Rafi Israel, MD
Factors such as increased patient expectation have led to the rapid growth in the popularity of premium intra-ocular lens (IOL) implantation over the past few years.
Eliminating visually significant corneal astigmatism is arguably one of the key factors in a successful multi-focal and/or accommodative IOL implantation surgery. This ophthalmologic trend has led physicians to revisit Limbal Relaxing Incision (LRI) procedures. Recent Study by Independent ophthalmologist, Dr. Ray Oyakawa, MD showed a 96% success rate in treating patients who had visually significant astigmatism during cataract surgery. This study was performed using the PalmScan P2000E surgical pachymeter with LRI software and built-in cataract induced astigmatism vector analysis. (ASCRS 2008).
Throughout the 1990’s, a number of authors recognized the advantages of moving corneal astigmatic relaxing incisions peripherally toward the limbus. LRI has become the most popular way to manage astigmatism for patients undergoing cataract extraction with intra-ocular lens implants.
LRI involves making a pair of incisions at the corneal limbus just anterior to the vascular arcade. By adjusting the length, depth, and location of the arcuate incision, one can induce changes in the corneal astigmatism. Specifically, changes in corneal astigmatism are achieved by flattening the steep corneal meridian with a simultaneous increase in corneal curvature in the flat meridian. The effect of the foregoing is to alleviate the corneal astigmatism while keeping the average corneal power untouched.
LRI procedures have gained widespread acceptance among cataract surgeons in recent years. The benefits of LRI procedures include almost immediate recovery of vision and excellent quality of vision after LRI. LRIs are often combined with a cataract operation to reduce preexisting astigmatism and thus, resulting in better postoperative uncorrected vision. When using the Premium IOL implants in patients with over one diaptor of astigmatism, LRI might be required to reduce the pre-op astigmatism, thereby increasing the patient’s overall satisfaction.
A number of published nomograms are available to aid ophthalmologists in astigmatic reduction. The Louis D. Nichamin MD’s, Age and Pachymetry adjusted intra-limbal arcuate Astigmatic (NAPA) nomogram is one of the most widely used nomograms. The NAPA nomogram is likely to yield the accurate and predictable results because of the Pachymeter adjusted factor. Dr. Nichamin recommends setting the blade to 90% of peripheral corneal thickness at the incision location.
For success in performing the NAPA LRI procedure, it is necessary to obtain accurate peripheral corneal pachymetry and to set the adjustable diamond knife at the appropriate depth. It is also necessary to obtain the arcuate incision size and the location of the cuts according to patient’s age and keratometry. Accurate measurements of the cornea are absolutely necessary to ensure against corneal perforations while reaching the 90% corneal depth necessary for best results.
While LRI’s might appear to be simple; many surgeons are still hesitant to perform LRI especially, if they have never performed this procedure before. This is in part due to the possibility to make a number of errors when working with a nomogram table. For example, one may not select the proper table (with-the-rule or against-the rule). One can also misread the row for pre-op cylinder value or the column for patient’s age. There can also be errors of documentation as well as size, length, depth and axis of the incision (Table 1). In addition, since many of the existing pachymeters have difficulty to accurately measure peripheral corneal thickness, there are increased probability to perforate the globe with the thinner corneas, and under-correction of astigmatism in patients with thicker corneas.
PalmScan has streamlined this process by providing surgeons a detailed surgical plan and graphical representation of the procedure based on accepted NAPA LRI nomogram. As well as cataract induced astigmatism vector analysis for concurrent cataract and LRI surgery.
Table 1: NAPA Nomogram
MMD’s PalmScan P2000E equipped with the LRI option greatly simplifies the LRI process, therefore reducing the risk of errors and improving the result. PalmScan P2000E combines user friendly LRI nomogram software with its state-of-art pachymeter capable of easily and accurately measuring corneal thickness at the limbus (Figure 1).
First, the user captures the peripheral corneal map pachymetry. See figure 1. The system then automatically imports the results into the LRI nomogram software and quickly and precisely performs the table lookup based on a few entries (Flat K, Steep K, Steep Axis and patient age). PalmScan P2000E’s high resolution TFT touch screen monitor provides the user with a clear and concise graphical picture of the location, size, depth and axis of the Limbal Relaxing Incisions (Figure 2).
In the Full Screen option, by displaying a nose-like graphic on the display, PalmScan allows the physician to align the instrument with the patient’s face during surgery to ensure the correct eye and axis are selected for the incision (Figure 3). PalmScan also permits the surgeon to flip the graphical picture such that it is oriented toward the top of the patient (Figure 4). PalmScan also is capable of printing the LRI results in a report format further reducing the risk of documentation errors.
In conclusion, this system will likely provide physicians with a faster, safer and easier way to perform the LRI procedure and thus will improve patient outcomes. MMD’s PalmScan, the first and only Pachymeter with LRI software, is setting the bar higher for all pachymeters and biometers on the market.
Rafi Israel MD is a board certified ophthalmologist and the director of Beverly Hills Eye Institute located at 9025 Wilshire Blvd #209 Beverly Hills, CA 90211, phone 310-276-3450, Fax 310-276-3548. He is an associated clinical professor of ophthalmology at Cedar Sinai Medical Center in Los Angeles, CA.