Interoperator variability in images obtained by laser polarimetry of the nerve fiber layer

To study operated-related variability in images obtained by laser polarimetry of the nerve fiber layer, a new imaging technique that attempts to estimate thickness of the nerve fiber layer by using the fact that it is birefringent.

Measurements were made using a commercial device, the Nerve Fiber Analyzer (Laser Diagnostic Technologies, San Diego, CA), which uses a dedicated scanning laser ophthalmoscope to produce a retardation map of the retina adjacent to the optic nerve head. Four trained operators tested 11 subjects twice each, resulting in 88 images. Standard circles were placed around the optic disk for analysis. We analyzed five indices computed from these images: mean thickness in each of four quadrants and mean thickness under the entire circle.

Repeated-measures analyses of variance showed significant effects of operator for four of these indices. Mean values for a given index varied by 11-14 muUm across operators, and the maximum difference across operators was approximately 22 of the mean value across subjects.

The clinical usefulness of the device will be limited until it has been shown that new modifications successfully reduce interoperator variability.