Simultaneous noninvasive clinical measurement of lens autofluorescence and rayleigh scattering using a fluorescence biomicroscope

Lens Autofluorescence Based Advanced Glycation End Products (AGEs) Measurement to Assess Risk of Osteopenia Among Individuals Under the Age of 50

INTRODUCTION

Simple non-invasive biomarker is urgently needed to detect the largely silent osteopenia in order to prevent osteoporosis-related fracture later in life. The accumulation of advanced glycation end products (AGEs) has been related to reduced bone density and osteoporotic fractures. Whether lens autofluorescence (LAF) based AGEs (LAF-AGEs) measurement could be used to assess the risk of osteopenia is aimed to investigate in this paper.

METHODS

Through routine health examination, 368 individuals under the age of 50 were enrolled. A dual-energy X-ray absorptiometry (DXA) device was used to measure bone mineral density (BMD) of the forearm and determine osteopenia. AGE levels were derived with LAF along with the other demographic and laboratory parameters. After deriving the age-adjusted AGE levels (AALs), a linear regression analysis and an ordered logistic regression analysis were applied to examine the associations between osteopenia and LAF-AGEs as well as AALs.

RESULTS

Negative correlations (Pearson r = -0.16, p < 0.001) were found between LAF-AGEs and T-scores. Higher AALs were significantly associated (p = 0.004) with escalated level of osteopenia in the ordered logistic analysis.

DISCUSSION

After reviewing the relevant studies, it is concluded that LAF-AGE is a more stable measure of long-term metabolic dysfunction than circulating AGE. LAF-AGEs are a valid, practical and non-invasive parameter for osteopenia risk evaluation. Further studies with longer follow-up will be helpful to clarify its effectiveness for osteoporosis risk assessment.

Long-term development of lens fluorescence in a twin cohort: Heritability and effects of age and lifestyle

The blue-green autofluorescence of the ocular lens increases with age, glycemia and smoking, as the irreplaceable structural proteins of the lens slowly accumulate damage from the encounter with reactive molecular species. We have conducted a prospective study of lens autofluorescence over two decades in a twin cohort. The study included 131 phakic, non-diabetic adult twins (median age at follow-up 58 years, range 41-66 years) who were examined twice at an interval of 21 years. Change in anterior lens peak autofluorescence was analyzed in relation to age, current and baseline glycemia, cumulative smoking and heritability. The level of lens autofluorescence in the study population increased as a function of age and smoking (p ≤.002), but not as a function of glycemia (p ≥.069). Lens autofluorescence remained a highly heritable trait (90.6% at baseline and 93.3% at follow-up), but whereas the combined effect of age and cumulative smoking explained 57.2% of the variance in lens autofluorescence at baseline in mid-life, it only accounted for 31.6% at follow-up 21 years later. From mid to late adulthood, the level of blue-green fluorescence remained overwhelmingly heritable, but became less predictable from age, smoking habits and glycemic status. Presumably, as the lens ages, its intrinsic characteristics come to dominate over environmental and systemic factors, perhaps in a prelude to the development of cataract.

Exploration of Noninvasive Detection of Advanced Glycation End Products in the Lens to Screen for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a complication of diabetes, which is the most common cause of end-stage renal disease (dialysis). DKD has a high mortality rate, and only early detection can nip this disease in the bud. Advanced glycation end products (AGEs)are generally believed to be involved in the occurrence of DKD. Studies have shown that the lens AGEs fluorescence for noninvasive detection has high consistency with the gold standard OGTT, has high sensitivity and specificity, and could be used as a practical tool for the early screening of type 2 diabetes mellitus (T2DM).Therefore, we speculated that the noninvasive lens AGEs fluorescence detection method can be used to predict the occurrence of DKD. This study detected levels of AGEs in multiple cellular and tissues and analyzed the relationships between AGEs and lens, eyeballs, peripheral blood mononuclear cell (PBMC), serum, and kidney. Additionally, we examined the possible role of lens AGEs fluorescence in DKD screening. Our preexperimental study found that lens AGE levels in patients with T2DM were positively correlated with PBM and serum AGE levels. Lens AGE levels in patients with T2DM were negatively correlated with eGFR and positively correlated with urinary ACR. The animal and cell experiments showed that the AGE levels in the eyeballs of DM mice were also positively correlated with those in the serum and kidney. To increase the reliability of the experiment, we increased the sample size. In our results, lens AGEs levels were positively correlated with the occurrence of DKD, and the incidence of DKD in the high lens AGEs group was 2.739 times that in the low lens AGEs group. The receiver operating characteristic (ROC) curves showed that patients with T2DM with a lens AGEs value ≥ 0.306 were likely to have DKD. The area under the ROC curve of the noninvasive technique for identifying DKD was 0.757 (95% Cl: 0.677-0.838, p<0.001), and the sensitivity and specificity were 70.0% and 78.7%, respectively. These results suggest that noninvasive lens AGEs detection technology has certain clinical value in diagnosing whether patients with T2DM have DKD.

Lens fluorescence and skin fluorescence in the Copenhagen Twin Cohort Eye Study: Covariates and heritability

Lens and skin fluorescence are related to the systemic accumulation of advanced glycation end products, which is accelerated in diabetes. We have examined lens fluorescence and skin fluorescence in healthy adult twins. The study enrolled twins aged median 59 years from a national population-based registry. Diabetic individuals were excluded from analysis. The interrelatedness between fluorescence parameters and relations between fluorescence and age, current HbA1c and smoking pack years were examined using correlation tests and mixed model linear regression analyses. Broad-sense heritability was analyzed and compared for lens fluorescence, skin fluorescence and HbA1c. Lens fluorescence and skin fluorescence were crudely interrelated (R = 0.38). In linear regression analyses, age explained a larger fraction of the variance in lens fluorescence (R2 = 32%) than in skin fluorescence (R2 = 20%), whereas HbA1c explained smaller variance fractions (R2 = 3% and 8%, respectively) followed by smoking pack years (4% and 3%, respectively). In multivariate analyses, age, HbA1c and smoking pack years combined explained more of the variance in lens fluorescence (R2 = 35%) than in skin fluorescence (R2 = 21%), but the influence of HbA1c on lens fluorescence was not statistically significant (p = .2). Age-adjusted broad-sense heritability was 85% for lens fluorescence, 53% for skin fluorescence and 71% for HbA1c in best fitting heritability models. Both fluorescence parameters increased with age, current glycemia and cumulative smoking. Lens fluorescence was found to be a predominantly heritable trait, whereas skin fluorescence was more influenced by environmental factors and closer related to current glycemia. The results suggest that skin fluorophores have a faster turn-over than lens fluorophores.

Macular Pigment Response to Lutein, Zeaxanthin, and Meso-zeaxanthin Supplementation in Open-Angle Glaucoma

Purpose

To evaluate macular pigment response to carotenoid supplementation in glaucomatous eyes.

Design

Double-masked, randomized, placebo-controlled clinical trial, the European Nutrition in Glaucoma Management Study (ClinicalTrials.gov identifier, NCT04460365).

Participants

Sixty-two participants (38 men, 24 women) with a diagnosis of open-angle glaucoma were enrolled. Forty-two were randomized to receive the active supplement, 20 participants were allocated to placebo.

Methods

Macular pigment optical density (MPOD) was measured by autofluorescence using the Heidelberg Spectralis scanning laser ophthalmoscope. Macular pigment optical density volume within the central 6° of retinal eccentricity as well as MPOD at 0.23°, 0.51°, 0.74°, and 1.02° were recorded at baseline and at 6-month intervals over 18 months. Visual function was assessed using visual acuity, mesopic and photopic contrast sensitivity under glare conditions, photo stress recovery time, microperimetry, and Glaucoma Activities Limitation 9 questionnaire. Advanced glaucoma module scans of retinal nerve fiber layer thickness and ganglion cell complex thickness over the central 6° of retinal eccentricity also were completed at each study visit.

Main Outcome Measures

Change in MPOD after supplementation with 10 mg lutein, 2 mg zeaxanthin, and 10 mg meso-zeaxanthin or placebo over 18 months.

Results

A mixed-model repeated measures analysis of variance revealed a statistically significant increase in MPOD volume (significant time effect: F(3,111) = 89.31, mean square error (MSE) = 1656.9; P < 0.01). Post hoc t tests revealed a significant difference in MPOD volume at each study visit for the treatment group (P < 0.01 for all), but no change in the placebo group (P > 0.05 for all). A statistically significant increase in mesopic contrast sensitivity under glare conditions was noted at 18 months in the treatment group, but not placebo. No other structural or functional changes were observed. No serious adverse events were noted during the trial.

Conclusions

Macular pigment can be augmented in glaucomatous eyes by supplementation with a formulation containing the carotenoids lutein, zeaxanthin, and meso-zeaxanthin. The greatest relative benefit was observed in those with the lowest baseline levels, but increases were noted across all participants and each retinal eccentricity. The potential benefits of MP augmentation for macular health in glaucoma merit further long-term evaluation.

Assessment of lens autofluorescence in patients with well-controlled essential hypertension and those with renal failure secondary to hypertension undergoing hemodialysis

PURPOSE

To compare the lens autofluorescence (AF) levels among patients with end-stage renal failure and undergoing hemodialysis secondary to hypertension, patients with well-controlled hypertension, and healthy controls.

METHOD

This study was a prospective, cross-sectional, comparative study conducted between February and April 2018. Two groups of patients and a group of healthy individuals were included in the study. The first group of patients included individuals with a renal insufficiency due to essential hypertension who underwent regular hemodialysis treatment (dialysis group). The second group included patients with well-controlled essential hypertension (hypertension group). Lens autofluorescence was measured via a scanning confocal lens fluorescence biomicroscope optical system for all participants. The measurement of fluorescence ratio is given as a numerical data. The AF results were compared in all groups.

RESULTS

The study included 87 individuals. There were 29 individuals (33.3 %) in the dialysis group, 30 (34.5 %) in the hypertension group, and 28 (32.2 %) in the healthy group. The mean fluorescence ratio(FR) was 0.20 ± 0.06, 0.20 ± 0.04, and 0.17 ± 0.04 in the dialysis, hypertension, and healthy groups respectively. There was a significant difference in the mean FR measurements between the three groups (p = .004). As a result of a binary comparison, mean FR values for patients in the dialysis group were higher (0.20 ± 0.06) than for healthy individuals (0.17 ± 0.04), which was statistically significant (p = .025). Mean FR measurements of hypertensive patients were higher (0.20 ± 0.04) than healthy individuals (0.17 ± 0.04), which was also statistically significant (p = .02). However, there was no statistically significant difference among the mean FR measurements between the hypertension and dialysis groups (p = .63).

CONCLUSION

We demonstrated that lens autofluorescence increased in patients with renal failure undergoing hemodialysis and those with well-controlled hypertension. The mean lens autofluorescence levels were significantly higher in both patient groups than the healthy control group.

The assessment of autofluorescence of the crystalline lens in diabetic patients and healthy controls: can it be used as a screening test?

Background

Our purpose was to demonstrate if measuring lens autofluorescence (AF) with a scanning confocal biomicroscope may be used to identify subjects with undiagnosed type II diabetes mellitus (DM), and hence, for it to be used as a marker for the severity of diabetic retinopathy in diabetic patients.

Patients and methods

In this cross-sectional, comparative study, lens AF was measured with scanning confocal lens fluorescence biomicroscope in diabetic and healthy groups. Full ophthalmological examination was performed. Blood tests of fasting plasma glucose, and glycosylated hemoglobin were also analyzed. The correlation between lens AF results and blood tests was evaluated in both groups. The cutoff value for the diagnosis of DM using lens AF was investigated.

Results

The study included 191 subjects with a mean age of 52.09±6.75 years. One hundred and seven (56.0%) subjects were female, and 84 (44.0%) were male. Eighty-two (42.9%) patients had type II DM, and 109 (57.1%) subjects self-reported as normal. The fluorescence ratio (FR) values ranged from 0.09 to 0.46 (0.23±0.06) in the total group. Mean FR measurements of diabetic subjects were significantly higher (0.27±0.06) than those without DM (0.20±0.05), (p=0.001). A statistically significant correlation was found between glycosylated hemoglobin, fasting plasma glucose, and FR. The cutoff point for the FR according to the presence of DM was found to be 0.24 and above (p=0.001), with a sensitivity of 71.95% and a specificity of 80.73%.

Conclusion

Measuring AF of human lens as an indirect evidence of increased advanced glycaton end products may helpful in detecting impaired glucose metabolism. Our results show highly significant correlation between possibility of DM and FR.

Fundus autofluorescence beyond lipofuscin: lesson learned from ex vivo fluorescence lifetime imaging in porcine eyes

Fundus autofluorescence (FAF) imaging is a well-established method in ophthalmology; however, the fluorophores involved need more clarification. The FAF lifetimes of 20 post mortem porcine eyes were measured in two spectral channels using fluorescence lifetime imaging ophthalmoscopy (FLIO) and compared with clinical data from 44 healthy young subjects. The FAF intensity ratio of the short and the long wavelength emission (spectral ratio) was determined. Ex vivo porcine fundus fluorescence emission is generally less intense than that seen in human eyes. The porcine retina showed significantly (p<0.05) longer lifetimes than the retinal pigment epithelium (RPE): 584 ± 128 ps vs. 121 ± 55 ps 498-560 nm, 240 ± 42 ps vs. 125 ± 20 ps at 560-720 nm. Furthermore, the lifetimes of the porcine RPE were significantly shorter (121 ± 55 ps and 125 ± 20 ps) than those measured from human fundus in vivo (162 ± 14 ps and 179 ± 13 ps, respectively). The fluorescence emission of porcine retina was shifted towards a shorter wavelength compared to that of RPE and human FAF. This data shows the considerable contribution of fluorophores in the neural retina to total FAF intensity in porcine eyes.

Imaging Lenticular Autofluorescence in Older Subjects

Purpose

To evaluate whether a practical method of imaging lenticular autofluorescence (AF) can provide an individualized measure correlated with age-related lens yellowing in older subjects undergoing tests involving shorter wavelength lights.

Methods

Lenticular AF was imaged with 488-nm excitation using a confocal scanning laser ophthalmoscope (cSLO) routinely used for retinal AF imaging. There were 75 older subjects (ages 47–87) at two sites; a small cohort of younger subjects served as controls. At one site, the cSLO was equipped with an internal reference to allow quantitative AF measurements; at the other site, reduced-illuminance AF imaging (RAFI) was used. In a subset of subjects, lens density index was independently estimated from dark-adapted spectral sensitivities performed psychophysically.

Results

Lenticular AF intensity was significantly higher in the older eyes than the younger cohort when measured with the internal reference (59.2 ± 15.4 vs. 134.4 ± 31.7 gray levels; P < 0.05) as well as when recorded with RAFI without the internal reference (10.9 ± 1.5 vs. 26.1 ± 5.7 gray levels; P < 0.05). Lenticular AF was positively correlated with age; however, there could also be large differences between individuals of similar age. Lenticular AF intensity correlated well with lens density indices estimated from psychophysical measures.

Conclusions

Lenticular AF measured with a retinal cSLO can provide a practical and individualized measure of lens yellowing, and may be a good candidate to distinguish between preretinal and retinal deficits involving short-wavelength lights in older eyes.

Ocular autofluorescence in diabetes mellitus. A review

Diabetes mellitus is a metabolic disease with a considerable impact on healthcare owing to its increased prevalence and high mortality rate. Structural, morphological, and physiological changes in each of the ocular components have been described in detail. Autofluorescence has been described as a good indicator of metabolic activity. The aim of the present review is to provide an overview of ocular endogenous fluorophores in the cornea, the crystalline lens, and the retinal pigment epithelium, the effects of diabetes mellitus and therefore the potential of autofluorescence assessment for screening and monitoring changes in diabetic patients.

Protein profiles in cortical and nuclear regions of aged human donor lenses: A confocal Raman microspectroscopic and imaging study

A combination of Raman spectroscopy, imaging, hierarchical cluster analysis (HCA) and peak ratio analysis was used to analyze protein profiles in the superficial cortex (SC), deep cortex (DC) and nucleus of old human lenses with cortical, nuclear and mixed cataracts. No consistent differences were observed in protein spectra and after cluster analysis between the three locations irrespective of the presence or absence of cortical opacities and/or coloration. A sharp increase (∼15%-∼33%) in protein content from SC to DC, normal for human lenses, was found in 7 lenses. In 4 lenses, characterized by the absence of cortical opacities, the SC has a protein content of ∼35%. A significant increase in the disulfide-to-protein ratio is found only in the SC of the 7 cortical cataracts. No changes were found in sulfhydryl-to-protein ratio. The relative contents of α-helices and β-sheets increase from SC to nucleus. β-Sheets are more common in the SC of lenses with cortical cataract. The absence of significant and consistent changes in protein profiles between nucleus and cortex even in cases of severe coloration is not favoring the prevailing concept that ubiquitous protein oxidation is a key factor for age related nuclear (ARN) cataracts. The observations favor the idea that multilamellar bodies or protein aggregates at very low volume densities are responsible for the rise in Mie light scatter as a main cause of ARN cataracts leaving the short-range-order of the fiber cytoplasm largely intact. The absence of significant changes in the protein spectra of the deep cortical opacities, milky white as a result of the presence of vesicle-like features, indicate they are packed with relatively undisturbed crystallins.

Measurement of Lens Autofluorescence for Diabetes Screening

Many efforts have been made lately to develop cost-effective, simple, and reproducible tests for diabetes screening besides the already established fasting plasma glucose, the oral glucose tolerance test, and the glycated hemoglobin A1_c. Several tests have been proposed lately, based on the measurement of the so-called advanced glycation endproducts (AGEs). AGEs production is exacerbated during hyperglycemia, and their accumulation in different tissues reflects the degree and duration of dysglycemia. The human lens represents a tissue where AGEs accumulation can be particularly well assessed. The present article comments on the article by Cahn et al. published in this issue of the Journal of Diabetes Science and Technology. Cahn and coauthors tested a new scanning confocal biomicroscope for its accuracy to detect noninvasively subjects with diabetes or at risk for developing diabetes.

Measurement of Lens Autofluorescence Can Distinguish Subjects With Diabetes From Those Without

Lens autofluorescence is increased in patients with diabetes mellitus, but clinical application has been limited by the lack of an instrument suitable for routine clinical use. We investigate possible uses of a new scanning confocal biomicroscope (1) to identify subjects with undiagnosed type 2 diabetes and (2) as a marker for the progression of diabetes. One hundred seventy-eight subjects self-reported as normal and 53 subjects physician-diagnosed with diabetes or prediabetes were recruited. Measurements were collected using a ClearPath DS-120 Lens Fluorescence Biomicroscope calibrated with standards traceable to National Institute of Standards and Technology (NIST). Fluorescence intensities were corrected for age by subtracting the value expected from a regression of intensity versus age for normal subjects. This "fluorescence deviation" showed progressively higher values for normal, prediabetes, type 2 diabetes, and type 1 diabetes and a high degree of predictability of diabetes diagnosis. A receiver operating characteristics curve was used to determine sensitivity and specificity for prediction of diabetes type 2. At a fluorescence deviation of 2500, a sensitivity of 67% at 94% specificity was observed detection of type 2 diabetes. The progressively higher fluorescence deviations are consistent with the physiological mechanisms of accumulation of fluorescent advanced glycation end products as the subject ages. The sensitivity and specificity performance of the lens autofluorescence test for type 2 diabetes is comparable to the performance of glucose threshold tests. The statistically significant difference between fluorescence deviations of normal and type 2 diabetes supports the feasibility of lens autofluorescence to screen subjects for undiagnosed type 2 diabetes. Ophthalmic practices are points of care at which there may be a public health benefit for screening patients for undiagnosed diabetes.