Abstract
A thinning of intraretinal layers has been previously described in Parkinson's disease (PD) patients compared to healthy controls (HCs). Few studies evaluated the possible correlation between retinal thickness and retinal microvascularization. Thus, here we assessed the thickness of retinal layers and microvascular pattern in early PD patients and HCs, using, respectively, spectral-domain optical coherence tomography (SD-OCT) and SD-OCT-angiography (SD-OCT-A), and more interestingly, we evaluated a possible correlation between retinal thickness and microvascular pattern. Patients fulfilling criteria for clinically established/clinically probable PD and HCs were enrolled. Exclusion criteria were any ocular, retinal, and systemic disease impairing the visual system. Retinal vascularization was analyzed using SD-OCT-A, and retinal layer thickness was assessed using SD-OCT. Forty-one eyes from 21 PD patients and 33 eyes from 17 HCs were evaluated. Peripapillary retinal nerve fiber layer (RNFL) and macular RNFL, ganglionic cell layer (GCL), inner plexiform layer (IPL), and inner nuclear layer (INL), resulted to be thinner in PD compared to HCs. Among PD patients, a positive correlation between RNFL, GCL, and IPL thickness and microvascular density was found in the foveal region, also adjusting by age, sex, and, especially, hypertension. Such findings were already present in the early stage of disease and were irrespective of dopaminergic treatment. Thus, the retina might be considered a biomarker of PD and could be a useful instrument for onset and disease progression.
Highlights
Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease (AD), affecting up to 4% of the population in the oldest age groups
According to these literature data, we found a reduction in peripapillary retinal nerve fiber layer (RNFL) thickness in PD patients compared to healthy controls (HCs), and all retinal layers, except for retinal pigment epithelium (RPE), were found to be thinner in the macula of PD patients compared to healthy subjects
Compared to HCs, the retina resulted to be thinner in PD patients, especially considering RNFL and ganglionic cell layer (GCL)
Summary
Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease (AD), affecting up to 4% of the population in the oldest age groups. PD is traditionally related to a progressive loss of dopaminergic neurons in the substantia nigra pars compacta, leading to motor symptoms, such as bradykinesia, resting tremor, and rigidity [1]. PD patients may experience non-motor symptoms such as mood dysfunction, personality disorders [2, 3], autonomic failure [4], cognitive impairment [5], sleep disorders [6], and visual disturbances [7], probably related to alpha-synuclein (αSYN) inclusions in both central and peripheral nervous systems [8, 9]. Retinal Pattern in Parkinson’s Disease when at least 50–60% of dopaminergic neurons have been lost, non-motor symptoms may occur many years before onset of motor manifestations, playing an intriguing role as biomarker in the diagnosis of “Prodromal PD” [10]. Among non-motor symptoms, visual disorders are extremely common, in the early stage of disease, affecting up to 78% of patients with PD [7]. Microvascular retinal density has been described to be lower in PD patients compared to HCs, using spectral-domain OCT angiography (SD-OCT-A) [21]
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