Normative data for a user-friendly paradigm for pattern electroretinogram recording

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.

Head-down posture induces PERG alterations in early glaucoma

PURPOSE

To probe susceptibility of retinal ganglion cells (RGC) to physiological stressors associated with moderate head-down body tilt in patients with suspicion of glaucoma or early manifest glaucoma (EMG).

METHODS

One hundred nine subjects with best corrected visual acuity (BCVA) ≥ 20/20 and no disease other than glaucoma [glaucoma suspects (GS)=79, EMG=14, normal controls (NC)=16 and comparable age range were tested. Noncontact intraocular pressure (IOP), pattern electroretinogram (PERG), and brachial blood pressure/heart rate measurements were performed in 3 consecutive conditions (∼0038 min apart): seated (baseline), -10-degree whole body head-down tilt (HDT), and seated again (recovery). PERG amplitude and latency, IOP, and systolic/diastolic blood pressures, heart rate, calculated mean central retinal artery pressure, ocular perfusion pressure, and systolic/diastolic perfusion pressures were evaluated.

RESULTS

During HDT, IOP significantly (P<0.001) increased in all groups approximately to the same extent (approximately 20%). PERG amplitude did not change in NC but decreased significantly (P<0.001) in patients (GS, -25%, EMG -23%). PERG phase become delayed in NC (-1.6%, P=0.04) but more so in patients (GS, -2.7%, P<0.001; EMG, -6.0%, P<0.001). The proportion of patients with PERG alterations significantly (P<0.05) exceeding those occurring in age-adjusted and baseline-adjusted NC were, GS: amplitude 20%, phase 15%; EMG: amplitude 14%, phase 50%. All measures recovered baseline values after HDT.

CONCLUSIONS

Moderate HDT induces temporary worsening of RGC function in a subpopulation of GS and EMG patients. This noninvasive protocol may help disclose abnormal susceptibility of RGCs in a subset of the patients at risk of glaucoma.

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.

Electrophysiology and glaucoma: current status and future challenges

Visual electrophysiology allows non-invasive monitoring of the function of most processing stages along the visual pathway. Here, we consider which of the available methods provides the most information concerning glaucomatous optic nerve disease. The multifocal electroretinogram (ERG), although often employed, is less affected in glaucoma than two direct measurements of retinal ganglion cell function, namely the pattern ERG (PERG) and the photopic negative response (PhNR) of the ERG. For the PERG, longitudinal studies have been reported, suggesting that this method can be used for the early detection of glaucoma; for the PhNR, no longitudinal study is available as yet. The multifocal PERG can spatially resolve ganglion cell function but its glaucomatous reduction is typically panretinal, even with only local field changes and so, its topographic resolution is of no advantage in glaucoma. The multifocal visual evoked potential promises objective perimetry and shows sensitivity and specificity comparable with standard automated perimetry but has not been established as a routine tool to date.

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.

The bioelectric field of the pattern electroretinogram in the mouse

PURPOSE

To compare the bioelectric field associated with the pattern electroretinogram (PERG) with that of the flash electroretinogram (FERG) in the mouse.

METHODS

PERGs and FERGs were recorded from each eye in 32 C57BL/6J mice using corneal silver loops referenced to a subcutaneous needle on the back of the head. PERG stimuli were horizontal gratings of 0.05 cycles per degree and 98% contrast reversing 2 times per second. Light-adapted FERG stimuli were bright strobe flashes. Stimuli were presented either monocularly or binocularly. In some experiments, TTX was injected in one eye and saline in the contralateral eye.

RESULTS

The PERG recorded from the contralateral, occluded eye had slightly larger amplitude (1.14 ×, P < 0.01) and longer latency (+1.57 ms, P < 0.01) compared with the ipsilateral eye. Under binocular stimulation, the PERG amplitude was much larger (1.67 ×, P < 0.01) than the monocular amplitude. TTX injected in the stimulated eye drastically reduced the PERG in both eyes. Monocular FERGs were recordable from the stimulated eye only and were moderately reduced by TTX. Binocular and monocular FERGs had similar amplitudes.

CONCLUSIONS

PERG and FERG generate different bioelectric fields in the mouse. The PERG bioelectric field is consistent with a dipole model whose axis is orthogonal to the eye axis, whereas the standard dipole model for the FERG is coaxial. Possible sources of the PERG bioelectric field are unmyelinated optic nerve axons adjacent to the sclera. Results provide new insights on the generators of the PERG signal and its alterations in mouse models of glaucoma and optic nerve diseases.

Simultaneous retinal and cortical visually evoked electrophysiological responses in between migraine attacks

PURPOSE

People with migraine often report aversion to flickering lights and show abnormal results on behavioural tasks that require the processing of temporal visual information. Studies have reported that the cortically evoked electrophysiological response to a flickering visual stimulus is abnormal; however, none have considered whether there is an underlying pre-cortical abnormality. In this cross-sectional study, we consider whether people with migraine have retinal and cortical electrophysiological abnormalities to flickering stimuli.

METHODS

Monocular transient (1 Hz) and steady-state (8.3 Hz) pattern reversal electroretinograms (PERGs) and pattern visual evoked responses (PVERs) were measured simultaneously in 45 people with migraine (26 without aura, 19 with aura) and 30 non-headache controls at a time between migraine attacks.

RESULTS

PERG amplitude and timing did not differ significantly between groups. Transient PVER amplitude was significantly reduced (28%) in the migraine with aura group compared to the controls F(2,72) = 3.6, p = 0.03). Both migraine groups showed significant reductions (32%, 39%) in steady-state PVER amplitude relative to controls (F(2,70) = 4.3, p = 0.02).

CONCLUSIONS

This study finds normal retinal processing of flickering stimuli in the presence of abnormal cortical function between migraine attacks.

Innovative pattern reversal displays for visual electrophysiological studies

Pattern Reversal (PR) stimulation is a frequently used tool in the evaluation of the visual pathway. The PR stimulus consists of a field of black and white segments (usually checks or bars) of constant luminance, which change phase (black to white and white to black) at a given reversal rate. The Pattern Electroretinogram (PERG) is a biological potential that is evoked from the retina upon viewing PR display. Likewise, the Pattern Visual Evoked Potential (PVEP) is a biological potential recorded from the occipital cortex when viewing a PR display. Typically, PR stimuli are presented on a Cathode Ray Tube (CRT) or Liquid Crystal Display (LCD) monitor. This paper presents three modalities to generate pattern reversal stimuli. The three methods are as follows: a display consisting of array of Light Emitting Diodes (LEDs), a display comprised of two miniature projectors, and a display utilizing a modified LCD display in conjunction with a variable polarizer. The proposed stimulators allow for the recording of PERG and PVEP waveforms at much higher rates than are capable with conventional stimulators. Additionally, all three of the alternative PR displays will be able to take advantage of advanced analysis techniques, such as the recently developed Continuous Loop Averaging Deconvolution (CLAD) algorithm.

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.

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.

Erratum: Psychoneuroimmunology: application to ocular diseases

Psychoneuroimmunology (PNI) is a relatively new discipline within the field of neuroscience which researches the relationship between emotional states, the central and peripheral nervous systems, and the endocrine and immune systems. Negative psychological states, such as stress, anxiety, and depression, may alter immune system regulation and modulation of peripheral cytokines. A plethora of PNI studies have shown that increased psychological stress and depression are associated with an alteration of immune functioning and worsened health outcomes for many conditions. To date, application of PNI methodology has not been reported for ocular diseases. This article provides an historical perspective on the origins of the rift between the emotional and spiritual from physical aspects of disease. A review of how stress is mediated through sympathetic adrenomedullary and hypothalamic pituitary axis activation with shifts in immunity is provided. The literature which supports spirituality in healing is presented. Finally, ocular diseases which would be most amenable to a PNI approach are discussed.

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.

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.

Psychoneuroimmunology: application to ocular diseases

Psychoneuroimmunology (PNI) is a relatively new discipline within the field of neuroscience which researches the relationship between emotional states, the central and peripheral nervous systems, and the endocrine and immune systems. Negative psychological states, such as stress, anxiety, and depression, may alter immune system regulation and modulation of peripheral cytokines. A plethora of PNI studies have shown that increased psychological stress and depression are associated with an alteration of immune functioning and worsened health outcomes for many conditions. To date, application of PNI methodology has not been reported for ocular diseases. This article provides an historical perspective on the origins of the rift between the emotional and spiritual from physical aspects of disease. A review of how stress is mediated through sympathetic adrenomedullary and hypothalamic pituitary axis activation with shifts in immunity is provided. The literature which supports spirituality in healing is presented. Finally, ocular diseases which would be most amenable to a PNI approach are discussed.

Effect of epigallocatechin-gallate on inner retinal function in ocular hypertension and glaucoma: a short-term study by pattern electroretinogram

BACKGROUND

Epigallocatechin-gallate (EGCG) is a powerful antioxidant with suggested neuroprotective action. The aim of this study was to evaluate the effect of short-term supplementation of EGCG on inner retinal function in ocular hypertension (OHT) and open-angle glaucoma (OAG).

METHODS

Eighteen OHT and 18 OAG patients (perimetric mean deviation: >-10 dB) were randomly assigned to assume oral placebo or EGCG over a 3-month period in a randomized, placebo-controlled, double-blind, cross-over design clinical trial (clinicaltrials.gov identifier: NCT00476138). Pattern-evoked electroretinograms (PERGs) to 1.6 cycles/degree square-wave gratings, counterphased at 16 reversals/second, and standard automated perimetry (Humphrey 30-2) were assessed at the study entry (baseline), and after 3 months of placebo or EGCG.

RESULTS

After EGCG, PERGs of OAG, but not OHT patients were increased in amplitude, compared either to baseline values (mean amplitude change: 0.06 log microV, p < 0.05) or to PERG amplitude values found in the same patients after placebo administration (mean change: -0.02 log microV, p not significant; difference between EGCG and placebo: 0.08 log microV, p < 0.05). In both OHT and OAG patients, standard automated perimetry did not show significant changes after either EGCG or placebo. In individual OAG patients, the magnitude of PERG amplitude increment after EGCG was inversely related (r = -0.8, p < 0.01) to corresponding baseline amplitudes.

CONCLUSIONS

Although this study cannot provide evidence for long-term benefit of EGCG supplementation in OAG, and the observed effect is small, the results suggest that EGCG might favourably influence inner retinal function in eyes with early to moderately advanced glaucomatous damage.

Adaptive changes of inner retina function in response to sustained pattern stimulation

We have characterized adaptive changes of inner retina function in response to sustained pattern stimulation in 32 normal subjects with an age range 23-77 years by measuring changes of the pattern electroretinogram (PERG) as a function of time. Contrast-reversal stimuli had square-wave profile in space and time, with peak spatial and temporal frequency and high contrast to maximize response amplitude. The PERG signal was sampled over 5min with a resolution of 15s. PERG signals were non-stationary, resulting in either progressive amplitude decline or even enhancement to a plateau, with a time course that could be well described by an exponential function with a time constant of 1-2min. Higher initial amplitudes were generally associated with amplitude decline, and lower initial amplitudes with enhancement. The delta amplitude (plateau minus initial) was a linear function of the initial amplitude. The magnitude of delta decreased with decreasing initial amplitude and inverted its sign for initial amplitudes about 1/3 lower than the maximum initial amplitude measured, but still about 3-4 times larger than the noise. Amplitude decline was generally associated with phase lag, whereas amplitude enhancement was associated with phase advance. Altogether, PERG generators appear to slowly adjust their gain in order to keep their sustained activity at an intermediate level that is rather independent of the level of activity at stimulus onset. This behavior is reminiscent of a buffering mechanism, where glial cells may play a primary role. An energy-budget model of neural-vascular-glial interaction is provided together with an equivalent electrical circuit that accounts for the results.

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.

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.

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.

Symmetry between the right and left eyes of the normal retinal nerve fiber layer measured with optical coherence tomography (an AOS thesis)

PURPOSE

To determine the limits of the normal amount of interocular symmetry in retinal nerve fiber layer (RNFL) thickness measurements obtained with third-generation time domain optical coherence tomography (OCT3).

METHODS

Both eyes of normal volunteers were scanned using the peripapillary standard and fast RNFL algorithms of OCT3.

RESULTS

A total of 108 volunteers were included in the analysis. The mean +/- standard deviation (SD) of age of the volunteers was 46.0 +/- 15.0 years (range 20-82). Forty-two participants (39%) were male and 66 (61%) were female. Mean RNFL thickness correlated extremely well, with intraclass correlation coefficients of 0.89 for both algorithms (95% confidence interval [CI], 0.84-0.93). The mean RNFL thickness of the right eye measured 1.3 mum thicker than the left on the standard scan (SD 4.7, 95% CI 0.4-2.2, P = .004) and 1.2 mum on the fast scan (SD 5.2, 95% CI 0.1-2.2, P = .026). The 95% tolerance limits on the difference between the mean RNFL thicknesses of right minus left eye was -10.8 and +8.9 mum with the standard scan algorithm and -10.6 and +11.7 mum with the fast scan algorithm.

CONCLUSIONS

Mean RNFL thickness between the 2 eyes of normal individuals should not differ by more than approximately 9 to 12 mum, depending on which scanning algorithm of OCT3 is used and which eye measures thicker. Differences beyond this level suggest statistically abnormal asymmetry, which may represent early glaucomatous optic neuropathy.

Pattern electroretinogram in glaucoma

PURPOSE OF REVIEW

Several studies have shown that the pattern electroretinogram, a direct, objective method of measuring retinal ganglion cell function, is altered early in ocular hypertension and glaucoma. Renewed interest in the pattern electroretinogram for early detection of pre-perimetric glaucoma has been sparked by noninvasive and reproducible methods of recording using skin electrodes.

RECENT FINDINGS

With the noninvasive pattern electroretinogram, response abnormalities have been detected in up to 50% of glaucoma suspects with normal standard perimetry. In early glaucoma (with either normal or high intraocular pressure), a reduction of intraocular pressure has sometimes yielded improvement in pattern electroretinogram amplitude. A prolonged steady-state stimulus presentation reduces the pattern electroretinogram amplitude and increases optic nerve blood flow in normal subjects, suggesting that sustained activity of retinal ganglion cells is physiologically associated with autoregulatory changes of the neural-vascular system. It is unknown whether this autoregulation is altered in glaucoma. The multifocal pattern electroretinogram does not seem to have an advantage over the pattern electroretinogram in the early detection of glaucoma. The photopic negative response of the diffuse flash electroretinogram has shown changes in glaucoma, but may not be able to detect retinal dysfunction in normal tension glaucoma.

SUMMARY

The pattern electroretinogram is a noninvasive, direct, objective method that may be useful to clinicians in detecting early retinal ganglion cell dysfunction in glaucoma suspects. The pattern electroretinogram may also optimize treatment strategies based on improvement of retinal ganglion cell function.

The mouse pattern electroretinogram

Mouse models of optic nerve disease such as glaucoma, optic neuritis, ischemic optic neuropathy, and mitochondrial optic neuropathy are being developed at increasing rate to investigate specific pathophysiological mechanisms and the effect of neuroprotective treatments. The use of these models may be greatly enhanced by the availability of non-invasive methods able to monitor retinal ganglion cell (RGC) function longitudinally such as the Pattern Electroretinogram (PERG). While the use of the PERG as a tool to probe inner retina function in mammals is known since 25 years, relatively less information is available for the mouse. Here, the PERG technique and the main applications in the mouse are reviewed.

A new pattern electroretinogram paradigm evaluated in terms of user friendliness and agreement with perimetry

PURPOSE

To assess ease of use of the pattern electroretinogram optimized for glaucoma screening (PERGLA) paradigm by a novice operator; to study test-retest variability of the PERGLA parameters; and to compare results from the PERGLA to those from perimetry.

DESIGN

Cohort study.

PARTICIPANTS

Twelve healthy control subjects and 16 patients with moderate to advanced glaucoma in at least 1 eye.

METHODS

Pattern electroretinograms were recorded simultaneously from both eyes using a commercially available testing station. Each participant underwent PERGLA procedures in 2 sessions. One eye of each subject was tested on contrast sensitivity perimetry (CSP) in which a 0.4 cycles/degree Gabor patch served as a stimulus. Central visual fields results from conventional automated perimetry (CAP) were obtained from patients' records. Bland-Altman analysis was performed on PERGLA results to assess normal test-retest variability. Differences from mean normal (in decibels [dB]) were compared for PERGLA versus CSP and CAP.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude, noise, phase, and test-retest variability (coefficient of variation); contrast sensitivity from CSP; perimetric sensitivity from CAP; and differences from mean normal for PERGLA, CSP, and CAP.

RESULTS

The mean log amplitude (0.08+/-0.12 log muV) and the mean phase (1.92+/-0.07 pi rad) for the control group were consistent with published PERGLA norms, as was test-retest variability for both amplitude (coefficient of variation [CV] = 8.2+/-7.0%) and phase (CV = 1.1+/-0.9%). The mean signal-to-noise ratio (8.7+/-4.5) was lower than published norms. The test-retest variability increased as PERGLA log amplitude decreased (R2>0.12, P<0.05). On average, differences from mean normal were similar for PERGLA versus CSP and for PERGLA versus CAP (mean differences<0.5 dB) with 95% confidence intervals near +/-4 dB in both comparisons.

CONCLUSIONS

A novice operator successfully replicated published PERGLA norms in a young control group for amplitude, phase, and repeatability. Higher test-retest variability was found in eyes with smaller signals. On average, PERGLA results were in reasonable agreement with those from perimetry, although there existed large individual differences which may limit the usage of PERGLA in screening or in following progression of glaucoma.

The pattern electroretinogram as a tool to monitor progressive retinal ganglion cell dysfunction in the DBA/2J mouse model of glaucoma

PURPOSE

To determine the baseline characteristics, reliability, and dynamic range of the pattern electroretinogram (PERG) as a tool to monitor progressive RGC dysfunction in the DBA/2J mouse model of glaucoma with spontaneously elevated intraocular pressure (IOP).

METHODS

PERGs were recorded from 56 undilated eyes of 28 anesthetized (ketamine-xylazine-acepromazine) DBA/2J mice of different ages (2-4 months, n = 44 eyes; 12-14 months, n = 12 eyes) in response to contrast reversal of gratings that maximize PERG amplitude (95% contrast, 1-Hz reversal, 0.05 cyc/deg spatial frequency, 50 degrees x 56 degrees field size). Robust averaging (1800 sweeps) was used to isolate PERG from background noise. Cone-driven ERGs in response to diffuse light flashes superimposed on a rod-adapting background (FERG) were also recorded.

RESULTS

PERGs had consistent waveforms and were reproducible across batches of mice and operators. In 2- to 4-month-old mice (prehypertensive stage), the PERG amplitude (mean, 8.15 +/- 0.4 microV [SEM]) was considerably larger than the noise (mean 1.18 +/- 0.1 microV). The test-retest variability (two different sessions 1 week apart) and interocular asymmetry of PERG amplitude was approximately 30%, and that of PERG latency was approximately 17%. In 12- to 14-month-old mice (advanced hypertensive stage) the PERG amplitude (mean, 1.29 +/- 0.12 microV) was close to that of noise. In 12- to 14-month-old mice the FERG was reduced to a lesser extent compared with the PERG.

CONCLUSIONS

The PERG has an adequate signal-to-noise ratio, reproducibility, and dynamic range to monitor the progression of functional changes in the inner retina in DBA/2J mice.

The relationship between retinal ganglion cell function and retinal nerve fiber thickness in early glaucoma

PURPOSE

To compare relative reduction of retinal ganglion cell (RGC) function and retinal nerve fiber layer (RNFL) thickness in early glaucoma by means of steady-state pattern electroretinogram (PERG) and optical coherence tomography (OCT), respectively.

METHODS

Eighty-four persons with suspected glaucoma due to disc abnormalities (GS: mean age 56.6 +/- 13.8 years, standard automated perimetry [SAP] mean deviation [MD] -0.58 +/- 1.34 dB) and 34 patients with early manifest glaucoma (EMG, mean age 65.9 +/- 10.7 years, SAP MD -2.7 +/- 4.5 dB) were tested with PERG and OCT. Both GS and EMG patients had small refractive errors, corrected visual acuity > or =20/25, and no systemic or retinal disease other than glaucoma.

RESULTS

MDs from age-predicted normal values were larger for PERG amplitude (GS: -1.113 dB; EMG: -2.352 dB) compared with the PERG-matched RNFL thickness (GS: -0.217 dB; EMG: -0.725 dB). Deviations exceeding the lower 95% tolerance intervals of the normal population were more frequent for PERG amplitude (GS: 26%; EMG: 56%) than PERG-matched RNFL thickness (GS: 6%; EMG: 29%).

CONCLUSIONS

In early glaucoma, reduction in RGC electrical activity exceeds the proportion expected from lost RGC axons, suggesting that a population of viable RGCs in the central retina is dysfunctional. By combining PERG and OCT it is, in principle, possible to obtain unique information on reduced responsiveness of viable RGCs.

Electrophysiological assessment of glaucomatous visual dysfunction during treatment with cytidine-5'-diphosphocholine (citicoline): a study of 8 years of follow-up

In this study we assessed, by simultaneous recordings of visual evoked potentials (VEPs) and pattern-electroretinograms (PERGs), the effects cytidine-5'-diphosphocholine (citicoline) on retinal function and/or visual cortical responses in glaucoma patients. Thirty glaucoma patients were randomly divided into two age-matched groups: patients in group GC (15 patients) were treated with citicoline (1,000 mg/die intramuscularly) for 2 months; patients in group GP (15 patients) were treated with placebo for 2 months. After 4 months of wash-out (month 6), GC patients underwent a further 2-month period of citicoline treatment (months 7-8) followed by another 4-month period of wash-out (months 9-12). In GP patients the wash-out was extended for a further 6 months (months 7-12). During the following 13-96 months, GC patients received additional 2-month periods of treatment with citicoline (each period followed by 4 months of wash-out) for a total of 16 periods in 8 years. GP patients were also examined at months 24, 26, 48, 60, 72, 84 and 96. In GC patients the first two treatments with citicoline induced a significant (p <0.01) improvement of VEP and PERG parameters with respect to pre-treatment conditions. VEPs and PERGs recorded in GC patients after the first wash-out revealed that, although there was a worsening trend, the electrophysiological improvement was still maintained with respect to baseline conditions. The additional periods of citicoline treatment in GC patients during the subsequent 13-96 months induced a greater (p <0.01) improvement of VEP and PERG parameters with respect to pre-treatment conditions and when compared to GP patients. Thus, we observed that citicoline significantly improves retinal and cortical bioelectrical responses in glaucoma patients, suggesting a potential use of this substance in the medical treatment of glaucoma, as a complement to hypotensive therapy.

Habituation of retinal ganglion cell activity in response to steady state pattern visual stimuli in normal subjects

PURPOSE

To evaluate autoregulatory changes of retinal ganglion cell (RGC) activity, as measured by the pattern electroretinogram (PERG), when the eye is exposed to a steady state presentation of stimuli that maximize PERG amplitude and blood flow.

METHODS

The PERG was recorded from both eyes of 14 normal subjects in response to steady state presentation (4 minutes) of contrast-reversing (16.28/s) gratings (1.6 cyc/deg) with different contrast (12%-99%) and mean luminance (40-1.3 cd/m(2)). One temporal period of the stimulus (122.8 ms) was sampled and averaged in packets of 50 sweeps ( approximately 15 seconds each). PERG amplitude and phase were evaluated by Discrete Fourier Transform and displayed as a function of time. Data were fitted with an exponential decay function to evaluate PERG changes with time.

RESULTS

For patterns of 99% contrast, the PERG amplitude progressively decreased with time until reaching a plateau approximately 30% lower than the initial amplitude after approximately 2 minutes (habituation). The ratio between initial and plateau amplitude did not change by reducing the stimulus luminance by 1 log unit. However, reducing contrast decreased amplitude habituation. The habituation was abolished at 25% contrast.

CONCLUSIONS

Decrease of PERG amplitude with time is consistent with a slow adaptive change of RGC activity in response to high-contrast, steady state stimuli. The authors propose that the initial amplitude represents an index of RGC activity, and the plateau amplitude represents a dynamic equilibrium between RGC activity and the available energy supply. These results are relevant for a better understanding of glaucomatous optic neuropathy.

Pattern electroretinogram abnormality and glaucoma

PURPOSE

To determine the existence of retinal ganglion cell dysfunction and associated risk factors in glaucoma suspects with increased optic disc cupping and normal visual field.

DESIGN

Cross-sectional, observational study.

PARTICIPANTS

Two hundred glaucoma suspect (GS) patients were identified based on optic disc abnormalities (vertical cup-to-disc ratios [C/D]>0.5; vertical C/D asymmetry >or= 0.2; disc hemorrhages; notching) in association with known glaucoma risk factors (positive family history, African American descent, increased intraocular pressure [IOP]), but normal visual fields. Forty-two patients had early manifest glaucoma (EMG). Sixteen normal black subjects were added to update previous pattern electroretinogram (PERG) normative data and to establish a normal control (NC) group with a racial breakdown comparable with that of the study groups.

METHODS

Pattern electroretinograms were recorded simultaneously from both eyes using skin electrodes and automated analysis; visual fields were monitored with standard white-on-white automated perimetry (SAP) central 24-2 program; vertical C/D was evaluated by an independent reader from stereo disc photographs; and univariate and multivariate statistical analysis between PERG and other outcome measures was evaluated.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microV), phase (pi rad), and interocular asymmetry in amplitude and phase (%); and SAP mean deviation (MD; decibels), vertical C/D, age (years), IOP (mmHg), and race (black vs. nonblack).

RESULTS

The PERG results were abnormal in at least 1 of the outcome measures in 52% of GS patients and 69% of EMG patients. The PERG amplitude was correlated weakly with both MD (P<0.01) and vertical C/D (P = 0.05). The correlation between PERG amplitude and MD and C/D was stronger (P<0.001) for interocular differences rather than absolute measures. Interocular PERG amplitude asymmetry increased with severity of disease (EMG>GS>NC; P<0.01). The PERG amplitude decline with age was steeper in patients with a more negative MD (P<0.01) and in patients with a more negative MD and a larger vertical C/D (P = 0.06). Black race (but not family history) was associated with lower PERG amplitude (P = 0.005) in GS and EMG patients, but not in normal controls (P = 0.44).

CONCLUSIONS

The correlation between PERG abnormality and known risk factors for glaucoma indicates that PERG has a predictive potential for the development or progression of the disease, or both.

Restoration of retinal ganglion cell function in early glaucoma after intraocular pressure reduction: a pilot study

PURPOSE

To investigate the changes of pattern electroretinogram (PERG) after intraocular pressure lowering in glaucoma patients and normal controls.

DESIGN

Interventional retrospective cross-sectional study.

PARTICIPANTS

Twenty-five patients (49 eyes) with ocular hypertension or glaucoma undergoing topical treatment to lower IOP served as a study group; 22 patients (44 eyes) with ocular hypertension or glaucoma observed without treatment served as a control group for treated glaucoma patients; 9 normal subjects (18 eyes) receiving a 250-mg acetazolamide tablet served as a second study group; and 17 normal subjects (34 eyes) from a previous study served as a second control group for treated normal subjects.

METHOD

Pattern electroretinograms were recorded simultaneously from both eyes using skin electrodes and automated analysis. Visual field (VF) analyses were performed with white-on-white standard automated perimetry (SAP). Intraocular pressure was measured with Goldmann applanation tonometry; central corneal thickness was measured with pachymetry.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude (microvolts), phase (pi rads), and test-retest variability (test 2-to-test 1 ratio, in decibels), SAP mean deviation (decibels), and IOP (millimeters of mercury).

RESULTS

In 56% of right eyes and 21% of left eyes of the treated glaucoma subgroup, the PERG amplitude and/or phase improved beyond the 95% confidence intervals of the test-retest variability of the untreated glaucoma control group. Pattern electroretinogram improvement with IOP lowering occurred in both high- and low-tension glaucoma eyes. Eyes with severely impaired VFs showed little improvement in PERG; however, eyes of normal subjects treated with acetazolamide did not show significant PERG changes relative to the test-retest variability of normal controls.

CONCLUSIONS

Retinal ganglion cell function can be at least partially restored after IOP reduction in glaucomatous eyes with early VF impairment.

Pattern electroretinogram and glaucoma

Purpose of review

Several studies have shown that the pattern electroretinogram, a direct, objective method of measuring retinal ganglion cell function, is altered early in ocular hypertension and glaucoma. Renewed interest in the pattern electroretinogram for early detection of pre-perimetric glaucoma has been sparked by noninvasive and reproducible methods of recording using skin electrodes.

Recent findings

With the noninvasive pattern electroretinogram, response abnormalities have been detected in up to 50% of glaucoma suspects with normal standard perimetry. In early glaucoma (with either normal or high intraocular pressure), a reduction of intraocular pressure has sometimes yielded improvement in pattern electroretinogram amplitude. A prolonged steady-state stimulus presentation reduces the pattern electroretinogram amplitude and increases optic nerve blood flow in normal subjects, suggesting that sustained activity of retinal ganglion cells is physiologcally associated with autoregulatory changes of the neuralvascular system. It is unknown whether this autoregulation is altered in glaucoma. The multifocal pattern electroretinogram does not seem to have an advantage over the pattern electroretinogram in the early detection of glaucoma. The photopic negative response of the diffuse flash electroretinogram has shown changes in glaucoma, but may not be able to detect retinal dysfunction in normal tension glaucoma.

Summary

The pattern electroretinogram is a noninvasive, direct, objective method that may be useful to clinicians in detecting early retinal ganglion cell dysfunction in glaucoma suspects. The pattern electroretinogram may also optimize treatment strategies based on improvement of retinal ganglion cell function.