Pharmacologically defined components of the normal porcine multifocal ERG

Multifocal Electroretinography Changes over 12 Months after Resolution of Central Serous Chorioretinopathy: Prospective Observational Study

INTRODUCTION

This prospective observational study aimed to evaluate the changes in retinal function after the anatomical resolution of central serous chorioretinopathy by multifocal electroretinography.

METHODS

Thirty-two eyes of 32 patients with unilaterally resolved central serous chorioretinopathy were prospectively studied. Serial multifocal electroretinography examinations were performed at the initial visit for active central serous chorioretinopathy, the time of anatomical resolution (resolved central serous chorioretinopathy), and 3, 6, and 12 months after resolution. The peak amplitudes of the first kernel responses were analysed and compared with those in 27 age-matched normal controls.

RESULTS

Compared with controls, the N1 amplitudes of rings 1-4 and P1 amplitudes of rings 1-3 showed statistically significant reductions at 12 months after the resolution of central serous chorioretinopathy (p < 0.05). The multifocal electroretinography amplitude substantially increased at the time of resolution and gradually improved until 3 months after the resolution of central serous chorioretinopathy.

CONCLUSION

Serial examinations with multifocal electroretinography showed that retinal responses increased mostly after the resolution of central serous chorioretinopathy, and this improvement slowly progressed until 3 months; however, the multifocal electroretinography amplitudes remained statistically reduced 12 months after the anatomical resolution of central serous chorioretinopathy, indicating the residual functional deficits detected by multifocal electroretinography.

The p-ERG spatial acuity in the biomedical pig under physiological conditions

Pigs are becoming an important pre-clinical animal species for translational ophthalmology, due to similarities with humans in anatomical and physiological patterns. Different models of eye disorders have been proposed, and they are good candidates to assess biocompatibility/functionality of retinal prostheses. Electroretinography is a common tool allowing to gain information on retinal function, with several types of electroretinogram (ERG) been implemented including full field (ff-ERG), multifocal (mf-ERG) and pattern (p-ERG). p-ERG represents a valuable tool to monitor Retinal Ganglion Cells (RGCs) activity and can be used to calculate p-ERG spatial acuity. Unfortunately, scarce methodological data are available regarding recording/interpretation of p-ERG and retinal acuity in biomedical pigs yet enhancing knowledge regarding pig vision physiology will allow for more refined and responsible use of such species. Aim of this study was to record p-ERG in juvenile pigs to functionally assess visual acuity. Six female hybrid pigs underwent two p-ERG recording sessions at 16 and 19 weeks of age. Photopic ff-ERG were also recorded; optical coherence tomography (OCT) and histology were used to confirm retinal integrity. ff-ERG signals were repeatable within/across sessions. All p-ERG traces consistently displayed characterizing peaks, and the progressive decrease of amplitude in response to the increment of spatial frequency revealed the reliability of the method. Mean p-ERG spatial acuities were 5.7 ± 0.14 (16 weeks) and 6.2 ± 0.15 cpd (19 weeks). Overall, the p-ERG recordings described in the present work seem reliable and repeatable, and may represent an important tool when it comes to vision assessment in pigs.

Efficacy of 0.01% atropine for myopia control in a randomized, placebo-controlled trial depends on baseline electroretinal response

This study aimed to evaluate the efficacy of 18-month 0.01% atropine in 61 myopic children (aged 7–10) and the relationship with central retinal response (by multifocal electroretinogram [mfERG]) in a double-masked randomized placebo-controlled clinical trial. Global-flash mfERG was measured at baseline, while cycloplegic spherical equivalent refraction (SER) and axial length (AL) were measured at baseline and at 6-month intervals. Annualized change in SER and AL were compared between atropine and control groups, and the relationships with baseline mfERG were evaluated. Changes in SER (−0.70 ± 0.39D vs. −0.66 ± 0.41D, p = 0.63) and AL (0.32 ± 0.16 mm vs. 0.30 ± 0.22 mm, p = 0.52) were similar in atropine and control groups. Interestingly, in the placebo group, mfERG amplitude was negatively correlated with axial elongation (R_p = −0.44, p = 0.03) as in our previous study. However, in the atropine group, an opposite trend was observed that axial elongation was positively correlated with mfERG amplitude (R_a = 0.37, p = 0.04). Annualized myopia progression demonstrated similar opposite effect between atropine and placebo groups but did not reach statistical significance. An ERG screening protocol may be warranted to identify suitable candidates to reduce the likelihood of an unfavorable treatment response by 0.01% atropine.

Retinal and visual function in infants with non-accidental trauma and retinal hemorrhages

PURPOSE

To investigate retinal function and visual outcomes in infants with retinal hemorrhages due to non-accidental trauma (NAT).

METHODS

This is a retrospective review of full-field or multifocal electroretinogram (ERG) recordings, visual acuity in log minimum angle of resolution (logMAR), clinical status, and neuroimaging. Multifocal ERGs from the central 40° were compared to corresponding fundus imaging. Visual acuity was measured by Teller cards at follow-up. ERGs were compared to controls recorded under anesthesia.

RESULTS

Sixteen children met inclusion criteria (14 recorded during the acute phase and 2 during long-term follow-up). During the acute phase, ERGs (n = 4 full field; n = 10 multifocal ERG) showed abnormal amplitude, latency, or both in at least one eye. Ten subjects had significantly reduced responses in both eyes, 3 of which had an ERG dominated by a negative waveform (absent b-wave or P1). The remaining six subjects had responses in one eye that were near normal (≥ 50% of controls). ERGs were sometimes abnormal in local areas without hemorrhage. ERGs could be preserved in local areas adjacent to traumatic retinoschisis. Two subjects with reduced visual acuity had belated ERGs: One had an abnormal macular ERG and the other had a normal macular ERG implying cortical visual impairment. At follow-up, 10 of 14 subjects had significant visual acuity loss (≥ 0.7 age-corrected logMAR); four subjects had mild vision loss (≤ 0.5 age-corrected logMAR). Visual acuity outcome was not reliably associated with the fundus appearance in the acute phase. All subjects with a negative ERG waveform had severe vision loss on follow-up.

CONCLUSIONS

Retinal dysfunction was common during the acute phase of NAT. A near normal appearing fundus did not imply normal retinal function, and ERG abnormality did not always predict a poor visual acuity outcome. However, a negative ERG waveform was associated severe visual acuity loss. Potential artifacts of retinal hemorrhages and anesthesia could not fully account for multifocal ERG abnormalities. Retinal function can be preserved in areas adjacent to traumatic retinoschisis.

Subretinal surgery: functional and histological consequences of entry into the subretinal space

BACKGROUND AND OBJECTIVES

Gene-therapy, stem-cell transplantation and surgical robots hold the potential for treatment of currently untreatable retinal degenerative diseases. All of the techniques require entry into the subretinal space, which is a potential space located between the retina and the retinal pigment epithelium (RPE). Knowledge about obstacles and critical steps in relation to subretinal procedures is therefore needed. This thesis explores the functional and histological consequences of separation of the retina from the RPE, extensive RPE damage, a large cut in the retina (retinotomy) and RPE phagocytosis in a porcine model.

METHODS

Experiments were performed in 106 female domestic pigs of Danish landrace distributed over five studies. Under general anesthesia, different procedures for expansion of the subretinal space were conducted. Outcomes were visual function measured electrophysiologically with multifocal electroretinogram (mfERG) and retinal morphology examined histologically. Study I: The effect of anesthesia on mfERG was examined by repeated recordings for 3 hr in isoflurane or propofol anesthesia. Outcome was mfERG amplitude. Study II: Consequences of a large separation of the photoreceptors from the RPE were examined by injecting a perfluorocarbon-liquid (decalin) into the subretinal space. Two weeks after, in a second surgery, decalin was withdrawn. Outcomes were mfERG and histology 4 weeks after decalin injection. Study III: Extensive RPE damage was examined by expanding the subretinal space with saline and removing large sheets of RPE-cells through a retinotomy. Outcomes were mfERG and histology 2, 4 and 6 weeks after the procedure. Study IV: Consequences of a large retinotomy were examined by similar procedures as in Study III, but in study IV only a few RPE cells were removed. Outcomes were mfERG and histology 2 and 6 weeks after surgery. Study V: Clearance of the subretinal space was examined by injecting fluorescent latex beads of various sizes into the subretinal space. Outcome was histologic location of the beads at different time intervals after the procedure.

RESULTS

Study I: MfERG amplitudes decreased linearly as a function of time in propofol or isoflurane anesthesia. Duration of mfERG recording could be decreased without compromising quality, and thereby could time in anesthesia be reduced. Study II: MfERG and histology remained normal after reattachment of a large and 2-week long separation of the photoreceptors and RPE. Repeated entry into the subretinal space was well tolerated. Fluid injection into the subretinal space constitutes a risk of RPE-damage. Study III: Removal of large sheets of retinal pigment epithelial cells triggered a widespread rhegmatogenous-like retinal detachment resulting in visual loss. Study IV: A large retinotomy with limited damage of the RPE was well tolerated, and visual function was preserved. Study V: Subretinal latex beads up to 4 μm were phagocytosed by the RPE and passed into the sub-RPE space. Beads up to 2 μm travelled further through the Bruch's membrane and were found in the choroid, sclera and inside blood vessels.

CONCLUSION

A large expansion of the subretinal space, repeated entry, a large retinotomy and limited RPE damage is well tolerated and retinal function is preserved. Subretinal injection of fluid can damage the RPE and extensive RPE damage can induce a rhegmatogenous-like retinal detachment with loss of visual function. Foreign substances exit the subretinal space and can reach the systemic circulation.

Neuropeptide Y treatment induces retinal vasoconstriction and causes functional and histological retinal damage in a porcine ischaemia model

PURPOSE

To investigate the effects of intravitreal neuropeptide Y (NPY) treatment following acute retinal ischaemia in an in vivo porcine model. In addition, we evaluated the vasoconstrictive potential of NPY on porcine retinal arteries ex vivo.

METHODS

Twelve pigs underwent induced retinal ischaemia by elevated intraocular pressure clamping the ocular perfusion pressure at 5 mmHg for 2 hr followed by intravitreal injection of NPY or vehicle. After 4 weeks, retinas were evaluated functionally by standard and global-flash multifocal electroretinogram (mfERG) and histologically by thickness of retinal layers and number of ganglion cells. Additionally, the vasoconstrictive effects of NPY and its involved receptors were tested using wire myographs and NPY receptor antagonists on porcine retinal arteries.

RESULTS

Intravitreal injection of NPY after induced ischaemia caused a significant reduction in the mean induced component (IC) amplitude ratio (treated/normal eye) compared to vehicle-treated eyes. This reduction was accompanied by histological damage, where NPY treatment reduced the mean thickness of inner retinal layers and number of ganglion cells. In retinal arteries, NPY-induced vasoconstriction to a plateau of approximately 65% of potassium-induced constriction. This effect appeared to be mediated via Y1 and Y2, but not Y5.

CONCLUSION

In seeming contrast to previous in vitro studies, intravitreal NPY treatment caused functional and histological damage compared to vehicle after a retinal ischaemic insult. Furthermore, we showed for the first time that NPY induces Y1- and Y2- but not Y5-mediated vasoconstriction in retinal arteries. This constriction could explain the worsening in vivo effect induced by NPY treatment following an ischaemic insult and suggests that future studies on exploring the neuroprotective effects of NPY might focus on other receptors than Y1 and Y2.

Time-Dependent Decline in Multifocal Electroretinogram Requires Faster Recording Procedures in Anesthetized Pigs

Purpose

The time-dependent effect of anesthetics on the retinal function is debated. We hypothesize that in anesthetized animals there is a time-dependent decline that requires optimized multifocal electroretinogram (mfERG) recording procedures.

Methods

Conventional and four-frame global-flash mfERG recordings were obtained approximately 15, 60, and 150 minutes after the induction of propofol anesthesia (20 pigs) and isoflurane anesthesia (nine pigs). In six of the propofol-anesthetized pigs, the mfERG recordings were split in 3-minute segments. Two to 4 weeks after initial recordings, an intraocular injection of tetrodotoxin (TTX) was given and the mfERG was rerecorded as described above. Data were analyzed using mixed models in SAS statistical software.

Results

Propofol significantly decreases the conventional and global-flash amplitudes over time. The only significant effect of isoflurane is a decrease in the global-flash amplitudes. At 15 minutes after TTX injection several of the mfERG amplitudes are significantly decreased. There is a linear correlation between the conventional P1 and the global-flash DR mfERG-amplitude (R² = 0.82, slope = 0.72, P < 0.0001). There is no significant difference between the 3-minute and the prolonged mfERG recordings for conventional amplitudes and the global-flash direct response. The global flash–induced component significantly decreases with prolonged mfERG recordings.

Conclusions

A 3-minute mfERG recording and a single stimulation protocol is sufficient in anesthetized pigs. Recordings should be obtained immediately after the induction of anesthesia. The effect of TTX is significant 15 minutes after injection, but is contaminated by the effect of anesthesia 90 minutes after injection. Therefore, the quality of mfERG recordings can be further improved by determining the necessary time-of-delay from intraocular injection of a drug to full effect.

Translational Relevance

General anesthesia is a possible source of error in mfERG recordings. Therefore, it is important to investigate the translational relevance of the results to mfERG recordings in children in general anesthesia.

A Third-Generation Lipid Emulsion that Contains n-3 Long-Chain PUFAs Preserves Retinal Function in Parenterally Fed Neonatal Piglets

BACKGROUND

Preterm neonates and those with intestinal failure require prolonged parenteral nutrition (PN) during a critical time of early central nervous system maturation. Conventional lipid emulsions fed to preterm neonates lack n-3 (ω-3) long-chain polyunsaturated fatty acids (LC-PUFAs; >20 carbon chain in length). Recently, fish oil lipid emulsions have been developed that provide both n-6 (ω-6) and n-3 LC-PUFAs, precursors of very long-chain PUFAs (VLC-PUFAs; >24 carbon chain in length).

OBJECTIVE

Our objective was to determine the effect of fish oil lipid on retinal function in neonatal piglets fed total PN with the use of the lipid emulsions available in clinical practice. We hypothesized that fish oil-containing parenteral lipid would preserve retinal function more than conventional parenteral lipid.

METHODS

Male neonatal piglets (2-5 d of age) were fed isonitrogenous (16 g · kg^-1 · d^-1), isocaloric (1.1 MJ · kg^-1 · d^-1) PN that varied only in the lipid emulsion: Intralipid or SMOFlipid at 10 g · kg^-1 · d^-1 (n = 8/group). Retinal function was assessed after 14 d of treatment by recording electroretinograms under various light intensity conditions. Retinas were then harvested for histology and to determine fatty acid composition.

RESULTS

Electroretinogram intensity response curves showed greater photoreceptor a-wave amplitude in piglets fed SMOFlipid than in those fed Intralipid (percentage), for postsynaptic depolarizing bipolar cell b-waves (percentage) and for flicker electroretinogram amplitudes (percentage) (P < 0.05). Compared with those fed Intralipid, SMOFlipid-fed piglets had greater retinal total n-3 LC-PUFAs (15.7% compared with 18.4%; P = 0.04) and n-3 VLC-PUFAs (0.9% compared with 1.5%; P = 0.02), whereas Intralipid-fed piglets had greater total n-6 LC-PUFAs (13.1% compared with 10.5%; P < 0.01) and n-6 VLC-PUFAs (0.7% compared with 0.5%; P = 0.01). Histologically, retinas were indistinguishable between groups.

CONCLUSIONS

In a neonatal piglet model of PN feeding, the inclusion of fish oil-based n-3 LC-PUFAs in the lipid emulsion leads to their accretion and endogenous elongation to VLC-PUFAs in the retina, which is associated with better retinal function.

Mechanisms of secondary degeneration after partial optic nerve transection

Secondary degeneration occurs commonly in the central nervous system after traumatic injuries and following acute and chronic diseases, including glaucoma. A constellation of mechanisms have been shown to be associated with secondary degeneration including apoptosis, necrosis, autophagy, oxidative stress, excitotoxicity, derangements in ionic homeostasis and calcium influx. Glial cells, such as microglia, astrocytes and oligodendrocytes, have also been demonstrated to take part in the process of secondary injury. Partial optic nerve transection is a useful model which was established about 13 years ago. The merit of this model compared with other optic nerve injury models used for glaucoma study, including complete optic nerve transection model and optic nerve crush model, is the possibility to separate primary degeneration from secondary degeneration in location. Therefore, it provides a good tool for the study of secondary degeneration. This review will focus on the research progress of the mechanisms of secondary degeneration using partial optic nerve transection model.

Effect of lycium barbarum (wolfberry) polysaccharides on preserving retinal function after partial optic nerve transection

Lycium Barbarum Polysaccharides (LBP) are the active components of Wolfberry (a traditional Chinese medicine) which has long been used for improving visual function. This study aims to investigate localized changes of retinal function in a partial optic nerve transection (PONT) model, and effects of LBP on visual function. The multifocal electroretinograms (mfERG) were obtained from 30 eyes of 30 Sprague-Dawley rats. The rats were divided into 6 groups (five treatment groups and one control group). Starting from the first day of the experiment, the rats in the (PONT+LBP) group and the (LBP) group were dosed with LBP; rats in the (PONT+PBS (phosphate buffered saline)) group and the (PBS) group were dosed with PBS via nasogastric tube every day until euthanized. The dorsal part of the optic nerve was transected in the (PONT), (PONT+LBP) and (PONT+PBS) groups at the end of week 1 (day 7 after LBP or PBS feeding began). The mfERG was measured at three time points: week 2, week 3 and week 5. Significant reduction of P1 and PhNR amplitudes of the mfERG were observed in all retinal regions a week after PONT. Feeding with LBP prior to PONT preserved retinal function. All mfERG responses returned to the normal range in the superior retina, which corresponds to the transected dorsal region of the optic nerve, while most of the inferior retinal responses were significantly increased at week 4 after PONT. The ventral part of the retina had secondary degeneration which was not only limited to the ganglion cell layer, but is a widespread effect affecting the outer retina. LBP altered the functional reduction caused by PONT by regulating the signal from the outer retina.

The influence of brightness on functional assessment by mferg: a study on scaffolds used in retinal cell transplantation in pigs

To determine the effect of membrane brightness on multifocal electroretinograms (mfERGs), we implanted poly lactic-co-glycolic acid (PLGA) membranes in the subretinal space of 11 porcine eyes. We compared membranes with their native shiny white color with membranes that were stained with a blue dye (Brilliant Blue). Histological and electrophysiological evaluation of the overlying retina was carried out 6 weeks after implantation. Histologically, both white and blue membranes degraded in a spongiform manner leaving a disrupted outer retina with no preserved photoreceptor segments. Multifocal ERG revealed the white membranes to have a significantly higher P1-amplitude ratio than the blue (P = 0.027), and a correlation between brightness ratio and P1-amplitude ratio was found (r = 0.762). Based on our findings, we conclude that bright subretinal objects can produce normal mfERG amplitude ratios even when the adjacent photoreceptors are missing. Functional assessment with mfERG in scaffold implant studies should therefore be evaluated with care.

Toxicity profiles of subretinal indocyanine green, Brilliant Blue G, and triamcinolone acetonide: a comparative study

BACKGROUND

This study introduces a novel porcine model to examine the histopathological and electrophysiological consequences of retinotoxicity exerted by dyes commonly used for internal limiting membrane (ILM) staining.

METHODS

Indocyanine green (ICG) 0.5 mg/ml, Brilliant Blue G (BBG) 0.25 mg/ml and triamcinolone acetonide (TA) 13 mg/ml was injected subretinally in 12 vitrectomized pig eyes. At 6 weeks, retinas were examined by multifocal electroretinography (mfERG), ophthalmoscopy, fluorescein angiograpy, histopathology, and apoptosis assay.

RESULTS

mfERG responses were significantly lower in ICG-injected eyes than in healthy fellow eyes (p = 0.039). The ratio between injected eyes and healthy fellow eyes was lower in the ICG group than in the BBG (p = 0.009) and TA group (p = 0.025). No difference between BBG and TA existed. All retinas were reattached, and fluorescein angiographies showed a window defect corresponding to the injected areas but no blood-retina barrier break-down. Histopathology confirmed damage to the outer retina after ICG, but not after BBG and TA. No apoptosis was found at 6 weeks.

CONCLUSIONS

Subretinal ICG induces histological and functional damage to the retina, suggesting that ICG should be used with caution in macular hole surgery, where subretinal migration can occur. In contrast, BBG and TA appear safe after subretinal injection.

Forward and backward adaptive effects in global flash multifocal electroretinogram stimulation

PURPOSE

The present study investigated retinal adaptive responses in concert with the modulation of forward and backward adaptation induced by periodic global flashes using the global flash multifocal electroretinogram (mfERG).

METHODS

Six normal subjects were recruited for global flash mfERG measurements, which consisted of 103 scaled hexagonal elements followed by a global flash frame. In experiments I and II, with constant luminance maintained in both local and global flash frames, the number of dark frames was independently varied and these frames were either inserted prior to or following the global flash frame to investigate the forward or backward adaptive effect of the global flash on the mfERG. In experiment III, the number of dark frames was fixed but the luminance of the global flash frame was varied with constant luminance of the focal flash. This was used to demonstrate that the adaptive effect related not to time but to variation of luminance.

RESULTS

All the central, para-central and peripheral direct component amplitudes were found to be significantly influenced by variation of the number of dark frames (p < 0.01). Reducing the forward adaptive effect of the global flash enhanced the direct component response and it became steady after five dark frames were inserted following the global flash. Reducing the backward adaptive effect of the global flash also enhanced the direct component response but it started reducing after four dark frames were inserted prior to the global flash frame. These changes were different with luminance modulation of the global flash intensity with fixed dark frames, while the direct component amplitude grew approximately linearly with decreasing mean luminance of the global flash stimulation.

CONCLUSION

The retina plays a major role in visual adaptation. Both forward and backward adaptive effects of the global flash on the direct component have been illustrated in this study. The results show that the forward and backward adaptive phenomena in the global flash mfERG are different and demonstrate that backward adaptation is found at the retinal level.

Pharmacological dissection of multifocal electroretinograms of rabbits with Pro347Leu rhodopsin mutation

PURPOSE

To determine whether photoreceptor degeneration in transgenic (Tg) rabbits carrying the Pro347Leu rhodopsin mutation alters the neural activity of the middle and inner retinal neurons.

METHODS

Multifocal electroretinograms (mfERGs) were recorded from eight 12-week-old Tg rabbits both before and after intravitreal injection of the following: tetrodotoxin citrate (TTX), N-methyl-DL: -aspartic acid (NMDA), 2-amino-4-phosphonobutyric acid (APB), and cis-2,3-piperidine-dicarboxylic acid (PDA). Digital subtraction of the mfERGs recorded after the drugs were administered from those recorded before was used to extract the components that were eliminated by these drugs. Eight agematched, wild-type (WT) rabbits were studied with the same protocol.

RESULTS

There was no reduction in the amplitude of the cone photoreceptor response of the mfERGs in Tg rabbits. Both the first positive and the first negative waves of the ON-bipolar cell responses were significantly larger in the Tg than in the WT rabbits. Late negative waves of the ON-bipolar cell response were recorded only in the WT rabbits. The first negative wave of the inner retinal responses was larger in the Tg than in the Wt rabbits. The late positive waves were seen mainly in the WT rabbits.

CONCLUSIONS

The ON-bipolar cell and inner retinal responses were altered at the early stage of photoreceptor degeneration in Tg rabbits despite the preservation of the cone photoreceptor responses.

Effects of luminance combinations on the characteristics of the global flash multifocal electroretinogram (mfERG)

PURPOSE

This study aims to ascertain the characteristics of the response triggered by the global flash multifocal electroretinogram (MOFO mfERG) under various combinations of global and focal flash luminance, and to determine the optimal conditions for this measurement.

METHODS

Ten normal subjects with mean age 23.2 yrs (+/- 1.14 yrs) were recruited for the MOFO mfERG measurement. The visual stimulation consisted of four video frames (stimulus frame with 103 scaled hexagonal focal flashes, followed by a dark frame, a global flash and then another dark frame). The focal and global flash intensities were varied independently for four levels (50, 100, 200 and 400 cd/m(2)). The subjects then underwent measurements with sixteen combinations of focal and global flash luminance. The direct component (DC) and induced component (IC) of the MOFO mfERG were grouped into central and peripheral regions for analysis.

RESULTS

The central and peripheral DC amplitude increased with the focal flash luminance under constant global flash luminance. Moreover, the proportion of the global flash and focal flash intensity was shown to be important to achieve an optimal IC response. When the ratio of global flash luminance to focal flash luminance (g/f ratio) was kept at about 2:1, the central and peripheral IC amplitude reached the peak value, and further increasing the global flash luminance would not enhance the IC response magnitude. The implicit time of both central and peripheral DC generally decreased with the increase of g/f ratio. However, the implicit time of central and peripheral IC increased with the g/f ratio.

CONCLUSION

The g/f ratio is important in the MOFO mfERG paradigm, since the DC and IC responses change with this ratio. In order to obtain both optimal DC and IC responses, a g/f ratio of 1:1 with focal flash luminance between 100 cd/m(2) and 200 cd/m(2) would be recommended. As the global flash mfERG paradigm is studying the interaction triggered by both flashes, the g/f ratio is a vital parameter for measurement in future studies.

Delayed administration of glial cell line-derived neurotrophic factor (GDNF) protects retinal ganglion cells in a pig model of acute retinal ischemia

This study investigates whether intravitreal administration of glial cell line-derived neurotrophic factor (GDNF) enhances survival of NeuN positive retinal cells in a porcine model of retinal ischemia. 16 pigs were subjected to an ischemic insult where intraocular pressure was maintained at 5 mmHg below mean arterial blood pressure for 2 h. The mean IOP during the ischemic insult was 79.5 mmHg (s.e.m. 2.1 mmHg, n = 15). Three days after the insult the pigs received an intravitreal injection of GDNF microspheres or blank microspheres. The pigs were evaluated by way of multifocal electroretinography (mfERG), quantification of NeuN positive cells and evaluation of the degree of retinal perivasculitis and inflammation 6 weeks after the insult. In the post-injection eyes (days 14, 28 and 42), the ratios of the iN1 and the iP2 amplitudes were 0.10 (95% CI: 0.05-0.15) and 0.09 (95% CI: 0.04-0.16) in eyes treated with blank microspheres, and 0.24 (95% CI: 0.18-0.32) and 0.23 (95% CI: 0.15-0.33) in eyes treated with GDNF microspheres. These differences were statistically significant (P < 0.05). The number of NeuN positive cells in the area of the visual streak area was significantly higher in eyes injected with GDNF microspheres compared to eyes injected with blank microspheres. In eyes injected with GDNF microspheres the ganglion cell count was 9.5/field (s.e.m.: 2.1, n = 8), in eyes injected with blank microspheres it was 3.5/field (s.e.m.: 1.2, n = 7). This difference was statistically significant (P < 0.05). There was also a significant difference (P < 0.01) in the degree of perivasculiitis between GDNF treated eyes (median perivasculitis score 1.5) and blank treated eyes (median perivasculitis score 3.0). In conclusion, injection of GDNF microspheres 3 days after an ischemic insult results in functional and morphological rescue of NeuN positive cells in a porcine model of acute ocular ischemia.

Multifocal electroretinogram in rhodopsin P347L transgenic pigs

PURPOSE

Neural ectopic rewiring in retinal degeneration such as retinitis pigmentosa (RP) may form functional synapses between cones and rod bipolar cells that cause atypical signal processing. In this study, the multifocal electroretinograms (mfERGs) of a large animal model of RP, the rhodopsin P347L transgenic (Tg) pig, were measured to examine the sources and nature of altered signal processing.

METHODS

mfERG responses from a 6-week-old Tg pig were recorded before and after sequential application of tetrodotoxin (TTX), N-methyl-D-aspartate (NMDA), 2-amino-4-phosphonobutyric acid (APB), and cis-2,3-piperidinedicarboylic acid (PDA), to identify contributions to the retinal signal from inner retinal neurons, the ON-pathway, the OFF-pathway, and photoreceptors. The mfERG response contributions from different retinal components of in the Tg eyes were estimated and compared with control data from eyes of age-matched wild-type (WT) pigs.

RESULTS

There was a prominent difference in the estimates of the inner retinal response and ON-bipolar cell pathway contribution between the Tg and WT mfERG responses. In particular, the early components of the inner retinal contribution were obviously altered in the Tg mfERG. The inner retinal components at approximately 24 and 40 ms appeared to be inverted. Differences in the estimates of OFF-bipolar cell pathway contributions were minimal. There was no change in cone cell responses in the Tg mfERG.

CONCLUSIONS

In Tg retinas, ectopic synapses formed between cones and rod bipolar cells probably altered signal processing of the ON-bipolar cell pathway. In response to the altered visual signal input from the outer retina, signal processing in inner retinal neurons was also modified.