Alzheimer's disease and glaucoma: imaging the biomarkers of neurodegenerative disease

Abstract

Imaging through the visual system in Alzheimer's disease, with the technology currently in widespread use for the diagnosis and management of eye disease such as glaucoma and macular degeneration, is proving to be promising. In vivo cross-section imaging during an annual comprehensive eye exam has been available for a decade for glaucoma and macular degeneration, and this same imaging, using Optical Coherence Tomography, has been demonstrated to show deficits specific to AD and mild cognitive impairment. These deficits are in the form of nerve fiber layer tissue drop out in the retina and optic nerve. The retrograde loss of nerve fiber layer tissue in the retina and optic nerve may be an early biomarker of AD, and these deficits in the nerve fiber layer of the retina and optic nerve may be the earliest sign of AD, even prior to damage to the hippocampal region that impacts memory.

Figure 1

The top three images depict the nerve fiber layer (NFL) generated by the older technology; Stratus-OCT. The y axis is NFL thickness in microns and the x axis is the circumference of the optic nerve in degrees; TEMP = temporal, SUP = superior, NAS = nasal and INF = inferior. None of the participants had a significant refractive error. The top left figure is from a 73 year old control participant with no known risk factors for glaucoma; Caucasian and age matched to the AD participant. The NFL had an average thickness of 101 microns. The top right image was obtained from a 72 year old participant with no known risk factors for glaucoma; Caucasian, with AD. The NFL had an average thickness of 75 microns. The middle image was from a Caucasian participant, with no known risk factors for glaucoma; that had both Parkinson's disease and glaucoma. The average NFL thickness was 58 microns. The yellow arrows show regions of thinning hypothesized to be due to retrograde neurologic degeneration. The red arrow indicates areas of thinning attributed to glaucoma. The bottom three images are cross sections of the optic nerve. Sections of red indicate the nerve fiber layer. The bottom left image is of the control participant, the bottom middle image is of the AD participant and the bottom right image is of the participant with both Parkinson's disease and glaucoma.