Ocular haemodynamics and colour contrast sensitivity in patients with type 1 diabetes

Wide-field swept-source OCTA in the assessment of retinal microvasculature in early-stage diabetic retinopathy

BACKGROUND

To perform a quantitative analysis of retinal microvasculature in patients with early-stage diabetic retinopathy (DR) using wide-field swept-source optical coherence tomography angiography (SS-OCTA).  METHODS: One hundred nineteen eyes of 119 patents (67 eyes with no DR and 52 eyes with mild-moderate nonproliferative diabetic retinopathy (NPDR)) were enrolled in this observational and cross-sectional cohort study, and an age-matched group consisting of 39 eyes of 39 non-diabetic subjects were set as the control. Each participant underwent a full ophthalmic examination, including wide-field SS-OCTA imaging. On OCTA scans (12 mm * 12 mm), the mean perfusion area (PA) and vessel density (VD) were independently measured in all 16 Early Treatment Diabetic Retinopathy Study (ETDRS) sectors. Linear regression analyses were conducted to evaluate the influences of PA.

RESULTS

In the central ring, there were no significant differences in the average PA and VD among the groups. In the 3 mm radius, the PA and VD of the no DR and mild-moderate NPDR were significantly decreased compared with the control group in superior and inferior quadrants. In the wide-field scans (9 and 12 mm radius), there was no significant difference in average PA and VD between the groups in each sectors (p > 0.05). Regression analysis found that the effect of VD on PA was statistically different (b = 1.311, p < 0.001).

CONCLUSION

Wide-field OCTA imaging is useful for evaluating peripheral capillary perfusion in eyes with early-stage DR. Decrease in PA and VD was greater in the S3 and I3 sectors, and reductions in PA and VD were uneven in wide-filed sectors (9 and 12 mm radius).

Zone-wise examination of optical coherence tomography features and their correspondence to multifocal electroretinography in eyes with nonproliferative diabetic retinopathy

PURPOSE

To examine (1) the retinal structure by optical coherence tomography (OCT) and function by means of multifocal electroretinography (mfERG) in eyes with and without nonproliferative diabetic retinopathy (NPDR) (2) for correspondence between local retinal function and OCT zones with retinal lesions.

METHODS

One hundred and thirty-two eligible participants (30 with nonproliferative DR (NPDR) and 102 with diabetes with no DR) underwent comprehensive ophthalmic examination, optical coherence tomography for retinal thickness measures, mfERG, and ultra-wide field fundus photography. OCT Early Treatment Diabetic Retinopathy Study (ETDRS) grid was overlaid on to mfERG plots.

RESULTS

Those with NPDR had significantly thicker full retinal measures in the nine (ETDRS) zones compared to no DR. mfERG P1 latencies in rings 1-6 were significantly delayed, while the response densities in rings 4-6 were lower in the NPDR group. Significant negative correlation was noted between OCT thickness and mfERG P1 response densities in many ETDRS zones. Significant positive correlation was noted between P1 latencies and OCT thickness in a few zones. The combination of cystic spaces, microaneurysms, and hard exudates were present in all zones and were associated with a decrease in P1 response densities compared to no lesions. Reduced P1 response densities were associated with a sporadic delay in the mfERG latencies and vice versa. The number of lesions did not show correspondence to the mfERG measures.

CONCLUSIONS

In eyes with NPDR, retinal function is differentially correlated with the DR lesions on OCT and can be assessed using multimodal imaging modalities.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

[Impact of antiangiogenic therapy on ocular blood flow and microcirculation in diabetic macular edema]

Today, diabetic macular edema (DME) is still one of the main causes of vision loss in patients with diabetes.

PURPOSE

To identify changes in the ocular blood flow and microvascular network of the macular zone in patients with DME after antiangiogenic therapy.

MATERIAL AND METHODS

In the course of the study, 25 patients (50 eyes) with monolateral clinically significant DME aged 67.5±3.85 years were examined. Control group consisted of 75 healthy subjects (150 eyes). All patients underwent ultrasound examination of the eyes and orbits (in Color Doppler Imaging (CDI) and Pulse-Doppler modes) and OCT-angiography (OCT-A) before the intravitreal injection of ranibizumab, as well as 3 days, 2 weeks, and 1 month after the treatment.

RESULTS

According to OCT-A, the initial values of microvascular network parameters were significantly below the norm (p<0.05). After intravitreal ranibizumab injection (IRI), no significant changes in the density of microcapillaries or in the parameters of foveal avascular zone (FAZ) were recorded. However, a transient increase of the FAZ area was revealed 2 weeks after the injection, as well as an increase of microcapillaries density in the central quadrant together with a decrease of density in the peripheral quadrants 1 month after IRI. By the end of the follow-up period, a decrease in the initially raised maximum systolic velocity (Vsyst) and resistance index (RI) in the ophthalmic artery (OA) of the affected eye were documented. Additionally, an increase in Vsyst and 2-fold increase in end-diastolic velocity (Vdiast), as well as a decrease in RI in the central retinal artery (CRA) on the affected and paired eyes were detected.

CONCLUSION

The study revealed no negative effects of the angiogenesis inhibitor ranibizumab on retinal microcirculation or ocular blood flow. The registered changes in blood flow may indicate improvement of hemodynamic parameters after resorption of macular edema.

The relationship of dietary fish intake to diabetic retinopathy and retinal vascular caliber in patients with type 2 diabetes

In this cross-sectional study, we evaluated the association of dietary fish intake with varying severity of diabetic retinopathy (DR) and retinal vascular caliber in Asians with type 2 diabetes mellitus. 357 Asians (median age: 58 years; 31% women; 78% Chinese) were recruited from a tertiary eye care institution in Singapore. Fish consumption was evaluated using a validated food frequency questionnaire. Digital retinal photographs assessed for DR severity and retinal vascular caliber. Ordered logistic and linear regression models were used to investigate the association of fish intake with DR severity and vascular caliber. Increasing frequency of fish consumption was significantly associated with lower odds of having severe DR (odds ratio [OR] = 0.91, 95% CI: 0.84–0.99 per 1-unit increase of fish intake; P = 0.038). Among those with no retinopathy, persons in quartile 4 fish intake had a wider retinal vascular caliber for arteriolar (β = 22.27 µm, 95% CI: 12.64–31.90; P-trend < 0.001) and venular (β = 32.00 µm, 95% CI: 17.56–46.43; P-trend < 0.001), than those in quartile 1 fish intake. Persons with higher fish intake had a decreased likelihood of having severe DR. In diabetics without retinopathy, higher fish intake was associated with wider retinal vascular caliber. Future research is needed to reinforce the direction of the casualty.

Retinal blood flow is increased in type 1 diabetes mellitus patients with advanced stages of retinopathy

BACKGROUND

Diabetic retinopathy (DRP) is a common microvascular complication seen in patients with type 1 diabetes mellitus (T1DM). The effects of T1DM and concomitant (proliferative) DRP on retinal blood flow are currently unclear. Therefore, we measured retinal vascular blood flow in T1DM patients with and without DRP and non-diabetic controls. We further assessed the acute effects of panretinal photocoagulation on retinal microvascular bloodflow in eight patients with diabetes.

METHODS

Thirty-three T1DM patients with proliferative DRP, previously treated with panretinal photocoagulation (pDRP), 11 T1DM patients with untreated non-proliferative retinopathy (npDRP) and 32 T1DM patients without DRP (nDRP) were compared with 44 non-diabetic gender-matched controls. Using scanning laser Doppler flowmetry (HRF, Heidelberg) blood flow in the retinal microvasculature was measured temporal and nasal of the optic disc and averaged into one flow value per eye. The right eye was used as a default for further analyses. Eight patients with novel proliferative retinopathy (4 T1DM and 4 with type 2 diabetes) were measured before and several months after photocoagulation. Between-group differences in retinal blood flow were assessed using ANOVA corrected for multiple comparisons (Bonferroni).

RESULTS

Retinal blood flow was higher in the treated pDRP compared with the nDRP group and controls (all P Bonferroni < 0.01). Furthermore, there was a positive linear trend for blood flow with lowest blood flow in the control group and highest in the pDRP group (P-for-trend < 0.01). In the eight patients with novel proliferative retinopathy, blood flow did not significantly change before and after panretinal photocoagulation (P > 0.05). Using regression analysis, no variables were found as predictors of retinal blood flow.

CONCLUSIONS

In comparison with controls and nDRP patients, retinal blood flow significantly increased in the pDRP group, which previously underwent photocoagulation treatment, but not in the npDRP patients. These changes may be a consequence of a failing vascular autoregulation in advanced diabetic retinopathy.

Vascular Dysfunction in Diabetes and Glaucoma: A Complex Relationship Reviewed

Open-angle glaucoma (OAG) is a multifactorial disease characterized by progressive retinal ganglion cell death and visual field loss. Intraocular pressure, ocular perfusion pressure, and systemic vascular irregularities have all been identified as contributing factors for glaucoma onset and progression. Focal and systemic vascular abnormalities have also been well documented in diabetic patients. The relationship between diabetes mellitus and OAG remains enigmatic in the literature. As the pathogenesis of both diabetes mellitus and OAG involves compromised vascular regulation, this review was undertaken to further investigate their precise relationship. A literature review of published population-based studies was performed, with a focus on studies regarding blood flow abnormalities. Although current studies support the role of vascular contributions to both diseases, the association between glaucoma and diabetes yields contrasting results.

Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

Diabetic retinopathy: pathogenic mechanisms and current treatments

Since diabetes is now a global epidemic, the incidence of retinopathy, a leading cause of blindness in patients aged 20-74 years, is also expected to rise to alarming levels. The risk of development and progression of diabetic retinopathy is closely associated with the type and duration of diabetes, blood glucose, blood pressure and possibly lipids. It is an unmet medical need that can lead to severe and irreversible loss of vision in people of working age worldwide. The aim of this review is to give an overview of the clinical and anatomical changes during the progression of retinopathy, the underlying pathogenic mechanisms that link hyperglycemia with retinal tissue damage, current treatments, and the emerging pharmacological therapies for this sight-threatening complication of diabetes.

Retinal blood flow in type 1 diabetic patients with no or mild diabetic retinopathy during euglycemic clamp

OBJECTIVE

To compare total retinal blood flow in diabetic patients with no or mild nonproliferative diabetic retinopathy and healthy control subjects and to investigate in patients whether there is a difference between retinal blood flow before morning insulin and under normoglycemic conditions using a glucose clamp.

RESEARCH DESIGN AND METHODS

Twenty patients with type 1 diabetes with no or mild diabetic retinopathy were included in this open parallel-group study, and 20 healthy age- and sex-matched subjects were included as control subjects. Retinal blood flow was assessed by combining velocity measurements using laser Doppler velocimetry and diameter measurements using a commercially available dynamic vessel analyzer. Measurements were performed before and during a euglycemic clamp.

RESULTS

Total retinal blood flow was higher in diabetic patients (53 +/- 16 microl/min) than in healthy subjects (43 +/- 16 microl/min; P = 0.034 between groups). When plasma glucose in diabetic patients was reduced from 9.3 +/- 1.7 to 5.3 +/- 0.5 mmol/l (P < 0.001) retinal blood flow decreased to 49 +/- 15 microl/min (P = 0.0003 vs. baseline). Total retinal blood flow during the glucose clamp was not significantly different from blood flow in normal control subjects (P = 0.161).

CONCLUSIONS

Type 1 diabetic patients with no or only mild diabetic retinopathy have increased retinal blood flow before their morning insulin dosage. Blood flow is reduced toward normal during euglycemic conditions. Retinal blood flow may fluctuate significantly with fluctuating plasma glucose levels, which may contribute to the microvascular changes seen in diabetic retinopathy.

Topographical alterations of inner retinal activity during systemic hyperoxia-hypercapnia in normal subjects and patients with type 1 diabetes

The purpose of this study was to investigate whether an increase in the circulating oxygen supply can alter inner retinal function, assessed by recordings of multifocal oscillatory potentials. We studied 9 subjects with type 1 diabetes (8 without overt retinopathy, one with 2 microaneurysms) and 10 similar-aged normal subjects. The central 60 degrees of the retina was stimulated by an array of 61 hexagonal elements, and mfOP recordings were obtained while breathing room air or carbogen. First-order kernel analysis of the recordings shows 2 potentials (first-order OP1, OP2), whereas second-order kernel analysis produces 3 potentials (second-order OP1, OP2, OP3). Two methods were used to analyze the results: First, we performed a ring analysis for each subject and measured the amplitudes and latencies of the five potentials. We demonstrate that during carbogen inhalation, the control subjects, but not the patients with diabetes, showed significantly increased second-order OP3 amplitudes, for a retinal ring from around 1.8-13 degrees eccentricity. Secondly, a topographical analysis was performed on the amplitude of the second-order OP3 in all 61 traces (from the average recordings of each subject group), which revealed significant alterations not visible in a ring analysis. A similar topographical analysis of the amplitude of the first-order OP2 revealed a small increase in its amplitude during carbogen inhalation for both subject groups. This study demonstrates that some aspects of inner retinal function are modified by the inhalation of carbogen. The reduced effect of carbogen inhalation on the recordings from the patients with diabetes may be due to compromised vascular perfusion in these subjects.

Effect of a drug combination treatment on ocular perfusion in recurrent idiopathic intermediate uveitis

PURPOSE

To test the effect of a drug combination therapy on ocular perfusion in human eyes affected by idiopathic intermediate uveitis.

METHODS

Seven patients (12 eyes) showing active signs of intermediate uveitis, with at least two more similar episodes reported within the previous 12 months, were enrolled in a prospective case series. Two fellow healthy eyes of two of the enrolled patients were studied as internal controls. Color Doppler imaging of the central retinal artery (CRA), the ophthalmic artery (OA), and the posterior ciliary arteries (PCAs) was performed at the time of enrollment, and at 6 and 12 months after starting treatment with oral fluorocortolone, cyclosporine, and parenteral methotrexate. The best-corrected visual acuity was concurrently measured as a second parameter.

RESULTS

In the 12 affected eyes, the mean visual acuity (+/-SD) improved from 0.15(+/-0.12) to 0.04(+/-0.18) LogMAR (paired samples Student's t-test: p = 0.015). The resistivity index (RI +/- SD) of the CRA decreased from 0.81(+/-0.13) to 0.71(+/-0.13)(p = 0.0091). Further, the variation of the RI in the PCAs reached a borderline significance (p = 0.062), decreasing from 0.71(+/-0.12) to 0.61(+/-0.12). No significant changes were observed in the OA. Moreover, eyes showing a visual improvement of > or =0.1 (LogMAR) were more likely to show a > or =10% improvement of the RI for the CRA (Fisher's exact test: p = 0.018; power = 90%; alpha probability = 5%; odds ratio = 2,4).

CONCLUSIONS

In eyes affected by idiopathic intermediate uveitis, treated with a systemic drug combination therapy, the improvement of the visual acuity seems to correlate with a proportional improvement of the retrobulbar circulation.

Ocular blood flow in diabetes and age-related macular degeneration

The 2 leading causes of blindness in adults in the industrialized nations, diabetic retinopathy and age-related macular degeneration, have been investigated thoroughly with respect to their pathogenesis. In recent years, it has been discovered that dysfunctional ocular microcirculation appears to play a part in the development of both diseases. In diabetic retinopathy, it has been shown that the disease is associated with early retinal vascular dysregulation. In the later states of the disease, retinal tissue hypoxia is a major trigger of sight-threatening neovascularization. In age-related macular degeneration, there is increasing evidence that reduced blood flow in the choroid is associated with the development and progression of the disease. Knowledge of the pathophysiological vascular states underlying these diseases is essential for the assessment and development of future therapies.

Regulation of retinal blood flow in health and disease

Optimal retinal neuronal cell function requires an appropriate, tightly regulated environment, provided by cellular barriers, which separate functional compartments, maintain their homeostasis, and control metabolic substrate transport. Correctly regulated hemodynamics and delivery of oxygen and metabolic substrates, as well as intact blood-retinal barriers are necessary requirements for the maintenance of retinal structure and function. Retinal blood flow is autoregulated by the interaction of myogenic and metabolic mechanisms through the release of vasoactive substances by the vascular endothelium and retinal tissue surrounding the arteriolar wall. Autoregulation is achieved by adaptation of the vascular tone of the resistance vessels (arterioles, capillaries) to changes in the perfusion pressure or metabolic needs of the tissue. This adaptation occurs through the interaction of multiple mechanisms affecting the arteriolar smooth muscle cells and capillary pericytes. Mechanical stretch and increases in arteriolar transmural pressure induce the endothelial cells to release contracting factors affecting the tone of arteriolar smooth muscle cells and pericytes. Close interaction between nitric oxide (NO), lactate, arachidonic acid metabolites, released by the neuronal and glial cells during neural activity and energy-generating reactions of the retina strive to optimize blood flow according to the metabolic needs of the tissue. NO, which plays a central role in neurovascular coupling, may exert its effect, by modulating glial cell function involved in such vasomotor responses. During the evolution of ischemic microangiopathies, impairment of structure and function of the retinal neural tissue and endothelium affect the interaction of these metabolic pathways, leading to a disturbed blood flow regulation. The resulting ischemia, tissue hypoxia and alterations in the blood barrier trigger the formation of macular edema and neovascularization. Hypoxia-related VEGF expression correlates with the formation of neovessels. The relief from hypoxia results in arteriolar constriction, decreases the hydrostatic pressure in the capillaries and venules, and relieves endothelial stretching. The reestablished oxygenation of the inner retina downregulates VEGF expression and thus inhibits neovascularization and macular edema. Correct control of the multiple pathways, such as retinal blood flow, tissue oxygenation and metabolic substrate support, aiming at restoring retinal cell metabolic interactions, may be effective in preventing damage occurring during the evolution of ischemic microangiopathies.

Characteristics of myogenic tone in the rat ophthalmic artery

The pressure-induced constriction in the rat ophthalmic artery was characterized. Ophthalmic arteries were isolated, cannulated in an arteriograph, and pressurized. Arteries developed 25% constriction at 70 mmHg of intraluminal pressure. Arteries maintained almost similar diameter over the range of pressures 50–210 mmHg, and forced dilatation was observed at pressures >210 mmHg. Denudation of endothelium increased the sensitivity of arteries to pressure-induced constriction, and significantly higher myogenic tone was observed in the pressure range of 10–100 mmHg. Indomethacin and cyclooxygenase-2 inhibition by SC-236 decreased myogenic tone, whereas cyclooxygenase-1 inhibition by SC-560 potentiated myogenic tone in a lower concentration range and decreased at a higher concentration. Pressure-induced constriction was completely blocked by 1 μM nifedipine. Phospholipase C inhibition by 6 μM U-73122 decreased myogenic tone by 39%, whereas PKC inhibitor GF-109203X (3 μM) had no effect. Constriction to phenylephrine was significantly decreased by U-73122 (1 μM) and GF-109203X (3 μM) at an intraluminal pressure of 10 mmHg. Rho-kinase inhibition by Y-27632 (30 μM) and HA-1077 (30 μM) decreased myogenic tone by 75% and 73%, respectively, and 1 μM Y-27632 significantly decreased myogenic tone developed in response to graded increases in pressure. These results suggest that rat ophthalmic artery has an efficient pressure-dependent autoregulatory function that is modulated by endothelium. Contribution of phospholipase C-activation to myogenic tone is minimal, whereas Rho-kinase activation plays a predominant role in the myogenic reactivity in this artery.

Effect of atorvastatin on ocular blood flow velocities in patients with diabetic retinopathy

AIM

To investigate blood flow velocities in the ophthalmic and central retinal arteries (CRAs) in patients with diabetic retinopathy before and after atorvastatin treatment.

METHODS

45 patients with type 2 diabetes were included in this double-blind, placebo-controlled study. The patients with diabetes were divided into three subgroups: group 1 (n = 15) included patients with non-proliferative diabetic retinopathy (NPDR); group 2 (n = 15) had patients with proliferative diabetic retinopathy (PDR); and group 3 (n = 15; placebo group) included 8 patients with NPDR and 7 patients with PDR. The patients in groups 1 and 2 (atorvastatin group) received 10 mg atorvastatin daily for 10 weeks. Pre-treatment and post-treatment serum levels of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol and triglyceride were recorded before and after treatment. Ocular blood flow velocities of the ophthalmic artery and CRA were evaluated by colour Doppler imaging before and after treatment in each group.

RESULTS

The baseline haemodynamic parameters were similar between atorvastatin and placebo groups (p>0.05 for both). Atorvastatin significantly decreased serum levels of total cholesterol, low-density lipoprotein cholesterol and triglycerides in groups 1 and 2 compared with pretreatment levels (p<0.001 for both). The mean peak systolic flow velocities (PSVs) of the ophthalmic artery in group 2, and the mean PSV and resistive indices of the CRA in groups 1 and 2 decreased significantly after atorvastatin treatment (p<0.05 for both), whereas the mean end diastolic flow velocity of the ophthalmic artery and CRA did not change (p>0.05). There was no significant difference in ocular blood flow velocities in the placebo group (p>0.05).

CONCLUSION

Atorvastatin may have a role in reducing diabetic retinal complications, with improvement in vascular resistance and decrease in the mean PSVs of the ophthalmic artery and CRA. However, further studies with large numbers of patients are needed to obtain the long-term results of this drug.

Hyperoxia, hyperglycemia, and photoreceptor sensitivity in normal and diabetic subjects

The aim of this study was to investigate the effects of an increase in the saturation of blood oxygen (SaO2) and/or serum glucose on photoreceptor sensitivity in normal subjects and in patients with diabetes mellitus. We monitored cone and rod sensitivity by recording dark-adaptation curves to both green and red test stimuli while inhaling either air (20% O2 + 80% N2) or 100% oxygen in 12 normal subjects and 12 diabetic patients with no (10) or mild (2) retinopathy. We also repeated the experiment in 10 of the normal subjects under hyperglycemia (mean serum glucose: 161 mg/dl). Results show that in normal subjects the dark-adapted cone sensitivity is improved by an increase in SaO2 or by hyperglycemia. Final rod sensitivity is unchanged during hyperoxia and during hyperglycemia when measured with a green test spot. However the kinetics of dark adaptation are altered during hyperglycemia, and an increase in final sensitivity is observed when measured with the red test spot. Inhalation of oxygen during hyperglycemia in normal subjects reduces cone sensitivity compared to that found during hyperglycemia alone (Pasteur effect). In diabetic subjects the dark-adapted cone threshold is comparable to that found in normal subjects, and sensitivity also increases with an increase in SaO2. The final rod threshold, however, is impaired compared to that of the control group, and rod sensitivity is improved by increasing the SaO2. The results suggest that the metabolism of rods and cones may differ in normal subjects: in cones, the rate of metabolism can be augmented by increasing the available oxygen or glucose, whereas rods appear more insensitive to increased blood oxygen saturation and hyperglycemia. In diabetic subjects, both cone and rod metabolism can be increased by supplemental oxygen, indicative of an early rod deficit. The study lends weight to the hypothesis that dark-adapted rods in diabetics are hypoxic before the onset of retinopathy.

Contrast sensitivity and color vision in HIV-infected individuals without infectious retinopathy

PURPOSE

To investigate the relationship between abnormal contrast sensitivity and abnormal color vision among human immunodeficiency virus (HIV)-infected individuals who have normal visual acuity and to seek host factors that predict these abnormalities.

DESIGN

Noninterventional, cross-sectional study.

METHODS

We evaluated 71 HIV-infected subjects with visual acuity of 20/25 or better, clear media, and no vision-threatening retinal lesions. Visual function was determined using the Pelli-Robson contrast sensitivity test and the Farnsworth-Munsell 100-Hue color test (FM-100). Results were compared with published values for normal populations and to measures of HIV disease severity. We evaluated two levels of impairment for each visual function. "Mild dysfunction" was defined as > or =1 standard deviation (SD), but <2 SD from normal means. "Abnormal" was defined as > or =2 SD from normal means.

RESULTS

The prevalences of abnormal contrast sensitivity and abnormal color vision were 7.0% and 9.9%, respectively. We did not identify relationships between impaired contrast sensitivity and impaired color vision. Impaired color vision was associated with increasing age (r = 0.36, P = .002). We could not identify significant correlations between either contrast sensitivity or color vision values and the following factors: current or nadir (lowest previous) CD4+ T-lymphocyte count, HIV blood level, and Karnofsky score.

CONCLUSIONS

Abnormal contrast sensitivity and abnormal color vision can occur independently in HIV-infected individuals and can be present in the absence of severe immunosuppression.

Foveolar choroidal hemodynamics in proliferative diabetic retinopathy

PURPOSE

We studied the choroidal circulation in patients with proliferative diabetic retinopathy (PDR) to assess whether choroidal hemodynamic abnormalities may exist in PDR.

METHODS

Eighteen eyes of 18 patients with PDR and high-risk characteristics for visual loss were included in this study. Mean duration of diabetes was 20 +/- 9 years (mean +/- SD), hemoglobin A1c was 8.9 +/- 2.3%, and blood glucose at the time of blood flow measurement was 188 +/- 90 mg/dl. Choroidal circulatory parameters obtained in these patients were compared to those of 35 eyes of 35 age and blood pressure matched, healthy controls using a Wilcoxon rank sum test. Laser Doppler flowmetry (Oculix) was used to calculate relative choroidal blood velocity (Chvel), volume (Chvol), and flow (Chflow) in the center of the foveola.

RESULTS

No significant differences in average age, mean blood pressure (BPm), or perfusion pressure (PP) were observed between diabetic patients and control subjects. In diabetic patients, Chvol was 0.29 +/- 0.08 (mean +/- 1 SD) arbitrary units (AU); this value was 15% lower than that of control subjects, 0.34 +/- 0.10 AU (p = 0.04). In contrast, average Chvel was not significantly different between subjects with PDR (0.39 +/- 0.07 AU) and control subjects (0.41 +/- 0.07 AU). The average Chflow in subjects with PDR (9.4 +/- 2.9 AU) was 27% lower than that of control subjects (12.8 +/- 4.2 AU; p = 0.003). No significant correlation was detected between the circulatory measurements and age, BPm, or PP. There was a statistically significant negative correlation between duration of diabetes and Chvel (R = -0.55; p = 0.03).

CONCLUSIONS

Our results suggest that Chvol and Chflow are significantly reduced in patients with PDR.

Twelve hour reproducibility of choroidal blood flow parameters in healthy subjects

AIMS/BACKGROUND

To investigate the reproducibility and potential diurnal variation of choroidal blood flow parameters in healthy subjects over a period of 12 hours.

METHODS

The choroidal blood flow parameters of 16 healthy non-smoking subjects were measured at five time points during the day (8:00, 11:00, 14:00, 17:00, and 20:00). Outcome parameters were pulsatile ocular blood flow as assessed by pneumotonometry, fundus pulsation amplitude as assessed by laser interferometry, blood velocities in the opthalmic and posterior ciliary arteries as assessed by colour Doppler imaging, and choroidal blood flow, volume, and velocity as assessed by fundus camera based laser Doppler flowmetry. The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter.

RESULTS

None of the techniques used found a diurnal variation in choroidal blood flow. Coefficients of variation were within 2.9% and 13.6% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 11.2% to 58.8%.

CONCLUSIONS

These data indicate that in healthy subjects the selected techniques provide adequate reproducibility to be used in clinical studies. Variability may, however, be considerably higher in older subjects or subjects with ocular disease. The higher individual differences in flow parameter readings limit the use of the techniques in clinical practice. To overcome problems with measurement validity, a clinical trial should include as many choroidal blood flow outcome parameters as possible to check for consistency.

Ocular blood flow parameters after pars plana vitrectomy in patients with diabetic retinopathy

BACKGROUND

Whereas the anatomic result of vitrectomy in patients with vitreoretinal complications due to diabetes is usually satisfying, the functional outcome is sometimes poor. The authors investigated whether this may be related in part to effects of vitrectomy on ocular perfusion.

METHODS

Ocular hemodynamics were measured before vitrectomy and 1 and 4 weeks postoperatively in 13 consecutive diabetic patients. Pulsatile choroidal blood flow was assessed with laser interferometric measurement of fundus pulsation amplitude. In addition, mean blood flow velocity and resistive index in the ophthalmic artery, the central retinal artery, and the posterior ciliary arteries were measured with color Doppler imaging.

RESULTS

Fundus pulsation amplitude was significantly reduced after surgery as compared to baseline (baseline: 3.7 +/- 1.0 microm; 4 weeks: 3.1 +/- 0.8; P < 0.001). Postoperatively, mean blood flow velocity in the central retinal artery (P = 0.009) and the posterior ciliary arteries (P = 0.0006) was significantly reduced, whereas resistive index was increased in the central retinal artery (P = 0.028) but not in the posterior ciliary arteries.

CONCLUSIONS

The current data suggest that vitrectomy induces significant reductions in ocular blood flow in patients with diabetic retinopathy. Whether this may affect the visual outcome after vitrectomy or whether this reflects improved retinal oxygenation after vitrectomy remains to be established.

Retinopathy in juvenile diabetes: a 10-year (1990-2000) review

Diabetic retinopathy (DR) is the most frequent complication of diabetes and a leading cause of impaired vision in the Western world. There is general agreement that early diagnosis and treatment of DR can slow its progression and help to prevent blindness. However, as a result of its asymptomatic nature and its etiopathogenesis, which is still unclear due to its multifactorial complexity, DR-related blindness has a growing social impact in industrialized countries. Therefore, in order to gain a better understanding of this serious disease, the author performed an updated 10-year review of risk factors and management of DR in type 1 diabetes.