Lens fluorescence in relation to nephropathy in insulin-dependent diabetes mellitus

GUNN's DOTS AS INDICATORS OF RENAL FUNCTION, FINDINGS FROM THE TONGREN HEALTH CARE STUDY

PURPOSE

To investigate the prevalence of Gunn's dots (GDs) and associated systemic factors in adult Chinese.

METHODS

A cross-sectional study enrolling participants older than 45 years from a community-based study. Gunn's dots were evaluated using fundus photography, and associated systemic factors were analyzed. Patients with any retinal or optic neuropathy were excluded.

RESULTS

The study included 4,118 participants (mean age: 58.3 ± 9.9 years; male: 1,699/41.3%). Gunn's dots were found in 931 participants, with a prevalence of 22.6 ± 0.8% (95% confidence interval [CI]: 21.3-23.9). Systemic factors associated with a higher GD prevalence were younger age (odds ratio [OR]: 0.92; 95% CI: 0.91-0.93; P < 0.001), higher estimated glomerular filtration rate (eGFR) (OR: 1.01; 95% CI: 1.001-1.02; P = 0.022), and higher serum concentration of triglycerides (OR: 1.08; 95% CI: 1.004-1.16; P = 0.040). The GD prevalence was 3.5 (OR = 3.46; 95% CI: 1.06-11.35) and 4.4 (OR = 4.37; 95% CI: 1.27-15.09) times greater for participants with an eGFR of ≥90 mL/minute/1.73 m2 and an eGFR of ≥100 mL/minute/1.73 m2, respectively, as compared with participants with an eGFR of <60 mL/minute/1.73 m2.

CONCLUSION

The GD prevalence (mean: 22.6%) was associated with younger age, higher eGFR, and higher serum triglyceride concentrations. The presence of GDs may serve as indicators of healthy renal function.

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.

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.

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.

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

BACKGROUND

Lens autofluorescence increases with the age of the subject, and the fluorophores responsible are associated with cataract, retinopathy, and other complications of diabetes. We built a scanning confocal lens fluorescence biomicroscope suitable for routine clinical measurement of lens autofluorescence and light scattering and report data from 127 healthy subjects.

METHOD

The fluorescence biomicroscope focuses a beam of light from a blue light-emitting diode on the lens and measures fluorescent green light and blue scattered light using a sensitive silicon photomultiplier. The system includes a target fixation light and a video camera for alignment and automatic pupil tracking. Under software control, a volume of measurement is scanned from behind the posterior lens capsule, through the lens to the aqueous humor, and then back again. Software computes the average ratio of lens autofluorescence to scattered light in the central portion of the lens. Self-reported healthy nondiabetic subjects were examined by an optometrist; if their eyes were healthy and without significant cataract, they were entered into the study.

RESULTS

Valid lens autofluorescence data were collected from 127 subjects between 21 and 70 years of age. A linear model for lens autofluorescence intensity with age was highly statistically significant, and the improvement in fit for higher-order polynomial models was not statistically significant. The ratio of lens autofluorescence to light scatter was also calculated; regression analysis showed significant curvature for the relationship of the fluorescence ratio to age, so a nonlinear model was used to estimate the mean ratio of autofluorescence to scatter and its prediction intervals as a function of age.

CONCLUSIONS

Our observation of a strongly significant linear regression of fluorescence intensity with age of the subjects agrees with the results from previous studies, as does a nonlinear model for the fluorescence ratio. The fluorescence biomicroscope enables the clinician to identify patients with fluorescence ratio significantly higher than expected for their age.

Lens fluorescence and metabolic control in type 1 diabetic patients: a 14 year follow up study

BACKGROUND/AIMS

In this prospective study the authors followed the post-translational modification of the proteins of the lens of the eye by fluorometry over a period of 14 years in patients with type 1 diabetes mellitus.

METHODS

Twenty patients were examined at 6 years (baseline) and 20 years (follow up) after onset of diabetes mellitus. Glycaemic levels were assessed from HbA1c measured at regular intervals from the onset of diabetes mellitus.

RESULTS

Lens fluorescence at follow up was significantly related to mean HbA1c during the study period and to lens fluorescence at baseline (p<0.0001). Sixty per cent of the variation in rate of increase in lens fluorescence during the study period was statistically attributable to glycaemia levels.

CONCLUSION

The results confirm that the rate of fluorophore accumulation in the lens of adult diabetic patients is increased in proportion to glycaemic control. This parameter alone is, however, not sufficient to explain the entire variation in lens fluorophore accumulation. Consequently, lens fluorescence must be influenced by other factors before initiation and during the study period, and possibly even before onset of diabetes mellitus. The underlying mechanism could be a variation in susceptibility to lens protein denaturation by glycation.

Corneal fluorescence in relation to genetic and environmental factors: a twin study

PURPOSE

Corneal fluorescence is believed to be caused by advanced glycation end products formed by non-enzymatic glycation on corneal proteins. The purpose of the present twin study was to examine whether the process is related to genetic or environmental factors.

METHODS

Corneal fluorescence was measured in 59 monozygotic and 54 dizygotic twin pairs. The influences of genetic and environmental factors were estimated using structural equation modelling.

RESULTS

Interindividual variation in corneal fluorescence was attributable to environmental factors, whereas the effect of genetic factors was of little or no significance. Corneal fluorescence correlated significantly with smoking habits (r = 0.38) and the 2-hour oral glucose tolerance test response (r = 0.27), and increased with age (p < 0.0001).

CONCLUSION

Fluorophore accumulation in the cornea was attributable to age and environmental effects, of which smoking was the most conspicuous identifiable factor, although glucose was also of relevance. However, the greater part of interindividual variation in corneal fluorescence remains unexplained.

Spatial visual filtering in diabetes mellitus

PURPOSE

To investigate spatial visual filtering in a group of diabetic patients and compare the results with those of a group of controls.

METHODS

The luminance threshold of a moving 2 degrees achromatic target, viewed against a 17 degrees achromatic background grating, was measured as a function of grating periodicity from 0.21 to 31.4 cpd in 22 diabetic patients and 12 controls, giving a response characteristic of the spatial function of a sustained-response type of visual channel. A previously published model of spatiotemporal filtering, integrating photoreceptor kinetics with difference-of-Gaussian circularly symmetric receptive fields, was used to analyse the data.

METHODS

The model gave a good fit to the data in the control group, with a mean central space constant of 0.046 degrees and centre:surround ratio of 1:5.2 and mean R(2)=0.78 (SD 0.12). The mean central space constant in the diabetic group was 0.051 degrees and the centre:surround ratio 1:4.2, although best fit was significantly worse, at R(2)=0.54 (SD 0.19), P=0.001. The best fit for diabetic subjects with grade 2 maculopathy was significantly worse than for those with no maculopathy ( P=0.03).

CONCLUSION

The study demonstrates a disruption of circularly symmetric centre-surround receptive field structure of the sustained-response channel in the diabetic retina to a degree that is consistent with the retinal level of anatomical change in diabetic maculopathy.

The Hermann-Hering grid illusion demonstrates disruption of lateral inhibition processing in diabetes mellitus

BACKGROUND/AIM

The Hermann-Hering grid illusion consists of dark illusory spots perceived at the intersections of horizontal and vertical white bars viewed against a dark background. The dark spots originate from lateral inhibition processing. This illusion was used to investigate the hypothesis that lateral inhibition may be disrupted in diabetes mellitus.

METHOD

A computer monitor based psychophysical test was developed to measure the threshold of perception of the illusion for different bar widths. The contrast threshold for illusion perception at seven bar widths (range 0.09 degrees to 0.60 degrees) was measured using a randomly interleaved double staircase. Convolution of Hermann-Hering grids with difference of Gaussian receptive fields was used to generate model sensitivity functions. The method of least squares was used to fit these to the experimental data. 14 diabetic patients and 12 control subjects of similar ages performed the test.

RESULTS

The sensitivity to the illusion was significantly reduced in the diabetic group for bar widths 0.22 degrees, 0.28 degrees, and 0.35 degrees (p = 0.01). The mean centre:surround ratio for the controls was 1:9.1 (SD 1.6) with a mean correlation coefficient of R(2) = 0.80 (SD 0.16). In the diabetic group, two subjects were unable to perceive the illusion. The mean centre:surround ratio for the 12 remaining diabetic patients was 1:8.6 (SD 2.1). However, the correlation coefficients were poor with a mean of R(2) = 0.54 (SD 0.27), p = 0.04 in comparison with the control group.

CONCLUSIONS

A difference of Gaussian receptive field model fits the experimental data well for the controls but does not fit the data obtained for the diabetics. This indicates dysfunction of the lateral inhibition processes in the post-receptoral pathway.

Study of lens autofluorescence by fluorophotometry in pregnant patients with diabetes

PURPOSE

Lens autofluorescence originates from an accumulation of fluorescent substances such as the tryptophan-derived residues and glycosylated protein aggregations, which are associated with the process of cataractogenesis and lens aging. The purpose of this investigation is to determine whether pregnancy alters the typical constituents of the lens autofluorescence in patients with diabetes and, if so, to what degree this may occur.

METHODS

Lens autofluorescence was studied with fluorophotometry in 127 eyes of 72 individuals: 23 control subjects, 6 healthy pregnant women, 21 patients with diabetes, and 44 pregnant patients with diabetes.

RESULTS

The autofluorescence values were 311 +/- 130 ng/ml, 253 +/- 40 ng/ml, 378 +/- 110 ng/ml, and 562 +/- 164 Eq ng/ml (Eq ng/ml = Ng/ml equivalent fluorescein) in the four groups, respectively. The difference between the nonpregnant and pregnant patients with diabetes was significant (P < 0.001).

CONCLUSION

These results suggest that there is an important deterioration in the metabolic state of the lens during gestation in patients with diabetes, as is the case for diabetic retinopathy.

Impaired contrast sensitivity in adolescents and young type 1 (insulin-dependent) diabetic patients with microalbuminuria

We compared neurosensorial visual function by psychophysical tests (macular recovery time and contrast sensitivity) in two well matched groups of young Type 1 (insulin-dependent) diabetic patients with micro- and normoalbuminuria, respectively. The patients had normal visual acuity (> or = 1.0) and either no retinopathy or non-proliferative retinopathy. Thirty patients with microalbuminuria (albumin excretion > or = 15 micrograms/min in a least two out of three timed overnight urine samples) were matched (age, diabetes duration, mean one-year HbA1c, gender) with normoalbuminuric (n = 27) patients. Retinopathy (50 degree colour fundus photography) was assessed by counting microaneurysms and hemorrhages as 'red spots'. Contrast sensitivity was examined for the spatial frequencies of 1.5, 3, 6, 12 and 18 cycles per degree (cpd). Macular recovery time (nyctometry) refers to the time-related (2 min) ability of the retina to regain visual acuity following exposure to bright light (photostress). Contrast sensitivity score was reduced in patients with microalbuminuria compared to those without; 18 cpd (mean and 95% confidence intervals): [4.2 (3.8-4.7) vs 5.0 (4.6-5.4), p = 0.03]. Macular recovery performance was not significantly reduced: [21.0 arbitrary units (17.5-24.6) vs 26.0 (22.6-30.7), p = 0.12]. We conclude that impaired contrast sensitivity independent of background retinopathy is shown in a group of young Type 1 (insulin-dependent) diabetic patients with low-grade microalbuminuria compared to a group of patients with normoalbuminuria.

Type I diabetic nephropathy: clinical characteristics and economic impact

Approximately one-third of type I diabetic patients develop diabetic nephropathy with confounding pathogenesis--frequently manifested as heavy persistent proteinuria, fall in glomerular filtration rate, and increased arterial hypertension. There is increasing incidence and prevalence of type I diabetes, particularly in northern Europe and the United States. Increased morbidity and mortality occur in type I diabetic patients with renal disease. Among type I patients with persistent proteinuria, death occurs on the average within 5-10 years. The economic impact of endstage renal disease due to diabetic nephropathy is overwhelming, and the cost is increasing at an alarming rate.