Purpose:
Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by progressive decline in learning, memory, and executive functions. In addition to cognitive and behavioral deficits, vision disturbances have been reported in early stage of AD, well before the diagnosis is clearly established. To further investigate ocular abnormalities, a novel AD transgenic rat model was analyzed.
Methods:
Transgenic (Tg) rats (TgF344-AD) heterozygous for human mutant APPswe/PS1ΔE9 and age-matched wild type (WT) rats, as well as 20 human postmortem retinal samples from both AD and healthy donors were used. Visual function in the rodent was analyzed using the optokinetic response. Immunohistochemistry on retinal and brain sections was used to detect various markers including amyloid-β (Aβ) plaques.
Results
As expected, Aβ plaques were detected in the hippocampus, cortex, and retina of Tg rats. Plaque-like structures were also found in two AD human whole-mount retinas. The choroidal thickness was significantly reduced in both Tg rat and in AD human eyes when compared with age-matched controls. Tg rat eyes also showed hypertrophic retinal pigment epithelial cells, inflammatory cells, and upregulation of complement factor C3. Although visual acuity was lower in Tg than in WT rats, there was no significant difference in the retinal ganglion cell number and retinal vasculature.
Conclusions:
Further studies are needed to elucidate the significance and mechanisms of this pathological change and luminance threshold recording from the superior colliculus.
The authors present profiles of performance on a behavioral task (Visual Paired Comparison) using infrared eye tracking that could potentially be useful in predicting the onset of Alzheimer's Disease. Delay intervals of 2 sec and 2 min were used between the initial viewing of a picture and when the picture was displayed alongside a novel picture. Eye-tracking revealed that at the 2 second delay, 6 mild cognitively impaired patients (MCI), 15 matched control subjects (NC), and 4 neurological control subject's with Parkinson's Disease (PD) performed comparably, i.e., viewed the novel picture greater than 71% of the time. When the delay increased to 2 minutes, MCI patients viewed the novel picture only 53% of the time (p < .05), while NC and PD remained above 70%. These findings are consistent with the idea that the MCI patients did not remember well which picture was recently viewed. These findings demonstrate the usefulness of this task for assessing normal as well as impaired memory function.