Confirmatory results in suspect glaucoma patients with normal visual field and abnormal retinal nerve fiber layer findings

Purpose: To investigate eyes with a normal visual field and an abnormal retinal nerve fiber layer, as measured with the Scanning Laser Polarimeter (GDx), with a battery of diagnostic tests to assess the agreement between the different diagnostic tests in this subset of eyes. Methods: Thirty-two eyes of 21 patients were selected. All eyes had, on at least three consecutive visits, demonstrated normal visual fields (Humphrey Field Analyzer 24-2 full threshold program, GHT within normal limits) and loss of retinal nerve fiber layer (GDx parameters outside normal limits). Each eye was further examined with the Heidelberg Retina Tomograph (HRT) and multifocal visual evoked potential (mVEP). Color stereoscopic photographs of the optic nerve head were classified by three, masked, glaucoma specialists. Each test classified the eyes as normal, borderline or glaucomatous. The classification was tabulated and the percentage of agreement between the individual tests was calculated. Results: Using a polling system of the five diagnostic tests to decide if an eye was normal or suspect/glaucomatous resulted in 63% of the eyes being falsely labeled suspect/glaucomatous by GDx and 37% being falsely labeled normal by the visual field test. Excluding parameters sensitive to variations in corneal birefringence improved the diagnostic performance of GDx to 43%, and the visual field decreased to 57%. The highest level of agreement was found between the visual field and mVEP data (74%). GDx showed relatively poor agreement with all the tests, even when potential errors from a fixed corneal compensator were largely removed. Conclusions: GDx demonstrated relatively poor agreement with the other diagnostic tests in this small proportion of patients. When disparities exist between diagnostic tests for glaucoma, it is important to do a battery of tests before making clinical decisions.