Assessment of macular function by multifocal electroretinogram before and after macular hole surgery

Morphological and Functional Features in Patients with Idiopathic Macular Hole Treatment

Purpose

To evaluate the multifocal electroretinogram (mfERG) and optical coherence tomography (OCT) angiography features in patients with idiopathic macular hole (IMH) before and after vitrectomy.

Patients and Methods

This prospective study was conducted at Shanxi Eye Hospital from January 2019 to December 2021. Twenty-five eyes of 25 patients with unilateral IMH, the unaffected fellow eyes, and 30 eyes of healthy patients were investigated. All unilateral IMH eyes underwent vitrectomy.

Results

The IMH eyes had significantly delayed latency (rings 2-5) of mfERG compared with the healthy control eyes, and the amplitude density of all rings of mfERG was reduced (P < 0.05). When comparing the mfERG components before surgery and at the follow-up, the amplitude density of IMH eyes (ring 1, 3, 4 and 5) was increased significantly (P < 0.05). The delayed implicit times of the second and fifth ring were significantly shortened compared with those of preoperative eyes (P < 0.05). The mean delayed implicit time of mfERG in six months after surgery was negatively correlated with visual acuity (r = -0.890, P = 0.043). Significant differences of superficial retinal blood flow density (SRBFD, P < 0.001) and choroidal blood flow density (CBFD) (P < 0.05) got via OCTA were found between IMH before surgery and healthy control eyes. SRBFD of the fellow eyes were significantly different with the healthy control eyes (P = 0.038). Statistically significance of SRBFD and CBFD changes in IMH eyes were found before and after surgery (P < 0.05).

Conclusion

IMH eyes had a decreased amplitude density and a delayed implicit time in some regions. Additionally, SRBFD and CBFD were both increased after vitrectomy, which suggests that the blood supply of the retina and choroid is partially restored after vitrectomy.

Postoperative Changes in Vessel Density according to Macular Hole and Macular Pseudohole Subtypes

Purpose: To determine the postoperative changes in vessel density according to macular hole and macular pseudohole (MPH) subtypes and to investigate the differences in the mechanisms underlying their development. We also investigated whether changes in vessel density are correlated with changes in the multifocal electroretinogram (mfERG) and best corrected visual acuity (BCVA).Methods: We reviewed the medical records of patients with MPH or a macular hole who underwent pars plana vitrectomy. We included 15 eyes of 15 patients with a full thickness macular hole (FTMH), nine eyes of nine patients with a tractional lamellar macular hole (LMH), eight eyes of eight patients with a degenerative LMH, and nine eyes of eight patients with a MPH. The BCVA, foveal avascular zone (FAZ), foveal and parafoveal vessel density, and mfERG ring 1 and ring 2 P1 amplitudes were analyzed before and 1 and 6 months after surgery.Results: One month postoperatively, the foveal vessel density of patients with a MPH or tractional LMH increased (p = 0.011, p = 0.008). The parafoveal vessel density of patients with a MPH, tractional LMH, and FTMH increased (p = 0.007, p = 0.038, p = 0.031). There was no significant increase in foveal or parafoveal vessel density in patients with a degenerative LMH (p = 0.201, p = 0.171). There was a significant correlation between the change in parafoveal vessel density and that in BCVA 6 months postoperatively in patients with a FTMH (r = -0.543, p = 0.037).Conclusions: By assessing changes in vessel density after vitrectomy, it is possible to estimate the effect of traction according to the type of macular hole. There was a significant correlation between parafoveal vessel density and BCVA in patients with a FTMH. Restoration of the retinal structure and vessel density might improve visual acuity.

Asymmetric extent of distortion measured using the Watzke-Allen Test in patients with macular hole

Visual dysfunction in patients with macular hole is believed to occur because of cone cell displacement, often measured by the Watzke-Allen test (WAT). However, it is unknown if the horizontal and vertical measurements recorded by WAT reflect the true extent of photoreceptor displacement. This study aimed to measure the extent of photoreceptor displacement in patients with macular hole using WAT and compare the displacement value with the hole diameter measured by optical coherence tomography (OCT). This prospective, observational study at a single tertiary referral center included 43 patients with macular hole. WAT thresholds were assessed for their ability to detect macular hole. The slit was presented vertically and horizontally, and the brightness of the monitor screen was 180 cd/m². Horizontal and vertical WAT thresholds for distortion were measured. Correlations and performance evaluations were assessed by Pearson's correlation analysis and Wilcoxon rank-sum test, respectively, between WAT threshold values and hole diameters. Horizontal and vertical WAT thresholds and diameters were compared using paired t-tests. The mean vertical WAT threshold (1.95° ± 0.87°) was significantly higher than the mean horizontal threshold (1.71° ± 0.73°; P < 0.0001). The mean minimum horizontal hole diameter (303.42 ± 111.16 mm; visual angle, 1.01°) was significantly greater than the mean minimum vertical diameter (264.12 ± 107.88 mm; visual angle, 0.88°; P = 0.0149). The minimum vertical and horizontal macular hole diameters were positively correlated with the vertical and horizontal WAT threshold values (r = 0.514, P < 0.01; r = 0.447, P < 0.01, respectively). The WAT threshold values were greater than the respective minimum macular hole diameters, indicative of cone cells displacement over an area larger than that of the hole. The difference in the extent of vertical and horizontal distortions suggests asymmetric hole formation. Hence, WAT threshold values may help evaluate visual function in patients with macular hole.

Effect of optical defocus on multifocal ERG responses

BACKGROUND

Multifocal electroretinography (mfERG) is a sensitive technique to probe retinal function topographically. Various conditions such as macular degeneration decrease the first-order kernel (K1) response magnitude of mfERG. Previous studies have given inconsistent results on the effect of optical defocus due to poor controls. This study investigated the effect of optical defocus on the K1 response of the central retina using a well-controlled method.

METHODS

Twenty subjects were recruited to undergo mfERG measurement using the VERIS 4.0 system. A four millimetre artificial pupil was fitted before each fully-dilated right eye, optically corrected for the viewing distance. The implicit times and response amplitudes of n1 (first negative trough) and p1 (first positive peak) under three different optical defocus conditions (zero dioptres, +1.00 D and +3.00 D) were measured.

RESULTS

The implicit times of n1 and p1 did not demonstrate any significant variation from the central macula to para-macula under different optical defocus conditions. The response amplitude of n1 did not show any changes from the central macula to para-macula but the response amplitude of the central macular p1 showed a significant reduction by 12 per cent under +1.00 D defocus and +3.00 D defocus.

CONCLUSIONS

Optical defocus causes mild reduction in mfERG at the central macula but there are no significant changes in the periphery. A full optical correction is recommended for mfERG measurement to minimise the reduction of the macular response due to optical defocus.

Epiretinal membrane: A review

The prevalence of epiretinal membrane (ERM) is 7% to 11.8%, with increasing age being the most important risk factor. Although most ERM is idiopathic, common secondary causes include cataract surgery, retinal vascular disease, uveitis and retinal tears. The myofibroblastic pre-retinal cells are thought to transdifferentiate from glial and retinal pigment epithelial cells that reach the retinal surface via defects in the internal limiting membrane (ILM) or from the vitreous cavity. Grading schemes have evolved from clinical signs to ocular coherence tomography (OCT) based classification with associated features such as the cotton ball sign. Features predictive of better prognosis include absence of ectopic inner foveal layers, cystoid macular oedema, acquired vitelliform lesions and ellipsoid and cone outer segment termination defects. OCT-angiography shows reduced size of the foveal avascular zone. Vitrectomy with membrane peeling remains the mainstay of treatment for symptomatic ERMs. Additional ILM peeling reduces recurrence but is associated with anatomical changes including inner retinal dimpling.

Inverted ILM Flap Technique in Idiopathic Full-Thickness Macular Hole Surgery: Functional Outcomes and Their Correlation with Morphologic Findings

Objectives

The inverted internal limiting membrane (ILM) flap technique has been shown to increase the success rate in large full-thickness macular holes (FTMHs) and in FTMHs associated with high myopia. The aim of our study was to confirm the efficacy and safety of inverted ILM flap technique in idiopathic FTMHs independent of their dimensions and to assess functional outcomes and their correlation to morphologic findings.

Methods

Sixteen consecutive patients affected by idiopathic FTMH were enrolled in this prospective study. The preoperative mean (±SD) diameter of the FTMH was 422 (±106) µm. All patients underwent vitrectomy and ILM peeling with inverted ILM flap. At 1-, 3-, and 6-month postoperative visits, visual acuity measurement, indirect ophthalmoscopy, and microperimetry were performed, and the foveal contour and the integrity of the ellipsoid zone (EZ) and external limiting membrane (ELM) were investigated using spectral domain optical coherence tomography (SD-OCT).

Results

At six months postoperatively, 15 out of 16 (93.75%) patients obtained FTMH closure. The mean best corrected visual acuity (BCVA) improved from 1.1 LogMAR to 0.3 LogMAR, and the mean retinal sensitivity (MS) improved from 7.2 to 23.4 dB. ELM defects were evident in 1 out of 16 (6.25%) eyes, and EZ defects were detected in 2 out of 16 (12,50%) eyes. A statistically significant relationship was observed between BCVA, MS, and EZ reconstitution at each follow-up visit.

Conclusions

Results confirm that the inverted ILM flap technique is a safe and effective option for FTMH treatment and show a strong correlation between higher BCVAs and MSs and EZ reconstitution after surgery.

A multifocal electroretinography study to evaluate risk of developing macular hole in the fellow eye of patients suffering with unilateral macular hole

Background

Visual outcome of eyes has often been found to be unsatisfactory even after successful closure of a macular hole, owing to factors like persistent metamorphopsia, scotoma, and reduced sensitivity. Therefore, it becomes critical to evaluate and study the probability and risk of developing a macular hole in the fellow eyes of the patient. This study analyzed the multifocal electroretinographic responses to help predict the risk of macular hole development in fellow eyes.

Methods

In total 26 fellow eyes, 26 eyes with macular hole, and 50 eyes of 25 controls were enrolled prospectively. The retinal responses from the different rings were compared in the three groups. Optical coherence tomography was done to rule out macular pathology or vitreomacular traction in the fellow eyes.

Results

All the fellow eyes under observation showed significantly reduced mean amplitudes of retinal response densities, in all rings as compared with controls (31.45 ± 10.38 versus 48.87 ± 7.55, p = 0.00). Three of the fellow eyes developed a macular hole during the 24 months observation period. The prevalence of fellow eye involvement was 11.5%. Relative risk of developing macular hole in the fellow eye ranged from 25 to 75.

Conclusion

All the fellow eyes, including those that did not develop a macular hole, showed significantly reduced responses on multifocal electroretinogram. This indicates that macular hole may not be a focal disease. It may have widespread functional deficit which is bilateral in nature and suggestive of a degenerative or ischemic insult.

Detection and monitoring of subclinical ocular siderosis using multifocal electroretinogram

BACKGROUND

Although full-field electroretinogram (ffERG) is the gold standard test to detect physiological dysfunction in siderosis, it measures overall retinal function. This study aims to determine if multifocal electroretinogram (mfERG) can detect subclinical siderosis in eyes with an iron intraocular foreign body (IOFB).

METHODS

Twenty eyes of 20 patients with retained iron IOFB, clear ocular media and good visual acuity (≥20/120) were enroled in this prospective case-control study. The fellow eyes served as control. These were evaluated with ffERG and mfERG at baseline. Serial mfERG was done till six months after pars plana vitrectomy with IOFB removal. Primary outcomes measures were amplitude and peak time of P1 and N1 wave of mfERG.

RESULTS

The median age was 25 years (range 18-55). Most patients (n = 14/20) presented within a month of trauma. Baseline ffERG showed no difference in either 'a' or 'b' wave amplitude or peak time between cases and controls. However, on mfERG, there was a significant decrease in P1 and N1 wave amplitude and delay in P1 wave peak time in <2° retinal ring in cases as compared to controls (p = 0.001, 0.001 and 0.02 respectively) despite variability in results. At 6 months, P1 amplitude showed significant improvement from baseline in cases (p = 0.010). However, P1 peak time did not show significant recovery (p = 0.65).

CONCLUSIONS

mfERG may reveal subclinical electrophysiological retinal dysfunction in eyes with iron IOFB in cases with normal ffERG. P1 peak time may serve as an electrophysiological marker for past retinal damage.

[Dynamics of electrophysiological parameters of the retina after surgical treatment of idiopathic macular hole]

AIM

to study the dynamics of recovery of electrophysiological parameters of the retina after surgical treatment of idiopathic macular hole (IMH) and to assess their relevance to functional prognosis of the operation.

MATERIAL AND METHODS

The study included 118 patients (120 eyes) examined before and after successful IMH surgery. The patients underwent electroretinography (Ganzfeld and multifocal), static computed perimetry, and optical coherence tomography. They were also tested for the electrical sensitivity of the retina, lability of the visual analyzer, and critical fusion frequency. Postoperative functional parameters of the retina (electrophysiological included) were followed up at 1-2, 5-6, and 12-plus months and then compared to those obtained before surgery. Parameter dynamics, relationships, and the prognostic value of particular indicators were of interest.

RESULTS

It was found that after successful restoration of retinal anatomy, functional parameters of the retina gradually improve and reach their maximum at 3 to 12 months, however, remain below the normal range in all cases. In 58 cases, postoperative visual acuity was 0.5 or higher (regarded as 'high postoperative visual acuity' - the HPVA group) and was accompanied by high density of foveal biopotential and foveal light sensitivity. In the HPVA group, the majority (62%) were patients with preoperative 'shift phenomenon' (a shift of the maximum of bioelectric potential from the fovea to parafovea and perifovea, its amplitude and density being supernormal for these retinal regions).

CONCLUSION

Changes in electrophysiological and other functional parameters of the retina can be detected within 3-12 months after successful IMH surgery. Their recovery is not full and goes with a delay relative to restoration of retinal structure. The probability of high functional result of the operation, which includes an increase in visual acuity, foveal light sensitivity, and amplitude and density of foveal biopotential, is higher in patients with biopotential shift at baseline.

Inverted Internal Limiting Membrane Flap Technique for Repair of Large Macular Holes: A Short-term Follow-up of Anatomical and Functional Outcomes

Background:

Inverted internal limiting membrane (ILM) flap technique has recently been reported in a limited number of studies as an effective surgical technique for the management of large macular holes (MHs) with fair MH closure rates as well as gains in visual acuity. In the current study, longitudinal changes in multi-focal electroretinogram (mfERG) responses, best-corrected visual acuity (BCVA) and spectral-domain optical coherence tomography (SD-OCT) were evaluated in eyes with large MHs managed by this technique.

Methods:

A prospective noncontrolled interventional study of eight patients (eight eyes) with large MHs (minimum diameter >400 μm) was conducted. All MHs were treated with pars plana vitrectomy and indocyanine green-assisted inverted ILM flap technique. SD-OCT images were used to assess the anatomical outcomes of surgery while BCVA and mfERG were used to evaluate the functional outcomes during a 3-month follow-up.

Results:

All patients underwent successful intended manipulation and translocation of the ILM flap without flap dislocation and achieved complete anatomical closure. Partial microstructural reconstruction, demonstrated on SD-OCT as restoration of the external limiting membrane and the ellipsoid zone, was observed in all cases as early as 1 month after surgery. Functionally, as compared to baseline, all patients showed improvements in BCVA and all but one in mfERG response during follow-up. However, Pearson's test revealed no significant correlations between BCVA and mfERG responses of the fovea and of the macular area at each evaluation time point.

Conclusions:

Inverted ILM flap technique appeares to be a safe and effective approach for the management of large idiopathic MHs with favorable short-term anatomical and functional results. Postoperative reconstruction of the microstructure generally shows good consistency with improvements in both BCVA and mfERG response, of which the latter might be a supplement for the former in postoperative functional follow-up.

[Electrophysiological parameters of the retina in idiopathic macular hole]

AIM

To investigate the nature and range of electrophysiological disturbances in idiopathic macular hole (IMH) and establish their relationship with structural parameters of the retina.

MATERIAL AND METHODS

The study included 249 patients (280 eyes) with IMH. All of them underwent ganzfeld and multifocal electroretinography (ERG), optical coherence tomography, and evaluation of retinal electrical sensitivity and analyzer lability. The results were then compared to those of non-IMH patients (196 paired eyes) and controls (25 people, 49 eyes).

RESULTS

Multifocal ERG findings prove that IMH is always associated with significant changes in bioelectrical potential of the central retina. In 62% of cases its decreased density and extended latency were registered in not only the fovea, but also the para- and perifovea. In 8% of cases the changes involved everything within a 30-degree area of the central retina. In 30% of cases the maximum bioelectric potential was found to have shifted from the centre to para- and perifovea, its amplitude and density being supernormal for these regions (shift phenomenon). A weak correlation between electrophysiological parameters and retinal thickness around the hole has been also established.

CONCLUSION

Of all methods used to assess retinal function in IMH, multifocal ERG is the most informative. In 100% of cases foveal biopotential is sharply reduced in density and disfigured. In 70% of cases these changes spread outside the fovea.

Changes in Inner and Outer Retinal Layer Thicknesses after Vitrectomy for Idiopathic Macular Hole: Implications for Visual Prognosis

Purpose

To investigate sequential post-operative thickness changes in inner and outer retinal layers in eyes with an idiopathic macular hole (MH).

Methods

Retrospective case series. Twenty-four eyes of 23 patients who had received pars plana vitrectomy (PPV) for the closure of MH were included in the study. Spectral domain optical coherence tomography C-scan was used to automatically measure the mean thickness of the inner and outer retinal layers pre-operatively and up to 6 months following surgery. The photoreceptor outer segment (PROS) length was measured manually and was used to assess its relationship with best-corrected visual acuity (BCVA).

Results

Compared with the pre-operative thickness, the inner layers significantly thinned during follow-up (P = 0.02), particularly in the parafoveal (P = 0.01), but not perifoveal, area. The post-operative inner layer thinning ranged from the ganglion cell layer to the inner plexiform layer (P = 0.002), whereas the nerve fiber layer was unaltered. Outer layer thickness was significantly greater post-operatively (P = 0.002), and especially the PROS lengthened not only in the fovea but also in the parafovea (P < 0.001). Six months after surgery, BCVA was significantly correlated exclusively with the elongated foveal PROS (R = 0.42, P = 0.03), but not with any of the other thickness parameters examined.

Conclusions

Following PPV for MH, retinal inner layers other than the nerve fiber layer thinned, suggestive of subclinical thickening in the inner layers where no cyst was evident pre-operatively. In contrast, retinal outer layer thickness significantly increased, potentially as a result of PROS elongation linking tightly with favorable visual prognosis in MH eyes.

Cone implicit time as a predictor of visual outcome in macular hole surgery

PURPOSE

To investigate whether preoperative retinal function measured by full-field ERG and multifocal ERG is correlated to postoperative visual acuity after macular hole surgery.

METHODS

Standard pars plana vitrectomy with removal of the internal limiting membrane (ILM) was performed on 19 consecutive patients undergoing macular hole surgery. Intraocular gas tamponade with a C2F6 gas-air mixture was employed, followed by a face-down position for at least 5 days. The patients were examined with the ETDRS chart, full-field ERG (Espion), multifocal ERG (Veris 6), and optical coherence tomography (OCT) preoperatively, and 6 weeks, 6 months, and 18 months after surgery.

RESULTS

The cone 30-Hz flicker implicit time in the full-field ERG reflecting retinal function was prolonged (p = 0.016) before surgery compared to aged-matched controls. After macula hole surgery, longstanding alteration of cone function reflected by mfERG and full-field ERG was verified 18 months after surgery. The prolonged cone 30-Hz flicker implicit time in the full-field ERG before surgery was significantly correlated to the ETDRS visual acuity 6 months postoperatively (p = 0.03).

CONCLUSIONS

Preoperative evaluation of retinal function with multifocal ERG and full-field ERG improves the understanding of the retinal recovery process after macular hole surgery. The cone implicit time in full-field 30-Hz flicker ERG could be a valid predictor of long-term visual outcome, which may be useful for selecting patients suitable for surgery.

Electrophysiological examination in uveitis: a review of the literature

Purpose

Uveitis is the inflammation of the uveal tract, which usually also affects the retina and vitreous humor. The electrophysiological examination is an objective ocular examination that includes the electroretinogram, visual evoked potentials, the electrooculogram, the multifocal electroretinogram, and multifocal visual evoked potentials. Our aim is to review the literature of the use of the electrophysiological examination in cases of uveitis.

Methods

We performed a systematic search of the literature of published papers until October 2012 using the PubMed search engine. The key terms that were used were “uveitis”, “electrophysiological examination”, “electroretinogram”, “visual evoked potentials”, “electrooculogram”, “multifocal electroretinogram”, and “multifocal visual evoked potentials” in multiple combinations. To the best of our knowledge, this is the first review concerning the assessment of electrophysiology in uveitis.

Results

Our search of the literature demonstrated that the electrophysiological examination, mainly by means of electroretinogram, multifocal electroretinogram, and visual evoked potentials, is performed in several cases of uveitis for many purposes, including diagnosis and monitoring of disease progression and treatment efficacy. The electrophysiological examination is more useful in patients with multiple evanescent white dot syndrome, acute posterior multifocal placoid pigment epitheliopathy, birdshot chorioretinopathy, Vogt–Koyanagi–Harada disease, Adamantiades–Behçet disease, ocular syphilis, and Fuchs heterochromic cyclitis.

Conclusion

This review summarizes the use of the electrophysiological examination in uveitic patients and underlines its value as a useful tool in the objective assessment and the monitoring of the disease.

Multifocal electroretinography in type 2 idiopathic macular telangiectasia

BACKGROUND

To characterize the electroretinographic response of the macula by multifocal electroretinography (mfERG) in patients with type 2 idiopathic macular telangiectasia (MacTel).

METHODS

A prospective study of mfERG in patients with type 2 MacTel was conducted from April 2009 to November 2009. mfERGs were recorded using a visual evoked response imaging system (MonElec2, Metrovision, Perenchies, France). The International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines were followed. Patients with type 2 MacTel confirmed by fundus fluorescein angiography without subretinal neovascularisation were included. For recording purposes, 61 stimulus hexagonal elements were used. The first-order kernel mfERG responses were analyzed. Individual mfERG responses for the hexagons were grouped into concentric rings centered on the fovea for analysis (< 2, 5-10, 10-15 and >15°). Student's t-test and Mann-Whitney U test and linear regression analysis was performed with STATA ver 11.1 (StataCorp, College Station , TX, USA).

RESULTS

Twenty eight eyes of 14 patients and 20 eyes of ten normal controls were included in the study. The mean logMAR visual acuity of the patients was 0.51 (Snellen equivalent 20/63). The mean N1 amplitude (nv/deg(2)) of patients were significantly reduced compared to controls and were as follows: 8.91 ± 14.00 vs 43.44 ± 9.55 (p < 0.0001) in less than 2°, 9.24 ± 10.47 vs 22.00 ± 3.87 (p < 0.0001) in 5-10°, 8.57 ± 10.02 vs 15.24 ± 1.89 (p < 0.0001) in 10-15°, and 7.03 ± 6.52 vs 12.47 ± 2.62 in > 15° (p < 0.001). The mean P1 amplitude (nv/deg(2)) was also significantly reduced in patients compared to controls and was as follows: 27.66 ± 37.44 vs 96.20 ± 12.41 (p < 0.0001) in less than 2°, 22.61 ± 19.38 vs 53.78 ± 9.79 (p < 0.0001) in 5-10°, 18.75 ± 20.21 vs 35.22 ± 4.16 (p < 0.001) in 10-15°, and 17.10 ± 12.54 vs 25.71 ± 3.93 (p < 0.001). The implicit time of N1 and P1 were also delayed significantly in all the rings. The mean central foveal thickness assessed by optical coherence tomography (OCT) scan was 84.78 ± 45.12 μm. There was poor correlation between mfERG amplitudes or implicit times with either the visual acuity or OCT central thickness.

CONCLUSION

mfERG showed significant reduction in amplitudes and implicit times of the waveforms in patients with type 2 MacTel in all the rings, suggesting a more generalized affection of the macula. The maximum reductions were seen in the <2(o) rings. Although there was poor correlation between the visual acuity and the amplitudes a of the waveforms, mfERG is a useful investigative modality for functional assessment of macula in type 2 MacTel patients.

Optical coherence tomography and multifocal electroretinogram findings in chronic solar retinopathy

PURPOSE

To correlate the structural and functional retinal defects, which are induced photochemically in chronic solar retinopathy.

DESIGN

Observational case report.

METHODS

Four emmetropic eyes of two patients, previously diagnosed with chronic solar retinopathy, were evaluated by optical coherence tomography (OCT), multifocal electroretinography, and fluorescein angiography.

RESULTS

Visual acuity ranged from 20/80 to 20/50 and all subjects had central and steady fixation. In all eyes, OCT demonstrated a hyporeflective space at the level of outer retinal and retinal pigment epithelium (RPE) layers, which was limited to the fovea. The foveal contour was preserved with normal vitreoretinal interface. Multifocal electroretinogram (mfERG) trace array of the first-order kernel demonstrated attenuated responses extending to a larger area, the para- and perifovea. A foveal RPE window defect was angiographically evident in all cases.

CONCLUSIONS

A model of centrifugal neuronal damage is proposed for chronic solar retinopathy, with more functional than structural neuroretinal defects.

Simultaneous structural and functional imaging of the macula using combined optical coherence tomography ophthalmoscope and multifocal electroretinogram

Multimodal imaging (MMI) is a new imaging technique that combines an electrophysiological test (multifocal electroretinogram) with an optical coherence tomography ophthalmoscope. MMI allows the two technologies to operate simultaneously yet independently to provide accurate correlation of macular structure and function at multiple sites. Preliminary work with MMI in patients with macular holes showed that functional deficits existed beyond the geographical area of structural alterations and that macular hole size did not always correlate with the severity of functional loss. Functional information may therefore be important when assessing prognosis in these patients. We envisage that MMI may prove a useful new tool in the assessment of many macular pathologies.

The clinical applications of multifocal electroretinography: a systematic review

Multifocal electroretinography (mfERG) is an investigation that can simultaneously measure multiple electroretinographic responses at different retinal locations by cross-correlation techniques. mfERG therefore allows topographic mapping of retinal function in the central 40-50 degrees of the retina. The strength of mfERG lies in its ability to provide objective assessment of the central retinal function at different retinal areas within a short duration of time. Since the introduction of mfERG in 1992, mfERG has been applied in a large variety of clinical settings. This article reviews the clinical applications of mfERG based on the currently available evidence. mfERG has been found to be useful in the assessment of localized retinal dysfunction caused by various acquired or hereditary retinal disorders. The use of mfERG also enabled clinicians to objectively monitor the treatment outcomes as the changes in visual functions might not be reflected by subjective methods of assessment. By changing the stimulus, recording, and analysis parameters, investigation of specific retinal electrophysiological components can be performed topographically. Further developments and consolidations of these parameters will likely broaden the use of mfERG in the clinical setting.

Changes in multifocal oscillatory potentials after internal limiting membrane removal for macular hole: multifocal OPs after ILM removal

PURPOSE

To determine whether removal of the internal limiting membrane (ILM) during macular hole (MH) surgery alters the retinal function.

METHODS

Multifocal electroretinograms (mfERGs) were recorded preoperatively and 3 months after surgery from 11 eyes of 10 patients with an idiopathic MH treated successfully by pars plana vitrectomy accompanied by ILM removal. A low frequency (9.4 Hz) pseudorandom binary m-sequence stimulus was used to elicit the mfERGs from different retinal loci. The bandpass of the amplifier was set at 10-300 Hz to record the mfERGs and at 100-300 Hz to record the oscillatory potentials (OPs).

RESULTS

An anatomical closure of the MH was achieved in all patients, and the mean visual acuity was significantly improved postoperatively. No significant difference was observed in both the amplitudes and implicit times of the negative and positive waves of the mfERGs and the OPs recorded preoperatively to those recorded postoperatively.

CONCLUSIONS

MH surgery with ILM removal does not alter the electrophysiological function of both the outer and inner retina of the posterior pole where the ILM was removed.

Functional assessment of the possible toxicity of indocyanine green dye in macular hole surgery

PURPOSE

To evaluate the possible toxicity of indocyanine green (ICG) dye in macular hole surgery by comparing functional results after successful surgeries performed with and without staining.

DESIGN

Prospective observational case series.

METHODS

In a study conducted at our department, 30 eyes of 29 patients with idiopathic macular hole underwent pars plana vitrectomy, with peeling of the internal limiting membrane (ILM). In 21 eyes (group A), ICG staining was used to visualize the membrane; in nine eyes (group B), no dye was applied. Pre- and postoperative examinations (at three, six, 12, and 20 months) included visual acuity (VA) (Snellen chart), slit-lamp biomicroscopy, multifocal electroretinography (mfERG), and optical coherence tomography (OCT). For statistical analysis, the Mann-Whitney U test and Newman-Keuls post hoc analysis were used.

RESULTS

The macular hole was closed in all patients. At 20 months, VA improvement (logarithm of minimal angle of resolution units) compared with baseline was more pronounced in group B (P < .001) than in group A (P = .022); VA was also better for group B compared directly with group A (P = .048). For mfERG, preoperative responses were subnormal. Postoperatively, responses initially decreased, but at 20 months significant improvement was seen in both groups (P < .001). When data from the groups are compared at 20 months, significantly greater mfERG improvement was found in group B in both central and perimacular areas (P < .001).

CONCLUSIONS

The significantly better outcomes without staining may suggest dye toxicity. Alternative internal limiting membrane visualization substances with fewer adverse effects (trypan blue, triamcinolone) may be preferable.

Assessing Responses of the Macula in Patients with Macular Holes using a New System Measuring Localized Visual Acuity and the mfERG

PURPOSE

To evaluate acuity and multifocal electroretinogram (mfERG) responses from the macula in affected and unaffected fellow eyes of patients with macular holes.

METHODS

We tested 10 eyes with macular hole and 10 fellow eyes from 11 patients. We measured local visual acuity thresholds at 27 discrete locations within 21 degrees diameter using the Functional Fundus Imaging System (FFIS), a psychophysical system that measures visual acuity as a function of visual field location, and local ERG responses within 45 degrees diameter using the mfERG.

RESULTS

In the affected eyes, the mean FFIS visual acuity thresholds were significantly elevated within the central 21 degrees diameter area, compared to a group of control eyes. No significant differences were found between the acuities of the fellow eyes compared to those of the control group. The amplitudes of the first positive peak of the mfERG were reduced in the central 7.8 degrees in affected eyes. In the central 2 degrees , 4 out of 10 affected eyes showed non-measurable ERG signals. The remaining six eyes showed significantly reduced mean amplitudes, but not delayed implicit times, when compared to the control group. For the fellow eyes, the mean amplitudes of the mfERG and implicit times did not differ from the means of the control eyes.

CONCLUSIONS

Both local psychophysical and electrophysiological testing demonstrated retinal dysfunction extending beyond the site of the macular holes in some patients (three of the patients had central mfERG amplitudes falling within the normal range).

Scanning laser ophthalmoscope-evoked multifocal ERG (SLO-mfERG) in patients with macular holes and normal individuals

AIMS

A scanning laser ophthalmoscope (SLO) has been used for multifocal electroretinography (mf ERG) measurements under simultaneous fundus monitoring. The aim of this study was to prove if the SLO-mfERG measurement reflects reliably the clinically registered underlying disease, and to demonstrate the importance of its main advantage, fixation monitoring.

METHODS

In all, 10 patients with macular hole stage II/III were included in the study, and 19 normal individuals served as the control group. The mf ERG device was combined with an SLO, which was used both as a stimulus and trigger unit as well as a fundus-monitoring system. Monitoring of the fundus was guaranteed by an infrared laser (780 nm). The stimulus matrix consisted of 61 hexagonal elements, covering 24 degrees of the posterior pole. We examined both, patients with macular holes and healthy individuals.

RESULTS

Compared to normal controls, patients with a macular hole (Gass stage III) showed a significant decrease in response density in the centre of the stimulus array, which correlated well with the morphological alteration observed by clinical examination. However, variation of response density of the central hexagonal area has been proved to be high.

CONCLUSIONS

SLO-mfERG is a feasible and reliable new technique to investigate macular function under simultaneous fundus control. The main advantage is that control of fixation can be used in order to obtain more reliable results that correlate well with visible fundus abnormalities such as in patients with macular holes. However, further investigations have to be performed in order to overcome sufficiently the problem of fixation instability.

Beyond visual acuity: new and complementary tests of visual function

Visual acuity is an essential component of the routine ophthalmic examination and the most common measure of visual function. There is increasing recognition, however, of the need to evaluate visual function beyond the limited extent afforded by visual acuity. The primary objective of this article is to introduce a variety of new and lesser-used techniques for measuring visual function that complement visual acuity assessment, each of which has been shown to detect visual dysfunction in patients with normal visual acuity.

Variation of multifocal electroretinogram with axial length

INTRODUCTION

The first-order kernel response of multifocal electroretinogram (mfERG) decreases in myopia. A recent study indicates that the flash ERG is also reduced with increased axial length. The aim of this study was to investigate the variations in the first-order response (K1) and the first slice of second-order response (K2.1) across the retina for different axial lengths.

METHODS

Thirty healthy subjects with axial length from 23.72 to 28.13 mm (spherical equivalent refractive errors from plano to -10.50 D) were recruited for mfERG measurement using VERIS 4.0. All subjects were fully corrected after cycloplegic refraction and pupils were dilated prior to mfERG recording. There is one trough, n1, and one peak, p1, in the K1 response and three troughs, n1, n2, n3, and three peaks, p1, p2, p3, in the K2.1 response. The amplitudes and implicit times of K1 and K2.1 responses were analysed to determine the characteristic of the responses across retina and the correlation to axial length.

RESULTS

The amplitudes of p1 (in the first-order kernel-K1) decreased in the central region and the paracentral region (ring 3) as the axial length increased. The central retinal region showed high rates of reduction in both n1 and p1 (in K1). The amplitudes of n1p1 and n2p2 (in the first slice of the second-order kernel-K2.1) were reduced in the paracentral region (from ring 2 to ring 5) as axial length increased. The average n1 and p1 in K1, and n1p1 and n2p2 in K2.1 mfERG responses are decreased in amplitude by 6-10% per millimetre elongation of axial length.

CONCLUSION

Eyes with longer axial lengths, usually with high myopia, have a weaker mfERG response and this attenuation is across the measured retina (from central to paracentral regions) but different kernel responses show a different pattern of attenuation at different retinal eccentricities. The weaker mfERG responses may be related to the morphological changes associated with increased axial length.

Preoperative and postoperative assessment by multifocal electroretinography in the management of optic disc pits with serous macular detachment

PURPOSE

To evaluate the macular function by means of multifocal electroretinogram (MF ERG) in eyes with congenital optic disc pit and serous macular detachment. The evaluation was performed before and after the successful surgical intervention.

DESIGN

Nonrandomized, comparative (self-controlled), interventional trial.

PARTICIPANTS

Ten patients (10 eyes) with optic disc pit with serous macular detachment were treated with the macular buckling procedure and followed up from March 1999 through May 2001.

METHODS

In all patients included in the study, MF ERG was recorded before and after treatment. For recording, the VERIS III system (Visual Evoked Response Imaging System; Tomey, Nagoya, Japan) was used.

MAIN OUTCOME MEASURES

The retinal response densities were studied before and after treatment in areas 1 and 2 and were compared with visual acuity.

RESULTS

The MF ERG before treatment showed decreased retinal response densities in all 10 cases. Twelve months after the surgical intervention, the electrical response densities in areas 1 (foveal area) and 2 (parafoveal area) improved. Further improvement was noted in 3 of the 10 patients who completed a follow-up of 18 months after treatment. In 8 of the 10 patients, postoperative visual acuity also increased. In the remaining two patients, visual acuity did not change after treatment, despite improvement of the retinal response densities.

CONCLUSIONS

In eyes with congenital optic disc pit with serous macular detachment, the decrease in retinal electrophysiologic response before treatment was not limited to the fovea, but also involved the perifoveal area. In all 10 eyes 12 months after treatment, the electrical activities in areas 1 and 2 improved. This improvement was not always followed by an increase in visual acuity. In 2 of the 10 patients, visual acuity remained unchanged. The values of retinal response densities before treatment cannot be used alone as a prognostic factor for the postoperative functional retinal results. It should also be stressed that the results of this study cannot be compared with the results of studies where spontaneous resolution of the macular detachment occurred.

Evaluation of successful macular hole surgery by optical coherence tomography and multifocal electroretinography

PURPOSE

To evaluate successful macular hole surgery using optical coherence tomography (OCT) and multifocal electroretinography (MFERG).

DESIGN

Interventional case series.

METHODS

In a prospective study, 20 eyes of 20 patients with successful surgery for stage II, III, or IV idiopathic macular hole were evaluated by best-corrected visual acuity (BCVA), ocular examination, OCT, and MFERG preoperatively and 1, 3, 6, and 12 months postoperatively. For statistical analysis, the paired t test and nonparametric methods were used, as well as the Spearman analysis.

RESULTS

Postoperatively, all 20 eyes of 20 patients had anatomic closure of the macular hole confirmed by OCT. The center of the fovea, measured by OCT from the retinal pigment epithelium to the inner retinal surface, had a mean +/- SD thickness of 116.5 +/- 30.9 microm (range, 68-175 microm) 1 year postoperatively. Best-corrected visual acuity significantly improved (preoperative mean +/- standard deviation [SD] value, 0.131 +/- 0.081 and 1 year postoperative mean +/- SD value, 0.407 +/- 0.193). Multifocal electroretinography values area 1 (0-2.8 degrees) and area 2 (2.8-9 degrees from the center of the fovea) significantly improved (preoperative mean +/- SD values 3.10 +/- 1.334 nV/deg(2) and 3.573 +/- 1.545 nV/deg(2), respectively, and 1 year postoperative +/- SD mean values, 5.53 +/- 1.208 nV/deg(2) and 4.748 +/- 1.404 nV/deg(2), respectively). The thickness of the fovea, measured by OCT, significantly correlated with the BCVA 1 year postoperatively. One year postoperative MFERG values areas 1 and 2 were not correlated with 12-month BCVA and OCT findings.

CONCLUSIONS

Twelve months postoperatively BCVA and MFERG values significantly improved in this series of eyes with successful macular hole surgery. Optical coherence tomography findings were correlated to BCVA, but MFERG values were not correlated to BCVA and OCT findings, 1 year postoperatively.

Reduced amplitude and delayed latency in foveal response of multifocal electroretinogram in early age related macular degeneration

AIM

To explore the use of multifocal electroretinograms (MERG) in detecting early changes in age related macular degeneration (AMD).

METHOD

15 pre-AMD or early AMD eyes showing retinal drusen or irregular fundus pigmentation with window defects by fluorescein angiography (FA) and mildly decreased visual acuity were examined and compared with their asymptomatic fellow eyes. 20 age matched normal eyes were included as controls. MERG was recorded by a Veris system (version 3.0) using a 103 hexagon stimulus and 218 second total recording time per eye. The first order kernel was used to calculate amplitudes and latencies in three configurations: the nasal and the temporal areas, the superior and the inferior areas, and six concentric rings centred on the fovea.

RESULTS

There were no significant differences in the amplitudes and the latencies between the different regions (nasal versus temporal and superior versus inferior) of the retina as well as between the different groups of eyes (normal, pre-AMD or early AMD, and the asymptomatic fellow eyes) in each region. Using the concentric configuration, the foveal amplitude of pre-AMD or early AMD eyes was significantly suppressed when compared with the age matched control group and their average latency was longer in the fovea than in outer rings and significantly prolonged when compared with the normal control group. Similar changes in amplitude and latency were also observed in the asymptomatic fellow eyes.

CONCLUSION

Significant abnormality in the foveal amplitude and the foveal latency of MERG could be detected in pre-AMD or early AMD eyes as well as their asymptomatic contralateral eyes, suggesting MERG as a sensitive tool in detecting early foveal abnormalities in AMD.

Clinical applications of multifocal electroretinography

The multifocal ERG using the m-sequence stimulation technique allows the derivation of 61 - 241 local ERG signals in a central visual field of about 60 degree diameter in a short time between 4 and 16 min. A recording in a light adapted state offers local information comparable to cone responses in the full-field ERG. Retinal functional losses due to regional disorders in outer retinal layers can be described in detail with this technique. In maculopathies decreased or absent central ERGs are found surrounded by normal ERG. The extent of the central lesion can be estimated. In diseases of the outer retina the pattern of distribution of multifocal ERG activity is similar to the the pattern of the visual field defect. In addition to decreased ERG amplitudes a delay of implicit time may be an important sign of pathology, i.e. the pronounced delay of implicit times in the periphery in retinitis pigmentosa and the implicit time delays in regions associated with retinal edema like CRVO and cystoid macula edema in intermediate uveitis. No simple correlation of the first order kernel multifocal ERG and field defects could be found in disorders of the ganglion cell layer. The multifocal ERG is therefore useful in the differential diagnosis of retinal and optic nerve diseases.

Multifocal ERG changes before and after macular hole surgery

To evaluate the visual function of 15 eyes suffering from macular hole the multifocal ERG was used pre and postoperatively. In all the cases a successful vitrectomy has been done with macular hole closure in all the eyes. The Multifocal ERG shows an improvement of retinal response density in regions 1 and 2, even in the 2 eyes with unchanged visual acuity postoperatively. Although a relationship exist between the postoperative retinal response density and the visual acuity, the retinal response density varies between eyes with the same visual acuity.

Assessing retinal function with the multifocal technique

With the multifocal technique, as developed by Erich Sutter and colleagues, scores of focal electroretinogram (ERG) responses can be obtained in a matter of minutes. Although this technique is relatively new, it has already provided insights into the mechanisms of retinal disease. However, because it is new, there also remain questions about how it works and what it measures. This chapter considers some of these insights and some of these questions. The first part (Section 2) describes how the multifocal ERG (mERG) is recorded and considers its relationship to the full-field ERG. The mERG responses are shown to be from relatively local regions of the retina and are comprised of the same components as the full-field ERG. The diagnostic advantage of the mERG as compared to the full-field ERG is also illustrated. In Section 3, the effects of damage to different cell layers of the retina are shown to affect the mERG differently, and these changes are summarized within a conceptual framework. It is argued, for example, that when diseases of the receptor outer segment, like retinitis pigmentosa, result in small, depressed mERG responses, then the damage is, as expected, at the outer segment. However, when these diseases result in mERG responses that are reasonably large but very delayed, then the damage is beyond the outer segment, probably in the outer plexiform layer. The implicit time of the mERG, not amplitude, is the more sensitive measure of damage in degenerative diseases of the receptors. On the other hand, diseases, like glaucoma, which act on the ganglion axon, do not result in easily identified changes to the mERG unless inner retinal damage is involved as well. Inner retinal damage changes the waveform of the mERG and decreases the naso-temporal variation normally observed. Finally, diseases, like diabetes, that act on more than one layer of the retina can have a range of effects. In Section 4, recent work with the monkey mERG is reviewed, with emphasis on the relevance to human diseases. For example, blocking the sodium-based action potentials produced by ganglion and amacrine cells eliminates the naso-temporal variation in the monkey mERG and these altered mERG responses resemble those from some patients with diabetes or glaucoma. Finally, in Section 5 the second-order kernel is described. The presence of a second-order kernel has important implications for understanding the shape of the mERG response (first-order kernel). Full-field simulations of the mERG paradigm illustrate that the first-order kernel is comprised of responses with different waveforms. Further, it is argued that the nonlinear, adaptive mechanisms that produce the second-order kernel are involved in shaping the time course of the response. Patients with large, but abnormally delayed mERG responses (first-order kernel), do not have a detectable second-order kernel. It is speculated that a markedly diminished second-order kernel is diagnostic of outer plexiform layer damage, not inner plexiform layer damage as is commonly assumed.

Tomographic features of early macular hole closure after vitreous surgery

PURPOSE

To report the optical coherence tomographic features of macular hole closure in the first months after vitreous surgery.

METHODS

We studied prospectively the tomographic features of 28 eyes (28 patients) with idiopathic macular holes before and after vitreous surgery by optical coherence tomography. We compared the best-corrected visual acuity levels with the postoperative tomographic features.

RESULTS

The 25 eyes with successfully sealed macular holes had one of two tomographic features within 1 month postoperatively: simple closure (normal foveal configuration) in 14 eyes (56%) or a bridge formation at the fovea that mimicked a foveal retinal detachment in 11 eyes (44%). It took an average of 2.0 months (range, 0.8 to 3.5 months) for the bridge tissue to attach to the retinal pigment epithelium. Best-corrected visual acuity quickly improved in the former group; visual improvement began 1 month after attachment of the bridge tissue in the latter group. A closed hole reopened 4 months postoperatively in one eye with a bridge formation.

CONCLUSIONS

Idiopathic macular holes have one of two patterns early after surgical closure, simple closure or a bridge formation. Visual improvement starts after the fovea assumes a normal configuration. The bridge formation appears to reflect an early phase and fragile condition in the anatomic closure of macular holes.