Pattern electroretinogram abnormality and glaucoma

Structural and Functional Evaluations for the Early Detection of Glaucoma

The early detection of glaucoma is imperative in order to preserve functional vision. Structural and functional methods are utilized to detect and monitor glaucomatous damage and the vision loss it causes. The relationship between these detection measures is complex and differs between individuals, especially in early glaucoma. Using both measures together is advised in order to ensure the highest probability of glaucoma detection, and new testing methods are continuously developed with the goals of earlier disease detection and improvement of disease monitoring. The purpose of this review is to explore the relationship between structural and functional glaucoma detection and discuss important technological advances for early glaucoma detection.

Bilateral Glaucomatous Optic Neuropathy Caused by Eye Rubbing

In this report, we describe a particular condition of a 52-year-old man who showed advanced bilateral glaucomatous-like optic disc damage, even though the intraocular pressure resulted normal during all examinations performed. Visual field test, steady-state pattern electroretinogram, retinal nerve fiber layer and retinal tomographic evaluations were performed to evaluate the optic disc damage. Over a 4-year observational period, his visual acuity decreased to 12/20 in the right eye and counting fingers in the left eye. Visual fields were severely compromised, and intraocular pressure values were not superior to 14 mm Hg during routine examinations. An accurate anamnesis and the suspicion of this disease represent a crucial aspect to establish the correct diagnosis. In fact, our patient strongly rubbed his eyes for more than 10 h per day. Recurrent and continuous eye rubbing can induce progressive optic neuropathy, causing severe visual field damage similar to the pathology of advanced glaucoma.

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.

Photopic negative response in diagnosis of glaucoma: an experimental study in glaucomatous rabbit model

AIM

To determine whether the photopic negative response (PhNR) elicited by transient white flash on white background is characterizing for glaucoma model in rabbits.

METHODS

Glaucoma was induced in twelve rabbits by subconjunctival injection of 0.05 mL of betamethasone in right eyes (each 1 mL contain betamethasone dipropionate 5 mg and betamethasone sodium phosphate 2 mg).The intraocular pressure (IOP), electroretinogram (ERG) and visual evoked potential (VEP) were measured successively prior and on the 3, 7d, two weeks and four weeks postglaucoma induction. After four weeks, the animals were sacrificed and the globes were histopathologically examined.

RESULTS

The IOP increased significantly after one week (P=0.0001), then it gradually returned to the control level. In ERG examination, the means of a and b wave amplitude and latency were not affected significantly. PhNR amplitude decreased significantly within one week (P=0.0001), but its latency was not affected significantly (P=0.132). The means of VEP latency and amplitude were significantly affected after two weeks and four weeks of glaucoma induction (P=0.0001 and 0.02, respectively). The histopathologic examination of the globes showed reduced number of cells in the retinal ganglion cell layer with multiple vacuoles in the retinal nerve fibre layer.There was significant positive correlation between ganglion cell layer cells and PhNR amplitude (r=0.8, P=0.002).

CONCLUSION

The rise in IOP resulted in irreversible changes or incomplete recovery of VEP and PhNR amplitude. Both PhNR and VEP represented good additional tools in early diagnosis of glaucoma.

Can Variability of Pattern ERG Signal Help to Detect Retinal Ganglion Cells Dysfunction in Glaucomatous Eyes?

Objective. To evaluate variability of steady-state pattern electroretinogram (SS-PERG) signal in normal, suspected, and glaucomatous eyes. Methods. Twenty-one subjects with suspected glaucoma due to disc abnormalities (GS), 37 patients with early glaucoma (EG), and 24 normal control (NC) were tested with spectral-domain optical coherence tomography (SD-OCT), standard automated perimetry (SAP), and SS-PERG. Mean deviation (MD), pattern standard deviation (PSD), retinal nerve fiber layer (RNFL), and ganglionar complex cells (GCC) were evaluated. The SS-PERG was recorded five consecutive times and the amplitude and phase of second harmonic were measured. PERG amplitude and coefficient of variation of phase (CVphase) were recorded, and correlation with structural and functional parameters of disease, by means of one-way ANOVA and Pearson's correlation, was analysed. Results. PERG amplitude was reduced, as expression of retinal ganglion cells (RGCs) dysfunction, in EG patients and GS subjects compared to NC patients (P < 0.0001). CVphase was significantly increased in EG patients and GS subjects, compared to healthy (P < 0.0001), and it was also correlated with PSD (P = 0.0009), GCC (P = 0.028), and RNFL (P = 0.0078) only in EG patients. Conclusions. Increased intrasession variability of phase in suspected glaucomatous eyes may be a sign of RGCs dysfunction.

Treatment with citicoline eye drops enhances retinal function and neural conduction along the visual pathways in open angle glaucoma

PURPOSE

To evaluate the retinal function and the neural conduction along the visual pathways after treatment with citicoline eye drops in patients with open angle glaucoma (OAG).

METHODS

Fifty-six OAG patients (mean age 52.4 ± 4.72 years, IOP <18 mmHg with beta-blocker monotherapy only) were enrolled. Of these, 47 eyes completed the study: 24 OAG eyes were treated with topical citicoline (OMK1®, Omikron Italia, 3 drops/day) (GC eyes) over a 4-month period (month 4) followed by a 2-month period of citicoline wash-out (month 6), and another 23 OAG eyes were only treated with beta-blocker monotherapy (GP eyes). In GC and GP eyes, pattern electroretinogram (PERG) and visual evoked potentials (VEP) were assessed at baseline and at months 4 and 6 in both groups.

RESULTS

At baseline, similar (ANOVA, p > 0.01) PERG and VEP values in GC and GP eyes were observed. After treatment with topical citicoline, a significant (p < 0.01) increase of PERG P50-N95 and VEP N75-P100 amplitudes, and a significant (p < 0.01) shortening of VEP P100 implicit times were found. In GC eyes, the shortening of VEP P100 implicit times was correlated significantly (p < 0.01) with the increase of PERG P50-N95 amplitudes. After a 2-month period of topical Citicoline wash-out, PERG and VEP values were similar (p > 0.01) to baseline ones. GP eyes showed not significant changes of PERG and VEP values during the entire follow-up.

CONCLUSIONS

Topical treatment with citicoline in OAG eyes induces an enhancement of the retinal bioelectrical responses (increase of PERG amplitude) with a consequent improvement of the bioelectrical activity of the visual cortex (shortening and increase of VEP implicit time and amplitude, respectively).

Adaptation of the steady-state PERG in early glaucoma

PURPOSE

Previous studies have shown that the onset of high-contrast, fast reversing patterned stimuli induces rapid blood flow increase in retinal vessels in association with slow changes of the steady-state pattern electroretinogram (PERG) signal. We tested the hypothesis that adaptive PERG changes of normal controls differed from those of glaucoma suspects and patients with early manifest glaucoma.

METHODS

Subjects were 42 glaucoma suspects (Standard Automated Perimetry-MD -0.89±1.8 dB), 22 early manifest glaucoma (MD -2.12±2.4 dB) with visual acuity of ≥20/20 and 16 age-matched normal controls from a previous study. The PERG signal was sampled every ~15 seconds over 4 minutes in response to gratings (1.6 cyc/degree, 100% contrast) reversing 16.28 times/s. Amplitude/phase values of successive PERG samples were fitted with a nonparametric locally weighted polynomial regression smoothing function to retrieve the initial and final values and calculate their difference (δ) and the residual SD around the fitted function. The magnitude of PERG adaptive change compared to random variability was calculated as log10 of percentage coefficient of variation (CoV)=100×residual SDr÷δ. Grand-average PERGs were also obtained by averaging all samples of the same series.

RESULTS

The grand-average PERG amplitude [analysis of variance (ANOVA), P=0.02], but not phase (ANOVA, P=0.63), decreased with increasing severity of disease. Adaptive changes [log10 (CoV)] of PERG amplitude were not significantly associated with disease severity (ANOVA, P=0.27) but adaptive changes [log10 (CoV)] of PERG phase were (ANOVA, P=0.037; linear trend, P=0.011).

CONCLUSIONS

The steady-state PERG signal displayed slow adaptive changes over time that could be isolated from random variability. PERG adaptive changes differed from those of grand-average PERGs (corresponding the standard steady-state PERG), thus representing a new source of biological information about retinal ganglion cell function that may have potential in the study of glaucoma and optic nerve diseases.

Hemifield pattern electroretinogram in ocular hypertension: comparison with frequency doubling technology and optical coherence tomography to detect early optic neuropathy

BACKGROUND

To assess the sensitivity and specificity of hemifield pattern electroretinogram (HF-PERG) for detecting early retinal ganglion cell (RGC) damage in ocular hypertensive (OH) patients.

METHODS

Fifty-two OH patients (mean age 56±9.6 years) with an intraocular pressure (IOP) .21 mmHg were assessed. All subjects underwent HF-PERG, optical coherence tomography (OCT), and frequency doubling technology (FDT) visual field.

RESULTS

OH patients showed a significant increase of peak-time of the N95 (P=0.027) compared to controls. The amplitude of the N95 of the lower and upper HF-PERG showed significant differences (P=0.037 and P=0.023, respectively) between the two groups. A significant intraocular (P=0.006) and interocular (P=0.018) asymmetry of N95 amplitude was found. Receiver operating characteristic (ROC) curve analysis revealed a sensitivity of 93% for the N95 of the lower HF-PERG, whereas full-field pattern electroretinogram (PERG) N95 peak-time had a sensitivity of 88%. In OH patients, we found a thinning of OCT - retinal nerve fiber layer (RNFL), especially in the superior and inferior quadrant, although not statistically significant, and a significantly higher FDT pattern standard deviation (FDT-PSD; P=0.001). In the OCT-RNFL inferior quadrant, a sensitivity of 82% was recorded. Finally, the sensitivity of the FDT-PSD was 92%.

CONCLUSION

Our study shows that HF-PERG is a very sensitive test for detecting early damage of the RGC.

Trial end points and natural history in patients with G11778A Leber hereditary optic neuropathy : preparation for gene therapy clinical trial

IMPORTANCE Establishing the natural history of G11778A Leber hereditary optic neuropathy (LHON) is important to determine the optimal end points to assess the safety and efficacy of a planned gene therapy trial. OBJECTIVE To use the results of the present natural history study of patients with G11778A LHON to plan a gene therapy clinical trial that will use allotopic expression by delivering a normal nuclear-encoded ND4 gene into the nuclei of retinal ganglion cells via an adeno-associated virus vector injected into the vitreous. DESIGN, SETTING, AND PARTICIPANTS A prospective observational study initiated in 2008 was conducted in primary and referral institutional practice settings. Participants included 44 individuals with G11778A LHON, recruited between September 2008 and March 2012, who were evaluated every 6 months and returned for 1 or more follow-up visits (6-36 months) as of August 2012. EXPOSURES Complete neuro-ophthalmic examination and main measures. MAIN OUTCOMES AND MEASURES Visual acuity, automated visual field testing, pattern electroretinogram, and spectral-domain optical coherence tomography. RESULTS Clinical measures were stable during the follow-up period, and visual acuity was as good as or better than the other visual factors used for monitoring patients. Based on a criterion of 15 or more letters from the Early Treatment Diabetic Retinopathy Study chart, 13 eyes of 8 patients (18%) improved, but 24 months after the onset of symptoms, any further improvements were to no better than 20/100. Acuity recovery occurred in some patients despite continued marked retinal nerve fiber layer thinning indistinguishable from that in patients who did not recover visual acuity. CONCLUSIONS AND RELEVANCE Spontaneous improvement of visual acuity in patients with G11778A LHON is not common and is partial and limited when it occurs, so improvements in vision with adeno-associated virus-mediated gene therapy of a synthetic wild-type ND4 subunit gene should be possible to detect with a reasonable sample size. Visual acuity appears to be the most suitable primary end point for the planned clinical trial.

Retinal ganglion cell dysfunction in asymptomatic G11778A: Leber hereditary optic neuropathy

PURPOSE

To report the serial evaluation of asymptomatic eyes of subjects with mutated G11778A mitochondrial DNA.

METHODS

Forty-five asymptomatic G11778A Leber hereditary optic neuropathy (LHON) carriers and two patients with the mutation who developed unilateral visual loss underwent testing that included visual acuity, automated visual field, pattern electroretinogram (PERG), and spectral-domain optical coherence tomography every 6 months between September 2008 and March 2012.

RESULTS

Visual acuity, visual fields, and retinal nerve fiber layer thickness remained stable within the normal range. Mean PERG amplitudes of carriers dropped progressively by ∼ 40% from baseline to 36 months. In addition, comparisons with the fellow eyes of patients with unilateral optic neuritis revealed a 3.4 ETDRS (Early Treatment Diabetic Retinopathy Study) letter loss in the LHON carriers. A single carrier developed visual loss, with PERG amplitudes dropping by half. In one of two LHON cases who presented with unilateral visual loss, visual acuity in the asymptomatic eye was ∼ 20/40 at baseline. The PERG amplitude of this eye was reduced to ∼ 30% of normal. Six months later, his visual acuity had dropped to ∼ 20/500. A second patient who was ∼ 20/20 and had a visual field defect in the asymptomatic eye at baseline remained at this level for the 18 months of follow-up. His PERG amplitudes were similar to those of asymptomatic carriers, with 0.78 μV at baseline that did not decline with follow-up.

CONCLUSIONS

Declines of the PERG amplitude suggest subclinical retinal ganglion cell dysfunction in asymptomatic G11778A subjects, which is progressive.

Antiproliferative and cytotoxic properties of moxifloxacin on rat retinal ganglion cells

Abstract Purpose: To evaluate the antiproliferative and cytotoxic properties of moxifloxacin on cultured rat retinal ganglion cells (RGC5).

MATERIALS AND METHODS

Rat retinal ganglion cells were exposed to various concentration of moxifloxacin (5-1500 μg/mL). For antiproliferative properties, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) test was performed. Cellular cytotoxicity was assessed by using the Live/Dead viability/cytotoxicity assay and analyzed by fluorescence microscopy after 24 and 72 h of incubation, respectively.

RESULTS

Neither cytotoxic nor antiproliferative effect of moxifloxacin was observed below 50 μg/mL on RGC5 cells after 24 and 72 h of incubation. At higher concentrations of moxifloxacin (150 μg/mL, 500 μg/mL, and 1500 μg/mL (p < 0.001)) the number of viable cells and the proliferation rate of RGC5 were significantly reduced.

CONCLUSIONS

These results suggest a dose-dependent cytotoxic and antiproliferative effect of moxifloxacin on RGC5. Therefore, intracameral application of moxifloxacin should be used cautiously in patients with increased risk of retinal ganglion cells damage, particularly in glaucoma patients.

Pattern electroretinogram in neuromyelitis optica and multiple sclerosis with or without optic neuritis and its correlation with FD-OCT and perimetry

PURPOSE

To evaluate the ability of transient pattern electroretinogram (PERG) parameters to differentiate between eyes of patients with neuromyelitis optica (NMO), longitudinally extensive transverse myelitis (LETM), multiple sclerosis with optic neuritis (MS + ON), multiple sclerosis without optic neuritis (MS - ON), and controls, to compare PERG and OCT with regard to discrimination ability, and to assess the correlation between PERG, FD-OCT, and visual field measurements (VFs).

METHODS

Visual field measurements and full-field stimulation PERGs based on both 48- and 14-min checks were obtained from patients with MS (n = 28), NMO (n = 20), LETM (n = 18), and controls (n = 26). In addition, FD-OCT peripapillary retinal nerve fiber layer (RNFL) and segmented macular layer measurements were obtained and their correlation coefficients were determined.

RESULTS

Compared to controls, PERG amplitude measurements were significantly reduced in eyes with NMO and MS + ON, but not in eyes with LETM and MS - ON. PERG amplitudes were significantly smaller in NMO and MS + ON eyes than in MS - ON eyes. PERG and OCT performance was similar except in NMO eyes where macular thickness parameters were more efficient at detecting abnormalities. A significant correlation was found between N95 amplitude values and OCT-measured macular ganglion cell layer thickness, total retinal thickness, and temporal peripapillary RNFL thickness. PERG amplitude was also significantly associated with VF sensitivity loss. No statistically significant difference was observed with regard to the best-performing parameters of the two methods.

CONCLUSIONS

Pattern electroretinogram measurements were able to detect RNFL loss in MS + ON and NMO eyes, with a performance comparable to OCT. PERG amplitude measurements were reasonably well correlated with OCT-measured parameters.

Pattern electroretinography in glaucoma suspects and early primary open angle glaucoma

PURPOSE

To explore retinal ganglion cell (RGC) dysfunction in glaucoma suspects and patients with early primary open angle glaucoma (POAG) using pattern electroretinography (PERG).

METHODS

Twenty glaucoma suspects (glaucomatous optic disc appearance), 15 early POAG (based on abnormal discs and abnormal visual fields) and 16 normal controls were enrolled. Transient PERG was recorded in response to 0.8° and 16° black and white checkerboard stimuli. Amplitude and peak time (latency) of the P50 and N95 components of the PERG response, and the ratio of N95 amplitude in response to 0.8° and 16° checks were measured.

RESULTS

N95 peak time (latency) was significantly increased in both early manifest POAG and glaucoma suspects as compared to normal controls (P<0.001). In early POAG, N95 amplitude in response to small (0.8°) checks and the small/large check ratio were reduced in comparison to normal eyes (P<0.05). However, in glaucoma suspects no significant N95 amplitude reduction was observed. No significant difference was observed among the study groups in terms of P50 amplitude or peak time.

CONCLUSION

The N95 PERG response demonstrated uncoupled peak time and amplitude alterations in glaucoma. N95 peak time was significantly increased both in glaucoma suspects and early POAG; N95 amplitude reduction was present only in early POAG. PERG may detect RGC dysfunction (increased latency) before cell death (decreased amplitude) occurs.

Progressive loss of retinal ganglion cell function precedes structural loss by several years in glaucoma suspects

PURPOSE

We determined the time lag between loss of retinal ganglion cell function and retinal nerve fiber layer (RNFL) thickness.

METHODS

Glaucoma suspects were followed for at least four years. Patients underwent pattern electroretinography (PERG), optical coherence tomography (OCT) of the RNFL, and standard automated perimetry testing at 6-month intervals. Comparisons were made between changes in all testing modalities. To compare PERG and OCT measurements on a normalized scale, we calculated the dynamic range of PERG amplitude and RNFL thickness. The time lag between function and structure was defined as the difference in time-to-criterion loss between PERG amplitude and RNFL thickness.

RESULTS

For PERG (P < 0.001) and RNFL (P = 0.030), there was a statistically significant difference between the slopes corresponding to the lowest baseline PERG amplitude stratum (≤50%) and the reference stratum (>90%). Post hoc comparisons demonstrated highly significant differences between RNFL thicknesses of eyes in the stratum with most severely affected PERG (≤50%) and the two strata with least affected PERG (>70%). Estimates suggested that the PERG amplitude takes 1.9 to 2.5 years to lose 10% of its initial amplitude, whereas the RNFL thickness takes 9.9 to 10.4 years to lose 10% of its initial thickness. Thus, the time lag between PERG amplitude and RNFL thickness to lose 10% of their initial values is on the order of 8 years.

CONCLUSIONS

In patients who are glaucoma suspects, PERG signal anticipates an equivalent loss of OCT signal by several years.

Pattern electroretinogram progression in glaucoma suspects

PURPOSE

To prospectively monitor progressive changes of retinal ganglion cell function in early glaucoma using the pattern electroretinogram (PERG).

METHODS

Fifty-nine patients enrolled as glaucoma suspects were observed untreated over an average of 5.7±1.4 years, during which they were tested with PERG (PERGLA paradigm) and standard automated perimetry (SAP) 2 times per year. PERG amplitude and phase were normalized for physiological age-related changes, and linear regressions fitted to the data to calculate progression slopes (signal), slope SE (noise), and corresponding signal-to-noise ratios (SNR=slope÷SE). Linear regressions were also used to fit SAP global indices mean deviation (MD) and pattern standard deviation (PSD).

RESULTS

On average, progression slopes of PERG amplitude/phase were skewed toward negative values, their mean being significantly (P<0.01) different from zero. In contrast, mean slopes of SAP-MD and PSD were not significantly different from zero. SNRs were higher for PERG than SAP (P<0.01). A substantial number of eyes displayed significant (P<0.05) progression of PERG amplitude (15% to 20%) or PERG phase (16% to 25%). Fewer eyes displayed significant progression of SAP-MD (0% to 2%) or SAP-PSD (4% to 8%).

CONCLUSIONS

The PERG displayed clear longitudinal loss of signal (diminished amplitude, phase delay, or both) in a substantial number of eyes of patients, indicating progressive deterioration of retinal ganglion cell function. Progression of SAP global indices MD and PSD was found in a relatively smaller number of eyes. It remains to be established whether PERG progression has predictive value for developing visual dysfunction.

Retrograde signaling in the optic nerve is necessary for electrical responsiveness of retinal ganglion cells

PURPOSE

We investigated the role of retrograde signaling in the optic nerve on retinal ganglion cell (RGC) electrical responsiveness in the mouse model.

METHODS

Electrical response of RGC was measured by pattern electroretinogram (PERG) in 43 C57BL/6J mice 4 to 6 months old under ketamine/xylazine anesthesia. PERGs were recorded before and at different times after blockade of axon transport with lidocaine at either the retrobulbar level (2 μL, 40 μg/μL) or at level of the superior colliculus (SC, 1 μL, 40 μg/μL). PERGs also were recorded before and at different times after optic nerve crush 1.5 mm behind the eye, followed by TUJ1-positive RGC counts of excised retinas. As controls, PERGs also were recorded after either saline injections or sham optic nerve surgery. The photopic flash electroretinogram (FERG) and visual evoked potential (FVEP) also were recorded before lidocaine and at relevant times afterwards.

RESULTS

Lidocaine injection caused rapid (retrobulbar ~10 minutes, SC 1 hour), reversible reduction of PERG amplitude (≥50%). Optic nerve crush caused rapid (10-20 minutes), irreversible reduction of PERG amplitude (70-75%), increase of PERG latency (>25%), as well as RGC loss (88%) 1 month after crush. FVEP was unaltered by lidocaine. For all procedures, the FERG was unaltered.

CONCLUSIONS

As experimental interventions were made at postretinal level(s), PERG changes were likely associated with altered supply of retrogradely-delivered material from the SC. This implies that retrograde transport of target-derived molecules is necessary for normal RGC electrical responsiveness. The time course of early PERG changes is consistent with the speed of fast retrograde axon transport.

Frequency doubling technology, optical coherence technology and pattern electroretinogram in ocular hypertension

BACKGROUND

To assess which of three methods, namely, optical coherence tomography (OCT), pattern electroretinogram (PERG) or frequency-doubling technology (FDT), is the most sensitive and specific for detecting early glaucomatous damage in ocular hypertension (OH).

METHODS

Fifty-two patients with OH (24 men and 28 women, mean age of 56 ± 9.6 years) with an intraocular pressure (IOP) > 21 mm Hg and fifty-two control patients (25 men and 27 women, mean age of 54.8 ± 10.4 years) with IOP < 21 mm Hg, were assessed. All the patients had normal visual acuity, normal optic disk and normal perimetric indices.All subjects underwent OCT, FDT and PERG. Data were analyzed with unpaired t-tests, Chi-square test and Receiver Operating Characteristic (ROC) curve analyses.

RESULTS

In patients with OH, OCT showed retinal nerve fiber layer (RNFL) thinner than in control group in the superior quadrant (130.16 ± 10.02 vs 135.18 ± 9.27 μm, respectively; p < 0.011) and inferior quadrant (120.14 ± 11.0 vs 132.68 ± 8.03 μm; p < 0.001). FDT showed a significantly higher pattern standard deviation (PSD) (3.46  ± 1.48 vs 1.89 ± 0.7 dB; p < 0.001). With respect to PERG, only the amplitude showed significant differences (p < 0.044) between the two groups. ROC curve analysis revealed a sensitivity and specificity of 92% and 86%, respectively, for FDT-PSD (with an area under the ROC curve of 0.940), whereas with OCT, a sensitivity of 82% and a specificity of 74% was recorded in the inferior RNFL quadrant (with an area under the ROC curve of 0.806) finally with PERG amplitude we found a sensitivity of 52% and specificity of 77% (with an area under the ROC curve of 0.595).

CONCLUSIONS

FDT is the most sensitive and specific method for detecting early glaucomatous damage in eyes with OH, and together with OCT, can be useful in identifying those patients who may develop glaucoma.

TRIAL REGISTRATION

ISRCT number: ISRCTN70295497.

Subfoveal choroidal blood flow and central retinal function in early glaucoma

PURPOSE

To assess subfoveal choroidal blood flow (ChBF) in patients with early manifest glaucoma (EMG) and to compare blood flow with functional measures of central retinal integrity, standard automated perimetry (SAP) and pattern electroretinogram (PERG).

METHODS

Subfoveal ChBF was determined by confocal, real-time laser Doppler flowmetry in 24 patients with EMG [>-6 dB mean deviation (MD), age range: 29-77 years, visual acuity: 20/25-20/20] and 23 age-matched control subjects. All patients had a therapeutically (topical beta-blockers with or without prostaglandin analogues) controlled intraocular pressure (IOP < 20 mmHg). Subfoveal choroidal blood volume (ChBVol), velocity (ChBVel) and ChBF were determined as the average of three 60 second recordings. In all patients and controls, the PERG and SAP (Humphrey 30-2), following standardized protocols, were also recorded.

RESULTS

  In patients with EMG, reductions in average ChBVel and ChBF were roughly equal, respectively, by 30% and 33.4% (p < 0.01), when compared to control subjects, so that there was no significant difference in ChBVol between the two groups. Pattern electroretinogram amplitudes were reduced by 46% (p < 0.01) in patients compared to controls. No correlation was found between any of the ChBF parameters and PERG amplitude, or Humphrey 30-2 MD and pattern standard deviation.

CONCLUSION

  The results suggest a significant alteration of both ChBVel and ChBF in EMG, which does not appear to be associated with the severity of central retinal dysfunction. These findings may contribute to a better understanding of the pathophysiology of early glaucomatous damage in EMG and have implications for the treatment of this pathologic condition.

Progressive loss of retinal ganglion cell function is hindered with IOP-lowering treatment in early glaucoma

PURPOSE

To investigate progressive changes of retinal ganglion cell (RGC) function in glaucoma suspects before and after IOP-lowering treatment.

METHODS

The authors retrospectively analyzed pattern electroretinograms (PERG) recorded twice a year in 32 glaucoma suspects over at least 6 years. Fifteen patients (28 eyes in the study group) received IOP-lowering treatment at intermediate points during the follow-up, thereby generating a break point between the untreated period and the treated period. Seventeen patients (31 eyes in the control group) were not treated; a break point in the follow-up period was randomly assigned. To assess the effect of treatment, linear regression slopes of PERG amplitude were calculated for periods before and after the break point, and compared both within and between groups. Linear mixed models applied to raw PERG amplitudes recorded over the entire follow-up period were also calculated.

RESULTS

Before the break point, slopes had a similar negative trend in both groups, whereas after the break point the slope became shallower in the treated group (P = 0.002). The linear mixed model revealed an interaction between groups, period relative to break point, and segment duration (P = 0.001). Both analyses agreed that after the break point, the rate of PERG amplitude decline slowed in treated eyes by 0.013-0.019 μV/year compared with the untreated eyes. Mean IOPs measured before and after break point were similar in control eyes (14.8 ± 3.20 vs. 14.8 ± 3.14 mm Hg) but different in treated eyes (16.84 ± 3.96 vs. 14.8 ± 3.24 mm Hg; P < 0.001).

CONCLUSIONS

Progressive loss of RGC function in early glaucoma may be alleviated after IOP lowering, as measured by PERG.

Retinal pathway origins of the pattern electroretinogram (PERG)

PURPOSE

To determine retinal pathway origins of pattern electroretinogram (PERG) in macaque monkeys using pharmacologic dissections, uniform-field flashes, and PERG simulations.

METHODS

Transient (2 Hz, 4 reversals/s) and steady state (8.3 Hz, 16.6 reversals/s) PERGs and uniform-field ERGs were recorded before and after intravitreal injections of L-AP4 (not APB) (2-amino-4-phosphonobutyric acid, 1.6-2.0 mM), to prevent ON pathway responses; PDA (cis-2,3-piperidinedicarboxylic acid, 3.3-3.8 mM), to block activity of hyperpolarizing second- and all third-order retinal neurons; and TTX (tetrodotoxin, 6 μM), to block Na+-dependent spiking. PERGs were also recorded from macaques with advanced unilateral experimental glaucoma, and were simulated by averaging ON and OFF responses to uniform-field flashes.

RESULTS

For 2-Hz stimulation, L-AP4 reduced both negative- and positive-going (N95 and P50) amplitudes in transient PERGs, and their counterparts, N2 and P1 in simulations, to half-amplitude. PDA eliminated N95 and N2, but increased P50 and P1 amplitudes, in that it enhanced b-waves. As previously reported, severe experimental glaucoma or TTX eliminated photopic negative responses, N95, and N2; glaucoma eliminated P50 and reduced P1 amplitude; TTX reduced P50 and hardly altered P1. For 8.3-Hz stimulation, L-AP4 eliminated the steady state PERG and reduced simulated PERG amplitude, whereas PDA enhanced both responses. TTX reduced PERG amplitude to less than half; simulations were less reduced. Blockade of all postreceptoral activity eliminated transient and steady state PERGs, but left small residual P1 in simulations.

CONCLUSIONS

Transient PERG receives nearly equal amplitude contributions from ON and OFF pathways. N95 reflects spiking activity of ganglion cells; P50 reflects nonspiking activity as well. Steady state PERG, in contrast, reflects mainly spike-related ON pathway activity.

Pattern electroretinogram association with spectral domain-OCT structural measurements in glaucoma

PURPOSE

To describe the association between pattern electroretinogram (PERG) amplitude and spectral domain-optical coherence tomography (SD-OCT) macular thickness, retinal nerve fibre layer (RNFL) thickness and optic disc topography measurements.

SUBJECTS AND METHODS

Both eyes (n = 132) of 66 glaucoma patients (mean age = 67.9 years) enrolled in the University of California, San Diego, CA, USA, Diagnostic Innovations in Glaucoma Study (DIGS) were included. Eyes were tested with PERG (Glaid PERGLA, Lace Elettronica, Pisa, Italy), RTVue SD-OCT (Optovue Inc., Fremont, CA, USA) GCC, and NHM4 protocols on the same day. Of the 66 enrolled patients, 43 had glaucoma defined by repeated abnormal standard automated perimetry (SAP) results in at least one eye and 23 were glaucoma suspects defined by a glaucomatous-appearing optic disc by physicians' examination in at least one eye and normal SAP results in both eyes. Associations (R(2)) were determined between PERG amplitude (μV) and SD-OCT macular ganglion cell complex (GCC) thickness (μm), macular thickness (μm), macular outer retinal thickness (macular thickness minus GCC thickness) (μm), RNFL thickness (μm), neuroretinal rim area (mm(2)), and rim volume (mm(3)).

RESULTS

PERG amplitude was significantly associated with GCC thickness (R(2) = 0.179, P < 0.001), RNFL thickness (R(2) = 0.174, P < 0.001), and macular thickness (R(2) = 0.095, P<0.001). R(2) associations with other parameters were not significant (all P > 0.624). Significant associations remained for GCC and average RNFL thickness when age and intraocular pressure at the time of testing were included in multivariate models (both P ≤ 0.030).

CONCLUSIONS

PERG amplitude is significantly (but weakly) associated with macular GCC thickness, RNFL thickness, and macular thickness. The lack of association between PERG amplitude and macular outer retinal thickness supports previous results, possibly suggesting that that the PERG is driven primarily by retinal ganglion cell (inner retinal) responses.

Reversal of retinal ganglion cell dysfunction after surgical reduction of intraocular pressure

PURPOSE

The pattern electroretinogram optimized for glaucoma screening (PERGLA) is a noninvasive method of objectively measuring retinal ganglion cell (RGC) function. This study was undertaken to quantify the RGC response to intraocular pressure (IOP) reduction after glaucoma surgery.

DESIGN

Prospective cohort study.

PARTICIPANTS

Forty-seven eyes of 47 patients with uncontrolled IOP or progressive glaucomatous optic neuropathy receiving maximal medical therapy requiring trabeculectomy or aqueous drainage device implantation who met eligibility criteria.

METHODS

Eyes with visual acuity less than 20/30, corneal or retinal pathologic features, or unreliable standard automated perimetry (SAP) results were excluded. All patients underwent complete ocular examination, arterial blood pressure, SAP, and PERGLA at 2 sessions before surgery and at 3 months after surgery. Mean ocular perfusion pressure (MOPP) was calculated. Each measure of PERGLA amplitude and phase was an average of 600 artifact-free signal registrations.

MAIN OUTCOME MEASURES

Intraocular pressure and PERGLA amplitude and phase.

RESULTS

Forty-seven eyes of 47 patients (mean age ± standard deviation [SD], 69.9 ± 11.3 years) were enrolled. Thirty-four eyes (72%) underwent trabeculectomy with antifibrosis therapy; 13 eyes (28%) underwent glaucoma drainage implant surgery. Mean ± SD postoperative IOP (10.4 ± 4.6 mmHg) was significantly (P< 0.001) reduced compared with that before surgery (19.7 ± 8.6 mmHg). Mean ± SD postoperative PERGLA amplitude (0.46 ± 0.22 μV) was significantly (P = 0.001) increased compared with preoperative PERGLA amplitude (0.37 ± 0.18 μV). Mean ± SD postoperative PERGLA phase (1.72 ± 0.20 π-radian) was significantly (P = 0.01) reduced compared with preoperative PERGLA phase (1.81 ± 0.22 π-radian). Mean ± SD postoperative MOPP (53.1 ± 6.4 mmHg) was significantly (P < 0.001) increased compared with mean ± SD preoperative MOPP (45.8 ± 10.1 mmHg). No correlation (P > 0.05) was identified between change in PERGLA amplitude and change in IOP or MOPP.

CONCLUSIONS

Reversal of RGC dysfunction occurs after surgical reduction of IOP and may be quantified using PERGLA.

Leber hereditary optic neuropathy gene therapy clinical trial recruitment: year 1

OBJECTIVE

To describe the patient profiles of the Leber hereditary optic neuropathy (LHON) Gene Therapy Clinical Trial, year 1. This study aims to identify and characterize affected patients and carriers with the G11778A mutation in mitochondrial DNA for planned gene therapy that will use "allotopic expression" by delivering a normal nuclear-encoded ND4 gene into the nuclei of retinal ganglion cells via an adeno-associated virus vector injected into the vitreous.

METHODS

Patients with LHON with visual loss as well as asymptomatic maternally related family members were molecularly screened for ND1, ND4, and ND6 mutations in mitochondrial DNA commonly associated with LHON. All patients and maternal relatives also underwent complete neuro-ophthalmic examination, automated visual field testing, pattern electroretinogram (PERG), and OCT3.

RESULTS

Twenty-five subjects with LHON and 21 carriers positive for the G11778A mitochondrial DNA mutation were recruited. Three additional mutations in the ND4 gene, G11719A, G11947A, or G11914A, were detected. Mean retinal nerve fiber layer (RNFL) thickness was 78.3 μm up to 32 months after visual loss. It was 63.5 μm for all affected patients and 100.7 μm for carriers (P < .01). Mean PERG amplitude was lower in affected patients (40% of normal) than in carriers (94% of normal) (P < .01). Four carriers with PERG amplitudes less than 75% of normal had Early Treatment Diabetic Retinopathy Study acuity more than 20/25, mean defect more than -2 dB, and average RNFL thickness more than 80 μm.

CONCLUSIONS

Potential candidates for future gene therapy may include affected patients, as late as 32 months after loss of vision, with mildly reduced RNFL thickness or carriers with low PERG amplitudes and normal RNFL thickness, if the PERG amplitude is a predictor of conversion to LHON in these carriers.

The impact of intraocular pressure reduction on retinal ganglion cell function measured using pattern electroretinogram in eyes receiving latanoprost 0.005% versus placebo

PURPOSE

To evaluate the impact of intraocular (IOP) reduction on retinal ganglion cell (RGC) function measured using pattern electroretinogram optimized for glaucoma (PERGLA) in glaucoma suspect and glaucomatous eyes receiving latanoprost 0.005% versus placebo.

METHODS

This was a prospective, placebo-controlled, double masked, cross-over clinical trial. One randomly selected eye of each subject meeting eligibility criteria was enrolled. At each visit, subjects underwent five diurnal measurements between 8:00 am and 4:00 pm consisting of Goldmann IOP, and PERGLA measurements. A baseline examination was performed following a 4-week washout period, and repeat examination after randomly receiving latanoprost or placebo for 4-weeks. Subjects were then crossed over to receive the alternative therapy for 4 weeks following a second washout period, and underwent repeat examination. Linear mixed-effect models were used for the analysis.

RESULTS

Sixty-eight eyes (35 glaucoma, 33 glaucoma suspect) of 68 patients (mean age 67.4 ± 10.6 years) were enrolled. The mean IOP (mmHg) after latanoprost 0.005% therapy (14.9 ± 3.8) was significantly lower than baseline (18.8 ± 4.7, p<0.001) or placebo (18.0 ± 4.3), with a mean reduction of -20 ± 13%. Mean PERGLA amplitude (μV) and phase (π-radian) using latanoprost (0.49 ± 0.22 and 1.71 ± 0.22, respectively) were similar (p > 0.05) to baseline (0.49 ± 0.24 and 1.69 ± 0.19) and placebo (0.50 ± 0.24 and 1.72 ± 0.23). No significant (p > 0.05) diurnal variation in PERGLA amplitude was observed at baseline, or using latanoprost or placebo. Treatment with latanoprost, time of day, and IOP were not significantly (p > 0.05) associated with PERGLA amplitude or phase.

CONCLUSION

Twenty percent IOP reduction using latanoprost monotherapy is not associated with improvement in RGC function measured with PERGLA.

The PERG in diabetic glaucoma suspects with no evidence of retinopathy

OBJECTIVE

To better understand the role of diabetes mellitus on retinal ganglion cell function of glaucoma suspects.

METHODS

Eighteen diabetic glaucoma suspects (GSD) without retinopathy (type-2, n=16, type-1, n=2) and 156 age-matched glaucoma suspects (GS) without diabetes were tested with steady-state pattern electroretinogram (PERG, PERGLA paradigm, Ophthalmology 2004,111:161) as surrogate measure of retinal ganglion cell function. Results were compared with previously published data of 48 similarly aged normal controls (NC). All subjects (NC, GS, GSD) had small refractive errors and corrected visual acuity > or =20/25.

RESULTS

The mean PERG amplitude of both GS and GSD was significantly (P<0.01) smaller than that of age-matched NC. The mean PERG amplitude of GSD patients was significantly (P<0.05) smaller than that of GS accounting for individual differences in age, visual acuity, visual field defect, and intraocular pressure. The mean PERG phase did not differ between GS and GSD.

CONCLUSIONS

In agreement with previous studies, our results show that on average, GS have reduced PERG amplitude compared with NC. PERG amplitude is further reduced in GSD compared with nondiabetic GS with otherwise comparable ophthalmologic and systemic conditions.

Pattern electroretinogram and psychophysical tests of visual function for discriminating between healthy and glaucoma eyes

PURPOSE

To compare the diagnostic accuracy of the pattern electroretinogram (pattern ERG) to that of standard automated perimetry (SAP), short-wavelength automated perimetry (SWAP), and frequency-doubling technology (FDT) perimetry for discriminating between healthy and glaucomatous eyes.

DESIGN

Cross-sectional study.

METHODS

Eighty-three eyes of 42 healthy recruits and 92 eyes of 54 glaucoma patients (based on optic disc appearance) from the University of California, San Diego, Diagnostic Innovations in Glaucoma Study were tested with pattern ERG for glaucoma detection (PERGLA; Lace Elettronica, Pisa, Italy), SAP, SWAP, and FDT within 9 months. Receiver operating characteristic (ROC) curves were generated and compared for pattern ERG amplitude and SAP, SWAP, and FDT mean deviation and pattern standard deviation (PSD). Sensitivities and specificities were compared and agreement among tests was described.

RESULTS

The area under the ROC curve for pattern ERG amplitude was 0.744 (95% confidence interval = 0.670, 0.818). The ROC curve area was 0.786 (0.720, 0.853) for SAP PSD, 0.732 (0.659, 0.806) for SWAP PSD, and 0.818 (0.758, 0.879) for FDT PSD. At 95% specificity, sensitivities of SAP and FDT PSD were significantly higher than that of pattern ERG amplitude; at 80% specificity, similar sensitivities were observed among tests. Agreement among tests was slight to moderate.

CONCLUSION

The diagnostic accuracy of the pattern ERG amplitude was similar to that of SAP and SWAP, but somewhat worse than that of FDT. Nevertheless, the pattern ERG may hold some advantage over psychophysical testing because of its largely objective nature.

Effect of operator and optical defocus on the variability of pattern electroretinogram optimized for glaucoma detection (PERGLA)

PURPOSE

To evaluate the effect of operator and optical defocus on the variability of pattern electroretinogram optimized for glaucoma detection (PERGLA).

METHODS

Two different operators obtained 2 PERGLA recordings each from 10 healthy participants (5 women, mean age 32.1+/-10.3 y). In addition, one of the operators obtained recordings in which corrective lenses of various diopters (+/-0.5, +/-1, +/-2, and +/-3) were used to generate optical defocus in both eyes. The effect of operator on PERGLA amplitude and phase variability was determined using a single nested variance components' analysis model and by using Bland-Altman plots. One-way analysis of variance (ANOVA) was used to determine the effect of optical defocus on amplitude and phase.

RESULTS

Differences in measurements between operators accounted for approximately 26.6% and 18.2% of the total variance for amplitude and phase, respectively. Results were confirmed by the use of Bland-Altman plots. ANOVA identified a significant effect of defocus on mean amplitude (F=2.65, P=0.01), but not phase (F=1.02, P=0.42).

CONCLUSIONS

Measurements obtained by different operators can result in significant differences in PERGLA amplitude. In addition, although optical defocus leads to a decrease in PERGLA amplitude by reducing visual acuity, this can be avoided by obtaining J1 or better vision before testing.

Relationship between pattern electroretinogram, standard automated perimetry, and optic nerve structural assessments

PURPOSE

To examine the relationship between retinal ganglion cell function measured using pattern electroretinogram optimized for glaucoma screening (PERGLA), retinal nerve fiber layer (RNFL) thickness, and optic nerve head topography.

METHODS

Twenty-nine normal, 28 glaucoma, and 37 glaucoma suspect volunteers were enrolled. All participants were age similar. One randomly selected eye underwent complete eye examination, standard automated perimetry (SAP), scanning laser polarimetry with enhanced corneal compensation (GDxECC), optical coherence tomography, Heidelberg retina tomograph (HRT), and PERGLA measurements. PERGLA amplitude (microV) was converted to dB for comparison with SAP mean deviation (MD) and pattern SD. The correlation between PERGLA amplitude in dB and the average of sensitivity values for 16 central test locations of SAP were calculated. Analysis of variance, Pearson and Spearman rank correlations, coefficient of variation, and intraclass correlation coefficients were calculated.

RESULTS

PERGLA amplitude in glaucomatous eyes was significantly lower than normal eyes (0.47+/-0.20 vs. 0.70+/-0.28 microV, P<0.001) but not glaucoma suspects (0.54+/-0.21 microV, P=0.84). PERGLA amplitude was inversely correlated with age (r=-0.31, P=0.002). PERGLA amplitude (in dB) was associated with the sensitivity values of the SAP central 16 test locations (r=0.40, P<0001) across the entire cohort, GDxECC superior RNFL thickness (r=0.38, P<0.001), and HRT Moorfields regression analysis classification (rho=-0.34, P=0.001). The coefficient of variation and intraclass correlation coefficients were 14.5% and 0.89 for PERGLA amplitude, 2.4% and 0.98 for optical coherence tomography average RNFL, 2.2% and 0.97 for GDxECC temporal superior nasal inferior temporal average, and 6.3% and 0.94 for HRT rim area.

CONCLUSIONS

Retinal ganglion cell function measured using PERGLA is reduced in glaucoma and demonstrates modest correlations with central SAP sensitivity values and structural measures of optic nerve topography and RNFL thickness.

Physiologic significance of steady-state pattern electroretinogram losses in glaucoma: clues from simulation of abnormalities in normal subjects

PURPOSE

To better understand pathophysiologic mechanisms underlying pattern electroretinogram (PERG) losses in glaucoma by simulating either retinal ganglion cell (RGC) dysfunction or RGC loss in normal subjects.

MATERIALS AND METHODS

The steady-state PERG has been recorded in 10 normal subjects (mean age: 31+/-8 y) according to the PERGLA paradigm by means of skin electrodes in response to horizontal gratings (1.7 cycles/degree, 99% contrast, 40 cd/m mean luminance, circular field size 25 degree diameter) alternating 16.28 times/seconds. Simulated RGC dysfunction has been obtained by reducing either contrast and mean luminance or blurring the visual stimulus. Simulated RGC loss has been obtained by reducing stimulus area. Outcome measures were PERG amplitude and phase obtained by discrete Fourier transform of PERG waveforms.

RESULTS

Progressive PERG amplitude reductions spanning the entire dynamic range of PERG response could be obtained by progressively reducing stimulus contrast and luminance, blurring the stimulus, and reducing stimulus area. The same variations in stimulus conditions caused phase changes of disparate sign and magnitude. Phase advanced (latency shortened) by reducing stimulus contrast or blurring the stimulus; phase lagged (latency increased) by reducing stimulus luminance; phase remained constant by reducing stimulus area.

CONCLUSIONS

PERG amplitude and phase are essentially uncoupled, implying that these measures reflect distinct aspects of RGC activity. On the basis of our results and known PERG physiology, we propose a model in which both RGC dendrites and RGC axons contribute to the PERG signal. PERG delays may represent an indication of synaptic dysfunction that is potentially reversible.

Improved retinal function after trabeculectomy in glaucoma patients

PURPOSE

To investigate retinal function after reduction of intraocular pressure (IOP) by filtration surgery in patients with medically uncontrolled glaucoma.

METHODS

Eleven patients (11 eyes) with medically uncontrolled glaucoma underwent trabeculectomy. Clinical investigation, visual field (testing with standard automated perimetry (SAP-Humphrey), optical coherence tomography (OCT), full-field electroretinography (full-field ERG) and multifocal electroretinography (mfERG) were performed preoperatively as well as 2 and 6 months after surgery.

DESIGN

Interventional prospective, consecutive case series.

RESULTS

No significant reduction was seen in mean log MAR visual acuity 2 or 6 months after filtration surgery. The mean preoperative intraocular pressure of 27.1 (+/-6.2) mmHg decreased to 19.0(+/-6.1) mmHg 2 months after surgery and to 17.1 (+/- 3.4) mmHg 6 months after surgery (both p = 0.001). The reduction in IOP significantly decreased the number of anti-glaucoma agents used, from 3.7 +/- 1.6 at baseline to 0.8 +/- 0.9 2 months after surgery and to 1.3 +/- 1.2 6 months after surgery (p = 0.004 and p = 0.008 respectively). The results of SAP, OCT and full-field ERG did not show any significant difference between pre- and postoperative values at any point in time. No significant improvement was found with regard to the first positive peak (P(1)) amplitudes in the macular retina (area 1) or in the perimacular retina/periphery (area 2) when measured with mfERG 2 months after surgery. The mfERG examinations revealed significantly improved P(1) amplitudes 6 months after surgery in both area 1 and area 2, compared with the preoperative values (p = 0.042 and p = 0.014 respectively). The implicit time of P(1) decreased significantly 6 months after surgery in area 2 compared with the preoperative values (p = 0.023).

CONCLUSION

A significant lowering of IOP seems to improve the function of the central retina, as demonstrated by increased amplitudes and reduced implicit times assessed with mfERG.

Repeatability of pattern electroretinogram measurements using a new paradigm optimized for glaucoma detection

PURPOSE

To determine the within-trial and between-trial repeatability of pattern electroretinogram (PERG) measurements in healthy and patient eyes, using a new clinical instrument, the PERGLA.

STUDY DESIGN

In all, 70 eyes of 35 healthy individuals (intraocular pressure <22 mm Hg, healthy optic disc by stereophotograph assessment, standard visual fields within normal limits) and 90 eyes of 45 clinic patients (ocular hypertensive, glaucomatous optic neuropathy by stereophotograph assessment and/or repeatable abnormal visual fields) enrolled in the University of California, San Diego Diagnostic Innovations in Glaucoma Study (DIGS) were evaluated. Average mean deviation of patient eyes on standard automated perimetry was -1.81 dB (SD=2.61).

METHODS

The PERG was recorded using the PERGLA paradigm from both eyes simultaneously twice (ie, 2 trials) by a single operator with electrodes being removed and reattached between recordings. Repeatability of PERG amplitude (microV) and phase (pi rad) between 2 runs within a single trial (within-trial condition) was compared with repeatability between 2 trials (ie, after electrode replacement, between-trial condition) by calculating the coefficients of variability (CVs) and the intraclass correlation coefficients (ICCs) and displaying Bland-Altman plots.

RESULTS

For healthy eyes, amplitude CVs (SD) were 11.5% (11.5) and 9.9% (0.79) for within-trial and between-trial conditions, respectively. ICCs were 0.91 and 0.85. Phase CVs were 1.3% (1.5) (within-trials) and 1.5% (1.4) (between-trials) and ICCs were 0.85 and 0.88. For patient eyes, amplitude CVs (SD) were 12.2% (10.1) and 11.2% (7.5) for within-trial and between-trial conditions, respectively. ICCs were 0.92 and 0.89. Phase CVs were 2.2% (2.2) (within-trials) and 2.4% (2.2) (between-trials) and ICCs were 0.82 and 0.83. Bland-Altman plots indicated good agreement between the repeated recordings and were similar within-trials and between-trials for healthy and patient eyes.

CONCLUSIONS

Repeatability of PERGLA recordings is good and is similar within-trials and between-trials for both healthy and patient eyes suggesting this technique is promising for monitoring change over time.

Retinal pathway origins of the pattern ERG of the mouse

This study investigated contributions from the retinal On and Off pathways, and the spiking and nonspiking activity of neurons in those pathways to the pattern ERG of the mouse. Light-adapted pattern and ganzfeld ERGs were recorded from anesthetized C57BL/6 mice 3-4 months of age. Recordings were made before and after intravitreal injections of PDA (cis-2,3-piperidine-dicarboxylic acid) to block transmission to hyperpolarizing 2nd order and all 3rd order neurons, TTX (tetrodotoxin) to block Na(+)-dependent spiking, APB (2-amino-4-phosphonobutyric acid) to block synapses between photoreceptors and ON-bipolar cells, and APB + TTX and PDA + TTX cocktails. The pattern stimuli consisted of 0.05 cy/deg gratings reversing in contrast at 1 Hz, presented at various contrasts (50-90%) and a rod saturating mean luminance. For flash ERGs, brief green ganzfeld flashes were presented on a rod-suppressing green background. Recordings were made 39-42 days after unilateral optic nerve crush (ONC) in a subset of animals in which ganglion cell degeneration was subsequently confirmed in retinal sections. Pattern ERGs were similar in waveform for all contrasts, with a positive wave (P1) peak for 90% contrast around 60 ms on average and maximum trough for a negative wave (N2) around 132 ms after each contrast reversal; amplitudes were greatest for 90% contrast which became the standard stimulus. ONC eliminated or nearly eliminated the pattern ERG but did not affect the major waves of the flash ERG. PDA and TTX both delayed P1 and N2 waves of the pattern ERG, and reduced their amplitudes, with effects of PDA on N2 greater than those of TTX. In the flash ERG, PDA reduced a-wave amplitudes, removed OPs but hardly affected b-wave amplitudes. In contrast, TTX reduced b-wave amplitudes substantially, as previously observed in rat. APB removed P1 of the pattern ERG, but left a negative wave of similar timing and amplitude to N2. In the flash ERG, APB removed the b-wave, producing a negative ERG. Addition of TTX to the APB injection removed most of N2 of the pattern ERG, while other waves of the pattern and flash ERG resembled those after APB alone. Addition of TTX to the PDA injection had little effect on the pattern ERG beyond that of PDA alone, but it prolonged the b-wave of the flash ERG. In conclusion, this study confirmed that a selective lesion of ganglion cells will practically eliminate the pattern ERG. The study also showed that P1 of the mouse pattern ERG is dominated by contributions, mainly spiking, from ON pathway neurons, whereas N2 reflects substantial spiking activity from the OFF pathway as well as nonspiking contributions from both pathways.

Diagnostic accuracy of pattern electroretinogram optimized for glaucoma detection

PURPOSE

To assess the ability of the new pattern electroretinogram optimized for glaucoma detection (PERGLA) paradigm to discriminate between healthy individuals and individuals with glaucomatous optic neuropathy (GON).

DESIGN

Cross-sectional study.

PARTICIPANTS

One hundred forty-two eyes of 71 participants (42 healthy and 29 with GON in at least 1 eye) enrolled in the University of California, San Diego, Diagnostic Innovations in Glaucoma Study were studied. Healthy individuals were those recruited as healthy with healthy-appearing optic disc by examination and masked stereoscopic optic disc photograph evaluation. Glaucomatous optic neuropathy was defined based on stereophotograph evaluation.

METHODS

The PERGLA (Glaid Elettronica, Pisa, Italy) recordings were obtained within 6 months of standard automated perimetry (SAP) testing. Dependent variables were PERGLA amplitude, phase, amplitude asymmetry, phase asymmetry, and SAP pattern standard deviation (PSD) and mean deviation (MD).

MAIN OUTCOME MEASURES

Diagnostic accuracy (sensitivity and specificity) of the PERGLA normative database for classifying healthy and glaucomatous individuals was determined. In addition, performance (areas under receiver operating characteristic curves [AUCs]) of PERGLA amplitude and phase for classifying healthy (n=84) and GON (n=50) eyes was determined. Results from both analyses were compared with those from SAP.

RESULTS

Sensitivity and specificity of the PERGLA normative database were 0.76 and 0.59, respectively, compared with 0.83 and 0.77 for SAP. The AUCs for PERGLA amplitude and phase were 0.75 and 0.50 (chance performance), respectively. The AUCs for SAP PSD and MD were 0.83 and 0.78, respectively.

CONCLUSIONS

Pattern electroretinograms recorded using the PERGLA paradigm can discriminate between healthy and glaucoma eyes, although this technique performed no better than SAP at this task. Low specificity of the PERGLA normative database suggests that the distribution of recordings included in the database is not ideal.

Morpho-functional follow-up of the optic nerve in treated ocular hypertension: disc morphometry and steady-state pattern electroretinogram

PURPOSE

To examine longitudinally optic disc structure and inner retinal function in treated ocular hypertension (OHT).

MATERIALS AND METHODS

A morphometric (Heidelberg Retina Tomograph, HRT) and functional (steady-state pattern electroretinogram, PERG) evaluation of 27 OHT patients treated with topical beta-blockers and/or prostaglandin analogues and prospectively followed over a 24 +/- 6 month period.

RESULTS

Compared with baseline, mean final PERG amplitude tended to increase (p < 0.01), while HRT was stable. Individual PERG amplitude increase was large (>or= 100%) in some patients (5/27), and unexplained by clinical parameters at baseline.

CONCLUSIONS

In treated OHT, functional responses may improve while disc structure remains stable. The findings suggest that OHT-associated inner retinal dysfunction is at least in part reversible with therapeutic intraocular pressure control.

Update on the pattern electroretinogram in glaucoma

PURPOSE

To review the efficacy of the pattern electroretinogram (PERG) in early diagnosis of glaucoma.

METHODS

Stimulation parameters of check size and temporal frequency are considered. Analyses of various peaks (P50, N95, the N95/P50) and Fourier steady-state are considered. The relation to visual field defects is explored.

RESULTS

The PERG is markedly alterated in glaucoma. It shows amplitude reductions in (still) normal areas of the visual field. Optical imaging on the retina needs to be optimal. Higher temporal frequency (>10 reversals/s) improves the sensitivity to detect glaucoma compared with transient stimulation. The ratio between the amplitudes to 0.8 degrees checks and to 16 degrees checks, "PERG ratio," exploits a check size-specific reduction in early glaucoma and reduces variability. Longitudinal studies suggest that the PERG can indicate incipient glaucoma damage before evidence from the visual field.

CONCLUSIONS

The PERG is a demanding electrophysiological technique that can serve as a sensitive biomarker for retinal ganglion cell function. With appropriate paradigms, PERG assists in identifying those patients with elevated interocular pressure in whom glaucoma damage is incipient before visual field changes occur.

Reversible dysfunction of retinal ganglion cells in non-secreting pituitary tumors

A large cohort of patients participated in a longitudinal study of early glaucoma progression. During follow up, six eyes of three patients displayed a relatively rapid deterioration of pattern electroretinogram (PERG) signal compared to changes in visual acuity, IOP, Standard Automated Perimetry, and Retinal Nerve Fiber Layer thickness measured by OCT. This deterioration prompted further testing including magnetic resonance imaging (MRI), which revealed pituitary tumors in all three patients, two of which were abutting but not compressing the chiasm. Following tumor resection, the PERG signal gradually recovered to baseline values in all six eyes. Results indicate that pituitary tumors may cause retrograde dysfunction of retinal ganglion cells (RGC) even in the absence of visible mechanical compression of the visual pathway, and such dysfunction may be reversed by tumor reduction. The results suggest that PERG is a useful tool in the early diagnosis and management of patients with chiasmal mass lesions.

Electrophysiological assessment of visual function in patients with non-arteritic ischaemic optic neuropathy

BACKGROUND AND PURPOSE

Our study aims to evaluate retinal function and neural conduction in post-retinal visual pathways of patients with non-arteritic ischaemic optic neuropathy (NION).

METHODS

Twenty patients (mean age: 63.7 +/- 5.96 year) with NION and 20 age-similar control subjects were enrolled. Simultaneous recording of pattern electroretinograms (PERGs) and visual evoked potentials (VEPs), and Log of minimum angle resolution (MAR) visual acuity (VA) were assessed in NION patients and controls.

RESULTS

Significantly (ANOVA, P < 0.01) abnormal PERG and VEP responses, delayed retinocortical time (RCT, difference between VEP P100 and PERG P50 implicit times), and reduced VA were found in NION patients with respect to control subjects. The delay in RCT was not significantly (Pearson's test, P > 0.01) correlated with the PERG impairment. The reduction in VA was significantly (Pearson's test, P < 0.01) correlated to the increase in VEP P100 implicit time and RCT, whereas no correlations (P > 0.01) were found with PERG abnormalities.

CONCLUSIONS

Non-arteritic ischaemic optic neuropathy patients with a reduction in VA may present two different, unrelated impairments: a dysfunction of the inner retinal layer (abnormal PERG) and abnormal post-retinal neural conduction (abnormal VEP and RCT). The reduction in VA seems to be related to the post-retinal impairment and seems to be independent from the retinal dysfunction.

Reproducibility of pattern electroretinogram in glaucoma patients with a range of severity of disease with the new glaucoma paradigm

PURPOSE

To determine the reproducibility of the pattern electroretinogram with the new Pattern Electroretinogram for Glaucoma (PERGLA) recording paradigm in glaucoma patients with a range of severity.

DESIGN

Experimental study.

PARTICIPANTS

Fifty-three glaucoma patients were recruited for the study (mean age +/- standard deviation [SD], 69+/-11 years). Their mean deviation (MD) global indices on static automatic perimetry ranged from 2.16 to -31.36 decibels (mean MD, -9.05).

INTERVENTION

All patients had pattern electroretinogram recordings done 5 times by the same operator, on 5 different days with the standardized PERGLA paradigm.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microvolts), phase (pi radians), response variability (coefficient of variation [CV] = SD/mean x 100) of amplitude and phase of 2 partial averages that build up the pattern electroretinogram waveform, interocular asymmetry in amplitude and phase (in terms of the CV generated by the pattern electroretinogram software), signal-to-noise (S/N) ratio, SDs, CV, and intraclass correlation coefficient (ICC). All analyses were done on one eye of each subject, except when interocular asymmetry was studied.

RESULTS

The CVs of intrasession variabilities in amplitude and phase were 12.08% and 2.20%, respectively, and those of intersession variabilities were 20.82% and 4.17%. The pattern electroretinogram produced intersession ICCs in amplitude and phase of 0.791 and 0.765, respectively. These ICCs were significantly higher than the ICCs for pattern electroretinogram interocular asymmetry in amplitude and phase (0.659 [P<0.05] and 0.571 [P<0.05], respectively). On average, the pattern electroretinogram S/N ratio in glaucomatous patients was about 5:1.

CONCLUSIONS

The reproducibility of PERGLA in glaucomatous patients is sufficiently good for it to be considered a useful complementary clinical tool. Being more reproducible, direct measures of amplitude and phase should be more useful in monitoring progression than interocular asymmetry comparisons.

Novel electrophysiological instrument for rapid and objective assessment of magnocellular deficits associated with glaucoma

PURPOSE

To introduce a rapid and objective electrophysiological technique that can assess visual function in the magnocellular pathway, which is thought to be affected in early-stage glaucoma.

METHODS

Low-contrast bright or dark isolated-checks were luminance-modulated against a static background at 10 Hz in order to drive preferentially the magnocellular ON or OFF pathway. Visual evoked potentials were recorded during 1-s epochs of stimulation and responses at the stimulus frequency were measured. Artifact rejection features ensured that eight valid runs were obtained per eye. Signal-to-noise ratios (SNR) were derived based on a multivariate statistic. In order to demonstrate its functionality, a small group of patients with glaucoma (N = 18, Snellen acuity of 20/30 or better) and control observers (N = 16) were tested. A participant failed the test if either eye yielded an SNR < or = 1. Receiver-operating-characteristic curve analysis was used to estimate the accuracy of group classification.

RESULTS

The instrument was found to elicit reliable responses from control observers. For the 15% bright condition, all control observers yielded significant isolated-check VEPs (icVEPs), whereas the majority of patients failed to do so, indicating significant losses in central visual function. This condition produced the highest classification accuracy (94%), followed by the 10% dark condition (91%).

CONCLUSIONS

Both ON and OFF divisions of the magnocellular pathway can be assessed rapidly through the application of the icVEP technique. This measure of central visual function may be of value in the detection of glaucomatous deficits and may complement tests of peripheral function.

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.

Evidence of the neuroprotective role of citicoline in glaucoma patients

The glaucomatous disease is currently considered a disease involving ocular and visual brain structures. This new approach to glaucoma introduces the possibility of inducing an improvement by means of a pharmacological approach similar to that used in different degenerative brain disorders. In line with this hypothesis, we studied the effects of oral (1600 mg/die, Cebrolux, Tubilux Pharma, Pomezia, Rome, Italy) or intramuscular (1000 mg/die, Cebroton, Tubilux Pharma) cytidine-5'-diphosphocholine (citicoline) treatment on retinal function and neural conduction in the visual pathways of glaucoma patients with moderate visual defects. Improvement of retinal function (objectively evaluated by pattern electroretinogram recordings) and of neural conduction along visual pathways (objectively evaluated by visual evoked potential recordings) were observed in glaucoma patients after two 60-day periods of oral or intramuscular treatment with citicoline. However, partial regression of this improvement was detected after two 120-day periods of washout. This suggests that the beneficial effects observed are in part treatment-dependent. The extension of citicoline treatment up to a period of 8 years lead to the stabilization or improvement of the glaucomatous visual dysfunction. These results suggest potential neuroprotective effects of citicoline in the glaucomatous disease.

Rodent models for glaucoma retinopathy and optic neuropathy

Animal models are useful to elucidate the etiology and pathology of glaucoma and to develop novel and more effective therapies for the disease. Because of the substantial similarities between the rodent and primate eyes, and the advances of relevant study techniques, rat and mouse models of glaucoma have recently become popular as research tools. This review surveys research techniques used in the measurement of rodent intraocular pressure, and also the evaluation of pertinent morphologic, biochemical, and functional changes in the retina, optic nerve head, and optic nerve. This review further describes in detail the individual rodent models, some of which serve as surrogate models and do not entail ocular hypertension, whereas others involve transient or chronic increases of intraocular pressure. The technical considerations and theoretical concerns of these models, their advantages, and limitations, are also discussed.

Decreased nasal-temporal asymmetry of the second-order kernel response of multifocal electroretinograms in eyes with normal-tension glaucoma

PURPOSE

To determine whether multifocal electroretinograms (mfERGs) can provide an index for identification of glaucomatous optic neuropathy in patients with normal-tension glaucoma (NTG).

METHODS

mfERGs were recorded in 30 normal volunteers (30 eyes) and 20 patients (20 eyes) with normal-tension glaucoma (NTG). Visual field examinations were performed with a Humphrey field analyzer, and all NTG patients had unilateral hemifield defects. The mfERGs were elicited by a binary m-sequence of flashes from 37 hexagonal elements that subtended an overall visual angle of 50 degrees x 40 degrees. The mfERGs were summed and analyzed for predetermined retinal loci. These mfERGs were compared with the perimetric findings of the corresponding visual fields.

RESULTS

In normal volunteers, the amplitude of the second-order kernel within the central 5 degrees of the nasal hemisphere was significantly smaller than in that of the temporal hemisphere (Wilcoxon signed-rank test, P = 0.0001). In NTG patients, this asymmetry of the two hemispheres was reduced or not present. The ratio of the amplitude of the mfERGs from the nasal and temporal hemispheres (N/T amplitude ratio) in normal control volunteers was significantly different from that of NTG patients with a hemifield defect (analysis of variance, P = 0.0001). When the cutoff value for the N/T amplitude ratio was set at 0.83 for discriminating glaucomatous eyes from normal eyes, the sensitivity was 65.0% with a specificity of 96.7%. The area under the receiver-operating characteristic curve of the N/T amplitude ratio was 0.86. The N/T amplitude ratio and the visual field indices were significantly correlated.

CONCLUSION

A decrease in the nasal-temporal asymmetry in the amplitude of the second-order kernel responses within the central 5 degrees of glaucoma patients' eyes indicated a dysfunction of the inner retinal layers, including of the retinal ganglion cells.