Comparison of focal macular cone ERGs in complete-type congenital stationary night blindness and APB-treated monkeys

Epiretinal Membrane Impairs the Inner Retinal Layer in a Traction Force-Dependent Manner

Purpose

To investigate the relationship between retinal traction force and impairment of the inner retinal layer in patients with epiretinal membrane (ERM).

Design

Nonrandomized, retrospective consecutive case series.

Participants

Two hundred nine eyes of 201 patients with idiopathic ERM who underwent vitrectomy for idiopathic ERM were enrolled.

Methods

Retinal folds caused by ERM were visualized using en face OCT, and the maximum depth of retinal folds within the parafovea (MDRF) was measured. Focal macular electroretinogram (ERG) was used to measure the amplitude and implicit time of each component for the ERM eyes and the normal fellow eyes. B-scan OCT images were used to measure the thicknesses of the inner nuclear layer (INL) and outer nuclear layer (ONL) + outer plexiform layer (OPL). Expression of α-smooth muscle actin (α-SMA) in surgically removed ERM specimens was quantified by reverse-transcription polymerase chain reaction.

Main Outcome Measures

We analyzed the relationship between MDRF and the relative amplitudes of focal macular ERG (affected eye/fellow eye), the relationships between MDRF and the mean INL thickness and ONL+OPL thickness, comparison of INL thickness and ONL+OPL thickness for each area when cases were classified according to MDRF localization in the ETDRS chart, and the relationship between MDRF and the relative expression of α-SMA in the ERM specimens.

Results

The MDRF significantly correlated with the relative amplitudes (affected eye/fellow eye) of b-waves and oscillatory potentials (r = -0.657, P = 0.015; r = -0.569, P = 0.042, respectively) and the mean INL thickness and ONL+OPL thickness (r = 0.604, P < 0.001; r = 0.210, P = 0.007, respectively). However, only the INL thickness progression rate was significantly correlated with the MDRF progression rate (r = 0.770, P < 0.001). On case stratification by localization of MDRF based on the ETDRS chart, in regions other than temporal regions, the INL thickness was significantly greater in regions with MDRF than in other regions. The MDRF significantly correlated with α-SMA expression in the ERM specimens (r = 0.555, P = 0.009).

Conclusions

The findings suggest that ERM impairs the inner retinal layer in a traction force-dependent manner.

Financial Disclosures

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Retinal temperature determination based on photopic porcine electroretinogram

OBJECTIVE

Subthreshold retinal laser therapy (SLT) is a treatment modality where the temperature of the retinal pigment epithelium (RPE) is briefly elevated to trigger the therapeutic benefits of sublethal heat shock. However, the temperature elevation induced by a laser exposure varies between patients due to individual differences in RPE pigmentation and choroidal perfusion. This study describes an electroretinography (ERG)-based method for controlling the temperature elevation during SLT.

METHODS

The temperature dependence of the photopic ERG response kinetics were investigated both ex vivo with isolated pig retinas and in vivo with anesthetized pigs by altering the temperature of the subject and recording ERG in different temperatures. A model was created for ERG-based temperature estimation and the feasibility of the model for controlling SLT was assessed through computational simulations.

RESULTS

The kinetics of the photopic in vivo flash ERG signaling accelerated between 3.6 and 4.7%/C, depending on the strength of the stimulus. The temperature dependence was 5.0%/C in the entire investigated range of 33 to 44C in ex vivo ERG. The simulations showed that the method is suitable for determining the steady-state temperature elevation in SLT treatments with a sufficiently long laser exposure and large spot size, e.g., during > 30 s laser exposures with > 3 mm stimulus spot diameter.

CONCLUSIONS

The described ERG-based temperature estimation model could be used to control SLT treatments such as transpupillary thermotherapy.

SIGNIFICANCE

The introduced ERG-based method for controlling SLT could improve the repeatability, safety, and efficacy of the treatment of various retinal disorders.

Ring analysis of multifocal oscillatory potentials (mfOPs) in cCSNB suggests near-normal ON-OFF pathways at the fovea only

PURPOSE

To investigate the center-periphery distribution of ON and OFF retinal responses in complete congenital stationary night blindness (cCSNB).

METHODS

Photopic full-field flash ERGs (photopic ffERGs) and OPs (photopic ffOPs) and slow m-sequence (to enhance OP prominence) mfERGs (and filtered mfOPs) evoked by a 37 hexagon stimulus array were recorded from normal subjects and cCSNB patients. Discrete wavelet transform (DWT) analysis of photopic ffERGs and mfERGs was also performed in order to assess the contribution of the ON and OFF retinal pathways (i.e., OFF-to-ON ratio) in both cohorts.

RESULTS

As expected, the photopic ffERG (and ffOPs) responses in cCSNB were devoid of the first two of the three OPs (i.e., OP2 and OP3 and OP4) normally seen on the ascending limb of the b-wave. A similar finding was also noted in the mfERGs (and mfOPs) of ring 4. In contrast, the mfERGs (and mfOPs) of ring 1 included all three OPs. DWT analysis revealed that while in normal subjects, the OFF-to-ON ratio of mfERGs slightly increased from rings 1 to 4 (from 0.61 ± 0.03 to 0.78 ± 0.04; p < 0.05; median: from 0.62 to 0.79; p < 0.05), in cCSNB this ratio increased significantly more [from 0.73 ± 0.13 (ring 1) to 1.18 ± 0.17 (ring 4); p < 0.05; median: 0.78 to 1.22; p < 0.05], hence from a normal ON-dominated ratio (central ring) to an OFF-dominated ratio (peripheral ring).

CONCLUSIONS

Our results show a clear discrepancy of ON and OFF mfOP components in cCSNB. Responses originating from the most central ring (i.e., ring 1) disclosed a near-normal electrophysiological contribution (as revealed with the presence of OP2, OP3 and OP4 as well as with the DWT OFF-to-ON ratio) of the retinal ON and OFF pathways in mfERG (and mfOPs) responses compared to responses from the more peripheral ring (and ffOP) which are devoid of the ON OPs (i.e., OP2 and OP3).

Macular function following intravitreal ranibizumab for macular edema associated with branch retinal vein occlusion

PURPOSE

To determine the physiology of the macula by the focal macular electroretinograms (fmERGs) in patients with branch retinal vein occlusion with macular edema (BRVOME) treated by intravitreal injections of ranibizumab (IVR).

METHODS

We studied 17 eyes of 17 patients with BRVOME. The contralateral unaffected eyes served as controls. All patients were treated with an IVR at monthly intervals for 3 consecutive months. The baseline best-corrected visual acuity (BCVA), optical coherence tomographic (OCT) findings, and fmERGs were compared to the post-treatment values. The fmERGs were elicited by a 15° circular spot or a superior or inferior semicircular spot. The center of the spot was placed on the fovea. The amplitudes of the a- and b-waves, photopic negative response (PhNR), and sum of the oscillatory potentials (ΣOPs: sum of OP1, OP2, and OP3 amplitudes) were measured. In addition, the implicit times of the a- and b-waves were also measured.

RESULTS

The BCVA improved significantly from 0.39 ± 0.28 logMAR units to 0.17 ± 0.18 logMAR units after the resolution of the central macular edema (P < 0.01). All components of the fmERGs elicited by the semicircular stimulus spot placed on the occluded side were smaller than that elicited from the corresponding area of the control eyes. The b-wave amplitudes increased significantly from 0.49 ± 0.25 to 0.75 ± 0.36 µV following the IVR injections, but the amplitudes of the a-wave and PhNR remained reduced (P < 0.05). The amplitudes of the PhNR and ΣOPs elicited by stimulating the non-occluded side were reduced with relative preservation of the a- and b-waves (P < 0.05). They recovered after the treatment from 0.27 ± 0.15 to 0.50 ± 0.30 and 0.33 ± 0.15 to 0.53 ± 0.19 µV, respectively.

CONCLUSIONS

IVRs improved the macular function not only on the occluded side but also on the non-occluded side. On the occluded side, the BRVOME affects the function of all retinal layers of the macula. Even after the IVR, the function of the photoreceptors and retinal ganglion cells remained abnormal. On the non-occluded side, the inner retinal function improved after the IVR.

ISCEV extended protocol for the stimulus-response series for light-adapted full-field ERG

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum protocol for clinical testing but encourages additional ERG testing when appropriate. This ISCEV extended protocol describes methods to record and evaluate a light-adapted (LA) ERG stimulus-response series with increasing flash strengths. The LA ERG stimulus-response series (also referred to as the luminance-response or intensity-response series in the published literature) can characterise generalised cone system function more comprehensively than the ISCEV standard LA ERGs alone. The amplitude of LA ERG a-waves, arising from cones and cone off-bipolar cells, typically shows a saturating function. The LA ERG b-wave amplitudes, which arise primarily from activity of retinal bipolar cells, show an amplitude peak followed by a nonzero plateau (the "photopic hill" phenomenon). This ISCEV extended protocol specifies a stimulus-response series suitable to evaluate generalised dysfunction affecting the LA retina, to aid in distinguishing between the on- and off-responses of the cone system and to monitor ERG changes in these characteristics. The LA ERG stimulus-response series for a- and b-waves is recorded to a sequence of nine flash stimuli ranging from 0.03 to 300 cd s m^-2, superimposed on a standard background of 30 cd m^-2. A shorter protocol is also presented to measure the mid-range of the function (the "photopic hill") using 5 flash stimuli.

Structures affecting recovery of macular function in patients with age-related macular degeneration after intravitreal ranibizumab

PURPOSE

To determine the retinal structures affecting the recovery of macular function in patients with exudative age-related macular degeneration (AMD) treated with intravitreal ranibizumab (IVR).

METHOD

Thirty eyes of 30 patients with exudative AMD who were treated with IVR at monthly intervals for 3 months were studied. Focal macular electroretinograms (fmERGs) and spectral-domain optical coherence tomography (SD-OCT) were performed before and 3 months after beginning the IVR injections. The fmERGs were elicited by a 15° white stimulus spot centered on the fovea. The thickness of different retinal layers, presence of a serous retinal detachment (SRD), and presence of a pigment epithelial detachment (PED) at the fovea was determined in the SD-OCT images. Measurements were made of the inner, middle, and outer layers of the retina and also of the SRD and PED in the horizontal and vertical meridians at 1.2 mm from the fovea (parafoveal regions). The significance of the correlations between these structural parameters and the a-wave amplitude of the fmERG was determined.

RESULTS

There was no significant correlation between the structural parameters of the fovea and the a-wave amplitude. In the parafoveal regions, the thickness of the outer retinal layer was significantly correlated with an increase of the a-wave amplitude (R = 0.56, P = 0.001). In addition, the SRD thickness was negatively and significantly correlated with the a-wave amplitude (R = -0.54, P = 0.002). The change in the parafoveal SRD thickness after IVRs was the only independent determinant of recovery of the a-wave amplitude after the treatments (P < 0.05).

CONCLUSIONS

The macular function measured by the fmERGs was determined by the parafoveal outer layer and SRD thickness in patients with exudative AMD. Of these, changes in the SRD thickness by IVRs most strongly affected the recovery of macular function.

Reduction of laser-induced choroidal neovascularization by intravitreal vasohibin-1 in monkey eyes

PURPOSE

To determine whether intravitreal vasohibin-1 will reduce the grade of the choroidal neovascularization in monkey eyes.

METHODS

Choroidal neovascularizations were induced in 12 monkey eyes by laser photocoagulation. Three monkeys were evaluated for the safety of the vasohibin-1 injections, 6 monkeys for the effects of a single injection, and 3 monkeys for repeated injections of vasohibin-1. Ophthalmoscopy, fluorescein angiography, focal electroretinograms, and optical coherence tomography were used for the evaluations. The level of vascular endothelial growth factor in the aqueous was determined by enzyme-linked immunosorbent assay. Immunohistochemistry was performed.

RESULTS

An intravitreal injection of 10 μg of vasohibin-1 induced mild intraocular inflammation. Eyes with an intravitreal injection of 0.1 μg and 1.0 μg of vasohibin-1 had significant less fluorescein leakage from the choroidal neovascularizations and larger amplitude focal electroretinograms than that of vehicle-injected eyes. Similar results were obtained by repeated injections of 0.1 μg of vasohibin-1. Immunohistochemistry showed that vasohibin-1 was expressed mainly in the endothelial cells within the choroidal neovascularizations. The vascular endothelial growth factor level was not significantly altered by intravitreal vasohibin-1.

CONCLUSION

The reduction of the laser-induced choroidal neovascularizations and preservation of macular function in monkey by intravitreal vasohibin-1 suggest that it should be considered for suppressing choroidal neovascularizations in humans.

Assessment of "non-recordable" electroretinograms by 9 Hz flicker stimulation under scotopic conditions

To refine methods of electroretinographical (ERG) recording for the analysis of low retinal potentials under scotopic conditions in advanced retinal degenerative diseases. Standard Ganzfeld ERG equipment (Diagnosys LLC, Cambridge, UK) was used in 27 healthy volunteers (mean age 28 ± SD 8.5 years) to define the stimulation protocol. The protocol was then applied in clinical routine and 992 recordings were obtained from patients (mean age 40.6 ± 18.3 years) over a period of 5 years. A blue stimulus with a flicker frequency of 9 Hz was specified under scotopic conditions to preferentially record rod-driven responses. A range of stimulus strengths (0.0000012-6.32 scot. cd s/m² and 6-14 ms flash duration) was tested for maximal amplitudes and interference between rods and cones. Analysis of results was done by standard Fourier Transformation and assessment of signal-to-noise ratio. Optimized stimulus parameters were found to be a time-integrated luminance of 0.012 scot. cd s/m² using a blue (470 nm) flash of 10 ms duration at a repetition frequency of 9 Hz. Characteristic stimulus strength versus amplitude curves and tests with stimuli of red or green wavelength suggest a predominant rod-system response. The 9 Hz response was found statistically distinguishable from noise in 38% of patients with otherwise non-recordable rod responses according to International Society for Clinical Electrophysiology of Vision standards. Thus, we believe this protocol can be used to record ERG potentials in patients with advanced retinal diseases and in the evaluation of potential treatments for these patients. The ease of implementation in clinical routine and of statistical evaluation providing an observer-independent evaluation may further facilitate its employment.

Retinal pathway origins of the pattern electroretinogram (PERG)

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Melanoma-associated retinopathy associated with intranasal melanoma

PURPOSE

To present a case of melanoma-associated retinopathy (MAR) associated with an intranasal melanoma.

CASE REPORT

A 77-year-old Japanese man visited us complaining of night blindness, blurred vision, and color vision difficulties in both eyes. His best-corrected visual acuity was 0.7 in the right and 1.0 in the left eyes. The rod response of the electroretinogram (ERG) was abolished, and the maximum response had a negative waveform. The a-wave of the single-flash cone response was square shaped, and the b-wave was delayed. The ON-response of the long-flash cone ERG was absent, but the OFF-response was preserved. A severe loss of retinal sensitivity was detected by static perimetry. Positron emission tomography showed no abnormal signs. Six months after the initial examination, an intranasal tumor was detected and surgically removed. The final diagnosis based on histopathology was malignant melanoma.

CONCLUSION

Our case demonstrates that MAR can be associated with an intranasal mucosal melanoma. Thus, in cases where the primary lesion cannot be identified in patients with MAR-like symptoms and signs, we recommend that preferential sites of mucosal melanomas be examined.