Retinal thickness profile is not linear throughout disease duration. Even in the absence of funduscopic disease, PR layer in diabetic patients seems to differ from nondiabetic subjects, thus suggesting that some form of neurodegeneration may take place before clinical signs of vascular problems arise.

Introduction Human coronavirus (HCoVs) are a group of viruses with recognized neurotropic and neuroinvasive capabilities. The reports on the neurological and ocular findings are increasing day after day and several central and peripheral neurological manifestations are already described. However, none specifically describes the neuro-ophthalmological manifestation of HCoVs. This is the first article specifically reviewing neuro-ophthalmological manifestations of HCoVs infection. Methods PubMed and Google Scholar databases were searched using the keywords: coronaviridae, coronavirus, COVID-19, SARS-CoV-2, SARS-CoV-1, MERS, ocular, ophthalmology, ophthalmological, neuro-ophthalmology, neurological, manifestations. A manual search through the reference lists of relevant articles was also performed. There were no restrictions concerning language or study type and publications not yet printed but available online were considered. Results Coronavirus eye involvement is not frequent and includes mostly a typical viral follicular conjunctivitis. Recently, retinal anatomical alterations were described using optic coherence tomography. Neuro-ophthalmological symptoms and signs can appear isolated or associated with neurological syndromes. The manifestations include headache, ocular pain, visual impairment, diplopia, and cranial nerve palsies secondary to Miller Fisher syndrome, Guillain-Barré syndrome, or encephalitis, and nystagmus. Conclusion Neurological and neuro-ophthalmological syndromes, symptoms, and signs should not be neglected and a complete ophthalmological examination of these patients should be performed to fully describe ocular manifestations related to HCoVs. We believe that major ocular and neuro-ophthalmological manifestations reports lack due to safety issues concerning detailed ophthalmological examination; on the other hand, in a large number of cases, the presence of life-threatening coronavirus disease hinders ocular examination and ophthalmologist’s visit to the intensive care unit.

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There seems to be a thickening of the choroid in diabetic patients without diabetic retinopathy. Moreover, this tissue may be functionally different in diabetes, as the pattern of associations seems to differ between groups.