Biology subjects

Barathi, V. A.

Publications and source records attributed to Barathi, V. A..

6 recordsLinked to original sources

bioRxiv2025

Optoretinography reveals rapid rod photoreceptor movement upon photoisomerization

Rod photoreceptors are essential for vision under dim light conditions. The onset of rod-mediated vision is marked by the isomerization of rhodopsin. Here we demonstrate that human and rodent rods undergo a minute and rapid contraction of their outer segments immediately upon photoisomerization. The contraction is explained as an electro-mechanical manifestation of the rod early receptor potential generated in the disk membranes, which is challenging to access in electrophysiology. The bleach-strength dependence of the contraction was accounted by a voltage-dependent membrane tension model, developed earlier to explain a similar behavior in cones. The in vivo optical imaging of light-evoked electrical activity in rodent rods was facilitated by an ultrahigh-resolution point-scan optical coherence tomography (OCT) system coupled with unsupervised learning, while in humans, an adaptive optics line-scan OCT facilitated high-speed recordings in individual rods. The non-invasive in vivo optical imaging of rhodopsin activation will have a significant impact on diagnostics and treatment of retinal disease, especially given the vulnerability of rods in inherited and age-related macular degeneration.

bioengineering↗

bioRxiv2025

Application of machine learning to discriminate photoreceptor cell species in xenotransplanted chimeric retinas

Photoreceptor transplantation is being studied to improve visual function in retinal diseases causing blindness, such as age-related macular degeneration, hereditary eye diseases, and traumatic retinopathy, among others. Preclinical studies often involve the delivery of exogenous human photoreceptor cells into the retinas of animal models. In such experiments, a key readout is the differential frequency of donor cell somatic integration versus artificial labeling secondary to material transfer of cytosolic or nuclear labels from donor to recipient cells. For this analysis, the ability to recognize photoreceptor nuclei as being of donor (human) versus animal is key, but purely immunohistology discrimination can be challenging because of antigenic species overlap or intercellular antigen transfer. To address this challenge, we sought to develop and validate a computational technique to discriminate between photoreceptor cells of different animal species based on machine learning of nuclear morphology. Here, we aimed to evaluate the feasibility of using computer-assisted detection of separate nuclei and employing random forest classification to automate the species differentiation, among DAPI-stained photoreceptors after xeno-transplantation of human photoreceptors into the retinas of mice and pigs. Our models were trained on single-species samples and validated with mixed-species samples. We then transplanted human embryonic stem cell-derived retinal organoid cells into rodent and pig retinal degeneration models. The random forest model accurately determined cell identity post-xenotransplantation, validated by histological assessment using an anti-human nuclear antibody. Our results support the potential efficacy of employing machine learning image analysis and classification techniques that may promote experimental rigor, minimize observer bias, and enable high throughput semi-automated workflows for transplantation outcomes analysis. The methodological framework reported here may enable a more nuanced and precise analysis of the behavior of transplanted photoreceptors for the purposes of human retinal regeneration.

neuroscience↗

bioRxiv2024

Interactions between high-intensity light and unrestricted vision in the drive for hyperopia

PURPOSETo evaluate the impact of optical versus illuminance factors and their duration-dependency on lens-induced hyperopia (LIH) in chick eyes. METHODSHyperopia was induced in one eye in chicks (10 groups, n=126) from day 1 (D1) post-hatching until D8 using +10 D lenses with fellow eyes as controls. One group (LIH) served as the control without any interventions. Remaining groups were exposed to 2, 4 or 6 hours of unrestricted vision (UnV), high intensity light (HL), or both (HL +UnV). Ocular axial length (AL), refractive error, and choroidal thickness were measured on days 1, 4, and 8. Inter-ocular difference (IOD = experimental - contralateral eye) {+/-} SEM was used to express outcome measures. RESULTSBy D8, LIH decreased AL (-0.42{+/-}0.03 mm) and produced hyperopic refraction (+3.48{+/-}0.32 D) and choroidal thickening (+85.81{+/-}35.23 {micro}m) in the LIH group (all, P<0.001). Exposure to UnV reduced LIH (i.e., hyperopic refraction, axial shortening, and choroidal thickening) in a duration-dependent manner, whereas HL potentiated the development of LIH in a duration-dependent manner. When combined, UnV overpowered HL, with resultant impact on refraction and AL being close to UnV alone, except after 6 hours, when HL+UnV induced shorter AL compared to UnV alone (P=0.03). CONCLUSIONDaily exposure to HL, UnV, and HL+UnV altered LIH in a duration-dependent manner with UnV and LIH producing competing signals. The signal generated by UnV was generally stronger than HL in combined exposure, yet longer durations of HL affected the drive for emmetropization in eyes with UnV.

developmental biology↗

bioRxiv2023

Automated, unbiased optoretinography reveals comprehensive nanoscopic dynamics of the outer retina in rodents

Phototransduction involves changes in concentration of ions and other solutes within photoreceptors and in subretinal space, which affect osmotic pressure and the associated water flow. Corresponding expansion and contraction of cellular layers can be imaged using optoretinography (ORG), based on phase-resolved optical coherence tomography (OCT). Until now, ORG could reliably detect only photoisomerization and phototransduction in photoreceptors, primarily in cones under very bright stimuli. By employing a novel subpixel bulk motion correction algorithm, which enabled imaging of the nanometer-scale tissue dynamics during minute-long recordings, and unsupervised learning of spatiotemporal patterns, we discovered optical signatures of the other retinal structures response to visual stimuli. These include inner and outer segments of rod photoreceptors, retinal pigment epithelium, and subretinal space in general. High sensitivity of our technique enabled detection of the retinal responses to very dim stimuli: down to 0.01% bleach level, corresponding to natural levels of scotopic illumination. We also demonstrated that with a single flash, the optoretinogram can map retinal responses across a 12{degrees}field of view, potentially replacing multifocal electroretinography, with its long acquisition time and low spatial resolution. This new technique expands the diagnostic capabilities and practical applicability of optoretinography, providing a more complete replacement of electroretinography, while combining structural and functional retinal imaging in the same OCT machine.

bioengineering↗

bioRxiv2022

Shot-noise limited phase-sensitive imaging of moving samples by phase-restoring subpixel motion correction in Fourier-domain optical coherence tomography

Phase-sensitive Fourier-domain optical coherence tomography (FD-OCT) enables in-vivo, label- free imaging of cellular movements with detection sensitivity down to the nanometer scale, and it is widely employed in emerging functional imaging modalities, such as optoretinography (ORG), Doppler OCT, and optical coherence elastography. However, when imaging tissue dynamics in vivo, tissue movement or bulk motion introduces decorrelation noise that compromises motion detection performance, particularly in terms of sensitivity and accuracy. Here, we demonstrate that the motion-related decorrelation noise in FD-OCT can be accurately corrected by restoring the initial sampling points using our proposed Phase-Restoring Subpixel Image Registration (PRESIR) method. Derived from a general FD-OCT model, the PRESIR method enables translational shifting of complex-valued OCT images over arbitrary displacements with subpixel precision, while accurately restoring phase components. Unlike conventional approaches that shift OCT images either in the spatial domain at the pixel level or in the spatial frequency domain for subpixel correction, our method reconstructs OCT images by correcting axial displacement in the spectral domain (k domain) and lateral displacement in the spatial frequency domain. We validated the PRESIR method through simulations, phantom experiments, and in-vivo optoretinography in both rodents and human subjects. Our approach significantly reduced decorrelation noise during the imaging of moving samples, achieving phase sensitivity close to the fundamental limit determined by the signal-to-noise ratio (SNR).

bioengineering↗

bioRxiv2021

Recovery from form-deprivation myopia in chicks is dependent upon the fullness and correlated colour temperature of the light spectrum

BackgroundTo evaluate the impact of full-spectrum light-emitting diodes (LEDs) mimicking sunlight on ocular axial elongation and refractive error development in a chicken model of myopia. MethodsA total of 39 chicks (Lohmann brown), 1 day-old, were randomly distributed into 3 groups. Animals were housed for 28 days in a temperature-controlled enclosure, under a 12/12h light/dark cycle of isoluminant ([~]285 Lux) fluorescent [n = 18, (4000K, FL-4000)] or Sunlike-LED [n=12, (4000K, SL-4000); n = 9, (6500K, SL-6500)] white lights. Myopia was induced monocularly in all chicks by random occlusion of one eye with a frosted diffuser, from day 1 post-hatching (D1) until D14. On D14, diffusers were removed, and recovery from myopia was monitored under the same experimental light condition. Axial length (AL), refractive status, choroidal thickness and anterior chamber depth were recorded on days 1, 7, 14, 22 and 28. Ex vivo scleral collagen fibre thicknesses were measured from scanning electron microscopy images. Differences in outcome measures between eyes and groups were compared using 2-way repeated-measures ANOVA. ResultsThere was no significant difference between groups in the AL and refraction of form-deprived (FD) eyes during form-deprivation (D1 to D14). FD eyes of animals raised under SL-4000 and SL-6500 recovered more rapidly from excessive axial elongation than those of animals raised under FL-4000, by D22 and D28. Correspondingly, the refractive status of FD eyes exposed to SL-4000 and SL-6500 was close to that of control eyes by D28. The choroid became thicker during recovery in FD eyes compared to control eyes, in all groups. Choroidal thickness was significantly greater in FD eyes of chickens raised under SL-6500 than in animals raised under FL-4000 (P < 0.01). The diameter of scleral collagen fibrils was significantly greater in recovering FD eyes of chickens raised under SL-6500, than in those raised under FL-4000 (P = 0.04) and SL-4000 (P = 0.002). ConclusionsCompared to fluorescent light, moderate intensities of full-spectrum Sunlike-LEDs can accelerate recovery from form-deprivation myopia in chickens, potentially through choroid-mediated pathways increasing the diameter of scleral collagen fibrils. This study highlights an important implication of the spectral content of white light on ocular growth and emmetropization.

neuroscience↗