Improvements to multi-offset adaptive optics scanning laser ophthalmoscopy for in vivo imaging of individual retinal ganglion cell layer neurons in humans

Retinal ganglion cells (RGCs) are the primary output neurons of the retina. RGC dysfunction and death can cause irreversible vision loss in glaucoma and other ocular diseases. However, no methods exist to evaluate RGCs at the level of single cell in the living human eye in the clinic. Our aim is to implement a technique revealing the retinal ganglion cell layer neurons whose contrast, robustness and acquisition time would make it suitable for clinical diagnosis and monitoring of patients. While previously we were able to demonstrate high contrast imaging in monkeys, here we propose a new adaptive optics scanning laser ophthalmoscope configuration that allows us to achieve similar results on humans in vivo. In particular we used a new detection scheme that allowed us to switch from two light sources to one thereby enabling us to increase the light power, eliminate problems caused by chromatic aberration and improve the image registration process. Here we show that this optimized detection scheme and image processing pipeline improve the multi-offset technique for imaging of human RGC layer neurons.

Frequency of retinal changes in patients with COVID-19: an observational study

In order to enter cells, SARS-CoV-2 virus uses the angiotensin-converting enzyme 2 receptor that is also expressed in retina. Aim. Determination of the frequency and nature of retinal changes, evaluation of visual functions in patients who have got over COVID-19. Materials and methods. This observational research includes 31 patients aged from 28 to 79 that got over COVID-19 (with severity according to computed tomography (CT): 1–3) in the period from 15 to 40 days before the research. Standard ophthalmological examination and optical coherence tomography (OCT) were performed; visual acuity measurement and threshold static perimetry were used to assess visual functions.Results. Pathology of the ocular surface wasn’t detected. Ophthalmoscopy revealed retinal changes in only one patient. At OCT, 27 (87%) patients proved to have de novo changes in the retinal neuroepithelium at the level of the internal plexiform layer and the retinal ganglion cell layer in the form of hyper-reflective polymorphic foci with clear borders; 18 (67%) patients had monocular lesions. The maximum corrected visual acuity didn’t differ from the previously defined one; no violations of retinal light sensitivity were detected. No association was found between the severity of CT lung changes and retinal changes. The detected retinal changes weren’t associated with symptoms of anosmia (hyposmia) and ageusia. OCT repeated after 12–15 days showed no dynamics of hyperreflective foci: they remained unchanged in their shape, echogenicity and size. Conclusion. De novo changes in retinal neuroepithelium at the level of the inner plexiform layer and the retinal ganglion cell layer were detected according to OCT data in 87% of patients who had undergone COVID-19. Anatomical changes in the retina weren’t manifested by functional visual disturbances. There is no association of retinal changes with lesions of I and IX cranial nerve pairs.

Elevated Intraocular Pressure Causes Abnormal Reactivity of Mouse Retinal Arterioles

Objective. Glaucoma is a leading cause of severe visual impairment and blindness. Although high intraocular pressure (IOP) is an established risk factor for the disease, the role of abnormal ocular vessel function in the pathophysiology of glaucoma gains more and more attention. We tested the hypothesis that elevated intraocular pressure (IOP) causes vascular dysfunction in the retina. Methods. High IOP was induced in one group of mice by unilateral cauterization of three episcleral veins. The other group received sham surgery only. Two weeks later, retinal vascular preparations were studied by video microscopy in vitro. Reactive oxygen species (ROS) levels and expression of hypoxia markers and of prooxidant and antioxidant redox genes as well as of inflammatory cytokines were determined. Results. Strikingly, responses of retinal arterioles to stepwise elevation of perfusion pressure were impaired in the high-IOP group. Moreover, vasodilation responses to the endothelium-dependent vasodilator, acetylcholine, were markedly reduced in mice with elevated IOP, while no differences were seen in response to the endothelium-independent nitric oxide donor, sodium nitroprusside. Remarkably, ROS levels were increased in the retinal ganglion cell layer including blood vessels. Expression of the NADPH oxidase isoform, NOX2, and of the inflammatory cytokine, TNF-α, was increased at the mRNA level in retinal explants. Expression of NOX2, but not of the hypoxic markers, HIF-1α and VEGF-A, was increased in the retinal ganglion cell layer and in retinal blood vessels at the protein level. Conclusion. Our data provide first-time evidence that IOP elevation impairs autoregulation and induces endothelial dysfunction in mouse retinal arterioles. Oxidative stress and inflammation, but not hypoxia, appear to be involved in this process.