Retinal oxygen metabolism is altered in patients with mild cognitive impairment and Alzheimer’s disease

Abstract

Purpose : There is evidence that systemic neuro-degenerative diseases such as mild cognitive impairment (MCI) or Alzheimer's disease (AD) are accompanied by structural and functional alterations in the neural tissue of the retina. The current study was performed to investigate a potential difference in retinal oxygen metabolism in patients with systemic neurodegenerative disease compared to age matched, healthy controls.

Methods : Patients with either MCI or with a mild to moderate degree of dementia due to AD were included in this case-control clinical trial. Inclusion criteria for MCI were abnormal memory function, normal general cognitive function and a Mini-Mental State Examination (MMSE) score > 26, for AD, a diagnosis of probable AD of mild to moderate degree according to the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria and an MMSE score in the range of 20 to 26.

Oxygen saturation in retinal vessels was measured using a Retinal Vessel Analyzer (Imedos, Jena, Germany). The arteriovenous difference in SO₂ was calculated by subtracting the mean venous SO₂ from the mean arterial SO₂. In addition, retinal nerve fiber layer thickness (RNFLT) was assessed using an optical coherence tomography system (Heidelberg Spectralis OCT, Germany).

Results : Forty-one patients and 23 healthy subjects (mean age 72.7±9.2 years vs. 70.0±7.7 years, p=0.23) were included in this study. Oxygen saturation in retinal vessels was not significantly different between patients with MCI or AD and healthy subjects (arteries: 94.4±4.9% vs. 95.6±3.1%, p=0.27, veins: 73.9±7.3% vs. 72.2±5.1%, p=0.32). In contrast, arteriovenous difference in retinal SO₂ was significantly reduced in patients with MCI or AD compared to healthy subjects (20.5±5.1% vs. 23.4±3.9%, p=0.02). RNFLT tended to be lower in patients compared to healthy controls (93.9±13.5 vs. 99.7±9.1µm, p = 0.07).

Conclusions : In patients with MCI and AD, the arteriovenous difference in SO₂ was reduced. This may reflect changes in retinal oxygen consumption. In addition, RNFLT was found to be lower in patients compared to healthy controls, although not statistically significant. These findings are in concordance with previous studies showing alterations in retinal oxygen metabolism as well as RNFLT in patients with neurodegenerative disease.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.