Glaucoma causes damage in the retinal nerve fiber layer (RNFL). Scanning laser polarimetry (SLP) assesses the integrity of the RNFL, a birefringent tissue, by measuring the total retardation in the light reflected from the retina. However, the anterior segment of the eye, mainly the cornea, is also birefringent, and its magnitude and axis vary over a wide range across the population. To accurately assess the RNFL retardation, Laser Diagnostic Technologies, Inc. has developed a new SLP system, GDx NFA, with custom corneal compensation (CCC).
The GDx NFA system has an imaging field of 40 1/4 (H) by 20 1/4 (V), covering both the peripapillary region and the macular region. CCC consists of two identical linear retarders; its magnitude and axis are both adjustable. Anterior segment birefringence of an examined eye is determined from the retardation distributions of the macula with the CCC set to a null retardance; then the magnitude and axis of the CCC are adjusted to null the anterior segment birefringence and the RNFL retardation image is obtained. A normative database is developed for the GDx NFA system to provide an assessment of the RNFL health at a single visit, and a neural network trained with both healthy RNFL patterns and glaucomatous RNFL patterns is provided to assist clinicians to detect RNFL damage.
The anterior segment birefringence can be determined accurately from the macular retardation image. With CCC, glaucomatous RNFL damage, both focal defect and diffuse defect, are readily identified. RNFL damages prior to visual field loss are observed in the early stages of glaucoma. There is a good correlation between the RNFL assessment by the GDx NFA and visual function test results.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.