[Determination of retinal nerve fiber density in vivo using laser polarimetry]

A direct in vivo measurement of the retinal nerve fiber layer thickness enables new possibilities for the detection of nerve fiber defects. Using the principle of polarimetry the Nerve Fiber Analyzer has been told to measure directly the nerve fiber layer thickness in vivo.

We measured the nerve fiber layer thickness along a peripapillary circle and investigated the reproducibility in 10 independent measurements of 10 left eyes of ten normals.

The nerve fiber layer thickness measurements varied between 10 and 130 microns for single pixel measurements. The coefficient of variation was 11.9 +/- 2.6 percent for a peripapillary circle while the temporal, nasal, superior and inferior quandrants were 19.2 +/- 3.6%, 19.5 +/- 4.7, 14.3 +/- 5.6 and 16.4 +/- 5.5 percent, respectively. Mean coefficient of variation in 10 time evaluation of 5 single examinations of 5 different eyes was 1.8 +/- 1.1%.

The first investigations demonstrate a good reproducibility of the measurements observed by the Nerve Fiber Analyzer. Supplementary to three-dimensional optic disc topography and perimetry, nerve fiber layer thickness assessment may become an additional tool for diagnosis and follow-up of early glaucoma. The option of measuring along circle segments or areas instead a peripapillary circle consisting of a single pixel would increase the clinical value and reproducibility. Further studies are warranted to evaluate the accuracy of this new method of polarimetry.