Electrophysiological methods in early glaucoma detection

Pattern Electroretinogram in Ocular Hypertension, Glaucoma Suspect and Early Manifest Glaucoma Eyes: A Systematic Review and Meta-analysis

Topic

To provide standardized confidence limits of the transient pattern electroretinogram (tPERG) P50 and N95 and steady state pattern electroretinogram (ssPERG) amplitudes in normal controls as compared to ocular hypertension (OHT), glaucoma suspect (GS), or early manifest glaucoma (EMG) eyes.

Clinical Relevance

The identification of standardized confidence limits in the context of pattern electroretinogram (PERG) might overcome the high intrinsic variability of the measure, and it might lead to a more intuitive understanding of the results as well as to an easier comparison of data from multiple tests, sites, and operators.

Methods

The study protocol was prospectively registered on the International Prospective Register of Systematic Reviews (ID: CRD42022370032). A literature search was conducted on PubMed, Web of Science, and Scopus. Studies comparing PERG raw data in normal control eyes as compared to OHT, GS, or EMG were included. The risk of bias was assessed using the National Institute for Health and Clinical Excellence quality assessment tool. The main outcome was the P50, N95, and ssPERG amplitude difference between the control and the study groups' eyes. The standardized mean difference was calculated as a measure of the effect size for the primary outcome. A subanalysis was conducted based on the type of electrodes adopted for the PERG measurements (invasive vs. noninvasive).

Results

Of the 4580 eligible papers, only 23 were included (1754 eyes). Statistically significant amplitude differences were found in the P50, N95, and ssPERG amplitudes between normal controls and OHT, GS, and EMG eyes. The highest standardized mean difference values were observed in the ssPERG amplitude in all 3 sets of comparison. The subanalysis did not reveal any statistically significant differences between invasive and noninvasive recording strategies.

Conclusions

The use of standardized values as the main outcome measures in the context of the PERG data analysis is a valid approach, normalizing several confounding factors which have affected the clinical utility of PERG both for individual patients and in clinical trials. Steady state PERG apparently better discriminates diseased eyes compared to tPERG. The adoption of skin-active electrodes is able to adequately discriminate between healthy and diseased statuses.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Electroretinogram and visual-evoked potential assessment of retinal and central visual function in a rat ocular hypertension model of glaucoma

PURPOSE/AIM

The aim of the study was to investigate the long-term functional changes that may occur in the retina and visual cortex in a rat ocular hypertension (OHT) model of glaucoma, used in our lab for treatment studies, using electroretinogram (ERG) and visual-evoked potential (VEP) cortical recordings in order to test the hypothesis that experimental glaucoma has differential retinal and central effects.

MATERIALS AND METHODS

Experimental glaucoma was induced unilaterally in Dark Agouti rats using hypertonic saline injection into the episcleral veins. After 3, 8, 16 and 26 weeks, ERGs and VEPs were recorded under scotopic conditions using brief full-field white flashes (10 μcd s m(-2) to 10.4 cd s m(-2)) and under photopic conditions using a rod-adapting background and white light flashes (0.13-10.4 cd s m(-2)).

RESULTS

At 16 and 26 weeks after OHT induction, there was a significant reduction in the amplitudes of the a- (50% and 30% of unoperated eye values, respectively) and b-waves (55% and 40%, respectively) of the scotopic ERG and the b-waves of the photopic ERG (55% and 45%, respectively) in the glaucomatous eyes. However, no significant changes in the VEPs simultaneously recorded over the visual cortex were seen at any of the time points.

CONCLUSIONS

The reductions in ERG amplitudes suggest that this model of glaucoma not only causes retinal ganglion cell (RGC) degeneration but also degeneration of the outer retinal cells, and this was confirmed by histology showing a reduction in the outer retinal layers in the glaucomatous eyes. Cortical VEPs did not show detrimental effects suggesting that the retinal damage in this model was not extensive enough to be detected with the VEP methods used or that there could be central compensation in this model of glaucoma.

Predictive value of short-wavelength automated perimetry: a 3-year follow-up study

PURPOSE

To determine whether structural changes in the retinal nerve fiber layer (RNFL) and functional abnormalities in short-wavelength automated perimetry (SWAP) can predict the onset of functional losses in standard automated perimetry patients suspected of having glaucoma.

DESIGN

Prospective observational case series.

PARTICIPANTS

A total of 160 eyes of ocular hypertensive subjects (intraocular pressure greater than 21 mmHg and normal standard automated perimetry) were included in the study.

INTERVENTIONS

The subjects underwent RNFL photographic evaluation and SWAP. Standard automated perimetries were repeated after 3 years to evaluate glaucomatous losses.

MAIN OUTCOME MEASURES

Onset of glaucomatous defects in conventional automated perimetry after 3 years of follow-up, with or without prior glaucomatous defects in RNFL and SWAP.

RESULTS

At the beginning of the study, 77 eyes showed RNFL losses (48%), and 58 eyes showed abnormalities in SWAP (36%). After the 3-year follow-up period, 14 of 77 eyes with RNFL losses had standard automated perimetry abnormalities (predicting sensitivity 93%), whereas 11 of 58 eyes with abnormal SWAP had standard automated perimetry losses (73% sensitivity).

CONCLUSIONS

RNFL and SWAP losses are signs of early glaucomatous damage and can predict functional losses in standard automated perimetry.

Glaucomatous damage patterns by short-wavelength automated perimetry (SWAP) in glaucoma suspects

PURPOSE

To determine the glaucomatous visual field damage patterns by short-wavelength automated perimetry (SWAP) in glaucoma suspects, and to compare the frequency of diffuse visual field losses and localized defects.

METHODS

157 eyes of 157 ocular hypertensive subjects who met the selection criteria (intraocular pressure greater than 21 mm Hg and normal standard visual fields) were studied. SWAP was done with a modified Humphrey Field Analyzer. Total (TD) and Pattern Deviation (PD) probability maps were calculated for SWAP. The frequency of abnormlities in the TD and PD were determined, analyzing the visual field loss components.

RESULTS

The involvement of the test points was more frequent on the TD plots than on the PD plots for all levels of defects (p< 0.001). The glaucomatous defects also showed certain topographical distribution.

CONCLUSIONS

A diffuse sensitivity component of visual field loss was found at all SWAP defect depths in glaucoma suspects.

Pilot study of the multifocal electroretinogram in ocular hypertension

AIMS

To investigate the variation of retinal function in ocular hypertension (OHT) using the multifocal electroretinogram (MERG), that can objectively assess regional retinal responses using kernel analysis.

METHODS

Patients with OHT were recruited for 61 flash MERG recording. The first and second order kernel responses were analysed and compared with responses from a normal group. All the patients with OHT had full eye examinations and visual field analysis to ensure they had no ocular pathology, apart from high IOP (>/= 22 mm Hg).

RESULTS

In OHT, both the first and the second order kernel responses showed a reduction in magnitude compared with control values. The second order kernel responses showed larger relative reduction of amplitude than the first order responses. In addition, the macula showed a greater reduction in response than the periphery.

CONCLUSIONS

First order and second order kernel analyses are useful for detecting changes of retinal response in OHT. The second order kernel analysis is important in measuring the inner retinal activity and is an important factor in detecting the early glaucoma case. Diminished macular response may be a useful sign in early glaucomatous changes.

[Study of electroretinogram components using pattern inversion in the early diagnosis of glaucoma]

Current electrophysiological techniques that help guide the diagnosis of glaucoma include pattern-electroretinogram (PERG) and pattern-visual evoked potential (PEVP) recordings. However, PERG has been recognized over the last decade as a good indicator of retinal ganglion cell function. One hundred seventy one eyes corresponding to 89 subjects were studied using both PERG (gold foil electrodes) and PEVP recordings. Two groups respectively including 32 subjects with ocular hypertension (OHT) and 27 subjects with simple chronic glaucoma (SCG) were compared with a control group composed of 30 healthy age-matched subjects. In regard to PERG recordings, the amplitudes of the P50 and N95 components were measured, but statistically significant differences were shown only for the N95 amplitudes both SCG (P < 0.01) and OHT (P < 0.05) groups. The amplitude and latency of the PEVP P100 component were analyzed. P100 latency was significantly delayed (P < 0.05) in SCG patients only. These findings suggest that the amplitude of the N95 component is the most sensitive electrophysiological parameter for early glaucoma detection.

Motion-onset visual evoked potentials improve the diagnosis of glaucoma

Chronic glaucoma has been shown preferentially to damage larger retinal cells and optic nerve fibres that provide the input to the magnocellular visual pathway. We compared the motion-onset visual evoked potentials (primarily the magnocellular system) with those to standard pattern reversal in 20 patients with bilateral chronic glaucoma. For motion-onset visual evoked potentials, the pattern (isolated 40' checks of 10% contrast) moved in four cardinal directions (varied randomly from trial to trial) at a velocity of 10 deg/s for 20 ms, with an interstimulus interval of 1 s. In pattern-reversal stimulation, the checkerboard reversed at a rate of 2 reversals per second. In 60% of the eyes investigated, the results of both types of visual evoked potentials correlated, showing either normal (27.5%) or increased (32.5%) latencies. In the remaining 40% of the eyes, the normal pattern-reversal visual evoked potential latencies were accompanied by prolonged motion-onset visual evoked potentials. The high occurrence of delayed motion-onset visual evoked potentials in our patients confirms the primary magnocellular loss in chronic glaucoma and suggests that the motion-onset VEPs are suitable for detection of glaucomatous changes.