JUL 09, 2008
Investigators with the NEI-sponsored Advanced Imaging for Glaucoma Study group reported in this article that combining several retinal nerve fiber layer (RNFL) parameters increases the diagnostic performance of the Stratus OCT instrument (Carl Zeiss Meditec, Jena, Germany). Specifically, they determined that an abnormally low value of less than the fifth percentile for overall, inferior quadrant, or superior quadrant RNFL thickness was the best predictor of glaucoma among the 89 age-matched normal subjects and perimetric glaucoma patients included in the current study. Adding more parameters to this combination decreased diagnostic performance, and other combinations of clock hours and quadrants did not perform as well.
For this study, the investigators purposefully chose to analyze simple combinations of parameters that do not require sophisticated computer algorithms or tedious calculations. The standard printout for the Stratus optical coherence tomography instrument (software version 4.0) shows dozens of parameters, and clinicians are left to determine whether or not their patients have glaucoma. Many clinicians base their diagnostic decisions on the overall thickness parameter results since they are intuitively the easiest to interpret. Indeed, in this study, overall thickness did provide the best diagnostic performance of any single parameter. However, the overall thickness measurement is not very sensitive for diagnosing glaucoma because small focal areas of thinning may not lower the overall thickness into the abnormal range. By also considering the inferior and superior quadrant thickness parameters, clinicians can improve the sensitivity of the Stratus OCT without significantly losing specificity.
This report's recommendations are very useful for diagnosing glaucoma and can be adopted easily for clinical practice. When treating patients with glaucoma risk factors, such as large optic cups, the best strategy is to look at each of the overall, inferior quadrant, and superior quadrant thickness parameter results. When any of these values are abnormal, clinicians should suspect glaucoma. This recommendation assumes that the signal strength is adequate (at least six) and the scan circle is centered well on the disk. Clinicians should also bear in mind that a diagnostic test's usefulness depends upon the prevalence in their patient population of the disease being tested and the level of suspicion that an individual patient being tested has the disease.
Dr. WuDunn is a consultant to Alcon Laboratories, Inc and Allergan, Inc. He also receives lecture fees from Alcon Laboratories, Inc. and Pfizer Ophthalmics.