VEP pattern after photostress: an index of macular function

Protective Effects of Adeno-associated Virus Mediated Brain-derived Neurotrophic Factor Expression on Retinal Ganglion Cells in Diabetic Rats

Adeno-associated virus vector plasmid carrying the expression cassette of brain-derived neurotrophic factor (BDNF), pAAV-BDNF, was constructed and packaged into recombinant adeno-associated virus (rAAV-BDNF). The rAAV-BDNF was intravitreally injected into streptzotocin (STZ)-induced diabetic Sprague-Dawley (SD) Rats. Data showed that over-expression of BDNF could increase alive retinal ganglion cell (RGC) number and improve its function in streptzotocin(STZ)-induced diabetic rats, which might be a new method to treat diabetic neuropathy and retinopathy.

[Ocular ischemic syndrome]

Ocular ischemic syndrome (OIS) is a group of ocular diseases caused by chronic artery occlusion usually involving the internal carotid artery. Patients suffer from visual loss and pain. OIS is a rare disease which can be confounded with diabetic retinopathy or an older central retinal vein occlusion. The only therapy is to treat the neovascular complications. Due to the high mortality of OIS patients, medical and neurological examinations are mandatory. We discuss the clinical findings and diagnostic and therapeutic options of OIS patients in this paper.

Evaluation of retinal function using the Dynamic Focal Cone ERG

The development of effective means of assessing visual function in retinal disease holds the key to improved understanding of pathogenesis, and better monitoring of treatment outcomes. In diseases such as age-related macular degeneration, in which the primary locus of dysfunction is the outer retina, tests which provide a direct measure of the functional integrity of the photoreceptor/retinal pigment epithelium (RPE) complex are of great importance. Recovery of retinal function following adaptation to a bright light requires the healthy function of photoreceptors, RPE, Bruch's membrane and choroidal circulation, making an assessment of this recovery a potentially useful clinical tool. However, current techniques are either subjective in nature, or are influenced by post-retinal processing of visual information. This report describes a novel technique, the 'Dynamic Focal Cone Electro-retinogram (ERG)', which allows direct, objective assessment of the recovery of macular function following photopigment bleach. A series of 41 Hz ERGs was recorded, and ERG amplitude was plotted as a function of time following cessation of the bleach. Normative data was collected from 10 healthy subjects. For all subjects, there was no measurable ERG immediately after the bleach, but the amplitude had returned to a pre-bleach level within 4 min. The amplitude recovery data were adequately described both by an exponential recovery function and by a model based on a rate-limited recovery process. We conclude that this technique provides a clinically applicable, objective measure of outer retinal recovery.

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.

Effects of antiepileptic drugs on evoked potentials in epileptic children

To evaluate the visual and auditory function in children and adolescents who are undergoing monotherapy with sodium valproate, carbamazepine, and phenobarbital visual-evoked potentials and brainstem auditory-evoked potentials were measured in 58 epileptic patients (30 males and 28 females), ages 13.7 +/- 6.9 years. Fifty healthy sex- and age-matched children served as controls. The measurements were performed before the beginning of therapy and after 12 months. Before the beginning of therapy, there were no significant differences in visual- and auditory-evoked potentials between the control group and the three groups of epileptic children. After 12 months of therapy, patients treated with carbamazepine demonstrated a significant (P < 0.001) increase of P100 latencies when compared with baseline data and control values; moreover, these patients exhibited a significant increase of peak latencies of waves I-III-V and interpeak interval I-V at auditory second evaluation. The patients treated with sodium valproate manifested a significant (P < 0.05) increase in VEP P100 latencies. On the contrary, children receiving phenobarbital did not manifest any significant abnormality at visual- and auditory-evoked potentials measurements. Our study demonstrates that for patients treated with carbamazepine and sodium valproate, an electrophysiologic dysfunction of visual and auditory sensory pathways can be present after 12 months of treatment.

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.

Extrafoveal photostress recovery test in glaucoma and idiopathic central serous chorioretinopathy

BACKGROUND/AIMS

A photostress recovery test was designed to differentiate macular diseases from optic nerve disorders, but recently an abnormal recovery time was reported in glaucoma. The purpose of this study was to search for the difference in abnormality of the photostress recovery test between glaucoma and idiopathic central serous chorioretinopathy (ICSC).

METHODS

This study involved 21 normal subjects, 14 patients, with ICSC and 10 patients with primary open angle glaucoma (POAG). A scanning laser ophthalmoscope (SLO) was used with microperimetry for bleaching the test point and measuring the recovery of sensitivity. Photostress recovery time (SLO-PSRT) could be measured at extrafoveal points outside and inside the affected area. The initial sensitivity change and the time constant of recovery after bleaching were calculated by fitting an exponential equation to the data.

RESULTS

In normal subjects, neither the initial sensitivity change nor the time constant were correlated with the location of the test point. In 14 patients with ICSC, the initial sensitivity change in the detached area was significantly smaller than that in the unaffected area which was not significantly different from that in the age matched normal subjects. The time constant in the detached area was significantly longer than that in the unaffected area, which was not significantly different from that in the normal subjects. In 10 patients with POAG, the initial sensitivity change inside and outside the scotoma was not significantly different from that of age matched normal subjects. The time constant inside the scotoma was significantly longer than that outside the scotoma, which was not significantly different from that of the age matched normal subjects.

CONCLUSION

Both ICSC and POAG showed a prolonged time constant of recovery, but the initial sensitivity change was reduced only in ICSC. The difference in our results between ICSC and POAG may be caused by the difference of the retinal pathology. Further, the SLO-PSRT is very useful when the lesion is located outside the fovea.

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.

Electrophysiological assessment of visual function in IDDM patients

Various electrophysiological tests have been employed to reveal functional abnormalities at different levels of the visual system in insulin-dependent diabetic (IDDM) patients. The aim of our work was to assess, with a comprehensive neurophysiological protocol evaluating the retinal, macular and visual pathways functions, whether and when such electrophysiological abnormalities do appear in IDDM patients free of any fluorangiographic sign of retinopathy with various disease duration. Flash-electroretinogram (ERG), oscillatory potentials (OPs), pattern-electroretinogram (PERG), and visual evoked potentials (VEPs) in basal condition and after photostress were assessed in 12 control subjects (C) and 42 aged-matched IDDM patients without clinical retinopathy (DR-) divided, on the basis of the disease duration, into 4 groups (1-5, 6-10, 11-15, 16-20 years). In addition another age-matched group of IDDM patients with a background retinopathy (DR+; n = 12; duration of disease 18 +/- 49 years) was evaluated. In all IDDM DR-patients PERG and VEP were significantly impaired. In addition, groups 11-15 and 16-20 years displayed impaired OPs. All electrophysiological parameters were further impaired in DR+ patients. In conclusion, retinal, macular and visual pathways functions are differently impaired in IDDM (DR-) patients with different disease duration. Electrophysiological impairment starts in the nervous conduction of the visual pathways with an early involvement, goes on in the innermost retinal layers and in the macula and ends in the middle and outer retinal layers.

Electrophysiological assessment of visual function in newly-diagnosed IDDM patients

Electrophysiological tests (electroretinogram, oscillatory potentials, visual evoked potentials, in the basal condition and after photostress) reveal an abnormal function of the visual system in insulin-dependent diabetic (IDDM) patients. The aim of our work was to assess whether electrophysiological abnormalities in visual function exist in newly-diagnosed diabetic patients free of any fluorangiographic signs of retinopathy. Ten control subjects (age 28.7 +/- 2.44 years) and then IDDM patients (age 25.2 +/- 6.78 years; disease duration 5.3 +/- 3.5 months) in stable metabolic control (HbA1C 7.5 +/- 1.1%) were evaluated. Flash-electroretinograms and oscillatory potentials were similar in both groups. Visual evoked potentials (VEP) recorded under basal conditions showed that P100 latency was significantly increased in the diabetic patients compared to control subjects (p < 0.01), while N75-P100 amplitude was similar in both groups. The recovery time of VEP after photostress was equivalent in diabetic patients and control subjects. The impaired basal VEPs suggest an early involvement of the nervous conduction in the optic nerve. However, the preserved flash-electroretinogram and the normal recovery time after photostress indicate that a short disease duration does not induce physiopathological changes in the outer retinal layers or in the macular function.

The pupil photostress test

PURPOSE

An objective, pupillographic photostress test was developed to assess the initial sensitivity loss and its rate of recovery in healthy eyes and in eyes affected by optic neuropathy.

METHODS

Pupillary light reflexes were recorded with an infrared pupillometer after a binocular photostress that subtended 30 degrees of the central visual field. The initial loss of light sensitivity (in log units) and its recovery with time were derived by analyzing subsequent increases in pupil contraction amplitude to a series of alternating light stimuli. The effects of photostress duration and intensity were studied in ten control subjects. Photostress recovery also was compared between eyes of nine patients with unilateral optic neuropathy.

RESULTS

In the ten control subjects, increasing photostress duration caused significantly increased sensitivity loss at time zero after the photostress (analysis of variance), but did not significantly affect the exponential recovery rate. Intense photostress brightness caused more initial sensitivity loss than did dimmer photostress lights. In addition, half-time of sensitivity recovery was prolonged after the brightest photostress. In nine patients with unilateral optic neuropathy, a 120-second photostress caused significantly less initial sensitivity loss in the affected eye than in the healthy fellow eye.

CONCLUSIONS

The pupil photostress test objectively can measure the eye's loss of light sensitivity after a photostress and its exponential rate of recovery. Loss of optic nerve function diminishes the initial stress-induced loss of light sensitivity and does not significantly affect the poststress rate of recovery in the patients tested.

A novel noninvasive videographic method for quantifying changes in the chromaticity of the optic nerve head with changes in the intraocular pressure, pulsatile choroidal blood flow and visual neural function in humans

Vision loss in glaucoma may be due to the compressive effects of the intraocular pressure (IOP) on the ganglion cell axons, impaired blood flow to the optic nerve, or some combination of these two factors. While reducing the IOP may preserve vision in patients with elevated IOP, not all patients experience longterm benefits from this therapeutic approach. The survival of ganglion cells may be more dependent upon the degree of vascular perfusion of the optic nerve head (ONH). In this report we present some preliminary data on a new noninvasive videographic technique for elaborating the capacity of the ONH vasculature to maintain perfusion constancy in the presence of transient elevations of the IOP and reductions of the ocular perfusion pressure (OPP). Shortterm, stepwise reductions of the OPP in the test eye of visually normal subjects (n = 5) systematically altered both the chromaticity (hue, saturation, brightness) of the ONH and the pulsatile ocular blood flow (POBF) in the choroid. Similar transient reductions in the OPP were seen to impair normal retinal physiology, as indicated by a significant attenuation of the bilateral pattern-reversal electroretinograms (pERGs) in visually normal subjects (n = 7). This technique was also used to reveal spontaneous rhythmical variations in the ONH chromaticity which were linked to the cardiac pulse rate. This so-called "chromatic pulse" of the ONH offers potential as a useful clinical index for evaluating the vascular perfusion of the ONH. The diagnostic and prognostic potential of dynamic digital imaging for the detection of abnormal hemodynamics in the ONH is discussed.

Visual evoked potentials after photostress in insulin-dependent diabetic patients with or without retinopathy

Visual evoked potentials (VEPs) were assessed under basal conditions and after photostress in normal control subjects, in insulin-dependent diabetic patients with retinopathy (IDDPWR) and in insulin-dependent diabetic patients without retinopathy (IDDP). The VEPs recorded under basal conditions showed a P100 latency significantly higher in IDDP and IDDP-WR eyes than in control eyes and in IDDPWR than in IDDP eyes (P < 0.01). N75-P100 amplitude was significantly lower in IDDP and IDDPWR eyes than in control eyes (P < 0.01). No difference was recorded in the N75-P100 amplitudes between IDDP and IDDPWR eyes. In all eyes, the VEPs recorded after photostress showed an increase in latency and a decrease in amplitude. In both IDDPWR eyes and IDDP eyes VEPs recorded at 20, 40 and 60 s after photostress showed higher mean increments in P100 latency than in C control eyes, and IDDPWR eyes showed higher mean increments in P100 latency than IDDP eyes (IDDP vs control P < 0.01, IDDPWR vs control P < 0.01, IDDPWR vs IDDP P < 0.017). The mean reductions in amplitude observed at 20, 40 and 60 s after photostress in IDDP and IDDPWR eyes were lower than in control eyes (IDDP vs control P = 0.01, IDDPWR vs control P < 0.01, IDDPWR vs IDDP P < 0.01). VEPs were superimposable on the basal VEP (recovery time) at 73.9 s in control eyes, at 88.17 s in IDDP eyes and at 113.3 s in IDDPWR eyes. VEPs after photostress in IDDP patients with normal visual acuity and no fluorangiographic signs of retinopathy may show multiple modifications. This may indicate the presence of an early functional deficiency of the central retinal layers.

The effects of altered retinal vascular perfusion pressure on the white flash scotopic ERG and oscillatory potentials in man

The oscillatory potentials (OPs) of the flash-elicited electroretinogram b-wave have been identified as sensitive indices of abnormalities within the retinal circulation. A recent study by Lovasik and Kothe has identified the rod system as being more vulnerable than the cone system to transient alterations of the retinal vascular perfusion pressure (RVPP). In view of these previous findings, we investigated the susceptibility of the scotopic OPs to altered retinal perfusion, in 10 normotensive paid volunteers between 21 and 31 years of age. A transient increase in RVPP was effected by body inversion, while a transient decrease in RVPP was obtained by suction ophthalmodynamometry. Group averaged data showed that OP-1 to OP-4 decreased in amplitude with either an increase or a decrease in RVPP. In contrast to all other OPs, OP-5 was reduced to a greater degree when RVPP was decreased and showed a pronounced gain in amplitude as RVPP was increased. Our study has isolated a component-specific vulnerability to altered retinal perfusion. This finding may be interpreted as indicating a different retinal site of origin for the generators of OP-5. The heightened sensitivity of OP-5 to alteration of the RVPP may offer diagnostic advantage for investigating chronic diseases causing retinal ischemia.