title: Diabetic brain or retina? Visual psychophysical performance in diabetic patients in relation to GABA levels in occipital cortex.
abstract: Visual impairment is one of the most feared complications of Type 2 Diabetes Mellitus. Here, we aimed to investigate the role of occipital cortex γ-aminobutyric acid (GABA) as a predictor of visual performance in type 2 diabetes. 18 type 2 diabetes patients were included in a longitudinal prospective one-year study, as well as 22 healthy age-matched controls. We collected demographic data, HbA1C and used a novel set of visual psychophysical tests addressing color, achromatic luminance and speed discrimination in both groups. Psychophysical tests underwent dimension reduction with principle component analysis into three synthetic variables: speed, achromatic luminance and color discrimination. A MEGA-PRESS magnetic resonance brain spectroscopy sequence was used to measure occipital GABA levels in the type 2 diabetes group. Retinopathy grading and retinal microaneurysms counting were performed in the type 2 diabetes group for single-armed correlations. Speed discrimination thresholds were significantly higher in the type 2 diabetes group in both visits; mean difference (95% confidence interval), [0.86 (0.32-1.40) in the first visit, 0.74 (0.04-1.44) in the second visit]. GABA from the occipital cortex predicted speed and achromatic luminance discrimination thresholds within the same visit (r = 0.54 and 0.52; p = 0.02 and 0.03, respectively) in type 2 diabetes group. GABA from the occipital cortex also predicted speed discrimination thresholds one year later (r = 0.52; p = 0.03) in the type 2 diabetes group. Our results suggest that speed discrimination is impaired in type 2 diabetes and that occipital cortical GABA is a novel predictor of visual psychophysical performance independently from retinopathy grade, metabolic control or disease duration in the early stages of the disease.
authors.affiliation: Institute for Nuclear Sciences Applied to Health (ICNAS), University of Coimbra, Coimbra, Portugal.|CNC.IBILI, University of Coimbra, Coimbra, Portugal.
authors.forename: Mafalda
authors.initials: M
authors.lastname: Sanches
authors.affiliation: Institute for Nuclear Sciences Applied to Health (ICNAS), University of Coimbra, Coimbra, Portugal.|CNC.IBILI, University of Coimbra, Coimbra, Portugal.|PhD Programme in Experimental Biology and Biomedicine (PDBEB), CNC - Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.|Institute for Interdisciplinary Research (IIIUC), University of Coimbra, Coimbra, Portugal.
authors.forename: Sulaiman I
authors.initials: SI
authors.lastname: Abuhaiba
authors.affiliation: Institute for Nuclear Sciences Applied to Health (ICNAS), University of Coimbra, Coimbra, Portugal.|CNC.IBILI, University of Coimbra, Coimbra, Portugal.|Visual Neuroscience Laboratory, Institute for Biomedical Imaging and Life Sciences (IBILI), Faculty of Medicine, University of Coimbra, Azinhaga de Santa Comba, Celas, 3000-548, Coimbra, Portugal.
authors.forename: Otília C
authors.initials: OC
authors.lastname: d'Almeida
authors.affiliation: CNC.IBILI, University of Coimbra, Coimbra, Portugal.|Visual Neuroscience Laboratory, Institute for Biomedical Imaging and Life Sciences (IBILI), Faculty of Medicine, University of Coimbra, Azinhaga de Santa Comba, Celas, 3000-548, Coimbra, Portugal.
authors.forename: Bruno
authors.initials: B
authors.lastname: Quendera
authors.affiliation: Department of Endocrinology, Coimbra University and Hospital Centre (CHUC), Coimbra, Portugal.
authors.forename: Leonor
authors.initials: L
authors.lastname: Gomes
authors.affiliation: Department of Endocrinology, Coimbra University and Hospital Centre (CHUC), Coimbra, Portugal.
authors.forename: Carolina
authors.initials: C
authors.lastname: Moreno
authors.affiliation: Department of Endocrinology, Coimbra University and Hospital Centre (CHUC), Coimbra, Portugal.
authors.forename: Daniela
authors.initials: D
authors.lastname: Guelho
authors.affiliation: Institute for Nuclear Sciences Applied to Health (ICNAS), University of Coimbra, Coimbra, Portugal. mcbranco@fmed.uc.pt.|CNC.IBILI, University of Coimbra, Coimbra, Portugal. mcbranco@fmed.uc.pt.|Visual Neuroscience Laboratory, Institute for Biomedical Imaging and Life Sciences (IBILI), Faculty of Medicine, University of Coimbra, Azinhaga de Santa Comba, Celas, 3000-548, Coimbra, Portugal. mcbranco@fmed.uc.pt.
authors.forename: Miguel
authors.identifier: http://orcid.org/0000-0003-4364-6373
authors.initials: M
authors.lastname: Castelo-Branco
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009778:Occipital Lobe / Q000000981:diagnostic imaging / Q000378:metabolism*; D010775:Photic Stimulation / Q000379:methods; D011446:Prospective Studies; D011597:Psychomotor Performance / Q000502:physiology*; D012160:Retina / Q000000981:diagnostic imaging / Q000378:metabolism*; D014786:Vision Disorders / Q000000981:diagnostic imaging / Q000378:metabolism*; D014787:Vision Tests / Q000379:methods; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005680:gamma-Aminobutyric Acid
keywords: Brain and retina; Brain spectroscopy; Diabetes; GABA; Occipital cortex; Psychophysics and visual performance