Pattern electroretinogram progression in glaucoma suspects

Sensitivity and specificity of the uniform field electroretinogram in glaucoma detection in comparison to the pattern electroretinogram

PURPOSE

To determine the ability of the photopic negative response (PhNR) of the uniform field electroretinogram (UF-ERG) to identify early glaucomatous changes in comparison to the checkerboard and bar stimuli of the pattern electroretinogram (PERG).

METHODS

Forty-nine glaucoma patients were classified into two groups: glaucoma-suspect (23 eyes) and early to moderate glaucoma (30 eyes), based on their clinical examination and the results of standard automated perimetry. Thirty patients (30 eyes) with intraocular pressures (IOP) of 21 mmHg or less, with no history of reported high IOP, were included as controls. PERG and UF-ERG recordings were obtained on a Diagnosys D-341 Attaché-Envoy System. Visual field testing was done only for glaucoma-suspect and glaucoma patients.

RESULTS

All three tests (PERG bar stimulus, PERG checkerboard stimulus and PhNR) displayed significantly prolonged peak times for glaucoma and glaucoma-suspect patients, with delays ranging from 7.8 to 14.8%, depending on the test. The PERG bar stimulus also showed a significantly lower N95 amplitude for both glaucoma groups (with reductions of 26.0% and 33.0% for glaucoma-suspect and glaucoma groups, respectively). The PERG checkerboard N95 amplitude component had high sensitivity for detecting glaucoma patients but a low specificity (97% and 37%, respectively; AUC = 0.61). Overall, the PhNR peak time showed the highest sensitivity and specificity (77% and 90%, respectively; AUC = 0.87).

CONCLUSIONS

PERG bar stimuli and the PhNR of the UF-ERG can be used in the clinical setting to detect glaucoma-related changes in glaucoma-suspect and glaucoma patients. However, our data confirm that the PhNR peak time has the best combined sensitivity and specificity.

The natural history of untreated ocular hypertension and glaucoma

Glaucoma is a chronic, progressive disease leading to irreversible blindness if left untreated; however, since reducing intraocular pressure has proven to be successful in slowing disease progression, little is known about the natural history of untreated glaucoma. This knowledge can be valuable in guiding management decisions in the era of personalized medicine. A systematic search was performed in Medline (PubMed), Embase, and Web of Science in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRIMSA) guidelines. The rate of structural and/or functional progression and conversion to glaucoma or to a more advanced stage of glaucoma are discussed for ocular hypertension and different types of open-angle glaucoma. Forty-three studies were included. Different rates of progression were found both among and within the different diagnostic groups that belong to the open-angle glaucoma spectrum. The highest rate was found in pseudoexfoliation glaucoma, followed by high tension glaucoma, normal tension glaucoma, and ocular hypertension, in decreasing order. The lowest rate was observed in glaucoma suspects. The known rates of progression provide valuable prognostic information for ophthalmologists and patients. Nonetheless, due to high variability among patients, individual progression cannot be accurately predicted and repeated follow-up examinations are required to estimate individual progression.

Attenuated Amplitude of Pattern Electroretinogram in Glaucoma Patients with Choroidal Parapapillary Microvasculature Dropout

This study aims to investigate whether parapapillary choroidal microvasculature dropout (MvD) is related to visual function measured by pattern electroretinogram (PERG) in glaucomatous eyes with β-zone parapapillary atrophy (PPA). A total of 79 patients with open angle glaucoma and preperimetric glaucoma with β-zone PPA was included in this cross-sectional study. Through the deep layer of the Swept-source optical coherence tomography angiography image, the angular width and the area of MvD were measured. Visual function was evaluated with a standard automated perimetry and PERG. N95 and P50 PERG amplitudes in eyes with MvD were noticeably decreased compared to those without MvD (p = 0.004 and p = 0.007, respectively), although the mean deviation was not significantly different (p = 0.107). The lower N95 amplitude was associated with the presence of MvD (β = −0.668, p = 0.017) and wider angular width of MvD (B = −7.612, p = 0.014). Old age (p = 0.001), average ganglion cell’s inner plexiform layer thickness (p = 0.003), and the presence of MvD (p = 0.020) were significantly related to low N95 amplitude. Association between the presence and extent of the MvD and PERG amplitudes suggests that the presence of MvD has relevance to the generalized dysfunction of retinal ganglion cells.

Pattern Electroretinogram Parameters Are Associated with Optic Nerve Morphology in Preperimetric Glaucoma after Adjusting for Disc Area

Purpose

We examined the relationships between pattern electroretinogram and optical coherence tomography derived optic nerve head measurements, after controlling for disc area.

Methods

Thirty-two eyes from 20 subjects with preperimetric glaucoma underwent pattern electroretinogram and optical coherence tomography. Pattern electroretinogram parameters (Magnitude, MagnitudeD, and MagnitudeD/Magnitude ratio) and optic nerve head measurements (rim area, average cup to disc ratio, vertical cup to disc ratio, cup volume, retinal nerve fiber layer thickness sectors, and Bruch's membrane opening-minimum rim width thickness sectors) were analyzed after controlling for disc area.

Results

Magnitude and MagnitudeD were significantly associated with rim area (r ≥ 0.503, p ≤ 0.004). All pattern electroretinogram parameters significantly correlated with Bruch's membrane opening-minimum rim width sectors—temporal superior and nasal inferior (r = 0.400, p=0.039)—and retinal nerve fiber layer sectors—superior, nasal superior, and inferior (r ≥ 0.428, p ≤ 0.026). Magnitude and MagnitudeD explained an additional 26.8% and 25.2% of variance in rim area (B = 0.174 (95% CI: 0.065, 0.283), p=0.003, and B = 0.160 (95% CI: 0.056, 0.265), p=0.004), respectively. MagnitudeD and MagnitudeD/Magnitude ratio explained an additional 13.4% and 12.8% of the variance in Bruch's membrane opening-minimum rim width global (B = 38.921 [95% CI: 3.872, 73.970], p=0.031, and B = 129.024 (95% CI: 9.589, 248.460), p=0.035), respectively. All Bruch's membrane opening-minimum rim width sectors and retinal nerve fiber layer sectors (nasal superior, nasal inferior, and inferior) were significantly correlated with rim area (r ≥ 0.389, p ≤ 0.045).

Conclusion

PERG abnormalities can predict rim area loss in preperimetric glaucoma after controlling for disc area. We recommend controlling for disc area to increase diagnostic accuracy in early glaucoma.

Steady-State Pattern Electroretinography in Eyes with Glaucoma and High Myopia

Purpose

To investigate features of the steady-state pattern electroretinogram (ssPERG) in subjects with glaucoma (G), high myopia (HM; spherical equivalent ≤-6D) and glaucoma with high myopia (GHM).

Patients and Methods

Our study included 48 participants divided into 3 groups (G, HM, and GHM) who each underwent monocular ssPERG testing with Diopsys NOVA PERG protocols. The ConStim protocol detects distinct topographic patterns of dysfunction 16° and 24° around the central macula. MagD is the amplitude of the average signal and MagD/Mag ratio indicates the consistency of the response. ssPERG indices were compared between groups and correlated with functional (ie, visual field mean deviation (VFMD)) and structural (ie, average retinal nerve fibre layer (RNFL) thickness; Cirrus optical coherence tomography) features.

Results

Participants had an average age of 59.4±7.6 years. Mean Humphrey VFMD was -14.22 ± 2.88dB, -2.62 ± 1.18dB and -12.80 ± 2.60dB for G, HM and GHM groups, respectively. Mean RNFL thickness was 63.0 ± 8.20μm, 69.5 ± 15.7μm and 60.6 ± 5.0μm for G, HM and GHM groups, respectively. For the 24° setting, no significant differences were noted for any of the parameters. For the 16° setting, MagD was lower in the GHM group compared to the HM group (0.29µV vs 0.52µV; p = 0.02). Significant differences were noted for the MagD/Mag ratio between HM and G groups (0.58 vs 0.40; p = 0.02) and between HM and GHM groups (0.58 vs 0.35; p = 0.002). There were positive correlations between both MagD 16° and MagD/Mag ratio 16° with VFMD (correlation coefficient [r]=0.37, p = 0.009; and r = 0.44, p = 0.002, respectively) and RNFL (r = 0.43, p = 0.002; and r = 0.48, p = 0.001, respectively).

Conclusion

MagD/Mag ratio at 16° was significantly lower in glaucomatous eyes (with or without high myopia) compared to those with high myopia without glaucoma, suggesting that glaucoma has a distinct impact on MagD/Mag ratio at 16° irrespective of the presence of myopia.

PERG adaptation for detection of retinal ganglion cell dysfunction in glaucoma: a pilot diagnostic accuracy study

It has been previously demonstrated that the adaptive phase changes of steady-state pattern electroretinogram (SS-PERG), recorded during 4-min presentation of patterned stimuli, are reduced in glaucoma suspects and patients compared to normal subjects. Our study aims at testing the hypothesis that adaptive changes of SS-PERG, recorded using the novel optimized Next Generation PERG (PERGx) protocol, differ between glaucoma patients and controls. In this pilot cross-sectional study, we included 28 glaucoma patients and 17 age-matched normal subjects. Both patients and controls underwent a full ophthalmologic examination, visual field testing, OCT and PERGx. The PERGx signal was sampled over 2 min (providing 1 noise and 9 signal packets) in response to alternating gratings generated on an OLED display. PERGx amplitude and phase were analyzed to quantify adaptive changes over recording time. Receiver operating characteristic (ROC) curves were used to study the diagnostic accuracy of PERGx parameters in distinguishing glaucoma patients from normal subjects. PERGx amplitude and phase data showed declining trends in both groups. PERGx amplitude slope and grand-average vector amplitude and phase were significantly different in patients compared to controls (p < 0.01), whereas phase angular dispersion was greater in patients but not significantly different between the two groups. The area under the ROC curves were 0.87 and 0.76 for PERGx amplitude slope and grand-average vector amplitude, and 0.62 and 0.87 for PERGx angular dispersion and grand-average vector phase, respectively. The PERGx paradigm resulted highly accurate in detecting the reduction of amplitude adaptive changes in glaucoma patients, presumably due to the loss of functional retinal ganglion cell autoregulation. Thus, PERG adaptation, recorded by this new protocol, might be helpful in the identification and diagnosis of early glaucomatous dysfunction.

Monitoring for glaucoma progression with SAP, electroretinography (PERG and PhNR) and OCT

Purpose

To investigate the value of pattern electroretinography (PERG) and photopic negative response (PhNR) in monitoring glaucoma compared to standard clinical tests (standard automated perimetry (SAP) and clinical optic disc assessment) and structural measurements using spectral-domain OCT.

Methods

A prospective study included 32 subjects (32 eyes) with ocular hypertension, suspect or early glaucoma monitored for progression with clinical examination, SAP, PERG, PhNR and OCT for at least 4 years. Progression was defined clinically by the documented change of the optic disc and/or significant visual field progression (EyeSuite™ trend analysis). One eye per patient was included in the analysis.

Results

During the follow-up, 13 eyes (40.6%) showed progression, whereas 19 remained stable. In the progressing group, all parameters showed significant worsening over time, except for the PhNR, whereas in the stable group only the OCT parameters showed a significant decrease at the last visit. The trend of change over time using linear regression was steepest for the OCT parameters. At baseline, only the ganglion cell complex (GCC) and peripapillary retinal nerve fibre (pRNFL) thicknesses significantly discriminated between the stable and progressing eyes with the area under the ROC curve of 0.72 and 0.71, respectively. The inter-session variability for the first two visits in the stable group was lower for OCT (% limits of agreement within ± 17.4% of the mean for pRNFL and ± 3.6% for the GCC thicknesses) than for ERG measures (within ± 35.9% of the mean for PERG N95 and ± 59.9% for PhNR). The coefficient of variation for repeated measurements in the stable group was 11.9% for PERG N95 and 23.6% for the PhNR, while it was considerably lower for all OCT measures (5.6% for pRNFL and 1.7% for GCC thicknesses).

Conclusions

Although PERG and PhNR are sensitive for early detection of glaucomatous damage, they have limited usefulness in monitoring glaucoma progression in clinical practice, mainly due to high inter-session variability. On the contrary, OCT measures show low inter-session variability and might have a predicting value for early discrimination of progressing cases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10633-021-09854-8.

1α,25-dihydroxyvitamin D3 protects retinal ganglion cells in glaucomatous mice

BACKGROUND

Glaucoma is an optic neuropathy characterized by loss of function and death of retinal ganglion cells (RGCs), leading to irreversible vision loss. Neuroinflammation is recognized as one of the causes of glaucoma, and currently no treatment is addressing this mechanism. We aimed to investigate the anti-inflammatory and neuroprotective effects of 1,25(OH)2D3 (1α,25-dihydroxyvitamin D3, calcitriol), in a genetic model of age-related glaucomatous neurodegeneration (DBA/2J mice).

METHODS

DBA/2J mice were randomized to 1,25(OH)2D3 or vehicle treatment groups. Pattern electroretinogram, flash electroretinogram, and intraocular pressure were recorded weekly. Immunostaining for RBPMS, Iba-1, and GFAP was carried out on retinal flat mounts to assess retinal ganglion cell density and quantify microglial and astrocyte activation, respectively. Molecular biology analyses were carried out to evaluate retinal expression of pro-inflammatory cytokines, pNFκB-p65, and neuroprotective factors. Investigators that analysed the data were blind to experimental groups, which were unveiled after graph design and statistical analysis, that were carried out with GraphPad Prism. Several statistical tests and approaches were used: the generalized estimated equations (GEE) analysis, t-test, and one-way ANOVA.

RESULTS

DBA/2J mice treated with 1,25(OH)2D3 for 5 weeks showed improved PERG and FERG amplitudes and reduced RGCs death, compared to vehicle-treated age-matched controls. 1,25(OH)2D3 treatment decreased microglial and astrocyte activation, as well as expression of inflammatory cytokines and pNF-κB-p65 (p < 0.05). Moreover, 1,25(OH)2D3-treated DBA/2J mice displayed increased mRNA levels of neuroprotective factors (p < 0.05), such as BDNF.

CONCLUSIONS

1,25(OH)2D3 protected RGCs preserving retinal function, reducing inflammatory cytokines, and increasing expression of neuroprotective factors. Therefore, 1,25(OH)2D3 could attenuate the retinal damage in glaucomatous patients and warrants further clinical evaluation for the treatment of optic neuropathies.

Impact of femtosecond laser-assisted in situ keratomileusis on retinal ganglion cell function

PURPOSE

To analyse the effect of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) on the electrical response of retinal ganglion cells using pattern electroretinography (pERG).

METHODS

This was a longitudinal, prospective, observational pilot study. We included consecutive myopic patients who underwent FS-LASIK to correct up to 6 dioptres of myopia and up to 2 dioptres of astigmatism. Patients with excessive blinking or tearing and those with Snellen uncorrected visual acuity less than 0.9 dec on postop day 1 were excluded. Diopsys NOVA^® (Diopsys Inc., NJ) pERG records, using high- and low-contrast patterns, were obtained 16 h and 1 month after FS-LASIK was performed. Magnitude (μV), Magnitude D (μV), Magnitude D/Magnitude ratio and signal-to-noise ratio (dB) were analysed. Wilcoxon test for nonparametric paired data was employed.

RESULTS

pERG data from 24 eyes were analysed from 24 patients who underwent FS-LASIK. Mean age was 35.79 ± 9.86 years. Mean preoperative refraction was -2.69 ± 7.6 D (spherical) and -0.38 ± 0.40 D (cylinder). Mean surgical time was 56.88 ± 7.6 s. No statistically significant differences were obtained for any of the studied parameters when comparing 16 h with 1 month after FS-LASIK, with the exception of Magnitude with low contrast, which increased from 1.21 ± 0.2 to 1.39 ± 0.29 µV at 16 h and 1 month postoperatively, respectively (p = 0.03).

CONCLUSIONS

FS-LASIK seems to induce a mild and transitory defect in retinal ganglion cell function. Only a mild decrease was detected in the magnitude value for low-contrast stimuli when pERG was performed 16 h postoperatively, and it returned to normal 1 month after surgery.

Relationship between N95 Amplitude of Pattern Electroretinogram and Optical Coherence Tomography Angiography in Open-Angle Glaucoma

Purpose: The pattern electroretinogram (PERG) is useful to detect retinal ganglion cell (RGC) damage in patients with glaucoma. Optical coherence tomography angiography (OCTA) measures retinal vessel density (VD), which is known to be reduced in glaucoma. There may be correlations between parameters of the PERG and OCTA in open-angle glaucoma (OAG). Methods: In total, 95 eyes of 95 OAG patients and 102 eyes of 102 normal controls were included in this study. N35, P50, and N95 latency along with P50 and N95 amplitude were obtained using the PERG. Retinal VD was measured around the peripapillary and macular area according to the ETDRS grid (concentric circles with diameters of 1, 3, and 6 mm), which is named a center (≤1 mm), an inner (1–3 mm), an outer (3–6 mm), and a full (≤6 mm) area. Pearson correlation analysis was done between parameters, and partial correlation analysis was done after adjusting confounding factors. Results: P50 amplitude, N95 amplitude, and VD of most measured areas were significantly lower in the OAG group compared to the normal group. N95 amplitude showed a statistically significant correlation with parameters of optical coherence tomography and visual field, peripapillary outer and full VD, and macular outer and full VD even after adjusting confounding factors. There was no significant correlation between parameters in the normal group. Conclusions: N95 amplitude was associated with structural and functional change including VD reduction in OAG. Microvascular alterations may be associated with dysfunctional changes of RGC recorded by the PERG in OAG.

P2X7 receptor antagonism preserves retinal ganglion cells in glaucomatous mice

To investigate the role of P2X7 receptor to preserve retinal ganglion cells (RGCs) structure and function in a genetic mouse model (DBA/2J mouse) of age-related glaucomatous neurodegeneration. Chronic treatment with P2X7 receptor antagonist eye drops was carried out in order to assess RGCs function and density by pattern electroretinogram (PERG) and RBPMS immunostaining, respectively. Further, microglia activation was assessed in flat-mounted retina by using Iba-1 immunostaining. Untreated glaucomatous eyes displayed significant microglia activation, alteration of PERG signal, and RGCs loss. In the P2X7 receptor antagonist-treated eyes, the PERG signal was significantly (p < 0.05) improved compared to controls, along with a significant (p < 0.05) reduction in terms of retinal microglial activation, and remarkable preservation of RGCs density. Altogether, these findings demonstrated that topical treatment with a P2X7 receptor antagonist has a neuroprotective effect on RGCs in glaucomatous mice, suggesting an appealing pharmacological approach to prevent retinal degenerative damage in optic neuropathy.

Long-term PERG monitoring of untreated and treated glaucoma suspects

PURPOSE

To investigate long-term structural and functional progression of untreated and treated glaucoma suspects (UGS and TGS).

METHODS

Retrospective analysis of serial steady-state pattern electroretinogram (PERG), mean retinal nerve fiber layer thickness (RNFLT), and standard automated perimetry mean deviation (SAP-MD) in UGS (N = 20) and TGS (N = 18). Outcome measures were the rates of change (linear regression slopes) of PERG amplitude, PERG phase, mean RNFLT, and SAP-MD over 9.8 ± 1.3 years (15.6 ± 4.2 visits).

RESULTS

The number of patients with significant (P < 0.05) progression slopes for PERG amplitude, PERG phase, RNFLT, and SAP-MD was, respectively, UGS: 5, 0, 4, 2; TGS: 8, 2, 6, 5. In UGS, outcome measures were not correlated with each other. In TGS, both PERG amplitude and RNFLT were significantly (P < 0.05) correlated with SAP-MD (R ≥ 0.58), while PERG amplitude and RNFLT were not correlated with each other (R = 0.43, P = 0.064). The rate of change of SAP-MD was predicted (P < 0.05) by a linear combination of RNFLT slope and PERG amplitude slope.

CONCLUSIONS

Results substantiate and extend previous results showing that steady-state PERG amplitude progressively decreased over time in a proportion of glaucoma suspects, with relatively steeper slope in TGS compared to UGS. RNFLT progression also had a steeper slope in TGS compared to UGS; however, progressions of PERG amplitude and RNFLT were not significantly correlated. Both PERG progression and RNFLT progression independently contribute to prediction of visual field progression.

Bilateral asymmetry improved accuracy when assessing glaucomatous vision-related quality of life impairment

Bilateral asymmetry has been used in optical coherence tomography tests to find early damage to the optic nerve. However, limited studies have quantitatively evaluated bilateral asymmetry in electrophysiological disorders in patients with glaucoma. The aim of the study was to evaluate bilateral asymmetry in pattern visual evoked potentials (PVEPs) and conventional clinical markers as well as its potential use in detecting glaucomatous impairment. After investigating 60 glaucomatous patients (120 eyes) and 65 age and sex-matched normal control subjects (130 eyes) using uni- and multivariable analysis, we found that vision-related quality of life (VRQOL) impairment was significantly associated with larger bilateral asymmetry index (BAI) of clinical markers. Rasch-calibrated National Eye Institute Visual Function Questionnaire-25 scores were significantly associated with the BAI in PVEPs latency in 15 minutes check size (β = -0.478, 95% confidence interval [CI], -0.708 to -0.248, P < .001) and the BAI in visual field mean deviation (β = -0.249, 95% CI, -0.454 to -0.044, P = .018) according to multivariable analysis. Bilateral asymmetry in objective and subjective functional measurements was quantitatively associated with glaucomatous VRQOL impairment. This finding may help bridge the gap in understanding between patients and clinicians, and increase awareness of how glaucomatous neuropathic progression may interfere with patients' daily life.

Rescue of retinal function by BDNF in a mouse model of glaucoma

Vision loss in glaucoma is caused by progressive dysfunction of retinal ganglion cells (RGCs) and optic nerve atrophy. Here, we investigated the effectiveness of BDNF treatment to preserve vision in a glaucoma experimental model. As an established experimental model, we used the DBA/2J mouse, which develops chronic intraocular pressure (IOP) elevation that mimics primary open-angle glaucoma (POAG). IOP was measured at different ages in DBA/2J mice. Visual function was monitored using the steady-state Pattern Electroretinogram (P-ERG) and visual cortical evoked potentials (VEP). RGC alterations were assessed using Brn3 immunolabeling, and confocal microscope analysis. Human recombinant BDNF was dissolved in physiological solution (0.9% NaCl); the effects of repeated intravitreal injections and topical eye BDNF applications were independently evaluated in DBA/2J mice with ocular hypertension. BDNF level was measured in retinal homogenate by ELISA and western blot. We found a progressive decline of P-ERG and VEP responses in DBA/2J mice between 4 and 7 months of age, in relationship with the development of ocular hypertension and the reduction of Brn3 immunopositive RGCs. Conversely, repeated intravitreal injections (BDNF concentration = 2 µg/µl, volume = 1 µl, for each injection; 1 injection every four days, three injections over two weeks) and topical eye application of BDNF eye-drops (12 µg/µl, 5 µl eye-drop every 48 h for two weeks) were able to rescue visual responses in 7 month DBA/2J mice. In particular, BDNF topical eye treatment recovered P-ERG and VEP impairment increasing the number of Brn3 immunopositive RGCs. We showed that BDNF effects were independent of IOP reduction. Thus, topical eye treatment with BDNF represents a promisingly safe and feasible strategy to preserve visual function and diminish RGC vulnerability to ocular hypertension.

Relationship between transient and steady-state pattern electroretinograms: theoretical and experimental assessment

PURPOSE

We determined if the overlap of transient (tr) pattern electroretinograms (PERG(tr)) can explain the generation of the steady-state (SS) pattern electroretinogram (PERG(SS)), and investigated the relationship between the two types of responses.

METHODS

Slightly jittered pattern reversals were used to generate quasi SS (QSS) PERG(SS) responses from eight normal subjects, recorded using lower eyelid skin electrodes, at rates between 6.9 and 26.5 reversals per second (rps). Jittered quasi PERG(SS) were deconvolved using the frequency domain continuous loop averaging deconvolution method. Additionally, conventional PERG(tr) at 2.2 rps and PERG(SS) at each of the QSS stimulation rates were obtained from all subjects. Two synthetic PERG(SS) responses were constructed at each stimulation rate, one using the PERG(tr) obtained at that rate, and the other using the conventional 2.2 rps PERG(tr). Synthetic responses then were compared to the recorded PERG(SS) using amplitude, latency, and spectral measurements.

RESULTS

Findings indicate that the PERG(SS) obtained at SS rates can be predicted using the superposition of deconvolved tr PERGs at each particular rate. Although conventional PERG(tr) can explain PERG(SS) obtained at rates below 15.4 rps (≥ 97% correlation), for higher reversal rates only deconvolved responses obtained at that rate can produce the recorded SS responses (96% vs. 65% correlation at 26.5 rps).

CONCLUSIONS

The study shows that PERG(SS) results from the overlapping of tr PERG(tr) waveforms generated at that reversal rate. The first two peaks (N(SS) and P(SS)) of the PERG(SS) reflect N35 and P50 waves of the tr PERG(tr). The N95 amplitude is reduced at conventional (16 rps) SS rates, but contributes to the overall PERG(SS) amplitude.

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.

Unwrapping of transient responses from high rate overlapping pattern electroretinograms by deconvolution

OBJECTIVE

Due to overlapping, temporal information is mostly lost in high rate steady-state pattern electroretinograms (PERGSS). This study develops a deconvolution method and a display/recording system to "unwrap" PERGSS and obtain a transient, "per stimulus" response (PERGtr) regardless of reversal rate.

METHODS

Processing and instrumentation, including high temporal resolution display and acquisition were developed for deconvolving PERGs acquired at high rates by slight jittering of reversal onsets at a given mean rate.

RESULTS

The system was successfully tested at eight rates from 2.2 to 78.1rps. At medium rates (17.4-41.2rps) recordings with conventional morphology (N35-P50-N95) but earlier peaks and higher amplitudes were extracted up to 40rps. At higher rates, smaller triphasic responses were obtained, exhibiting similar peak latencies, but reversed polarity. Oscillating potentials (OPs) were also recorded at all rates after deconvolution.

CONCLUSIONS

Transient PERGs and OPs can be extracted from quasi steady-state PERG recordings obtained at high rates with a deconvolution algorithm using high temporal resolution display and acquisition systems.

SIGNIFICANCE

The methodology to extract transient and oscillatory responses from steady-state PERGs could be useful in understanding high rate responses and diagnosis of various retinal diseases by revealing temporal information on waveform components which cannot be normally observed.

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.

Pattern electroretinogram (PERG) in the early diagnosis of normal-tension preperimetric glaucoma: a case report

INTRODUCTION

The purpose of this case is to present the use of pattern electroretinogram (PERG) in the early diagnosis of normal-tension preperimetric glaucoma in 56 years old woman.

METHODS AND RESULTS

At baseline the results were as follows: distance-corrected visual acuity in the right eye (RE) and left eye (LE) 1.0 and 0.7, respectively (Snellen table), normal anterior segments in both eyes, normal fundus in the RE and abnormal cup to disc ratio (0.6) in the LE. Intraocular pressure (IOP) was within normal limits in both eyes: RE-14 mmHg, LE-18 mmHg (Goldmann tonometer). Results of standard automated perimetry (SAP), short wavelength automated perimetry (SWAP) and nerve fiber analyzer (GDx) were normal in both eyes. PERG result was normal in the RE but in the LE reduced amplitudes of P50 and N95 waves were observed. After topical treatment (Xalacom to the LE), a reduction of IOP to 13 mmHg was achieved and was accompanied by amplitudes increase of PERG waves. After discontinuation of the therapy, IOP increased to 18 mmHg and P50 and N95 amplitudes decreased to the values before treatment, suggesting the influence of IOP lowering therapy on electrical function of retinal ganglion cells. After 4 years from the baseline, static perimetry results were still normal, but abnormalities in retinal nerve fiber layer thickness were detected in GDx.

CONCLUSIONS

PERG was a useful test not only for the early diagnosis of normal-tension preperimetric glaucoma, but also in evaluating the effectiveness of antiglaucomatous treatment.

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.

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.

Retinal ganglion cell morphology after optic nerve crush and experimental glaucoma

PURPOSE

To study sequential changes in retinal ganglion cell (RGC) morphology in mice after optic nerve crush and after induction of experimental glaucoma.

METHODS

Nerve crush or experimental glaucoma was induced in mice that selectively express yellow fluorescent protein (YFP) in RGCs. Mice were euthanized 1, 4, and 9 days after crush and 1, 3, and 6 weeks after induction of glaucoma by bead injection. All YFP-RGCs were identified in retinal whole mounts. Then confocal images of randomly selected RGCs were quantified for somal fluorescence brightness, soma size, neurite outgrowth, and dendritic complexity (Sholl analysis).

RESULTS

By 9 days after crush, 98% of RGC axons died and YFP-RGCs decreased by 64%. After 6 weeks of glaucoma, 31% of axons died, but there was no loss of YFP-RGC bodies. All crush retinas combined had significant decreases in neurite outgrowth parameters (P ≤ 0.036, generalized estimating equation [GEE] model) and dendritic complexity was lower than controls (P = 0.017, GEE model). There was no change in RGC soma area after crush. In combined glaucoma data, the RGC soma area was larger than control (P = 0.04, GEE model). At 3 weeks, glaucoma RGCs had significantly larger values for dendritic structure and complexity than controls (P = 0.044, GEE model), but no statistical difference was found at 6 weeks.

CONCLUSIONS

After nerve crush, RGCs and axons died rapidly, and dendritic structure decreased moderately in remaining RGCs. Glaucoma caused an increase in RGC dendrite structure and soma size at 3 weeks.