The attenuation of retinal nerve fiber layer thickness and cognitive deterioration

Differences in grading signal hyperintensities on magnetic resonance imaging may explain earlier reported conflicting results in studies of normal aging and dementia. We designed a new rating scale in which periventricular and white matter signal hyperintensities as well as basal ganglia and infratentorial signal hyperintensities are rated separately in a semiquantative way. In this study we compared the inter- and intra-observer agreements of this scale to the widely used rating scale of Fazekas. We confirmed the poor to reasonable intra- and inter-observer agreements of the Fazekas scale. The new scale, although more elaborate, provided good agreements with respect to the white matter, basal ganglia and infratentorial signal hyperintensities. In rating periventricular hyperintensities this scale yielded no advantage. It is concluded that this scale may be of use in studies especially focussing on deep white matter pathology on MRI, because it provides more detailed information, with good intra- and inter-observer reliability.

In this study we investigated the primary and secondary visual areas of normal and Alzheimer's disease brains by using the SMI32 antibody. It is known that in Alzheimer's disease primary sensory areas are usually less devastated than association cortices, although visual symptomatology has been documented early in the course of the disease. In area 17, the SMI32 antibody primarily labeled the perikarya and dentritic tree of the large Meynert cells and cells in layer IVB. Smaller neurons in layers III, V, and VI were also immunoreactive (ir). In area 18, very large SMI32-ir pyramidal neurons in layers III and V were observed. In both areas, staining intensity was correlated with cell size, the largest neurons being the most intensely stained. Only a few changes were observed in the Alzheimer's disease cases. The only statistically significant differences in SMI32-ir neuron counts between control and Alzheimer's disease brains occurred in layer IVB cells and Meynert cells in area 17, and in layer III cells in area 18. In contrast with association cortices, there were no changes in staining intensity in the visual areas. There were fewer neurofibrillary tangles and neuritic plaques in these areas than in prefrontal and inferior temporal cortex, and a correlation between neurofibrillary tangle counts and SMI32-ir neuron loss was only observed in layer III of area 18. These observations show that in the primary and secondary visual cortex, SMI32 also labeled a distinct subset of pyramidal cells that are known from data obtained in the monkey brain to furnish long corticocortical as well as subcortical projections. Interestingly, although there is much less cell and/or neurofibrillary tangle formation in these occipital regions than in prefrontal and temporal association areas, there is significant loss within key subsets of pyramidal cells. The selective loss of this particular subpopulation of pyramidal neurons will disrupt association pathways linking primary visual cortex with areas involved in higher level visual processing. The partial disconnection of such pathways may be relevant to the visual symptomatology frequently observed in Alzheimer's disease patients. These data further support the hypothesis that subtypes of pyramidal neurons with specific anatomical and molecular profiles may display a differential vulnerability in Alzheimer's disease.

To examine the relationship between signal strength and retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT). Observational cross-sectional study. Forty normal subjects were recruited. Retinal nerve fiber layer (RNFL) thickness was measured by Stratus OCT (Carl Zeiss Meditec, Dublin, CA). In each eye, the focusing knob was adjusted to obtain 6 images with different signal strengths ranging from 5 to 10. The relationships between signal strength and RNFL thickness were examined using the Spearman correlation coefficient. The differences of RNFL thicknesses were compared with repeated-measures analysis of variance. Retinal nerve fiber layer thicknesses measured at different signal strengths. Significant differences were observed between measurements obtained at signal strength of 10 and those obtained with signal strength of less than 10 at the superior, nasal, and temporal clock hours. RNFL thickness generally increased with the signal strength, with significant correlations found with the total average, superior, and nasal clock hours RNFL thicknesses. Optical coherence tomography RNFL measurements vary significantly with signal strength. Obtaining the maximal possible signal strength is recommended for RNFL thickness measurement.