Electrophysiological assessment of visual function in IDDM patients

Visual Dysfunction in Diabetes

Although diabetic retinopathy (DR) is clinically diagnosed as a vascular disease, many studies find retinal neuronal and visual dysfunction before the onset of vascular DR. This suggests that DR should be viewed as a neurovascular disease. Prior to the onset of DR, human patients have compromised electroretinograms that indicate a disruption of normal function, particularly in the inner retina. They also exhibit reduced contrast sensitivity. These early changes, especially those due to dysfunction in the inner retina, are also seen in rodent models of diabetes in the early stages of the disease. Rodent models of diabetes exhibit several neuronal mechanisms, such as reduced evoked GABA release, increased excitatory glutamate signaling, and reduced dopamine signaling, that suggest specific neuronal deficits. This suggests that understanding neuronal deficits may lead to early diabetes treatments to ameliorate neuronal dysfunction.

Visual Evoked Potentials for the Detection of Diabetic Retinal Neuropathy

Visual evoked potentials (VEP) are visually evoked signals that extract electroencephalographic activity in the visual cortex that can detect retinal ganglion cells, optic nerves, chiasmal and retrochiasmal dysfunction, including optic radiations, and the occipital cortex. Because diabetes causes diabetic retinopathy due to microangiopathy and neuropathy due to metabolic abnormalities and intraneural blood flow disorders, assessment of diabetic visual pathway impairment using VEP has been attempted. In this review, evidence on the attempts to assess the visual pathway dysfunction due to abnormal blood glucose levels using VEP is presented. Previous studies have provided significant evidence that VEP can functionally detect antecedent neuropathy before fundus examination. The detailed correlations between VEP waveforms and disease duration, HbA1c, glycemic control, and short-term increases and decreases in blood glucose levels are evaluated. VEP may be useful for predicting postoperative prognosis and evaluating visual function before surgery for diabetic retinopathy. Further controlled studies with larger cohorts are needed to establish a more detailed relationship between diabetes mellitus and VEP.

Optic Nerve Regeneration in Diabetic Retinopathy: Potentials and Challenges Ahead

Diabetic retinopathy (DR), the most common microvascular compilation of diabetes, is the leading cause of vision loss and blindness worldwide. Recent studies indicate that retinal neuron impairment occurs before any noticeable vascular changes in DR, and retinal ganglion cell (RGC) degeneration is one of the earliest signs. Axons of RGCs have little capacity to regenerate after injury, clinically leading the visual functional defects to become irreversible. In the past two decades, tremendous progress has been achieved to enable RGC axon regeneration in animal models of optic nerve injury, which holds promise for neural repair and visual restoration in DR. This review summarizes these advances and discusses the potential and challenges for developing optic nerve regeneration strategies treating DR.

Involvement of High Mobility Group Box 1 Protein in Optic Nerve Damage in Diabetes

Introduction

Diabetic patients routinely have high levels of high mobility group box 1 (HMGB1) protein in their plasma, vitreous and ocular membranes, which is strongly correlated with subclinical chronic inflammation in the eye. Our previous work has suggested that high HMGB1 in diabetes plays a role in retinal inflammation and angiogenesis, but its role in the optic nerve damage is unclear. Therefore, our goal is to examine the role of HMGB1 in optic nerve damage in diabetes.

Methods

Gene expression of HMGB1 was quantified in the optic nerve from streptozotocin-induced diabetic mice by qRT-PCR, and their protein expressions by Western blot analysis and immunofluorescence staining. Using immunohistochemical technique, expression of reactive astrogliosis (indicator of neuroinflammation) and nerve demyelination/damage were determined by quantifying glial fibrillary acid protein (GFAP) and myelin basic protein (MBP), respectively. The role of HMGB1 in the optic nerve damage and alteration visual pathways was confirmed in mice receiving glycyrrhizin, a HMGB1 inhibitor. Similar parameters were measured in the optic nerve from human donors with diabetes.

Results

Compared to normal mice, diabetic mice exhibited increased levels of HMGB1, higher GFAP expression, and decreased MBP in the optic nerve. Double immunofluorescence microscopy revealed that diabetes induced increased HMGB1 immunoreactivities were significantly colocalized with GFAP in the optic nerve. Glycyrrhizin supplementation effectively reduced HMGB1 and maintained normal axonal myelination and visual conduction. Results from mice optic nerve confirmed the results obtained from human donors with diabetes.

Discussions

Thus, diabetes-induced HMGB1 upregulation promotes optic nerve demyelination and inflammation. The regulation of HMGB1 activation has potential to protect optic nerve damage and the abnormalities of visual pathways in diabetic patients.

Clinical electrophysiology of the optic nerve and retinal ganglion cells

Clinical electrophysiological assessment of optic nerve and retinal ganglion cell function can be performed using the Pattern Electroretinogram (PERG), Visual Evoked Potential (VEP) and the Photopic Negative Response (PhNR) amongst other more specialised techniques. In this review, we describe these electrophysiological techniques and their application in diseases affecting the optic nerve and retinal ganglion cells with the exception of glaucoma. The disease groups discussed include hereditary, compressive, toxic/nutritional, traumatic, vascular, inflammatory and intracranial causes for optic nerve or retinal ganglion cell dysfunction. The benefits of objective, electrophysiological measurement of the retinal ganglion cells and optic nerve are discussed, as are their applications in clinical diagnosis of disease, determining prognosis, monitoring progression and response to novel therapies.

Reproducibility of Fixed-luminance and Multi-luminance Flicker Electroretinography in Patients With Diabetic Retinopathy Using an Office-based Testing Paradigm

BACKGROUND

We evaluated the reproducibility of office-based flicker electroretinography (ERG) in patients with nonproliferative diabetic retinopathy (NPDR).

METHODS

An observational study was conducted in which ultra-widefield fluorescein angiography (UWF-FA) was performed on 20 patients with mild-to-moderate NPDR; images were graded by the Fundus Photography Reading Center (Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, WI, USA). Fixed- and multi-luminance flicker ERG was repeated four times (greater than or equal to seven days apart). Recording consistency was assessed using intra-class correlation coefficients (ICCs), coefficients of variation, and Pearson correlations.

RESULTS

82.5% and 17.5% of eyes had mild and moderate NPDR using UWF-FA; 90% of the angiograms were given a high confidence grade. Fixed-luminance phase values were highly reproducible (ICC: 0.949; P < .001). There was a significant negative correlation between fixed-luminance phase and log-corrected ischemic index values (-0.426; P = .015).

CONCLUSIONS

Office-based, fixed-luminance phase values are highly reproducible and negatively correlate with retinal ischemia in NPDR, suggesting that global retinal dysfunction may be reliably quantified early in patients with diabetes.

The effects of early diabetes on inner retinal neurons

Diabetic retinopathy is now well understood as a neurovascular disease. Significant deficits early in diabetes are found in the inner retina that consists of bipolar cells that receive inputs from rod and cone photoreceptors, ganglion cells that receive inputs from bipolar cells, and amacrine cells that modulate these connections. These functional deficits can be measured in vivo in diabetic humans and animal models using the electroretinogram (ERG) and behavioral visual testing. Early effects of diabetes on both the human and animal model ERGs are changes to the oscillatory potentials that suggest dysfunctional communication between amacrine cells and bipolar cells as well as ERG measures that suggest ganglion cell dysfunction. These are coupled with changes in contrast sensitivity that suggest inner retinal changes. Mechanistic in vitro neuronal studies have suggested that these inner retinal changes are due to decreased inhibition in the retina, potentially due to decreased gamma aminobutyric acid (GABA) release, increased glutamate release, and increased excitation of retinal ganglion cells. Inner retinal deficits in dopamine levels have also been observed that can be reversed to limit inner retinal damage. Inner retinal targets present a promising new avenue for therapies for early-stage diabetic eye disease.

Neuroinflammation and oxidative stress act in concert to promote neurodegeneration in the diabetic retina and optic nerve: galectin-3 participation

Diabetes is a lifelong disease characterized by glucose metabolic imbalance, in which low insulin levels or impaired insulin signaling lead to hyperglycemic state. Within 20 years of diabetes progression, 95% of patients will have diabetic retinopathy, the leading cause of visual defects in working-age people worldwide. Although diabetes is considered a microvascular disease, recent studies have shown that neurodegeneration precedes vascular changes within the diabetic visual system, albeit its mechanisms are still under investigation. Neuroinflammation and oxidative stress are intrinsically related phenomena, since macrophage/microglia and astrocytes are the main sources of reactive oxygen species during central nervous system chronic degenerative diseases, and both pathological processes are increased in the visual system during diabetes. The present review will focus on recent findings of the contribution of oxidative stress derived from neuroinflammation in the early neurodegenerative aspects of the diabetic visual system and their relationship with galectin-3.

Citicoline and Retinal Ganglion Cells: Effects on Morphology and Function

BACKGROUND

Retinal ganglion cells (RGCs) are the nervous retinal elements which connect the visual receptors to the brain forming the nervous visual system. Functional and/or morphological involvement of RGCs occurs in several ocular and neurological disorders and therefore these cells are targeted in neuroprotective strategies. Cytidine 5-diphosphocholine or Citicoline is an endogenous compound that acts in the biosynthesis of phospholipids of cell membranes and increases neurotransmitters' levels in the Central Nervous System. Experimental studies suggested the neuromodulator effect and the protective role of Citicoline on RGCs. This review aims to present evidence of the effects of Citicoline in experimental models of RGCs degeneration and in human neurodegenerative disorders involving RGCs.

METHODS

All published papers containing experimental or clinical studies about the effects of Citicoline on RGCs morphology and function were reviewed.

RESULTS

In rodent retinal cultures and animal models, Citicoline induces antiapoptotic effects, increases the dopamine retinal level, and counteracts retinal nerve fibers layer thinning. Human studies in neurodegenerative visual pathologies such as glaucoma or non-arteritic ischemic neuropathy showed a reduction of the RGCs impairment after Citicoline administration. By reducing the RGCs' dysfunction, a better neural conduction along the post-retinal visual pathways with an improvement of the visual field defects was observed.

CONCLUSION

Citicoline, with a solid history of experimental and clinical studies, could be considered a very promising molecule for neuroprotective strategies in those pathologies (i.e. Glaucoma) in which morpho-functional changes of RGCc occurs.

Evaluation of visual pathways using visual evoked potentials in the patients with impaired fasting glucose and impaired glucose tolerance

PURPOSE

There are many studies on degeneration of the ganglion cells using visual evoked potential (VEP) in Diabetes mellitus (DM). The present study intended to investigate whether the retinopathy findings would be helpful for detecting the degeneration to develop or not in retinal ganglion cells with the VEP test before being detectable in ophthalmoscopic examination on prediabetic patients.

MATERIALS AND METHODS

The present study was conducted prospectively after obtaining approval from the Ethics Committee. In our study, the subjects were divided into three groups as impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and normal patients. They also underwent physical, ophthalmological and VEP examination. Three main components of VEP obtained from these groups were N75, P100, and N145 latency and N75-P100 amplitude.

RESULTS

The study participants consisted of the IFG group (n: 30, female/male ratio: 21/9; mean age: 49.17 ± 10.52 years), the IGT group (n: 30, female/male ratio: 23/7; mean age: 47.00 ± 11.09 years), and the Control Group (n: 40, female/male ratio: 30/10; mean age: 48.03 ± 10.96 years). Difference in sex and age between the study groups (p > 0.05). P100 latency was found to increase significantly in comparison between the IGT and Control Group for both eyes (p right: 0.003, p left: 0.001) whereas it did not increase significantly in the comparison between the IFG and the Control Group (p right: 0.065, p left: 0.116).

CONCLUSION

It was observed that VEP may be a parameter of predictive value that might be used in evaluating prediabetic cases in terms of retinopathies similar to DM.

Further Evidence for the Utility of Electrophysiological Methods for the Detection of Subclinical Stage Retinal and Optic Nerve Involvement in Diabetes

OBJECTIVE

To assess the utility of visual electrophysiological methods, visual evoked potentials (VEPs) and pattern electroretinograms (PERGs) were recorded for the detection of subclinical optic nerve and retinal involvement in patients with diabetes mellitus.

SUBJECTS AND METHODS

The data of 63 patients (126 eyes) with no vascular retinopathy or optic neuropathy were retrospectively analyzed. The patients were divided into polyneuropathic/nonpolyneuropathic groups to differentiate between early and late subclinical stages. The recorded parameters were compared with local reference values.

RESULTS

116 eyes (92%) had VEP and 76 (60%) had PERG abnormalities. The most frequent alteration was latency delay, but waveform and amplitude irregularities were also observed. The simultaneous use of the two methods allowed us to differentiate abnormal VEPs of purely optic nerve origin from those reflecting retinal involvement.

CONCLUSIONS

We suggest that regular electrophysiological screening should receive more attention in the ophthalmological care of diabetic patients.

Identifying cell class specific losses from serially generated electroretinogram components

Purpose. Processing of information through the cellular layers of the retina occurs in a serial manner. In the electroretinogram (ERG), this complicates interpretation of inner retinal changes as dysfunction may arise from “upstream” neurons or may indicate a direct loss to that neural generator. We propose an approach that addresses this issue by defining ERG gain relationships. Methods. Regression analyses between two serial ERG parameters in a control cohort of rats are used to define gain relationships. These gains are then applied to two models of retinal disease. Results. The PIII_amp to PII_amp gain is unity whereas the PII_amp to pSTR_amp and PII_amp to nSTR_amp gains are greater than unity, indicating “amplification” (P < 0.05). Timing relationships show amplification between PIII_it to PII_it and compression for PII_it to pSTR_it and PII_it to nSTR_it, (P < 0.05). Application of these gains to ω-3-deficiency indicates that all timing changes are downstream of photoreceptor changes, but a direct pSTR amplitude loss occurs (P < 0.05). Application to diabetes indicates widespread inner retinal dysfunction which cannot be attributed to outer retinal changes (P < 0.05). Conclusions. This simple approach aids in the interpretation of inner retinal ERG changes by taking into account gain characteristics found between successive ERG components of normal animals.

Retinal function in the von Hippel-Lindau disease

PURPOSE

To assess the retinal function in patients with von Hippel-Lindau disease (VHL).

PATIENTS

Studies were undertaken in 12 patients (17 eyes) with detected VHL gene mutation and 12 normal healthy controls (17 eyes).

METHODS

Pattern ERG (PERG), standard flash electroretinogram (ERG) recordings were performed in accordance with the International Society for Clinical Electrophysiology of Vision (ISCEV) standards.

RESULTS

In VHL patients, electrophysiological statistically significant changes were found. In PERG examination, increased latency of P50 was found in the total VHL group (p < 0.02) and in the VHL subgroup with retinal angiomas (p < 0.04). In ERG examination, photopic b-wave latency was increased in the total VHL group (p < 0.03) and also in the VHL subgroup without retinal angiomas (p < 0.05). In OPs, latency increase of OP2, OP3 waves and reduced amplitude of OP3 wave in the total VHL group (OP2 latency, p < 0.05; OP3 latency, p < 0.01; OP3 amplitude, p < 0.03) and in the VHL subgroup with retinal angiomas (OP2 latency, p < 0.02; OP3 latency, p < .008; OP3 amplitude, p < 0.02) were obtained.

CONCLUSIONS

It can be hypothesized that dysfunction of the inner retinal layer is present in individuals with VHL disease even in patients without retinal angiomas.

Analysis of sigma receptor (sigmaR1) expression in retinal ganglion cells cultured under hyperglycemic conditions and in diabetic mice

The type 1 sigma receptor (sigmaR1) is a nonopiate and nonphencyclidine binding site that has numerous pharmacological and physiological functions. In some studies, agonists for sigmaR1 have been shown to afford neuroprotection against overstimulation of the NMDA receptor. sigmaR1 expression has been demonstrated recently in retinal ganglion cells (RGC). RGCs undergo apoptosis early in diabetic retinopathy via NMDA receptor overstimulation. In the present study we asked whether RGCs cultured under hyperglycemic conditions and RGCs of diabetic mice continue to express sigmaR1. RGCs were cultured 48 h in RPMI medium containing either 45 mM glucose or 11 mM glucose plus 34 mM mannitol (osmolar control). C57BL/6 mice were made diabetic using streptozotocin. The retina was dissected from normal and streptozotocin-induced diabetic mice 3, 6 and 12 weeks post-onset of diabetes. sigmaR1 was analyzed in cells using semiquantitative RT-PCR and in tissues by semiquantitative RT-PCR, in situ hybridization, Western blot analysis and immunolocalization. The RT-PCR analysis of cultured RGCs showed that sigmaR1 mRNA is expressed under hyperglycemic conditions at levels similar to control cells. Similarly, analysis of retinas of diabetic mice showed no difference in levels of mRNA encoding sigmaR1 compared to retinas of control mice. In situ hybridization analysis showed that expression patterns of sigmaR1 mRNA in the ganglion cell layer were similar between diabetic and control mice. Western blot analysis suggested that levels of sigmaR1 in retina were similar between diabetic and control retinas. Immunohistochemical analysis of sigmaR1 showed a similar pattern of sigmaR1 protein expression between control and diabetic retina. These studies demonstrate that sigmaR1 is expressed under hyperglycemic conditions in vitro and in vivo.

Morphological and functional retinal impairment in Alzheimer's disease patients

OBJECTIVE

Our study aims to assess the optic nerve fiber layer thickness in vivo, the function of the innermost retinal layer and whether a correlation exists between morphological and functional parameters in patients affected by Alzheimer's Disease (AD).

METHODS

Seventeen AD patients (mean age 70.37+/-6.1 years, best corrected visual acuity >8/10 with refractive error between +/-3 sf, intra-ocular pressure (IOP)<18 mmHg) were enrolled. They were compared to 14 age-matched controls. Nerve fiber layer (NFL) thickness was measured by optical coherence tomography (OCT). Three different measurements in each quadrant (superior, inferior, nasal, and temporal) were taken and averaged. The data in all quadrants (12 values averaged) were identified as NFL Overall. Retinal function was assessed by pattern electroretinogram (PERG) recordings using high-contrast (80%) checkerboard stimuli subtending 15 min of the visual arc and reversed at the rate of two reversals/s.

RESULTS

In AD eyes, there was a significant (P<0.01) reduction in NFL thickness in each quadrant and in the NFL Overall evaluation compared with the values observed in control eyes. PERGs showed a significant (P<0.01) delay in N35, P50 and N95 implicit times, and reduction in N35-P50 and P50-N95 amplitudes. NFL Overall values were significantly correlated (P<0.01) to the PERG P50 and N95 implicit times and P50-N95 amplitude. No correlations (P>0.01) between NFL values and other PERG parameters (N35 implicit time, N35-P50 amplitude) were found.

CONCLUSIONS

Our results suggest that in AD patients, there is a reduction of NFL thickness evaluated in vivo by OCT and this morphological abnormality is related to a retinal dysfunction as revealed by abnormal PERG responses.

Electrophysiological evaluation of the macular cone adaptation: VEP after photostress. A review

In the present review, the methodologies and clinical applications of the visual evoked potentials (VEPs) after photostress, will be described. Photostress induces transient VEP changes consisting of an increase in response latency and a decrease in amplitude. When serial VEP recordings are obtained at discrete time intervals (i.e., every 20 s) after bleaching, the recovery of VEP waveform can be evaluated. The time needed for the VEP to recover to the pre-bleach, baseline status (recovery time after photostress) ranges in normal subjects between 68 and 78 s. Patients with different pathologies (maculopathies, ocular hypertension and glaucoma, diabetes with or without retinopathy, multiple sclerosis with optic neuritis) showed an abnormal response after photostress (higher increase in latency and decrease in amplitude and longer recovery time) with respect to age-matched controls. Our results indicate that the VEPs after photostress represent an objective, although not specific, index of the dynamic properties of macular performance after exposure to intense light stimulation.

Visual electrophysiological responses in persons with type 1 diabetes

Persons with type 1 diabetes show electrophysiological abnormalities of the visual system which are revealed by methods such as flash electroretinogram (FERG), oscillatory potentials (OPs), pattern electroretinogram (PERG), focal electroretinogram (focal ERG), visual evoked potentials (VEP) in basal condition and after photostress. This review reports the changes in electrophysiological responses of the different structures composing the visual system observed in persons with type 1 diabetes before the development of the overt clinical retinopathy. In persons with type 1 diabetes without retinopathy (IDD), the earlier abnormal electrophysiological responses are recorded from the innermost retinal layers and postretinal visual pathways, as suggested by impaired PERGs and delayed retinocortical time (RCT). These are observed in IDD persons with a disease duration shorter than 6 months. Further electrophysiological changes are recorded from the macula (abnormal focal ERG and VEP after photostress) in IDD persons with disease duration greater than 1 year. Additional electrophysiological changes are recorded from the middle and outer retinal layers (impaired FERG and OPs) in IDD persons with a disease duration greater than 10 years. All the electrophysiological tests show a greater degree of abnormal responses in persons with type 1 diabetes when a background retinopathy is present.

Effect of acute hyperglycemia on visual cortical activation as measured by functional MRI

To determine whether acute hyperglycemia changes the hyperemic response to functional activation of brain, the area and magnitude of the activation were measured in healthy volunteers maintained at euglycemia and then at hyperglycemia using the hyperglycemic clamp technique. Activation of the visual cortex (8-16 Hz) was assessed by functional MRI with blood oxygenation level dependent (BOLD) contrast using a 4 Tesla magnet and a multi-slice echo-planar imaging sequence (TE = 30 msec, TR = 1.5 sec). At euglycemia (4.8 +/- 0.2 mM, mean +/- SEM, n = 6), the number of activated pixels in the occipital lobe was 79 +/- 10 and the intensity of activation was 4.5 +/- 0.5%. During hyperglycemia (plasma glucose 300% of control), the number of activated pixels was 90 +/- 20% of control and the BOLD activation was 3.5 +/- 0.3%, respectively. The change in BOLD signal was below 0.2%/mM plasma glucose. This study demonstrates that acute hyperglycemia is without substantial effect on the size and intensity of activation of the occipital cortex. The results further suggest that fluctuations in blood glucose within the physiologic range are without effect on the functional activation of the cerebral cortex measured by BOLD fMRI.

Fluorescein-ERG, a sensitive method for the detection of vascular damage in diabetic patients

The purpose of this paper was to provide evidence for the reintroduction of simultaneously performed fluorescein angiography and electroretinography in the detection of diabetic retinopathy. ERG observations were made in conjunction with fluorescein angiography of 13 patients suffering from type I diabetes mellitus for five to 13 years. Only patients without any fluorescein leakage during angiography and without any morphologic changes in the fundus were involved in the study. Gold foil electrodes were used for recording. A stroboscopic lamp provided flashing light stimulation through a monochromatic blue filter. Intravenous fluorescein administration caused an immediate reduction in the ERG response. This reduction was seen both in the control subjects and in diabetes patients. In the control group, the reduction was over in 30-45 min, while in the diabetes group a considerable amplitude elevation was seen in all recordings between 15 and 60 min post-fluorescein. In the adaptation control group, where only repeated ERG recordings were employed every 15 min, a slight decrease in the a wave and a slight elevation of the b wave were observed during the whole recording period. No complaints or side-effects were detected during the observations. As all the patients displayed a normal fluorescein angiography besides elevated b wave after fluorescein administration, and this elevation was seen exclusively in the diabetic group, our study raises the possibility that this diagnostic method can be used in the detection of diabetic retinopathy.

Impaired saccadic eye movement in diabetic patients: the relationship with visual pathways function

The aim of this study was to evaluate whether a correlation existed between saccadic eye movements and visual pathways function in diabetic patients. Saccadic or fast Eye Movement System (EMS) and Visual Evoked Potentials (VEPs) were assessed in 20 insulin-dependent diabetic mellitus (IDDM) patients without long-term complications and in stable metabolic control and in 21 age-matched control subjects. In IDDM patients we observed significantly (p<0.01) longer EMS latency, while EMS velocity and accuracy were similar to those of controls; VEPs showed a significant delay in N75, P100, N145 latencies and significant reduction of N75-P100 and P100-N145 amplitudes. In IDDM patients no relationships between EMS and VEP parameters were found. In conclusion, EMS latency delay suggests an impairment of the saccadic eye movement system, while impaired VEPs may be ascribed to a dysfunction of the visual pathways. The lack of correlation between VEPs impairment and EMS latency delay suggests that in our IDDM patients the delay of saccadic latency cannot be exclusively related to a visual pathways dysfunction and could be ascribed to a diffuse neuronal involvement.

Visual electrophysiological responses in subjects with cerebral autosomal arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

OBJECTIVES

To evaluate visual electrophysiological responses in subjects with cerebral autosomal arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL).

METHODS

Three subjects (one male and two females, mean age 55.3+/-2.9 years) belonging to an Italian family already diagnosed with CADASIL through clinicopathological and genetic studies and 14 control subjects (6 males and 8 females, mean age 52.7+/-3.6 years) were enrolled in the study. Flash electroretinogram (ERG), oscillatory potentials (OPs) and simultaneous recordings of pattern electroretinogram (PERG) and visual evoked potentials (VEPs) were assessed in all 3 subjects with CADASIL and age-matched controls.

RESULTS

Subjects with CADASIL showed: reduced ERG, OP and PERG (N35-P50, P50-N95) amplitudes with respect to our normal limits; delayed PERG (N35, P50) and VEP (P100) implicit times when compared with our normal limits; and VEP (N75-P100) amplitudes and retinocortical times within our normal limits.

CONCLUSIONS

Subjects with CADASIL present a dysfunction in the outer, middle and innermost retinal layers when the index of neural conduction in the postretinal visual pathways is normal. The delay in visual cortical responses observed in subjects with CADASIL may be ascribable to retinal impairment with a possible functional sparing of the postretinal visual structures.

Electrophysiological evaluation of the macular cone system: focal electroretinography and visual evoked potentials after photostress

In this article, the methodologies and clinical applications of two electrophysiological tests, the focal electroretinogram (FERG) and the visual evoked potentials (VEPs) after photostress, are described. These techniques provide somewhat complementary results about macular function because they tap the activity of different neural substrates along the pathway of the cone system and allow evaluation of the macular function under steady-state (ie, the FERG) or dynamic (ie, the VEPs after photostress) conditions. The results obtained in patients with different macular pathologies indicate that while the FERG provides direct information about the extent and sites of macular dysfunction, the VEPs after photostress represent an objective, although not specific, index of the dynamic properties of macular performance after exposure to intense light stimulation. The combined use of both techniques appears to be promising for gaining further insights into the diagnosis and pathophysiology of macular diseases.

Neural conduction in visual pathways in newly-diagnosed IDDM patients

OBJECTIVES

Visual evoked potentials (VEPs) show abnormal responses in newly-diagnosed insulin-dependent diabetic (IDDM) patients. Electrophysiological methods allow one to dissect and explore different structures contributing to neural conduction in the visual pathways. The aim of our work was to assess whether the VEP abnormalities are due to impaired function of the retinal layers and/or a delayed conduction in the postretinal visual pathways.

METHODS

Simultaneous recordings of VEP and pattern-electroretinogram (PERG) were performed at two intervals (at entry of the study and after 3 months) in 14 newly-diagnosed IDDM patients (age: 24.8+/-6.8 years; duration of disease: 3+/-1.5 months), and in 14 age-matched control subjects.

RESULTS

In comparison with control subjects, IDDM patients showed: VEP P100 latencies significantly delayed (P < 0.01), a significant impairment of all PERG parameters (P < 0.01) and retinocortical time (RCT, difference between VEP P100 and PERG P50 latencies) and latency window (LW, difference between VEP N75 and PERG P50 latencies) also significantly increased (P < 0.01). All electrophysiological parameters were not significantly changed when retested after 3 months. No correlations were found between VEP P100 latency, RCT, LW and PERG parameters.

CONCLUSIONS

Impaired PERG indicates an involvement of the innermost retinal layers; increased values of RCT and LW represent an index of delayed neural conduction in the postretinal visual pathways. Therefore two sources, one retinal (impaired PERG) and one postretinal (delayed RCT and LW), may independently contribute in to the abnormal responses of VEP observed in newly-diagnosed IDDM patients. Three months of relatively-stable metabolic control have not normalized the VEP and PERG impairment.

Impaired VEP after photostress response in multiple sclerosis patients previously affected by optic neuritis

The aim of our work was to evaluate if an optic nerve involvement (multiple sclerosis patients previously affected by optic neuritis) may induce any change in visual evoked potential (VEP) after photostress response. VEP in basal conditions and after photostress were assessed in 10 patients with defined multiple sclerosis without a history of optic neuritis (MSWO); in 14 patients with defined multiple sclerosis previously affected by optic neuritis but with complete recovery of the visual acuity (MSON) and in 14 age-matched controls. In order to complete the investigation of the retinal function, Transient Pattern electroretinogram (PERG) and steady-state focal-ERG (counterphased gratings presented at 8 Hz in the macular region) were performed in MSON patients only. In MSWO eyes VEP parameters in basal condition and after photostress did not undergo significant changes compared to controls (ANOVA; P > 0.05). In MSON eyes we observed basal VEP with delayed P100 peak latency and reduced N75-P100 amplitude when compared with the control ones (P < 0.01). In MSON eyes the parameters of VEP after photostress underwent large changes and longer recovery time (RT) than in control and MSWO eyes (P < 0.01). In addition; in MSON eyes we found increased transient PERG P50 latency (P < 0.01) and reduced P50-N95 amplitude (P < 0.01); Focal-ERG (that displays a major component at 16 Hz; 2nd harmonic:2P) with reduced 2P amplitudes and delayed 2P phases (P < 0.01). Our results indicate that patients previously affected by optic neuritis present an abnormal VEP after photostress response and this may be ascribed predominantly to an involvement of the inner retinal layers as indicated by the concomitant impairment of PERG and focal-ERG responses.