Dyschromatopsia in diabetes mellitus and its relation to metabolic control

Visual function and retinal thickness in children with type 1 diabetes mellitus

CLINICAL RELEVANCE

The possibility that changes in blue-yellow visual thresholds and some retinal thickness measures in children with diabetes mellitus may be observed before any visible fundus changes points to the possibility of these measures being a useful predictor that the risks of diabetic retinopathy are higher in some children than in others.

INTRODUCTION

Previous studies showed mixed results on chromatic and achromatic contrast sensitivity early in the course of diabetes mellitus, and the findings of these studies may have been influenced by a lack of experimental sensitivity to visual deficits, a bias towards tritan-like errors or the cognitive demands of the tests and variations in sample composition. The purpose of this study was to evaluate colour and contrast thresholds and retinal thickness in children with type 1 diabetes mellitus compared with age-matched controls.

METHODS

A prospective case-control study was carried out on 9-14-year-old children with type 1 diabetes mellitus (49 cases) and age matched controls (49) in which isoluminant red-green and blue-yellow and achromatic luminance contrast thresholds were measured. Fundus photography was used to grade diabetic retinopathy. Retinal thickness parameters were measured using optical coherence tomography. Data on the duration of diabetes mellitus, glycaemic control (HbA1c), blood glucose level, body mass index, blood pressure and blood oxygenation at the time of testing were obtained.

RESULTS

The cases mostly had poorly controlled diabetes, HbA1c 8.6% (6.4-12.8%), for an average (range) duration of 5 (0.4-12) years. The cases had significantly higher blue-yellow thresholds (p = 0.02) and greater total retinal and inner retinal thickness (p < 0.05) than controls. No cases had diabetic retinopathy. Within the cases, poorer visual function and systemic health measures were associated with thinner retinal structures and greater global loss volume percentage in the ganglion cell complex.

CONCLUSION

Blue-yellow thresholds of cases were raised compared to normal. Within the cases, higher luminance contrast thresholds were also associated with, mostly, ganglion cell complex reductions.

Emerging Insights and Interventions for Diabetic Retinopathy

PURPOSE OF REVIEW

To introduce recent advances in the understanding of diabetic retinopathy and to summarize current and emerging strategies to treat this common and complex cause of vision loss.

RECENT FINDINGS

Advances in retinal imaging and functional analysis indicate that retinal vascular and neural pathologies exist long before the development of clinically visible retinopathy. Such diagnostics could facilitate risk stratification and selective early intervention in high-risk patients. Antagonists of the vascular endothelial growth factor pathway effectively reduce vision loss in diabetes and promote regression of disease severity. Promising new strategies to treat diabetic retinopathy involve novel systemic diabetes therapy and ocular therapies that antagonize angiogenic growth factor signaling, improve blood-retina barrier function and neurovascular coupling, modulate neuroretinal metabolism, or provide neuroprotection. Long considered a pure microvasculopathy, diabetic retinopathy in fact affects the neural and vascular retina as well as neurovascular communication. Emerging therapies include those that target neuroretinal dysfunction in addition to those modulating vascular biology.

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.

Blue flash ERG PhNR changes associated with poor long-term glycemic control in adolescents with type 1 diabetes

PURPOSE

To investigate the relationship between long-term glycemic control and photopic negative response (PhNR) changes in the blue flash ERG in adolescents with type 1 diabetes (T1D) without diabetic retinopathy (DR).

METHODS

After light adaptation, ERG responses to 1.60 cd·s/m(2) blue (420 nm) flashes (blue flash ERG) and 3.0 cd·s/m(2) white flashes (LA 3.0 ERG) were recorded in 22 patients (age range, 12 to 19 years) and 28 age-similar control subjects. The primary outcome measure was the amplitude of the PhNR. Secondary outcome measures were the amplitude and implicit time of the a-wave and b-wave. Multiple regression analyses were conducted with glycated hemoglobin (HbA(1c)) values and the time since diagnosis of T1D as covariates.

RESULTS

Blue flash ERG PhNR amplitudes were reduced (P = 0.005) in patients compared with control subjects. Multiple regression analysis demonstrated that a 1-unit increase in HbA(1c) was associated with a 15% decrease in the blue flash ERG PhNR amplitude (r = 0.61, P = 0.003). Compared with controls blue flash ERG a-waves (P = 0.03) and b-waves (P = 0.02) were delayed in patients but were not significantly associated with HbA(1c) or time since diagnosis of T1D. None of the ERG measures in the LA 3.0 ERG were significantly different in patients compared with controls.

CONCLUSIONS

Poorer long-term glycemic control is associated with worsening inner retinal dysfunction involving short-wavelength cone pathways of adolescents with T1D and no clinically visible DR. Future studies are warranted to determine whether changes in the blue flash ERG PhNR are a predictive marker of subclinical DR.

Do type 2 diabetes patients without diabetic retinopathy or subjects with impaired fasting glucose have impaired colour vision? The Okubo Color Study Report

AIMS

To investigate associations between fasting plasma glucose level and the prevalence of acquired colour vision impairment in type 2 diabetes patients without diabetic retinopathy.

METHODS

Participants in this cross-sectional study of male officials aged 20-60 yr in the Japanese Self Defence Force, underwent colour vision testing, ophthalmic examination, a standardized interview and examination of venous blood samples. Ishihara plates, a Lanthony 15-hue desaturated panel and Standard Pseudoisochromatic Plates Part 2 were used to examine colour vision. The Farnsworth-Munsell 100-hue test was performed to define acquired colour vision impairment. Cardiovascular disease risk factors were determined from serum blood samples, physical records and an interview. We performed logistic regression analysis adjusted for age, diagnosed hypertension, dyslipidaemia, cataract, glaucoma, being overweight, smoking status and alcohol intake. Crude and adjusted odds ratios were calculated for three glucose levels, which included normal fasting glucose, impaired fasting glucose and diabetes.

RESULTS

Out of a total of 1042 men enrolled, 872 were eligible for the study, and 31 were diagnosed with acquired colour vision impairment. As compared with the subjects with normal fasting glucose (< 5.6 mmol/l), the crude odds ratio for acquired colour vision impairment was 0.93 (95% CI 0.32-2.74) for the subjects with impaired fasting glucose (5.6-6.9 mmol/l) and 8.07 (95% CI 2.48-26.22) for the patients with type 2 diabetes. The multiple-adjusted odds ratios were 0.77 (95% CI 0.25-2.34) for the subjects with impaired fasting glucose and 5.89 (95% CI 1.55-22.40) for the patients with type 2 diabetes.

CONCLUSIONS

Our findings suggest that there is a dramatically increased prevalence of acquired colour vision impairment in type 2 diabetes patients without diabetic retinopathy which might be attributable to another pathogenesis associated with diabetic retinopathy.

Color vision impairment in type 2 diabetes assessed by the D-15d test and the Cambridge Colour Test

Color vision impairment emerges at early stages of diabetes mellitus type 2 (DM2) and may precede diabetic retinopathy or the appearance of vascular alterations in the retina. The aim of the present study was to compare the evaluation of the color vision with two different tests - the Lanthony desaturated D-15d test (a traditional color arrangement test), and the Cambridge Colour Test (CCT) (a computerized color discrimination test) - in patients diagnosed with DM2 without clinical signs of diabetic retinopathy (DR), and in sex- and age-matched control groups. Both color tests revealed statistically significant differences between the controls and the worst eyes of the DM2 patients. In addition, the degree of color vision impairment diagnosed by both tests correlated with the disease duration. The D-15d outcomes indicated solely tritan losses. In comparison, CCT outcomes revealed diffuse losses in color discrimination: 13.3% for best eyes and 29% for worst eyes. In addition, elevation of tritan thresholds in the DM2 patients, as detected by the Trivector subtest of the CCT, was found to correlate with the level of glycated hemoglobin. Outcomes of both tests confirm that subclinical losses of color vision are present in DM2 patients at an early stage of the disease, prior to signs of retinopathy. Considering the advantages of the CCT test compared to the D-15d test, further studies should attempt to verify and/or improve the efficiency of the CCT test.

A multifocal electroretinogram model predicting the development of diabetic retinopathy

The prevalence of diabetes has been accelerating at an alarming rate in the last decade; some describe it as an epidemic. Diabetic eye complications are the leading cause of blindness in adults aged 25-74 in the United States. Early diagnosis and development of effective preventatives and treatments of diabetic retinopathy are essential to save sight. We describe efforts to establish functional indicators of retinal health and predictors of diabetic retinopathy. These indicators and predictors will be needed as markers of the efficacy of new therapies. Clinical trials aimed at either prevention or early treatments will rely heavily on the discovery of sensitive methods to identify patients and retinal locations at risk, as well as to evaluate treatment effects. We report on recent success in revealing local functional changes of the retina with the multifocal electroretinogram (mfERG). This objective measure allows the simultaneous recording of responses from over 100 small retinal patches across the central 45 degrees field. We describe the sensitivity of mfERG implicit time measurement for revealing functional alterations of the retina in diabetes, the local correspondence between functional (mfERG) and structural (vascular) abnormalities in eyes with early nonproliferative retinopathy, and longitudinal studies to formulate models to predict the retinal sites of future retinopathic signs. A multivariate model including mfERG implicit time delays and 'person' risk factors achieved 86% sensitivity and 84% specificity for prediction of new retinopathy development over one year at specific locations in eyes with some retinopathy at baseline. A preliminary test of the model yielded very positive results. This model appears to be the first to predict, quantitatively, the retinal locations of new nonproliferative diabetic retinopathy development over a one-year period. In a separate study, the predictive power of a model was assessed over one- and two-year follow-ups. This permitted successful prediction of new retinopathy development in eyes with and without retinopathy at baseline. Finally, we briefly describe our current research efforts to (a) locally predict future sight-threatening diabetic macular edema, (b) investigate local retinal function change in adolescent patients with diabetes, and (c) better understand the physiological bases of the mfERG delays. The ability to predict the retinal locations of future retinopathy based on mfERG implicit time provides clinicians a powerful tool to screen, follow-up, and even consider early prophylactic treatment of the retinal tissue in diabetic patients. It also aids identification of 'at risk' populations for clinical trials of candidate therapies, which may greatly reduce their cost by decreasing the size of the needed sample and the duration of the trial.

Blue-light filtering intraocular lens in patients with diabetes: contrast sensitivity and chromatic discrimination

PURPOSE

To evaluate potential changes in contrast sensitivity and color discrimination in diabetic patients who had cataract surgery and implantation of the blue-light filtering AcrySof Natural (SN60AT) intraocular lens (IOL) compared with an ultraviolet-only filtering (AcrySof SA60AT) IOL.

SETTING

Refractive Surgery Unit, Hospital NISA Valencia al Mar, Valencia, Spain.

METHODS

Forty-four eyes of 22 diabetic patients were enrolled in a blue-light filtering fellow-eye control study. Patients received yellow-tinted IOLs (AcrySof Natural) in 1 eye and non-yellow-tinted IOLs (AcrySof SA60AT) in the fellow eye. Three months after surgery, monocular contrast sensitivity function was measured with the CSV 1000-E contrast sensitivity chart at distance and color discrimination was tested with the Farnsworth-Munsell 100-hue test.

RESULTS

Eyes implanted with the blue-light filtering IOLs showed better contrast sensitivity values than fellow eyes implanted with non-yellow-tinted IOLs (P<.05). The blue-light filtering IOL did not modify chromatic discrimination compared with the non-yellow-tinted IOL (P = .62). In the blue-yellow axis discrimination study, the eyes implanted with the AcrySof Natural IOL had statistically significant better color vision (P = .008).

CONCLUSIONS

In diabetic patients, the AcrySof Natural IOL provides better contrast sensitivity than the AcrySof SA60AT. The blue-light filter of the AcrySof Natural IOL did not cause chromatic discrimination defects based on total error scores and improved color vision in the blue-yellow chromatic axis in diabetic patients.

Extent of foveal tritanopia in diabetes mellitus

AIM

To use a colour matching technique to test the hypothesis that the foveal tritanopic zone is increased in size in diabetes mellitus.

METHOD

A Wright tristimulus colorimeter was adapted for small field colour matching and colour matches were performed on bipartite fields in the range 12' to 60' of arc. The reference stimulus was 490 nm desaturated with 650 nm and the matching stimulus consisted of either two wavelengths (530 nm and 650 nm) or three (460 nm, 530 nm, and 650 nm). The size of the zone of foveal tritanopia was measured using two alternative forced choice presentations of dichromatic and trichromatic matches made by the observer for different field sizes. 21 diabetic and 12 controls performed the experiment.

RESULTS

The results for the controls show a normal distribution, with a median foveal tritanopic zone of 18' of arc. The median for the diabetic patients was also 18' of arc, but the distribution showed a significant skew to the right. A non-parametric test shows a significant difference in comparison with the controls (p = 0.01), with several subjects having extensive zones of foveal tritanopia, reaching up to 1 degree.

CONCLUSIONS

In the majority of diabetic subjects the extent of foveal tritanopia is normal; however, there is good evidence that in a small number of subjects the size of the zone is significantly increased. This indicates S-cone pathway damage that is sufficiently severe to lead to dichromatic colour vision in the fovea.

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.

The short wavelength-sensitive cone electroretinogram in diabetes: relationship to systemic factors

The short wavelength-sensitive (S-) cone electroretinogram (ERG) is selectively reduced in diabetic patients both with and without retinopathy, but the exact mechanism of the vulnerability of the S-cone system is still unclear. This study examined relationships of the S-cone ERG to systemic factors in diabetes. Cone ERGs to different color flash stimuli were examined in the presence of bright white background illumination in 17 diabetic patients without retinopathy and in 17 diabetics with background retinopathy. Relationships of the amplitude and implicit time of the S-cone ERG to the following systemic factors were statistically analyzed: patients' age, hemoglobin A1 level, method of diabetic control, presence of retinopathy, and presence of nephropathy. The amplitude of the S-cone ERG b-wave was significantly reduced in diabetics treated with insulin and in those associated with nephropathy. No significant correlation was found between the S-cone ERG and patient's age, hemoglobin A1 level and presence or absence of retinopathy. A selective reduction of the S-cone ERG is observed in patients whose metabolic control has been poor for a longer period, suggesting that microvascular changes may play a role in the S-cone ERG impairment.

Colour vision and persistent microalbuminuria in children with type-1 (insulin-dependent) diabetes mellitus: a longitudinal study

In an attempt to elucidate colour vision in children with type 1 (insulin-dependent) diabetes mellitus without fluorescein angiographic signs of retinopathy, we studied a group of 50 patients of mean age + or - SD 10.27 + or - 2.89 (range 8.1-13.0 years). Results were compared with a sex-and age-matched control group. The Farnsworth-Munsell 100-hue test showed a significantly higher value in total error score (TES) in diabetics than in controls (64.07 + or - 18.32 and 54.27 + or - 12.87, respectively: P = 0.0004). Diabetic patients were divided in two groups as regards presence of persistent microalbuminuria and followed for 7 years. The HbAlc values of the two groups were: normoalbuminuric 7.10 +/- 2.92%, microalbuminuric 9.79 + or - 1.41 (P = 0.004). Microalbuminuric patients showed a significantly higher TES than normoalbuminuric subjects both at the beginning (94.79 + or - 13.98 vs. 58.10 + or - 11.98) and end of the study (103.07 + or - 14.61 vs. 61.04 + or - 13.36: P < 0.0001), and after follow-up they had a worse TES than at the beginning of the study (P = 0.01); no change in TES was found in normoalbuminuric patients during the study. The results suggest that a deficit in colour vision occurs in diabetic children before the onset of fluorescein angiographic signs of retinopathy. Our follow-up shows that microalbuminuric patients present a significant worsening of colour vision. When a patient shows persistent microalbuminuria, colour vision must be carefully evaluated, also in subjects without fluorescein angiographic signs of retinopathy.

Colour vision in diabetic patients after photocoagulation treatment. A five-year follow-up

Colour vision of 60 diabetic patients (60 eyes) was studied after photocoagulation treatment in 1986-87. For the follow-up study 5 years later in 1991-92, 32 of the patients were available. The ages of the patients in the follow-up study varied from 28 to 64 years, the duration of diabetes from 19 to 35 years, the amount of laser spots from 200 to 3174, and the visual acuity from 0.4 to 1.0. As colour vision tests, the Standard Pseudo-isochromatic Plates part 2, Lanthony Tritan Album, Farnsworth Panel D 15, and box III of the Farnsworth-Munsell 100 hue test were used. Of the 32 eyes, 22 (68.8%) had the same results in the colour vision tests, 4 (12.5%) had better results, and 6 (18.8%) had worse results than 5 years earlier. Between Group 1 (colour vision the same or better than 5 years earlier, 26 eyes) and Group 2 (colour vision worse than earlier, 6 eyes) there was a significant difference in the age and in the level of the visual acuity of the patients. The changes in the lens, fundus or visual acuity during 5 years did not seem to have an effect in colour vision.

Screening of diabetics who read incorrectly colour-dependent glucose test-strips

Forty-eight diabetic patients (82 eyes) were examined with four different colour vision tests and one blood glucose strip-test. The ages of the patients varied from 23 to 65 years (mean 44.3 years +/- 11.4, SD), the duration of diabetes from 13 to 41 years (mean 25.8 +/- 6.2), and the visual acuities from 0.2 to 1.0 (mean 0.8 +/- 0.2). Of the eyes, 77 had had photocoagulation, 25 had small peripheral lens opacities, and 55 had slight background retinopathy. The colour vision tests were: the Standard Pseudoisochromatic Plates part 2 (SPP2), the Lanthony Tritan Album, the Farnsworth Panel D 15 test and the box III of the Farnsworth-Munsell 100 hue (FM 100) test. The blood glucose test was Haemo-Glukotest 1-44. Of the 82 eyes, 38 incorrectly saw Haemo-Glukotest strips. The SPP2 test found 89% of the eyes, the Tritan Album 55%, the Panel D 15 71%, and the box III of the FM 100 test 76%. The strips were correctly interpreted in 44 of the eyes. However, 36% of them failed the SPP2, 16% the Tritan Album, 11% the Panel D 15 test and 18% the box III of the FM 100 test. The Panel D 15 test and the box III of the FM 100 test would be useful in screening those diabetics who cannot correctly interpret the colour-dependent glucose test-strips and would need a blood sugar meter for their blood glucose level testing.

Colour vision and dark adaptation in diabetic patients after photocoagulation

Colour vision and dark adaptation were studied in 60 diabetic patients treated with photocoagulation. An acquired colour vision defect was found in 50% and a defective dark adaptation in 77% of the patients. Both colour vision and dark adaptation were defective in 47% of the patients. Colour vision defect only was found in 3% and dark adaptation defect only in 30% of the patients. Neither of these defects was found in 20% of the patients. The Farnsworth-Munsell 100-hue test showed a blue-yellow axis in 24 of the 30 colour defective patients. In the patients with an impaired dark adaptation, the range of the cone and rod threshold elevations from the normal upper limit was from 0.2 to 1.4 log units. The Farnsworth-Munsell 100-hue test scores showed a significant positive correlation to the values of both cone and rod thresholds.

Color vision in diabetic school children

The color vision of 64 diabetic school children was studied. Acquired color vision defects due to diabetes could not be found in any of the children. Two of the children had a congenital red-green color vision defect. In the examination, three different pseudoisochromatic plate tests (Isihara, Standard Pseudoisochromatic Plates part 2, and Lanthony Tritan Album) were used as well as the Nagel anomaloscope and three different cap arrangement tests (Panel D 15, Lanthony Desaturated Panel, and Farnsworth-Munsell 100 hue). The plate tests and the anomaloscope examination were fast, reliable, and well accepted by the children. The cap arrangement tests took more time, and many of the children neither liked nor properly performed these tests. Twelve color dependent glucose strip tests for diabetes care at home were also studied. A few of the youngest school children made mistakes in interpreting the colors of these strips, although their color vision was normal.

Colour vision in long-standing diabetes mellitus

In 12 long-standing insulin-dependent diabetics with background diabetic retinopathy their 100-hue colour vision scores were positively related to the degree of retinopathy and negatively to fasting blood glucose levels. However, the 100-hue colour vision scores and types were not significantly different from those of normal subjects matched for age, sex, and social class.