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

PRE-RETINOPATHY OF TYPE 1 DIABETES IN THE CONTEXT OF FUNCTIONAL, STRUCTURAL AND MICROCIRCULATORY CHANGES IN THE MACULAR AREA

AIM

The authors assessed the development of intraocular changes in type 1 diabetes (T1DM) from the onset of the disease leading to diabetic retinopathy (DR). The quote: “There must be an intermediate stage between the physiological intraocular finding and the diabetic retinopathy itself “, (prof. Jan Vavřinec).

METHODS

A two-year study (2018 and 2019) was conducted at the Department of Ophthalmology of the Teaching Hospital Kralovske Vinohrady in Prague (Czech Republic). There were 54 patients aged 17-42 years, the detection of T1DM ranged between the 1st and 14th year of life, with a duration of 12-35 years. Individual patients were always examined simultaneously by three methods: CS (contrast sensitivity), SD-OCT (spectral domain optical coherence tomography) and OCT-A (optical coherence tomography-angiography). We examined 106 eyes once and in a comprehensive manner.

RESULTS

We have shown that there is an intermediate stage between the physiological finding on the retina and DR, so-called diabetic pre-retinopathy (DpR). Subsequent redistribution of the observed into two DpR subgroups was derived from the size of the FAZ, either with its smaller area or with a larger area determining the microvascularity of the central area of the retina. The results of both other methods were assigned to these values. For SD-OCT, the depth of the fovea (the difference between the central retinal thickness and the total average retinal thickness) was determined, which was affected by the increased the macular cubature. In all patients it was on average 10.3 μm3. The retina in the central area was significantly strengthened compared to the healthy population at the level of significance p 0,001. We divided the actual DpR into an image: DpR1 in 26.5 % of eyes - condition with an average shallower fovea only by 21.5 μm below the level of the surrounding retina and an average narrower FAZ: 0.165 mm2 and with a more significant decrease in CS; DpR2 in 40.5 % of eyes - condition with average deeper fovea by 42 μm, i.e., more significantly and average larger FAZ: 0.325 mm2 with lower decrease of CS. At the same time, other changes in microvascularity were noted, such as disorders in the sense of non-perfusion in the central part of the retina of various degrees. This finding differed significantly from changes in already established (non-proliferative) NPDR in 36 % of eyes, when a significant decrease in CS with normal visual acuity was found 4/4 ETDRS. Statistical differences in CS between DpR1 and DpR2 and NPDR were determined - always p 0.001. The average depth of the fovea was NPDR: 29.5 μm. NPDR had the largest average FAZ: 0.56 mm2. Also significant were the most significant changes in non-perfusion and especially the presence of microaneurysms.

CONCLUSIONS

These three non - invasive methods helped to monitor the dynamics of the development of ocular changes in T1DM of better quality than the determination of visual acuity and ophthalmoscopic examination. Increased retinal volume induced hypoxia of visual cells with subsequent dual autoregulatory mechanism conditioning two types of diabetic pre-retinopathy before the onset of DR.

Are Contrast Sensitivity Functions Impaired in Insulin Dependent Diabetics Without Diabetic Retinopathy?

Purpose: To confirm the influence of multilevel metabolic disturbance of insulin dependent diabetes mellitus (IDDM) on the vision even before the onset of the other changes routinely evaluated by ophthalmologists. Methods: Contrast sensitivity functions (CSFs) were estimated using the VCTS 6500 board. The standardised measurement procedure was performed. The value of the threshold contrast sensitivity was obtained for five spatial frequencies (1.5 - 3 - 6 - 12 - 18 c/deg). Other data was collected (duration of diabetes, BCVA, funduscopy, fluoresceine angiography, HbA1C). The study group consisted of 48 IDDM patients (94 eyes) without diabetic retinopathy and with Snellen BCVA > 1.0. The control group (56 normals, 98 eyes) was age and BCVA matched. Results: Highly statistically significant decrease of the CSFs in all spatial frequencies in the study group was obtained. Correlation between duration of the diabetes and impaired degree of CSFs was present in the middle spatial frequency. No significant changes in CSFs were found among patients with pathological value of glycated hemoglobin HbA1c (>7.8 %). Conclusions: If compared with routinely used Snellen visual acuity, the CSFs are more complex descriptors of the subjects vision abilities. IDDM has an influence on these sensitive functions, especially during examination in the middle spatial frequency of 6 and 12 c/deg, before disturbing visual acuity and before changes in the retinal morphology. Decrease of CSFs was influenced mainly by the patients’ age and partially (in the middle spatial frequency) by the IDDM duration.

Early inner retinal thinning and cardiovascular autonomic dysfunction in type 2 diabetes

Background

To investigate changes in the neural retina according to the presence of retinal nerve fiber layer (RNFL) defects in type 2 diabetes, and to determine the association between inner retina thickness and the severity of diabetic complications.

Methods

We studied non-glaucomatous patients with type 2 diabetes and control subjects Circumpapillary RNFL and macula ganglion cell-inner plexiform layer (GCIPL) thicknesses were measured by spectral-domain optical coherence tomography. In patients with type 2 diabetes, a cardiovascular autonomic function test (AFT) was performed, which included the heart rate parameter of beat-beat variation—with deep breathing, in response to the Valsalva maneuver, and on postural change from lying to standing. The results of each test were scored as 0 for normal and 1 for abnormal. A total AFT score of 1 was defined as early cardiovascular autonomic neuropathy (CAN), and an AFT score≥ 2 as definite CAN.

Results

We compared control eyes (n = 70), diabetic eyes with RNFL defects (n = 47), and eyes without RNFL defects (n = 30). The average RNFL and GCIPL thicknesses were significantly different among groups (all, P<0.05). On post-hoc testing, diabetic eyes with RNFL defects had a significantly thinner average GCIPL thickness than those without RNFL defects. On multivariate analyses, significantly thinner average GCIPL was seen in early CAN staging (B = -4.32, P = 0.016) and in definite CAN staging (B = -10.33, P<0.001), compared with no CAN involvement, after adjusting for confounding parameters.

Conclusions

Cardiovascular autonomic dysfunction was associated with early neurodegenerative changes in type 2 diabetes.

Contrast sensitivity to spatial gratings in moderate and dim light conditions in patients with diabetes in the absence of diabetic retinopathy

OBJECTIVE

To evaluate the ability of contrast sensitivity (CS) to discriminate loss of visual function in diabetic subjects with no clinical signs of retinopathy relative to that of normal subjects.

RESEARCH DESIGN AND METHODS

In this prospective cross-sectional study, we measured CS in 46 diabetic subjects with a mean age of 48±6 years, a best-corrected visual acuity of 20/20 and no signs of diabetic retinopathy. The CS in these subjects was compared with CS measurements in 46 normal control subjects at four spatial frequencies (3, 6, 12, 18 cycles per degree) under moderate (500 lux) and dim (less than 2 lux) background light conditions.

RESULTS

CS was approximately 0.16 log units lower in patients with diabetes relative to controls both in moderate and in dim background light conditions. Logistic regression classification and receiver operating characteristic curve analysis indicated that CS analysis using two light conditions was more accurate (0.78) overall compared with CS analysis using only a single illumination condition (accuracy values were 0.67 and 0.70 in moderate and dim light conditions, respectively).

CONCLUSIONS

Our results showed that patients with diabetes without clinical signs of retinopathy exhibit a uniform loss in CS at all spatial frequencies tested. Measuring the loss in CS at two spatial frequencies (3 and 6 cycles per degree) and two light conditions (moderate and dim) is sufficiently robust to classify diabetic subjects with no retinopathy versus control subjects.

Influence of retinopathy on the achromatic and chromatic vision of patients with type 2 diabetes

BACKGROUND

Luminance contrast sensitivity and colour vision are considered to have great predictive value in the evaluation of type 2 diabetic retinopathy. However, these two visual characteristics have seldom been investigated in the same group of patients. In the present study we measured contrast sensitivity and colour vision in a group of patients with type 2 diabetes and correlated the results with estimates of common metabolic markers for the disease. A subgroup of the patients had no clinical signs of retinopathy.

METHODS

The vision of 27 patients (n = 50 eyes) with type 2 diabetes, with retinopathy (n = 20 eyes), or without retinopathy (n = 30 eyes) were evaluated using two psychophysical tests, the Farnsworth-Munsell 100 hue test (FM 100), and measurements of the luminance contrast sensitivity at 11 spatial frequencies. The results were compared with measurements obtained from an age-matched control group (n = 32), and were correlated with the level of glycated haemoglobin, glycaemic level, and time of disease onset. Signs of retinopathy were identified during the ophthalmological examinations.

RESULTS

Contrast sensitivity and colour vision impairments were present at different levels in diabetes patients. Eyes with retinopathy showed more severe vision loss than eyes without retinopathy. The FM 100 test was more sensitive for separation of patients from controls. Colour vision loss had no colour axes preference. The contrast sensitivity test appeared to have some advantage in differentiating patients with retinopathy from patients without retinopathy.

CONCLUSIONS

Both methods can be useful to follow the visual function of diabetic patients and should be used together to discriminate patients from controls, as well as to identify early signs of retinal damage.

Spatial frequency threshold and contrast sensitivity of an optomotor behavior are impaired in the Ins2Akita mouse model of diabetes

Diabetic retinopathy can lead to progressive loss of vision and is a leading cause of blindness. The Ins2(Akita) mouse model of diabetes develops significant retinal and systemic pathology, but how these affect visual behavior is unknown. Here, we show that Ins2(Akita) mice have progressive, quantifiable vision deficits in an optomotor behavior. This mouse line is a promising model in which to understand the contribution of retinal neuronal injury during the chronic hyperglycemia and hypoinsulinemia of diabetes to deficits in vision.

Mesopic foveal contrast sensitivity is impaired in diabetic patients without retinopathy

BACKGROUND

Contrast sensitivity (CS) has been studied extensively to determine its effectiveness as a test for diagnosing early and advanced diabetic retinopathy. Various techniques have been adopted to measure CS, and most of them reported a significant difference between diabetic and normal eyes. Our purpose is to demonstrate differences in foveal CS between diabetic patients without retinopathy and healthy subjects under mesopic and photopic conditions, using a simple, rapid computerized test.

METHODS

Seventeen eyes of nine patients with type 2 diabetes without diabetic retinopathy were included. Fourteen eyes of seven non-diabetic patients served as controls. All the patients underwent a careful ophthalmologic examination, including ETDRS chart visual acuity, color photographs, and optical coherence tomography (OCT). Patients with any ocular disease were excluded. All eyes had a visual acuity of 20/25 or better, a normal eye examination and optical coherence tomography (OCT). Photopic and mesopic contrast sensitivity was tested using a computerized psychophysical static method involving four forced-choice procedures. The targets were Gabor patches with spatial frequencies of 3-12 cycles per degree (cpd). The mesopic testing was conducted in a completely darkened room; the monitor was covered with a neutral density filter, allowing luminance of only 0.9 cd/m(2).

RESULTS

The average age was similar: 59.1 ± 5.3 years in the diabetic group vs 61.4 ± 3.2 years in the control group. The average duration of diabetes was 16 years (range 6-26). The average visual acuity was 0.04 ± 0.01 logMAR and 0.01 ± 0.01 logMAR in the diabetic and control groups respectively. Photopic foveal CS was similar in both groups. Significantly lower CS was found in diabetic patients under mesopic conditions at a spatial frequency of 3 (p < 0.008). At higher spatial frequencies, the mesopic contrast sensitivity was very low in both groups and without a significant difference.

CONCLUSIONS

Mesopic foveal CS is impaired in diabetic patients despite good visual acuity, a normal fundus examination and normal OCT. Early central visual function impairment may occur in diabetic patients before the appearance of retinopathy.

Diabetes mellitus as a risk factor for glaucomatous optic neuropathy

Open-angle glaucoma (OAG) is an optic neuropathy characterized by progressive retinal ganglion cell (RGC) death and optic disk excavation. Evidence is accumulating that RGC apoptosis is the fundamental pathology of OAG. Among several risk factors for development and progression of OAG, inclusion of comorbid diabetes has been controversial. Some large population-based prevalence and incidence studies found a positive association between diabetes and OAG, whereas others did not. This inconsistency is derived from selection-, recall-, or survival-bias or misclassification due to low incidence of the two diseases. On the other hand, recent basic studies have shown that diabetes not only affects vascular tissues but also compromises neuronal and glial functions and metabolism in the retina, which ultimately gives rise to apoptotic death of retinal neurons including RGCs. The impaired metabolism of neurons and glia by diabetes may render RGCs susceptible to additional stresses related to OAG such as elevated intraocular pressure. In fact, our latest data demonstrate that retinas taken from rats with streptozotocin-induced diabetes, which underwent cauterization of three episcleral veins to become a chronic glaucoma model, had significantly more apoptotic cells than those from rats with diabetes alone or with chronic glaucoma alone. In this regard, diabetes is a 'risk factor' for glaucomatous optic neuropathy. Additionally, prospective studies are needed to determine if OAG patients with diabetes have a more aggressive course than those without diabetes.

Temporal visual filtering in diabetes mellitus

The background modulation method was used to investigate the temporal response of the magnocellular pathway in diabetic patients and controls. The luminance threshold for detecting a moving, 2 degrees, achromatic target was measured as a function of background flicker frequency from 5 to 45 Hz. A model of photoreceptor kinetics integrated with difference of Gaussian receptive fields [Vis. Neurosci. 13 (1996) 173] was used to analyse the data. Diabetic patients with significant maculopathy showed raised thresholds at 8.75, 12.5, 15 and 17.5 Hz. Estimates of photoreceptor summation time were the same in both groups, but receptive field centre-to-surround delay showed an increasing trend in the diabetic patients.

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.

Letter contrast sensitivity changes in early diabetic retinopathy

PURPOSE

To investigate the discriminative ability of letter contrast sensitivity (CS) and visual acuity (VA) in detecting functional losses in participants with type 2 diabetes.

METHODS

LogMAR VA and letter CS were measured on 20 type 2 diabetic and 24 age-matched control participants. The diabetic participants were sub-grouped according to the level of retinopathy present.

RESULTS

Letter CS was able to distinguish those participants with and without macular oedema and those with no or minimal diabetic retinopathy from the control group, whereas VA was not.

CONCLUSION

Letter CS may be used as an effective screening tool to assess damage to the visual pathway of diabetic participants both with and without clinically detectable signs.

A new view of diabetic retinopathy: a neurodegenerative disease of the eye

Diabetic retinopathy (DR) is a common complication of diabetes and a leading cause of legal blindness in working-age adults. The clinical hallmarks of DR include increased vascular permeability, leading to edema, and endothelial cell proliferation. Much of the research effort has been focused on vascular changes, but it is becoming apparent that other degenerative changes occur beyond the vascular cells of the retina. These include increased apoptosis, glial cell reactivity, microglial activation, and altered glutamate metabolism. When occurring together, these changes may be considered as neurodegenerative and could explain some of the functional deficits in vision that begin soon after the onset of diabetes. This review will present the current evidence that neurodegeneration of the retina is a critical component of DR. There are two basic hypotheses that account for loss of cells in the neural retina. First, the loss of blood-retinal barrier integrity, which initially manifests as an increase in vascular permeability, causes a failure to control the composition of the extracellular fluid in the retina, which in turn leads to edema and neuronal cell loss. Alternatively, diabetes has a direct effect on metabolism within the neural retina, leading to an increase in apoptosis, which in turn causes breakdown of the blood-retinal barrier. It is not clear which hypothesis will be found to be correct, and, in fact, it is likely that vascular permeability and neuronal apoptosis are closely linked components of DR. However, the gradual loss of neurons suggests that progress of the disease is ultimately irreversible, since these cells cannot usually be replaced. In light of this possibility, new treatments for DR should be preventive in nature, being implemented before overt clinical symptoms develop. While vascular permeability is the target that is primarily considered for new treatments of DR, evidence presented here suggests that apoptosis of neurons is also an essential target for pharmacological studies. The vision of people with diabetes will be protected only when we have discovered a means to prevent the gradual but constant loss of neurons within the inner retina.

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.

Seeing beyond retinopathy in diabetes: electrophysiological and psychophysical abnormalities and alterations in vision

Contrast sensitivity testing, in common with color vision (another test of psychophysical function), demonstrates significant changes in diabetic subjects compared with nondiabetic controls, and there is some evidence for a relationship with grade of retinopathy. Changes in contrast sensitivity have been demonstrated in children and adults with diabetes of short duration, and some evidence exists for a correlation with poor glycemic control, although prospective studies are required to assess this relationship over a longer time period. Although both color vision and contrast sensitivity demonstrate similar patterns, studies that directly compare the two tests suggest that measurement of contrast sensitivity is the more sensitive and specific.