Functional Imaging of Mitochondria in Age-Related Macular Degeneration Using Flavoprotein Fluorescence.

PURPOSE: Oxidative stress-induced mitochondrial dysfunction is implicated in the pathogenesis of age-related macular degeneration (AMD). Oxidized mitochondrial flavoprotein fluorescence (FPF) may serve as a quantifiable biomarker of oxidative stress, reported as either mean score for the entire image (intensity) or variability (heterogeneity). This study examines FPF intensity and heterogeneity across a large patient cohort of various Beckman stages of AMD. METHODS: This study enrolled patients with isolated AMD and healthy control patients with no retinopathy between 2018 and 2021. Multivariate logistic regression analysis included stage of AMD, age, gender, ethnicity, and smoking status. Analysis of Variance test compared mean FPF intensity and heterogeneity between disease states. RESULTS: Four hundred fifty-six eyes (228 AMD eyes, 228 age-matched control eyes) were included in the final multivariate analysis. Intermediate, geographic atrophy (GA), and neovascular AMD correlated with significantly increased FPF intensity (P < 0.001, respectively), while all AMD stages correlated with increased FPF heterogeneity (P < 0.001, respectively). FPF intensity and heterogeneity were significant negative predictors of visual acuity (P = 0.018 and 0.024, respectively). CONCLUSIONS: This prospective observational study further implicates mitochondrial damage in AMD pathophysiology. Long-term clinical trials will be needed to examine the predictive role of FPF imaging in patients over time. [Ophthalmic Surg Lasers Imaging Retina 2023;54:24-31.].

Mitochondrial Dysfunction in Primary Open-Angle Glaucoma Characterized by Flavoprotein Fluorescence at the Optic Nerve Head.

PURPOSE: To investigate the presence of flavoprotein fluorescence (FPF) at the optic nerve head (ONH) rim as a marker of mitochondrial dysfunction in primary open-angle glaucoma (POAG) and control eyes. DESIGN: Retrospective cross-sectional study of patients recruited from the New York Eye and Ear Infirmary of Mount Sinai. PARTICIPANTS: A total of 86 eyes (50 eyes of 30 patients with POAG and 36 eyes of 20 control participants) were enrolled. The presence of POAG was defined by circumpapillary retinal nerve fiber layer thickness (cpRNFLT) of less than the bottom fifth percentile of the normative database, glaucomatous ONH changes, and visual field defects on 24-2 tests. METHODS: Primary open-angle glaucoma and control eyes were imaged using the OcuMet Beacon. A 23° × 23° infrared scan was obtained, and an FPF scan was performed within a capture field spanning 13° in diameter. The ONH margins on the infrared image were identified by software algorithms. Then, FPF was measured within an elliptical annulus around the ONH rim, with the inner and outer boundaries corresponding to 0.5 to 1.1 times the ONH rim size. MAIN OUTCOMES MEASURES: Flavoprotein fluorescence at the OHN rim in POAG and control eyes. RESULTS: Differences in FPF between POAG and control eyes were characterized through mixed-effects logistic regression, adjusted for age and interocular pressure. Flavoprotein fluorescence was significantly higher in POAG versus control eyes, with a mean ± SD of 46.4 ± 27.9 versus 28.0 ± 11.7 (P < 0.001), respectively. Among POAG eyes, FPF showed correlation to visual field mean deviation (P < 0.001), visual field pattern standard deviation (P = 0.003), and cpRNFLT (P = 0.001) on linear mixed-effects models. CONCLUSIONS: Higher FPF in POAG versus control eyes suggests the presence of mitochondrial dysfunction at the ONH rim in eyes with glaucomatous damage. The degree of FPF corresponds to disease severity, as measured by visual field and nerve fiber layer thickness metrics. Thus, FPF may represent a metabolic indicator of disease status that reveals the extent of injury in glaucoma.

Functional imaging of mitochondria in genetically confirmed retinal dystrophies using flavoprotein fluorescence.

BACKGROUND: Whether by indirect oxidative stress or direct genetic defect, various genetic retinal dystrophies involve mitochondrial stress. Mitochondrial flavoprotein fluorescence (FPF), reported as either average signal intensity or variability (heterogeneity), may serve as a direct, quantifiable marker of oxidative stress. MATERIALS AND METHODS: This observational study enrolled patients with genetically confirmed retinal dystrophies between January and December 2021. Patients with concomitant maculopathy and ocular hypertension were excluded. Patients were FPF imaged with OcuMet Beacon® third generation device during routine outpatient visit. RESULTS: The final analysis cohort included 242 images from 157 patients. Mean FPF intensity was significantly increased between age matched controls and patients with confirmed rod-cone dystrophy, Stargardt disease, Bardet-Biedl syndrome (BBS), and Mitochondrial ATP synthase mutation (P ≤ 0.007). Mean FPF heterogeneity was significantly increased between age matched controls and patients with confirmed rod-cone dystrophy, Stargardt disease, and BBS (P ≤ 0.011). FPF lesions were noted to correlate with Fundus Autofluorescence (FAF) lesions in diseases examined. CONCLUSIONS: FPF intensity and heterogeneity significantly increased in patients with retinal dystrophies. The correlation of FPF lesions with FAF lesions implies FPF may be a clinically useful biomarker in patients with IRDs.

This study found increases in flavoprotein fluorescence signal in patients with genetically confirmed inherited retinal dystrophies compared to age matched controls. Flavoprotein fluorescence signal correlated with fundus autofluorescence findings, suggesting clinical utility of novel signal.

Functional imaging of mitochondria in retinal diseases using flavoprotein fluorescence.

Mitochondria are critical for cellular energy production and homeostasis. Oxidative stress and associated mitochondrial dysfunction are integral components of the pathophysiology of retinal diseases, including diabetic retinopathy (DR), age-related macular degeneration, and glaucoma. Within mitochondria, flavoproteins are oxidized and reduced and emit a green autofluorescence when oxidized following blue light excitation. Recently, a noninvasive imaging device was developed to measure retinal flavoprotein fluorescence (FPF). Thus, oxidized FPF can act as a biomarker of mitochondrial dysfunction. This review article describes the literature surrounding mitochondrial FPF imaging in retinal disease. The authors describe the role of mitochondrial dysfunction in retinal diseases, experiments using FPF as a marker of mitochondrial dysfunction in vitro, the three generations of retinal FPF imaging devices, and the peer-reviewed publications that have examined FPF imaging in patients. Finally, the authors report their own study findings. Goals were to establish normative reference levels for FPF intensity and heterogeneity in healthy eyes, to compare between healthy eyes and eyes with diabetes and DR, and to compare across stages of DR. The authors present methods to calculate a patient's expected FPF values using baseline characteristics. FPF intensity and heterogeneity were elevated in diabetic eyes compared to age-matched control eyes, and in proliferative DR compared to diabetic eyes without retinopathy. In diabetic eyes, higher FPF heterogeneity was associated with poorer visual acuity. In conclusion, while current retinal imaging modalities frequently focus on structural features, functional mitochondrial imaging shows promise as a metabolically targeted tool to evaluate retinal disease.

A 32 x 32 capacitive micromachined ultrasonic transducer array manufactured in standard CMOS.

As ultrasound imagers become increasingly portable and lower cost, breakthroughs in transducer technology will be needed to provide high-resolution, real-time 3-D imaging while maintaining the affordability needed for portable systems. This paper presents a 32 x 32 ultrasound array prototype, manufactured using a CMUT-in-CMOS approach whereby ultrasonic transducer elements and readout circuits are integrated on a single chip using a standard integrated circuit manufacturing process in a commercial CMOS foundry. Only blanket wet-etch and sealing steps are added to complete the MEMS devices after the CMOS process. This process typically yields better than 99% working elements per array, with less than ±1.5 dB variation in receive sensitivity among the 1024 individually addressable elements. The CMUT pulseecho frequency response is typically centered at 2.1 MHz with a -6 dB fractional bandwidth of 60%, and elements are arranged on a 250 µm hexagonal grid (less than half-wavelength pitch). Multiplexers and CMOS buffers within the array are used to make on-chip routing manageable, reduce the number of physical output leads, and drive the transducer cable. The array has been interfaced to a commercial imager as well as a set of custom transmit and receive electronics, and volumetric images of nylon fishing line targets have been produced.