Biology subjects

Mustafi, D.

Publications and source records attributed to Mustafi, D..

3 recordsLinked to original sources

bioRxiv2026

In vivo elastography of the human retina using light-evoked intrinsic actuation

The biomechanical properties of the retina govern its function, structural integrity, and susceptibility to disease, yet remain difficult to measure in vivo due to the lack of safe, spatially localized mechanical actuation. Here, we introduce a framework for probing retinal biomechanics in the living human eye by leveraging intrinsic optical actuation driven by phototransduction. Using phase-resolved optical coherence tomography with a local phase-referencing approach, we resolved signed, nanometer-scale displacements of the major outer retinal interfaces evoked by light. The resulting deformation field, originating in the photoreceptor outer segment, was distributed across retinal compartments in an eccentricity-dependent manner, with efficient axial transfer in the fovea and attenuated propagation in the parafovea. A hybrid analytical and finite-element framework was developed that retrieved the biomechanical properties of the retinal compartments based on their coordinated deformation and the anatomical variation in retinal structure versus eccentricity. In retinitis pigmentosa, the paradigm enabled the detection of light-evoked deformation in the transition zone despite the loss of native lamination, enabling a functional readout of the vulnerable photoreceptors at the leading edge of degeneration. Together, these results establish intrinsic optical stimulation as a basis for in vivo retinal elastography and enable the non-invasive, quantitative imaging of retinal biomechanics and function in the living human retina.

biophysics↗

bioRxiv2026

Optoretinography in R9AP-bradyopsia reveals the essential role of G-protein signaling in the human cone elongation response

Human cone and rod outer segments exhibit a rapid shrinkage followed by a slower elongation in response to light, forming the basis of the optoretinogram. The molecular basis of this optical assay of photoreceptor function remains incompletely understood. In mouse rods, the elongation response requires transducin, the G-protein -subunit activated in the initial amplifying step of the phototransduction cascade. Here, we measured human cone outer segment responses in subjects with bradyopsia arising from a triple-deletion mutation in R9AP, the anchor and transport protein for the GTPase-activating protein (GAP) RGS9. Immunoprecipitation showed that the mutant R9AP has greatly reduced affinity for RGS9, predictably reducing the level of RGS9 in the outer segment. The bradyopsia subjects elongation responses had normal activation kinetics, amplitude and photosensitivity, but markedly slowed recovery. These results indicate that normal levels of RGS9 are required for deactivation of the cone elongation response, situating the underlying molecular mechanism within the G-protein cascade at or prior to formation of the GAP complex. The recovery of the cone elongation response, measured in a paired-flash paradigm for stimuli isomerizing up to 75% of opsin, revealed that elongation requires a substrate that is depleted and recovers in a bleach-dependent manner. In particular, recovery from the highest bleaching exposure (75%) tracked the time course of cone opsin regeneration, implying that unregenerated cone opsin produces "dark light", known in rods to arise from constitutive activation of G-protein. Taken together, the results from controls and bradyopsia identify the inactive (GDP-bound) transducin complex as the essential substrate for the human cone elongation response. Suppression of the elongation response in the paired-flash paradigm further revealed the complete profile of the initial fast cone outer segment shrinkage response and reinforced its origin in opsin structural changes. Overall, these results identify key mechanistic elements of the optoretinogram and enable its use as a molecularly interpretable, non- invasive assay of cone function in disease and therapeutic response.

neuroscience↗

bioRxiv2019

Quantifying subclinical and longitudinal microvascular changes following episcleral plaque brachytherapy (EPB) using spectral-domain OCT angiography.

BackgroundI-125 episcleral plaque brachytherapy (EPB) is standard-of-care for globe-conserving treatment of medium-sized choroidal melanomas. Radiation retinopathy is a potential consequence of treatment, characterized by deleterious effects on retinal microvasculature. We investigated the application of Optical Coherence Tomography Angiography (OCTA) for detecting and longitudinally monitoring I-125 episcleral plaque brachytherapy induced radiation retinopathy. MethodsHigh resolution OCTA of the central 3x3mm macula were obtained from I-25 episcleral plaque brachytherapy treated and untreated fellow eyes of 62 patients. Capillary density (vessel skeleton density, VSD) and caliber (vessel diameter index, VDI) were quantified using previously validated semi-automated algorithms. Nonperfusion was also quantified as flow impairment regions (FIR). Exams from treated and fellow eyes obtained pre-treatment and at 6-month, 1-year, and 2-year intervals were compared using generalized estimating equation linear models. Dosimetry maps were used to evaluate spatial correlation between radiation dose and microvascular metrics. ResultsMean time from treatment to last follow-up was 10.8 months. Mean{+/-}SD and median radiation dose at the fovea were 64.5 {+/-} 76 Gy and 32.0 Gy, respectively. Preoperative logMAR (Snellen) mean visual acuity was 0.26 {+/-} 0.05 ([~]20/35) and 0.08 {+/-} 0.02 ([~]20/25) in treated and fellow eyes, respectively. At 6 months, treated eyes had significantly lower VSD (0.147 {+/-} 0.003 vs 0.155 {+/-} 0.002; p = 0.023) and higher FIR (1.95 {+/-} 0.176 vs 1.45 {+/-} 0.099; p = 0.018) compared to fellow eyes. There was a significant decrease in VSD and a corresponding increase in FIR even for treated eyes without clinically identifiable retinopathy at 6 months. VDI was significantly higher in treated eyes than in fellow eyes at 2 years (2.93 {+/-} 0.022 vs 2.84 {+/-} 0.016; p = 0.002). Microvascular changes were spatially correlated with a radiation gradient of 85-250 Gy across the fovea. ConclusionsOCTA can be used to quantify and monitor EPB induced radiation, and can detect vascular abnormalities even in the absence of clinically observable retinopathy. OCTA may therefore be useful in investigating treatment interventions that aim to delay EPB-induced radiation retinopathy.

scientific communication and education↗