16 D represents the average of all respondents). Corneal refractive surgical procedures for hyperopia, not widely used in the United States, appear to have a more limited range: from +1 D to +6 D, according to reports.

A zero refractive error, called emmetropia, is for the most part the desired state. Intraocular procedures beyond the scope of this article exist that can treat higher amounts of both myopia and hyperopia. People with refractive errors within 1 D of emmetropia (refractions between -1 D and +1 D) ordinarily are not considered candidates for refractive surgery.

People with refractions between -1 D and -16 D, and those with between +1 D and +6 D, therefore can be considered candidates for corneal refractive surgery, given that they qualify in other respects. A report by the consulting firm Arthur D. Little establishes the "vision-wear population" of the United States at 150 million citizens (EyeWorld, July 1997, page 30). From this, one might estimate that about half of the country's population falls into these two ranges, and thus perhaps half of the world's population as a whole.

The incidence of greater than 1 D of naturally occurring astigmatism in U.S. studies has variously been reported at 56%,(8) 39.5%,(9) and 32%.(10) One study estimated that astigmatism greater than 0.5 D was present in 44.4% of the population, with 8.44% of the total having astigmatism of 1.5 D or greater.(11) In one Australian PRK series, 70% of patients required an astigmatic correction as part of their treatment (Alpins N, personal communication).

One might therefore conclude that as many as half of the patients who are candidates for corneal refractive surgery, who may constitute half of the world's population, have astigmatism sufficient to be of concern to the refractive surgeon. These people could benefit from their surgeons' use of the Alpins method in astigmatism analysis and surgical planning.

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