Karteek Kunala

All Publications

• Multispectral label-free in vivo cellular imaging of human retinal pigment epithelium using adaptive optics fluorescence lifetime ophthalmoscopy improves feasibility for low emission analysis and increases sensitivity for detecting changes with age and eccentricity. Journal of biomedical optics Kunala, K., Tang, J. A., Parkins, K., Hunter, J. J. 2024; 29 (Suppl 2): S22707

  Abstract

  Adaptive optics fluorescence lifetime ophthalmoscopy (AOFLIO) provides a label-free approach to observe functional and molecular changes at cellular scale in vivo. Adding multispectral capabilities improves interpretation of lifetime fluctuations due to individual fluorophores in the retinal pigment epithelium (RPE).To quantify the cellular-scale changes in autofluorescence with age and eccentricity due to variations in lipofuscin, melanin, and melanolipofuscin in RPE using multispectral AOFLIO.AOFLIO was performed on six subjects at seven eccentricities. Four imaging channels ( λ ex / λ em ) were used: 473/SSC, 473/LSC, 532/LSC, and 765/NIR. Cells were segmented and the timing signals of each pixel in a cell were combined into a single histogram, which were then used to compute the lifetime and phasor parameters. An ANOVA was performed to investigate eccentricity and spectral effects on each parameter.A repeatability analysis revealed < 11.8 % change in lifetime parameters in repeat visits for 532/LSC. The 765/NIR and 532/LSC had eccentricity and age effects similar to previous reports. The 473/LSC had a change in eccentricity with mean lifetime and a phasor component. Both the 473/LSC and 473/SSC had changes in eccentricity in the short lifetime component and its relative contribution. The 473/SSC had no trend in eccentricity in phasor. The comparison across the four channels showed differences in lifetime and phasor parameters.Multispectral AOFLIO can provide a more comprehensive picture of changes with age and eccentricity. These results indicate that cell segmentation has the potential to allow investigations in low-photon scenarios such as in older or diseased subjects with the co-capture of an NIR channel (such as 765/NIR) with the desired spectral channel. This work represents the first multispectral, cellular-scale fluorescence lifetime comparison in vivo in the human RPE and may be a useful method for tracking diseases.

  View details for DOI 10.1117/1.JBO.29.S2.S22707

  View details for PubMedID 38962492

  View details for PubMedCentralID PMC11221116

• Near Infrared Autofluorescence Lifetime Imaging of Human Retinal Pigment Epithelium Using Adaptive Optics Scanning Light Ophthalmoscopy. Investigative ophthalmology & visual science Kunala, K., Tang, J. A., Bowles Johnson, K. E., Huynh, K. T., Parkins, K., Kim, H. J., Yang, Q., Sparrow, J. R., Hunter, J. J. 2024; 65 (5): 27

  Abstract

  To demonstrate the first near-infrared adaptive optics fluorescence lifetime imaging ophthalmoscopy (NIR-AOFLIO) measurements in vivo of the human retinal pigment epithelial (RPE) cellular mosaic and to visualize lifetime changes at different retinal eccentricities.NIR reflectance and autofluorescence were captured using a custom adaptive optics scanning light ophthalmoscope in 10 healthy subjects (23-64 years old) at seven eccentricities and in two eyes with retinal abnormalities. Repeatability was assessed across two visits up to 8 weeks apart. Endogenous retinal fluorophores and hydrophobic whole retinal extracts of Abca4-/- pigmented and albino mice were imaged to probe the fluorescence origin of NIR-AOFLIO.The RPE mosaic was resolved at all locations in five of seven younger subjects (<35 years old). The mean lifetime across near-peripheral regions (8° and 12°) was longer compared to near-foveal regions (0° and 2°). Repeatability across two visits showed moderate to excellent correlation (intraclass correlation: 0.88 [τm], 0.75 [τ1], 0.65 [τ2], 0.98 [a1]). The mean lifetime across drusen-containing eyes was longer than in age-matched healthy eyes. Fluorescence was observed in only the extracts from pigmented Abca4-/- mouse.NIR-AOFLIO was repeatable and allowed visualization of the RPE cellular mosaic. An observed signal in only the pigmented mouse extract infers the fluorescence signal originates predominantly from melanin. Variations observed across the retina with intermediate age-related macular degeneration suggest NIR-AOFLIO may act as a functional measure of a biomarker for in vivo monitoring of early alterations in retinal health.

  View details for DOI 10.1167/iovs.65.5.27

  View details for PubMedID 38758638

• Near-infrared adaptive optics fluorescence lifetime ophthalmoscopy of human retinal pigment epithelium reveals variations with eccentricity and disease Kunala, K., Tang, J., Johnson, K., Huynh, K. T., Parkins, K., Yang, Q., Hunter, J. J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2023

  View details for Web of Science ID 001053758301149

• Prolonged Fluorescence Lifetimes of the Retinal Pigment Epithelium in Human Subjects with Pentosan Polysulfate Sodium Toxicity Johnson, K., Tang, J., Kunala, K., Parkins, K., Yang, Q., Hunter, J. J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2023

  View details for Web of Science ID 001053758302351

• Erratum: Adaptive optics fluorescence lifetime imaging ophthalmoscopy of in vivo human retinal pigment epithelium: erratum. Biomedical optics express Tang, J. A., Granger, C. E., Kunala, K., Parkins, K., Huynh, K. T., Bowles-Johnson, K., Yang, Q., Hunter, J. J. 2023; 14 (4): 1544

  Abstract

  [This corrects the article on p. 1737 in vol. 13, PMID: 35414970.].

  View details for DOI 10.1364/BOE.485995

  View details for PubMedID 37078038

• Mapping the origin of two-photon excited fluorescence in macaque retinal layers with adaptive optics fluorescence lifetime ophthalmoscopy Huynh, K. T., Chadderdon, A. B., Kunala, K., Parkins, K., Yang, Q., Hunter, J. J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2022

  View details for Web of Science ID 000844401301061

• Calcium responses to optogenetic stimulation decay faster in primate retinal ganglion cells after photoreceptor ablation Xu, Z., Kunala, K., Murphy, P., Koo, E., Puthussery, T., McGregor, J. E. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2022

  View details for Web of Science ID 000844437002184

• In vivo measurement of light steering by single retinal cells optimizes phase-contrast AOSLO Feng, G., Yang, Q., Kunala, K., Schallek, J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2022

  View details for Web of Science ID 000844437006194

• Optogenetic therapy restores retinal activity in primate for at least a year following photoreceptor ablation MOLECULAR THERAPY McGregor, J. E., Kunala, K., Xu, Z., Murphy, P. J., Godat, T., Strazzeri, J. M., Bateman, B. A., Fischer, W. S., Parkins, K., Chu, C. J., Puthussery, T., Williams, D. R., Merigan, W. H. 2022; 30 (3): 1315-1328

  Abstract

  All retina-based vision restoration approaches rely on the assumption that photoreceptor loss does not preclude reactivation of the remaining retinal architecture. Whether extended periods of vision loss limit the efficacy of restorative therapies at the retinal level is unknown. We examined long-term changes in optogenetic responsivity of foveal retinal ganglion cells (RGCs) in non-human primates following localized photoreceptor ablation by high-intensity laser exposure. By performing fluorescence adaptive optics scanning light ophthalmoscopy (AOSLO) of RGCs expressing both the calcium indicator GCaMP6s and the optogenetic actuator ChrimsonR, it was possible to track optogenetic-mediated calcium responses in deafferented RGCs over time. Fluorescence fundus photography revealed a 40% reduction in ChrimsonR fluorescence from RGCs lacking photoreceptor input over the 3 weeks following photoreceptor ablation. Despite this, in vivo imaging revealed good cellular preservation of RGCs 3 months after the loss of photoreceptor input, and histology confirmed good structural preservation at 2 years. Optogenetic responses of RGCs in primate persisted for at least 1 year after the loss of photoreceptor input, with a sensitivity index similar to optogenetic responses recorded in intact retina. These results are promising for all potential therapeutic approaches to vision restoration that rely on preservation and reactivation of RGCs.

  View details for DOI 10.1016/j.ymthe.2021.09.014

  View details for Web of Science ID 000765833300013

  View details for PubMedID 34547460

  View details for PubMedCentralID PMC8899524

• Adaptive optics fluorescence lifetime imaging ophthalmoscopy of in vivo human retinal pigment epithelium BIOMEDICAL OPTICS EXPRESS Tang, J. H., Granger, C. E., Kunala, K., Parkins, K., Huynh, K. T., Bowles-Johnson, K., Yang, Q., Hunter, J. J. 2022; 13 (3): 1737-1754

  Abstract

  The intrinsic fluorescence properties of lipofuscin - naturally occurring granules that accumulate in the retinal pigment epithelium - are a potential biomarker for the health of the eye. A new modality is described here which combines adaptive optics technology with fluorescence lifetime detection, allowing for the investigation of functional and compositional differences within the eye and between subjects. This new adaptive optics fluorescence lifetime imaging ophthalmoscope was demonstrated in 6 subjects. Repeated measurements between visits had a minimum intraclass correlation coefficient of 0.59 Although the light levels were well below maximum permissible exposures, the safety of the imaging paradigm was tested using clinical measures; no concerns were raised. This new technology allows for in vivo adaptive optics fluorescence lifetime imaging of the human RPE mosaic.

  View details for DOI 10.1364/BOE.451628

  View details for Web of Science ID 000764563900001

  View details for PubMedID 35414970

  View details for PubMedCentralID PMC8973160

• Adaptive optics fluorescence lifetime ophthalmoscopy of iGlucoSnFR-TS suggests increased glucose in RPE of rho(-/-) compared to healthy mice Kunala, K., Xue, Y., Huynh, K., Yang, Q., Parkins, K., Steven, S., Dubra, A., Cepko, C., Hunter, J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021

  View details for Web of Science ID 000690760500051

• Adaptive optics fluorescence lifetime imaging ophthalmoscopy of the human RPE mosaic Tang, J., Granger, C. E., Parkins, K., Kunala, K., Huynh, K., Bowles-Johnson, K., Yang, Q., Hunter, J. J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2021

  View details for Web of Science ID 000690761100876

• Optogenetic activation of retinal ganglion cells persists for at least a year in primate fovea following photoreceptor loss McGregor, J. E., Kunala, K., Xu, Z., Parkins, K., Godat, T., Strazzeri, J. M., Bateman, B. A., Williams, D. R., Merigan, W. H. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2020

  View details for Web of Science ID 000554528300012

• Optical scattering measurements of random anti-reflection subwavelength surface structures on binary gratings Gadamsetti, P., Kunala, K., Poutous, M. K., Jiang, S., Digonnet, M. J. SPIE-INT SOC OPTICAL ENGINEERING. 2020

  View details for DOI 10.1117/12.2544368

  View details for Web of Science ID 000568488700026

• Optical Scattering of Deterministic Diffractive Elements with Antireflective Structured Surfaces Gadamsetti, P., Kunala, K., Poutous, M. K., IEEE IEEE. 2019: 223-225

  View details for Web of Science ID 000533584000048

• Random antireflective nanostructuring on binary near-wavelength period gratings OPTICAL ENGINEERING Kunala, K., Poutous, M. K. 2018; 57 (8)

  View details for DOI 10.1117/1.OE.57.8.087106

  View details for Web of Science ID 000444481600043

• Diffraction efficiency performance of random anti-reflecting subwavelength surface structures on prefabricated fused silica binary gratings APPLIED OPTICS Kunala, K., Poutous, M. K. 2018; 57 (16): 4421-4427

  Abstract

  Random anti-reflecting subwavelength surface structures have been reported to enhance transmission of optical windows and lenses. Specifically, for fused silica substrates, 99.9% specular transmission has been verified by various groups. Diffractive optical elements, such as gratings, also experience net Fresnel losses on both their planar and structured surfaces. We investigated the performance of prefabricated 50% duty-cycle, binary, fused silica linear gratings, with a period of 1.6 μm, before and after application of random anti-reflecting subwavelength surface structures, in order to reduce their initial Fresnel reflectivity. We compared the diffraction order directions and their efficiencies at three test wavelengths: 594, 612, and 633 nm, for both TE(s) and TM(p) incident light polarization states, under three different mountings: normal, first Bragg, and second Bragg incidence. We report transmission enhancement of the sum of all propagating grating orders for all cases tested by factors between 2% and 10%, with reduction of the respective reflected orders by similar ratios. Transmission enhancement of the -2 diffraction order at Bragg incidence suggests that the random etch has different rates between the raised and lowered linear grating topography.

  View details for DOI 10.1364/AO.57.004421

  View details for Web of Science ID 000433959100011

  View details for PubMedID 29877388

• Optical characterization of random anti-reflecting subwavelength surface structures on binary gratings Kunala, K., Sapkota, G., Poutous, M. K., Jiang, S., Digonnet, M. J. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2284523

  View details for Web of Science ID 000449778300015