A scanning laser polarimetry (SLP) system that measures in vivo retinal nerve fiber layer (RNFL) retardance (.delta..sub.N, .theta..sub.N) in a single measurement without a variable corneal compensator (VCC). The diagnostic signal is biased so that the detected RNFL retardance orientation angles are sufficiently similar at adjacent pixels in the retinal polarimetric image to permit resolution of the orientation angle ambiguity in a single polarimetric image without repeating the measurement at another signal polarization state. With a simple bias retarder, the effects of anterior segment retardance (.delta..sub.C, .theta..sub.C) can be removed from a single polarimetric image of the retina without a VCC. Alternatively, from two single polarimetric images obtained at two different bias retarder positions, the anterior segment retardance magnitude .delta..sub.C and orientation .theta..sub.C and the RNFL retardance magnitude .delta..sub.N and orientation .theta..sub.N can all be determined from the peripapillary RNFL image region alone.