Retinal nerve fiber layer split bundles are true anatomic variants.

PURPOSE The presence of retinal nerve fiber layer (RNFL) split bundles recently was described in normal eyes scanned using scanning laser polarimetry. In this study, the authors set out to ascertain whether RNFL split bundles can be found in histologic sections of normal human eyes. DESIGN Histologic study of postmortem human eyes. PARTICIPANTS Fourteen normal postmortem eyes obtained from 13 individuals. METHODS Peripapillary RNFL thickness measurements were plotted, for each eye, from ring sections of 3.0, 3.5, 4.0, and 4.5 mm in diameter. The presence of superior or inferior split RNFL patterns, or both, was sought. MAIN OUTCOME MEASURES The presence of superior or inferior split bundles or both in the histologic data. RESULTS Five of 14 eyes demonstrated a distinct histologic pattern of RNFL split bundles, of which 3 were found superiorly and 2 inferiorly. None of these 14 eyes demonstrated both a definite superior and a definite inferior split. CONCLUSIONS This study provides histologic evidence demonstrating that RNFL split bundles are likely a true anatomic finding, rather than an imaging artifact, and that their presence seems to be relatively common in normal eyes. The presence of a split bundle, being a normal variant, should be distinguished from RNFL loss.