Electrophysiological evidence that early glaucoma affects foveal vision

Correlations between Steady-State Pattern Electroretinogram and Humphrey Visual Field Analyzer Global Indices and Their Associations with Retinal Ganglion Cell Layer-Inner Plexiform Layer Thickness in Glaucoma Suspects

Purpose

The purpose of this study was to investigate the utility of steady state pattern electroretinogram (ss-PERG) in detecting retinal ganglion cell (RGC) dysfunction in glaucoma suspects (GS) who had normal 24-2 Humphrey Visual Fields (HFA).

Materials and Methods

This was a prospective cohort study of GS patients who were identified based on optic disc appearance with normal HFAs. Patients received a complete eye examination, standard automated perimetry (SAP), optical coherence tomography (OCT), and ss-PERG measurements. The ss-PERG parameters, Magnitude (Mag), Magnitude D (MagD), and MagD/Mag ratio, were examined, along with their relationships between HFA and OCT measurements.

Results

Twenty-five patients were included in this study, with a total of 49 eyes. Fifteen eyes had abnormal ss-PERG parameters and when compared to GS eyes with normal ss-PERG parameters, there were significant differences in HFA 24-2, retinal nerve fiber layer (RNFL) thickness, and ganglion cell layer and inner plexiform layer (GCL + IPL) thickness. All ss-PERG parameters were significantly correlated with 24-2 VF mean deviation (MD) and visual field index (VFI), as well as 10-2 VF MD after controlling for age, sex, intraocular pressure, central corneal thickness, and spherical equivalent. When controlled for age, spherical equivalent, and IOP, MagD/Mag ratio significantly contributed to the variance in average GCL + IPL thicknesses, whereas 24-2 VF MD and 10-2 VF MD did not. MagD/Mag ratio also significantly accounted for variance in all macular GCL + IPL sectors, while 10-2 VF MD did not.

Conclusions

ss-PERG has significant correlations with HFA global indices and was predictive of GCL + IPL thickness in GS patients. Clinical Significance. ss-PERG may serve as a useful functional tool for detecting and measuring RGC dysfunction in GS. It appears to be more sensitive than HFA in the detection of early changes in GCL + IPL thicknesses and may be helpful to use in conjunction with current diagnostic studies to improve the ability of monitoring GS progression.

Preferential Loss of Contrast Decrement Responses in Human Glaucoma

Purpose

The purpose of this study was to determine whether glaucoma in human patients produces preferential damage to OFF visual pathways, as suggested by animal experimental models, patient electroretinogram (ERG), and retinal imaging data.

Methods

Steady-state visual evoked potentials (SSVEPs) were recorded monocularly from 50 patients with glaucoma and 28 age-similar controls in response to equal Weber contrast increments and decrements presented using 2.73 hertz (Hz) sawtooth temporal waveforms.

Results

The eyes of patients with glaucoma were separated into mild (better than -6 decibel [dB] mean deviation; n = 28) and moderate to severe (worse than -6 dB mean deviation, n = 22) groups based on their Humphrey 24-2 visual field measurements. Response amplitudes and phases from the two glaucoma-severity groups were compared to controls at the group level. SSVEP amplitudes were depressed in both glaucoma groups, more so in the moderate to severe glaucoma group. The differences between controls and the moderate-severe glaucoma groups were more statistically reliable for decrements than for increments. Mean responses to decremental sawtooth stimuli were larger than those to increments in controls and in the mild glaucoma but not in the moderate to severe glaucoma group at the first harmonic. OFF/decrement responses at the first harmonic were faster in controls, but not in patients.

Conclusions

The observed pattern of preferential loss of decremental responses in human glaucoma is consistent with prior reports of selective damage to OFF retinal ganglion cells in murine models and in data from human ERG and retinal imaging. These data motivate pursuit of SSVEP as a biomarker for glaucoma progression.

The Relationship between Pupillometric Values and Visual Evoked Potential Test Results in Patients with Early Glaucoma

SIGNIFICANCE

Measuring pupil diameter may provide an additional objective method to detect and monitor glaucoma.

PURPOSE

The purposes of this study were to evaluate whether pupillometry can be used in the assessment of glaucomatous damage and to determine whether pupillometer can be used in glaucoma screening.

METHODS

In this retrospective study, patients with early stages of glaucomatous optic neuropathy were tested using visual evoked potential (VEP), standard automated perimetry, and pupillometer. The VEP record was made using two consecutive check sizes (1° and 15') at 1-Hz frequency. Patients with a mean deviation of <-2 and >-6 dB were included in the study. Pupil size measurements were performed under photopic conditions at 60-, 100-, and 130-cd/m luminance levels with the OPD Scan (Nidek, Gamagori, Japan) device.

RESULTS

In all, 24 eyes of 24 patients (14 women and 10 men) with newly diagnosed open-angle glaucoma were included, and 30 eyes of 30 healthy subjects (15 women, 15 men) were used as controls. There was no significant difference between sexes in photopic pupil diameters in either group. Comparing the pupil diameters in different luminance levels, the diameters were significantly larger in the patient group. When age-corrected values in the glaucoma group were compared with an age-matched control group, the differences in P100 latency and amplitudes were statistically significant. There were significant correlations between photopic pupil diameters and timing of VEP waveforms.

CONCLUSIONS

There is a relationship between pupil diameters and VEP results in eyes with early glaucoma.

Macular and Multifocal PERG and FD-OCT in Preperimetric and Hemifield Loss Glaucoma

PURPOSE

To evaluate the ability of macular and multifocal (mf) pattern electroretinogram (PERG) to differentiate preperimetric glaucoma (PG) and glaucoma with hemifield loss (GHL) from controls, to compare the discrimination ability of PERG and fourier-domain optical coherence tomography (FD-OCT), and to assess the relationship between measurements.

PATIENTS AND METHODS

Standard automated perimetry, steady-state and transient PERG and mfPERG measurements were obtained from PG (n=14, 24 eyes), GHL (n=5, 7 eyes), and controls (n=19, 22 eyes). Circumpapillary retinal nerve fiber layer (cpRNFL), full-thickness macula, and segmented macular layer thicknesses on FD-OCT were investigated. Measurements were compared using mixed effects linear models. The relationships between measurements and the diagnostic performance of each technology were assessed.

RESULTS

Compared with controls, average P50 peak time transient PERG responses were reduced in PG and GHL, whereas average latency and amplitude steady-state and mfPERG responses were abnormal only in GHL. cpRNFL and macular thickness measurements in PG and GHL differed significantly from controls. A significant relationship was found between PERG and most FD-OCT or SAP parameters. Partial least squares discriminant analysis revealed that OCT parameters, along with mfPERG and transient PERG parameters had similar ability to discriminate PG and GHL from healthy controls.

CONCLUSIONS

PERG and OCT parameters may be abnormal, with significant correlations between measurements, in PG eyes. Both technologies may be useful for detection of early glaucoma.

PERG and P-VEP after Surgical Trabeculectomy in Primary Open-Angle Glaucoma

Pattern-reversal electroretinograms (PERG) and visual evoked potentials (P-VEP) were measured for 10 eyes from 10 rigorously selected patients with bilateral advanced primary open angle glaucoma (POAG), before and after surgical trabeculectomy. The aim was to establish whether electrofunctional examinations improved after major IOP reduction. Only one eye at random was operated, and the fellow eye was used as control. The aim of this study, using electrofunctional examinations, was to clarify whether ganglion cell damage was reversible after marked reduction of IOP by surgery. The results indicate that glaucomatous damage seems to be irreversible.

Measurement of macular structure-function relationships using spectral domain-optical coherence tomography (SD-OCT) and pattern electroretinograms (PERG)

BACKGROUND

Retinal ganglion cell (RGC) death is a common cause of loss of vision during glaucoma. Pattern electroretinogram (PERG) is an objective measure of the central retinal function that correlates with macular GCL thickness. The aim of this study is to determine possible relationships between the N95 amplitude of pattern electroretinogram (PERGamp) and macular ganglion cell/inner plexiform layer thickness (GCIPLT).

METHODS AND FINDINGS

This was a retrospective and comparative study including 74 glaucoma patients (44 early stage and 30 advanced stage cases) and 66 normal control subjects. Macular GCIPLT was measured using Cirrus spectral domain-optical coherence tomography. Standard automated perimetry and pattern ERGs were used in all patient examinations. Three types of regression analysis (broken stick, linear regression, and quadratic regression) were used to evaluate possible relationships between PERGamp and GCIPLT. Correlations between visual field parameters and GCIPLT were evaluated according to glaucoma severity. The best fit model for the relationship between PERGamp and GCIPLT was the linear regression model (r2 = 0.22; P < 0.001). The best-fit model for the relationship between visual field parameters and GCIPLT was the broken stick model. During early glaucoma, macular GCIPLT was positively correlated with PERGamp, but not with visual field loss. In advanced glaucoma, macular GCIPLT was positively correlated with both PERGamp and visual field loss.

CONCLUSIONS

PERGamp was significantly correlated with macular GCIPT in early glaucoma patients, while visual field performance showed no correlation with GCIPLT. PERGamp can therefore assist clinicians in making an early decision regarding the most suitable treatment plan, especially when GCIPLT is thinning with no change in visual field performance.

M&S Smart System Contrast Sensitivity Measurements Compared With Standard Visual Function Measurements in Primary Open-Angle Glaucoma Patients

PURPOSE

To evaluate the nature and extent of letter contrast sensitivity (CS) deficits in glaucoma patients using a commercially available computer-based system (M&S Smart System II) and to compare the letter CS measurements to standard clinical measures of visual function.

METHODS

Ninety-four subjects with primary open-angle glaucoma participated. Each subject underwent visual acuity, letter CS, and standard automated perimetry testing (Humphrey SITA 24-2). All subjects had a best-corrected visual acuity (BCVA) of 0.3 log MAR (20/40 Snellen equivalent) or better and reliable standard automated perimetry (fixation losses, false positives, and false negatives <33%). CS functions were estimated from the letter CS and BCVA measurements. The area under the CS function (AUCSF), which is a combined index of CS and BCVA, was derived and analyzed.

RESULTS

The mean (± SD) BCVA was 0.08±0.10 log MAR (∼20/25 Snellen equivalent), the mean CS was 1.38±0.17, and the mean Humphrey Visual Field mean deviation (HVF MD) was -7.22±8.10 dB. Letter CS and HVF MD correlated significantly (r=0.51, P<0.001). BCVA correlated significantly with letter CS (r=-0.22, P=0.03), but not with HVF MD (r=-0.12, P=0.26). A subset of the subject sample (∼20%) had moderate to no field loss (≤-6 dB MD) and minimal to no BCVA loss (≤0.3 log MAR), but had poor letter CS. AUCSF was correlated significantly with HVF MD (r=0.46, P<0.001).

CONCLUSIONS

The present study is the first to evaluate letter CS in glaucoma using the digital M&S Smart System II display. Letter CS correlated significantly with standard HVF MD measurements, suggesting that letter CS may provide a useful adjunct test of visual function for glaucoma patients. In addition, the significant correlation between HVF MD and the combined index of CS and BCVA (AUCSF) suggests that this measure may also be useful for quantifying visual dysfunction in glaucoma patients.

Retinocortical Gain in the Foveal Pathway: The Effect of Spatial Frequency and Stimulus Size

The amplitude and the phase of the simultaneously recorded steady-state pattern electroretinogram (PERG) and visual evoked potential (VEP) were evaluated in humans as a function of the vertical diameter (D) of unidimensional Gabor stimuli. In the other dimension, parallel to the horizontal gratings, the patterns all had constant diameter (see Methods and Materials). Spatial frequencies (SFs) of 1 cycle per degree (cpd) and 5.3 cpd were counterphase modulated at a rate of 6.8 Hz. After off-line artifact rejection, the response was subject to Fast Fourier Transformation (FFT). Amplitude and phase of the first and second harmonics of both ERG and VEP were displayed for each SF and stimulus diameter.

Both ERG and VEP amplitude were found to increase as a function of D. Using trend analysis we found that ERG amplitude increased linearly as a function of D. VEP amplitude was found to be both linear and cubic, as a function of D. We calculated the ratio of VEP amplitude and ERG amplitude at each D and termed it retinocortical gain (G). G normalized to stimulus area was high for small D and decreased with D independently of SF. Unity gain occurred at stimulus sizes of 6° to 7°.

ERG phase was found to be more negative at 5.3 cpd than at 1 cpd. Although no significant difference was found between VEP phases at the two SFs tested, neither ERG nor VEP phase changed as a function of D.

The results suggest that retinocortical gain is highest for the foveally centered low spatial frequency small patch Gabors. The results provide support for the notion of the “foveal window” in human vision.

Clinical impact of migraine for the management of glaucoma patients

Migraine is a common and debilitating primary headache disorder that affects 10-15% of the general population, particularly people of working age. Migraine is relevant to providers of clinical eye-care because migraine attacks are associated with a range of visual sensory symptoms, and because of growing evidence that the results of standard tests of visual function necessary for the diagnosis and monitoring of glaucoma (visual fields, electrophysiology, ocular imaging) can be abnormal due to migraine. These abnormalities are measureable in-between migraine events (the interictal period), despite patients being asymptomatic and otherwise healthy. This picture is further complicated by epidemiological data that suggests an increased prevalence of migraine in patients with glaucoma, particularly in patients with normal tension glaucoma. We discuss how migraine, as a co-morbidity, can confound the results and interpretation of clinical tests that form part of contemporary glaucoma evaluation, and provide practical evidence-based recommendations for the clinical testing and management of patients with migraine who attend eye-care settings.

Pattern electroretinograms for the detection of neural loss in patients with permanent temporal visual field defect from chiasmal compression

PURPOSE

To evaluate the ability of full-field and hemifield pattern electroretinogram (PERG) parameters to differentiate between healthy eyes and eyes with band atrophy (BA) of the optic nerve.

METHODS

Twenty-six eyes from 26 consecutive patients with permanent temporal hemianopic visual field defects and BA of the optic nerve from previous chiasmal compression and 26 healthy subjects were studied prospectively. All patients were submitted to an ophthalmic examination including Humphrey 24-2 SITA Standard automated perimetry. Full-field and hemifield (nasal and temporal) stimulation transient pattern electroretinograms (PERG) were recorded using checkerboard screens. Amplitudes and peak times for the P50 and N95 as well as the overall P50+N95 amplitude were measured. The intraocular N95:P50 amplitude ratio was calculated. Comparisons were made using Student's t-test. Receiver operating characteristic (ROC) curves were used to describe the ability of PERG parameters to discriminate the groups.

RESULTS

Full-field P50, N95, and P50+N95 amplitude values were significantly smaller in eyes with BA than in control eyes (P < 0.001). Nasal and temporal hemifield PERG studies revealed significant differences in N95 and P50+N95 amplitudes measurements. No significant difference was observed regarding peak times or N95:P50 amplitude ratios. Nasal and temporal hemifield PERG values did not differ significantly in eyes with BA or in controls. Using the 10th percentile of normals as the lower limit of normal, 16 of 26 eyes were considered abnormal according to the best discriminating parameters.

CONCLUSIONS

Transient PERG amplitude measurements were efficient at differentiating eyes with BA and permanent visual field defects from normal controls. Hemifield stimulation PERG parameters were unable to detect asymmetric hemifield neural loss, but further studies are required to clarify this issue.

Baseline characteristics of the transient pattern electroretinogram in non-human primates: inter-ocular and inter-session variability

This study assessed the inter-ocular and inter-session variability of the transient pattern electroretinogram (PERG) in a group of non-human primates. The transient PERG was measured both eyes of 29 non-human primates, and again after three months in 23 eyes of 23 of these animals. Signals were elicited using a contrast (90%, 75 cdm(-2)) reversing (5 reversals sec(-1)) checkerboard pattern (0.56 cpd). PERGs were also measured for stimuli of varied spatial frequency (n=8, 0.07-2.22 cpd), contrast (n=4, 20-100%), mean luminance (n=4, 4.7-75 cdm(-2)) and defocus (n=5, +1, +2, +3 diopters). The inter-eye and inter-session limits-of-agreement (LOA; 95%) were determined for each PERG parameter. Variability was also compared with previous studies using the coefficient-of-variability (COV). Pharmacological blockade of the inner retinal contributions to the PERG measured under these conditions was conducted in one animal using intravitreal injection of tetrodotoxin (approximately 6 microM) and N-methyl-D-aspartic acid (approximately 6 microM). The N95 component of the primate transient PERG showed spatial tuning, with a peak between 0.14 and 0.28cpd. This spatial tuning was not as apparent for the P50 component. A linear relationship between P50 and N95 amplitude was found with contrast and mean luminance. Both components were attenuated with the introduction of +2 diopters or more of defocus. The inter-session COV for the P50 and N95 components were 23.8 and 19.2%, respectively, while the LOA were 58 and 46%, respectively. The N95:P50 ratio had smaller inter-session variability, was robust to changes in contrast, mean luminance and defocus, and was effective for characterization of inner-retinal dysfunction after pharmacologic block.

Correlation between optical coherence tomography, pattern electroretinogram, and visual evoked potentials in open-angle glaucoma patients

OBJECTIVE

[corrected] To correlate the nerve fiber layer (NFL) thickness and the visual function evaluated by electrophysiologic retinal and cortical responses assessed in open-angle glaucoma (OAG) eyes.

DESIGN

Prospective case-control study.

PARTICIPANTS

Thirty glaucoma patients (mean age, 47.1 +/- 7.15 years; refractive error range, +/- 2 spherical equivalent) with a mean deviation of computerized static perimetry (24/2 Humphrey, Dublin, CA) from -5 to -28 dB and intraocular pressure less than 21 mmHg on pharmacologic treatment and 14 age-matched control participants.

METHODS

Nerve fiber layer thickness was measured by optical coherence tomography. Retinal and visual pathway function was assessed by simultaneously recording pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) using high-contrast (80%) checkerboard stimuli (the single check edges subtend 15 minutes of the visual arc) reversed at the rate of two reversals per second. Linear regression analyses were adopted to establish the correlation between NFL thickness and PERG and VEP parameters.

MAIN OUTCOME MEASURES

Nerve fiber layer thickness measurements in each quadrant (superior, inferior, nasal, and temporal) were taken and then averaged (12 values averaged) and identified as NFL overall, whereas the data obtained in the temporal quadrant only (three values averaged) were identified as NFL temporal. PERG P50 implicit time and P50-N95 amplitude and VEP P100 implicit time and N75-P100 amplitude were also measured.

RESULTS

In OAG eyes, we found a significant (P < 0.01) reduction in NFL thickness in both NFL overall and NFL temporal evaluations with respect to the values observed in control eyes. PERG and VEP parameters showed a significant (P < 0.01) delay in implicit time and a reduction in peak-to-peak amplitude. In OAG eyes, the NFL overall and NFL temporal values were significantly correlated (P < 0.01) with the PERG P50 implicit time and P50-95 peak-to-peak amplitude. No correlations (P > 0.01) between NFL values and VEP parameters were found.

CONCLUSIONS

There is a correlation between PERG changes and NFL thickness, but there is no correlation between VEP changes and NFL thickness in patients affected by OAG.

Impaired visual function in glaucoma

OBJECTIVE

This work aims to evaluate whether glaucomatous visual field defects could be related to an impaired retinal function, to a delayed neural conduction in postretinal visual pathways, or both.

METHODS

Visual field by Humphrey perimeter (central 24-2 threshold test) and simultaneous recordings of visual evoked potential (VEP) and pattern electroretinogram (PERG) were assessed in 21 subjects with open angle glaucoma (POAG) and in 15 age-matched controls (C).

RESULTS

VEP: in POAG eyes we found P100 latency significantly (P<0.01) delayed when compared with controls and correlated with mean deviation (index of global visual field damage, MD) of 24-2 Humphrey perimetry (P<0.001); the P100 amplitudes were significantly (P<0.01) lower in POAG eyes than in control eyes and correlated with MD (P<0.001). PERG: POAG eyes showed P50 latency significantly (P<0.01) delayed when compared with controls and correlated with MD (P=0.002); the P50 and N95 amplitudes were significantly (P<0.01) lower in POAG than in control eyes and correlated with MD (P50: P=0.006; N95: P=0.002). Retinocortical time (RCT: difference between VEP P100 and PERG P50 latencies) and latency window (LW: difference between VEP N75 and PERG P50 latencies) were significantly (P<0.01) longer in POAG eyes than in control eyes and correlated with MD (RCT: P<0.001; LW: P<0.001). No significant correlations (P>0.05) were found between electrophysiological parameters and the corrected pattern standard deviation (index of localized visual field damage) of 24-2 Humphrey perimetry.

CONCLUSION

In patients with open angle glaucoma the reduction of the index of global visual field damage (MD) could be ascribed to two sources of functional impairment: one retinal (impaired PERG) and one postretinal (delayed RCT and LW). In the postretinal impairment, a postsynaptic degeneration at the level of the lateral geniculate nucleus could be suggested.

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 nicergoline on the retinal and cortical electrophysiological responses in glaucoma patients: a preliminary open study

PURPOSE

The retinal dysfunction and the delayed visual cortex responses shown by patients affected by glaucoma can be objectively assessed by Pattern Electroretinogram (PERG) and Visual Evoked Potentials (VEP) recordings. The present study aims to evaluate the effects of nicergoline on the retinal function and on the visual cortical responses in glaucoma patients.

METHODS

Sixty patients (mean age 44.6+/-3.7) with open angle glaucoma were enrolled. The patients were divided into two groups: NG Group, where 30 patients were treated with nicergoline (Cebran((R)), 2 cps day) for 30 days; and CG Group, where 30 patients were not treated. Simultaneous recordings of PERG and VEP were performed in NG patients at the baseline, at 30 days after treatment with nicergoline (day 30), and at 45 days from the end of the treatment (day 75). PERG and VEP were recorded in CG patients at the baseline and after 30 and 75 days. The visual stimulus for recording PERGs and VEPs was a checkerboard whose elements subtended a visual arc of 60' and 15' with a 70% contrast, and alternated at a frequency of 2 Hz.

RESULTS

At the baseline none of the electrophysiological parameters observed in NG Group patients differed (P>0.05) from those of CG Group patients. At days 30 and 75, in CG Group patients the values of the PERG and VEP parameters were unmodified (P>0.05) with respect to the baseline. In NG Group patients, the 30-day treatment period with nicergoline induced a significant (P<0.01) improvement of the PERG and VEP parameters. At day 75 all the electrophysiological parameters of NG Group did not differ significantly (P>0.05) from those at the baseline.

CONCLUSION

Treatment with nicergoline induces an improvement of the retinal function and of the visual cortical responses in patients affected by glaucoma. This effect disappears within 45 days after the suspension of the treatment.

Cytidine-5'-diphosphocholine (citicoline) improves retinal and cortical responses in patients with glaucoma

PURPOSE

To evaluate the effects of cytidine-5'-diphosphocholine (citicoline) on retinal function and on cortical responses in patients with glaucoma.

DESIGN

Randomized clinical trial.

PARTICIPANTS

Forty patients with open-angle glaucoma were randomly divided into two age-matched groups: citicoline group ([GC] n = 25) and placebo group ([GP] n = 15).

METHODS

The GC patients were treated with Neuroton (citicoline, 1000 mg/day intramuscularly) for 60 days; GP patients were treated with placebo (physiologic solution with additives) for 60 days. After 120 days of washout (day 180), the GC patients were divided into two age-matched groups: in 10 patients (GC1 group) the washout was prolonged for a further 120 days; in 15 patients (GC2 group) a second 60-day period of citicoline treatment was followed by a second 120-day period of washout. At day 180, the washout was extended for another 180 days in GP patients. In all subjects, retinal and cortical responses were evaluated by simultaneous recordings of visual evoked potentials (VEPs) and pattern-electroretinograms (PERGs) at baseline, after 60 days, and after 180 days. At day 300, VEPs and PERGs were also evaluated in GC1 patients, and at 240 and 360 days in GC2 and GP patients.

MAIN OUTCOME MEASURES

Visual evoked potential parameters (P100 latency and N75-P100 amplitude); PERG parameters (P50 latency and P50-N95 amplitude); and intraocular pressure.

RESULTS

The GP patients displayed similar VEP and PERG parameters in all examinations performed. In GC patients, the treatment with citicoline induced a significant (P < 0.01) improvement of VEP and PERG parameters, and their values were significantly different (P < 0.01) with respect to those of GP patients (P < 0.01). Visual evoked potentials and PERGs, recorded in GC patients after washout, revealed that although there was a worsening trend, the electrophysiologic improvement was still maintained. After a second period of washout, GC1 patients had VEP and PERG parameters similar (P > 0.05) to baseline ones and to those of GP patients. In GC2 patients, a second period of citicoline treatment induced a further (P < 0.01) improvement of VEP and PERG parameters

CONCLUSION

Citicoline may induce an improvement of the retinal and of the visual pathway function in patients with glaucoma.

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.

Little correlation of the pattern electroretinogram (PERG) and visual field measures in early glaucoma

Pattern-electroretinograms (PERG) to checkerboard reversal at 16/s. 0.8 degrees and 15 degrees check size and visual fields (Octopus G1) were retrospectively analyzed in 40 eyes of 30 patients with early glaucoma. The mean visual field defect was calculated separately for the central 26 degrees x 34 degrees covered by the PERG stimulus (MDc) and the more peripheral area (MDp) surrounding the stimulus. Deeper field loss was correlated with a reduced pattern electroretinogram amplitude (p < 0.01 for both MDp and MDc), indicating that the pattern electroretinogram deteriorates as glaucoma advances. If the analysis was confined to those 18 eyes (16 patients) that had no field defect within the area covered by the PERG stimulus (normal MDc but abnormal MDp), 13 of these had an abnormal PERG amplitude (p < 0.001). The results suggest that the PERG can reveal impairment of ganglion cell function that is not detected by conventional perimetry.

Responses to chromatic and luminance contrast in glaucoma: a psychophysical and electrophysiological study

Increasing anatomical evidence indicates that large retinal ganglion cells (M-cells) are preferentially damaged in primary open angle glaucoma (OAG), while the smaller ganglion cells (P-cells) are relatively spared. In 13 patients with defined OAG and modest visual field defects, we evaluated the responses to stimuli that are expected to involve primarily the function of the P-pathway and compared them with those of control subjects. The psychophysical contrast sensitivity (CS), the PERG and the VEPs were measured for red-green gratings of pure chromatic contrast, as well as yellow-black gratings of pure luminance contrast. As compared with controls, OAG patients had reduced CS for both luminance and chromatic contrast stimuli by about 6 dB. PERGs and VEPs to luminance stimuli were little affected, whereas those to chromatic stimuli were both reduced in amplitude and delayed. These results indicate that visual dysfunction in glaucoma is not selective for the M-pathway, and that responses to equiluminant colour-contrast stimuli may be of diagnostic value.

Neural conduction in the visual pathways in ocular hypertension and glaucoma

BACKGROUND

The aim of our work was to evaluate neural conduction in visual pathways in subjects with ocular hypertension and glaucoma.

METHODS

We assessed simultaneous recordings of pattern electroretinograms (PERG) and visual evoked potentials (VEP) in 16 subjects with ocular hypertension (OHT), in 16 subjects with primary open-angle glaucoma (POAG) and in 15 age-matched controls. The visual stimuli were checkerboard patterns (the check edges subtend 15 min of visual arc; contrast 70%) reversed at the rate of 2 reversals/s.

RESULTS

In OHT and POAG patients we found PERG and VEP latencies significantly longer than in controls. The P50-N95 PERG amplitudes were significantly reduced in OHT and POAG eyes. VEP amplitudes were significantly reduced in POAG eyes, while in OHT they were similar to controls. The retinocortical time (RCT; difference between VEP P100 latency and PERG P50 latency) was longer in POAG patients than in controls; no differences between patients with OHT and controls were observed. Moreover, we observed that in POAG the longer RCT was inversely related to the PERG amplitude.

CONCLUSION

Our results suggest that involvement of the innermost retinal layers in POAG is accompanied by slowed neural conduction in the visual pathways.

Electrophysiological methods in early glaucoma detection

Electrophysiological methods like pattern electroretinogram and pattern visual evoked potentials may be the best approach for early glaucoma detection, as they have demonstrated to be sensitive to the ganglion cells functional changes. Reported values of both P50 and N95 pattern electroretinogram components differ widely, a fact perhaps related to a heterogeneous grouping of patients suffering from ocular hypertension and glaucoma, rather than to the type of technique utilized. This study is based on a total of 42 subjects: 14 normals, 16 subjects suffering from ocular hypertension, and 12 patients with glaucoma, with 79 eyes examined. Pattern electroretinogram and pattern visual evoked potentials were used as successive techniques. Setting condition for pattern electroretinogram, such as low temporal frequency (2 Hz), 30 min check size, high contrast (99%) and luminance (93 cd/m2), identified the N95 component as the best index for early glaucoma detection. In the control group N95 mean amplitude was 1.62 muV +/- 0.59 SD and showed almost significant difference with ocular hypertension (p = 0.07) and highly significant difference with the glaucoma group (p < 0.01), with decrement of 58.6% in the glaucoma group. P50 mean amplitude, on the contrary, did not show significant differences among the groups (Newman-Keul test), its reduction in glaucoma being 28%. The mean pattern visual evoked potentials latency was alos highly significant between glaucoma and control groups, but not between ocular hypertension and control groups; the mean amplitude did not show significant differences. A proportion of 26.6% abnormal pattern electroretinogram was found in the group suspected of having glaucoma where conventional methods had proved normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of electrofunctional data following argon-laser trabeculoplasty in primary open-angle glaucoma

To establish whether or not glaucomatous damage is reversible, we obtained pattern-reversal electroretinograms (PERGs) and visual evoked potentials (VEPs) in 25 eyes of 25 patients suffering from bilateral primary open-angle glaucoma (POAG) before and after argon-laser trabeculoplasty. The laser treatment was carried out in only one eye chosen at random, and the fellow eye was used as a control. In the present study we intended to verify the possibility of using electrofunctional techniques to determine the two distinct and, probably, consecutive glaucomatous alterations occurring in ganglion cells: functional (reversible) and anatomical (irreversible). The results obtained indicate that glaucomatous damage is irreversible. We propose that such alterations differ very slightly and that the current electrofunctional techniques may not be sufficiently sophisticated to distinguish between them.

Association of Vistech contrast sensitivity and visual field findings in glaucoma

Single eye visual fields and contrast sensitivity were assessed in 60 subjects, who were being followed up in a glaucoma clinic for manifest glaucoma or a suspicion of glaucoma because of raised intraocular pressure. The Fieldmaster 5000 (static/kinetic perimeter) was used for the visual fields, and a Vistech wall chart sine wave grating test was used for contrast sensitivity measurements. The subjects were divided into three groups--defect (D), suspect (S) and normal (N)--on the basis of their perimetric findings by subjective grading of 16 perimetric scoring categories for each visual field. The mean Vistech sensitivity levels were not found to be significantly different between the D, S, and N field subgroups at any of the five spatial frequencies provided on the test charts (1.5, 3, 6, 12, and 18 cycles per degree). Complex algorithms combining results from two or more spatial frequencies also failed to yield any significant differences between the groups. Diagnostic sensitivity and specificities relating Vistech contrast sensitivity findings to groups N and D never concomitantly exceeded 60%.

The pattern electroretinogram

Physiological experiments and the exploitation of clinical conditions have provided compelling evidence that retinal ganglion cells and other inner retinal structures generate the pattern ERG (PERG). As an increasing number of clinical reports have been published some contradictory findings have been reported. These may be ascribed to variation in recording and measuring techniques. The PERG consists of two major portions, the early positive and the following negative component which can be investigated separately if the stimulus conditions allow isolated (or "transient") responses to be recorded. Care has to be taken in positioning the reference electrode, maintaining accurate refraction, and the influence of pupil size must be considered. Furthermore the PERG is contaminated by a luminance component which may be generated in the outer retina. The size of this increases with low spatial frequency (large check-sizes) and high mean luminance. The PERG permits the examination of an additional level of the retina and helps the understanding of pathophysiology of various eye diseases, and is of clinical importance in routine diagnosis and assessment. In glaucoma the PERG amplitude is often reduced before it is possible to detect a scotoma and it is therefore an important prognostic indicator in patients with ocular hypertension. In diabetic retinopathy, retinal ischaemia sufficient to lead to the pre-proliferative state can be demonstrated. The PERG also has a major clinical role in examining localised retinal pathology. If combined with VECP recording, it greatly extends the interpretations possible, since not only can damage to the optic nerve be detected by both tests, but the normal PERG in the presence of an abnormal PVECP implies that the losses are confined to the central pathway.