Photopic Electroretinogram Research Articles

Digoxin-Induced Reversible Dysfunction of the Cone Photoreceptors in Monkeys

To investigate functional alteration of the retina induced by digoxin in monkeys. Digoxin was intravenously administered to cynomolgus monkeys and standard full-field electroretinograms (ERGs) were serially recorded. In other digoxin-treated monkeys, the rod and cone a-waves to high-intensity flashes were obtained and analyzed by the a-wave fitting model (a-wave analysis). The following responses were also recorded: dark- and light-adapted responses to flashes of different intensities (dark- and light-adapted luminance responses), photopic ERG elicited by long-duration stimulus (ON-OFF response), and the photopic negative response (PhNR). Delayed b-wave was observed in all responses of the standard full-field ERGs; amplitude of the b-wave was increased in the rod response, but was decreased in the single-flash cone response and the 30-Hz flicker. These changes recovered gradually after elimination of digoxin from the blood. Digoxin enhanced and delayed the b-wave in the dark-adapted luminance-response analysis regardless of stimulus intensity. In the light-adapted luminance-response analysis, digoxin attenuated the a- and b-waves only at high and middle stimulus intensity, respectively. The a-wave analysis revealed selective decrease in the maximum response parameter (Rmax) in the cone a-wave. Both the b- and d-waves of the ON-OFF response were delayed. The selectively reduced Rmax in the cone a-wave indicated dysfunction of the cone photoreceptors in digoxin-treated monkeys. Meanwhile, the enhanced and delayed rod response suggested alteration of retinal components other than the cone photoreceptors. These results may contribute to the understanding of digoxin-induced visual disturbances in humans. It is suggested that the cone function is markedly, but not exclusively, affected in the retina of such patients.

Slight Alteration of the Electroretinogram in Mice Lacking Dystrophin Dp71

Aim: Most Duchenne muscular dystrophy patients and the mdx^Cv3 mouse strain, lacking expression of both dystrophins Dp260 and Dp71, show a high attenuation of the dark-adapted electroretinogram (ERG) b-wave amplitude, whereas mice lacking the expression of Dp260 show normal b-wave amplitude. Here, we completed our assessment of whether the sole absence of Dp71 affects the ERG. Methods: Ganzfeld ERGs were performed on dark-adapted Dp71-null mice and littermates. Scotopic flash ERGs were recorded at light intensities from 3.10−⁵ to 1 cd.s/m². Oscillatory potentials (OPs) were extracted at 1 cd.s/m². Photopic flash ERGs were recorded at 10 cd.s/m² after light adaptation. Results: Dp71-null mice showed a slight but significant reduction in b-wave amplitudes, normal a-wave amplitudes and nonaffected implicit times of the scotopic ERGs. No changes were observed in the amplitudes and implicit times of the OPs and the photopic ERGs. Conclusions: Our results demonstrate that together both Dp71 and Dp260 are required for the generation of the ERG b-wave in mice.

Protective effect of VEGF receptor 2 on cone photoreceptors under hypoxia condition

Objective To investigate the protective effect of VEGF receptor 2( VEGFR2) on retinal cone photoreceptors under hypoxia condition. Methods Eight-week-old cone-specific VEGFR2-knockout( KO) mice and wild-type( WT) C57BL /6 mice received intravenous injection of 8 mmol / L cobalt chloride in the right eyes for hypoxia condition and PBS in the left eyes for control, with 6 mice in each group. On the next day electroretinogram( ERG) was conducted to evaluate the photoreceptor function,and immunofluorescence colocalization was used to determine the density and morphology of cone photoreceptors. Results In KO and WT groups,hypoxia eyes had significantly decreased a-wave and b-wave amplitudes in scotopic ERG compared with PBS control eyes( P 0. 01),but with no significant difference between hypoxia eyes of KO and WT groups( P 0. 05). In both KO and WT groups,the hypoxia eyes also had significantly decreased a-wave and b-wave amplitude in photopic ERG compared with PBS control eyes( P 0. 01),and the decrease in KO mice was more significant than that in WT group( P 0. 05,P 0. 01),indicating the decrease of cone function in KO animal. Morphology examination showed noticeable changes under hypoxia condition in both KO and WT groups, showing decreased density,shortened appearance,and disordered arrangement,with the changes in KO group being more noticeable. Conclusion VEGFR2 has a protective effect on cone photoreceptors under hypoxia condition.

Electroretinogram and Visual-Evoked Potential Assessment of Retinal and Central Visual Function in a Rat Ocular Hypertension Model of Glaucoma

Purpose/aim: The aim of the study was to investigate the long-term functional changes that may occur in the retina and visual cortex in a rat ocular hypertension (OHT) model of glaucoma, used in our lab for treatment studies, using electroretinogram (ERG) and visual-evoked potential (VEP) cortical recordings in order to test the hypothesis that experimental glaucoma has differential retinal and central effects.Materials and methods: Experimental glaucoma was induced unilaterally in Dark Agouti rats using hypertonic saline injection into the episcleral veins. After 3, 8, 16 and 26 weeks, ERGs and VEPs were recorded under scotopic conditions using brief full-field white flashes (10 μcd s m−2 to 10.4 cd s m−2) and under photopic conditions using a rod-adapting background and white light flashes (0.13–10.4 cd s m−2).Results: At 16 and 26 weeks after OHT induction, there was a significant reduction in the amplitudes of the a- (50% and 30% of unoperated eye values, respectively) and b-waves (55% and 40%, respectively) of the scotopic ERG and the b-waves of the photopic ERG (55% and 45%, respectively) in the glaucomatous eyes. However, no significant changes in the VEPs simultaneously recorded over the visual cortex were seen at any of the time points.Conclusions: The reductions in ERG amplitudes suggest that this model of glaucoma not only causes retinal ganglion cell (RGC) degeneration but also degeneration of the outer retinal cells, and this was confirmed by histology showing a reduction in the outer retinal layers in the glaucomatous eyes. Cortical VEPs did not show detrimental effects suggesting that the retinal damage in this model was not extensive enough to be detected with the VEP methods used or that there could be central compensation in this model of glaucoma.

A Little Algae a Day Keeps the Retinal Degeneration Specialist Away?

Retinitis pigmentosa (RP) is a genetically heterogeneous inherited retinal degeneration that leads to slow but relentless vision loss, usually starting in the midperipheral field. Although there is no known cure for RP, many dietary supplements have been advocated to slow the progression of retinal degeneration. Based on several studies, the most frequently recommended supplements are vitamin A palmitate,1 docosahexaenoic acid,2 and lutein.3 The exact dietary formulations vary fromcenter to center, anddisagreement exists over the efficacy of one compoundvs another.4Nonetheless,most centers do advise some combination of nutritional supplements for individuals with RP. β-Carotene, a plant carotenoid commonly found in fruits andvegetables, is aprecursor tovitaminA.5 It is absorbed in the small intestine,where it is cleavedbyβ,β-carotene15,15’-monooxygenase to form 2 molecules of retinol. Because this reaction is inhibited by high levels of vitamin A, it has an inherent feedback mechanism toprevent high levels of thisvitaminfromaccumulating.β-Carotenehasalsobeenshown to be a potent antioxidant and is one of the components of the formulation currently recommended by the Age-Related Eye Disease Study to prevent the progression of age-relatedmacular degeneration.However, β-carotene supplementation is not without some risk. The incidence of lung and gastrointestinal cancers has been shown to be increased in smokers and asbestos workers who take this supplement.6 In the article by Rotenstreich et al,7 the authors describe a subset of patientswithRPwhodemonstrated improvement in their scotopic full-field electroretinograms (ERGs) after receiving β-carotene supplements. Such findingswill undoubtedly be exciting to patientswith RP, but these resultsmust be met with cautious optimism. This study, which included 34 patients with autosomal recessive and dominant RP, was designed as a randomized, double-masked, placebo-controlled, crossover study. The authors are to be commended for carrying out awell-designed trial. Patientswere treatedwith either placeboor capsules containingapproximately 20mgofβ-carotene derived from the alga Dunaliella bardawil. The primary end point of the study was change in the maximum scotopic ERGb-waveamplitudeat thebeginningof the trialperiodcompared with 90 days later. The secondary end points included photopic ERG b-wave amplitude, dark-adapted chromatic visual field area, light-adapted visual field area, and bestcorrectedvisualacuity.Therewasnosignificantchange inbestcorrected visual acuity or visual field area. For the primary end point, maximum scotopic ERG b-wave amplitude, patients demonstrated on average an 8-μV increase in amplitude while taking β-carotene as compared with a 6-μV decrease while receiving placebo. There are several important things to realize about these results. First, only 10 of 29 patients showed an improvement (defined by the authors as an increase of 10 μV). Because RP is a genetically heterogeneous disease, it is possible that only patients with a subset of mutations benefited from this therapy. Alternatively, as is common in many patients with advanced RP, the ERG amplitudes may have been so diminished that any improvement in amplitude may have been below the threshold of detectability. Second, it is important to note that the magnitude of the change, while statistically significant, is still quite small. Peak amplitudes vary from system to system, but it is not uncommon to obtain maximal scotopic b-wave amplitudes measuring 500 to 700 μV in healthy patients. Therefore, a change of 10 to 15 μV is small and must be compared with the intervisit variation for recording this signal. For example, Fishman et al8 demonstrated that in their ERG system when such variation is taken into account, the maximal b-wave needs to increase by 80% to be considered significant in low-amplitude cohorts and 25% in higher-amplitude cohorts. When both groups were pooled together, the threshold for a significant increase was 32%. In this study, the treatment group demonstrated a 40% improvement from baseline of the scotopic maximal b-wave compared with a 16% loss in the placebo group, which is suggestive of a significant improvement, although we cannot stratify the groups into lowand high-amplitude cohorts because 30-Hz flicker data were not provided. Light-adapted single-flash ERGs did show a change that was statistically significant (an 18% improvement), but when intervisit variation is taken into account, this change is less impressive. Measurements of the intervisit variation of the ERG system being used in this study would be important for fully interpreting the data. Finally, although the increase in ERG amplitude is suggestive of an improvement in the functioning of remaining cells in the retina, it does not necessarily indicate a sustainedprotective effect. Theamplitudeof 30-Hz flickerERG responses has been correlated with long-term prognosis in patientswith RP, but the same correlation has not beenmade for themaximal scotopic b-wave amplitude.9 Because β-carotene ismetabolized to vitaminA, it is tempting to compare its efficacy with previous trials using vitamin A supplementation for RP.1 Such a direct comparison is difficult, though, because the current study was of much shorter duration, inRelated article on page 985 Opinion

The Photopic Negative Response of the Mouse Electroretinogram: Reduction by Acute Elevation of Intraocular Pressure

To determine the presence and magnitude of the photopic negative response (PhNR) component of the electroretinogram (ERG) in the mouse eye and to test if it is altered by short-term elevation of intraocular pressure (IOP). Photopic and scotopic ERGs were recorded from 12-month-old C57BL/6J mice and analyzed for photoreceptoral responses (a-wave), bipolar cell responses (b-wave), scotopic threshold responses (STRs), and PhNRs. Electroretinogram signals were measured before and after short-term subischemic elevation of IOP (50 mm Hg for 30 minutes) induced by cannulation of the anterior chamber. Retinas were subsequently assessed for signs of retinal stress and cell survival using immunohistochemistry and quantitative PCR. The corneal negative PhNR of the photopic ERG was elicited in the mouse eye, and its amplitudes correlated with amplitudes of the positive STR (pSTR). Elevation of IOP significantly reduced amplitudes of both the PhNR and pSTR, while scotopic a-waves, scotopic b-waves, and photopic b-waves were unchanged. Pressure elevation was associated with upregulation of glial fibrillary acidic protein and heme oxygenase 1 expression in retinal macroglia in the absence of retinal cell death. The PhNR component of the full-field ERG can be recorded in mice and is sensitive to elevation of IOP. Correlation between PhNR and pSTR signals before and after IOP elevation suggests that the PhNR depends on inner retinal integrity and provides a means for evaluating inner retinal function in mouse models.

Retinal Changes Precede Visual Dysfunction in the Complement Factor H Knockout Mouse

We previously reported that aged mice lacking complement factor H (CFH) exhibit visual defects and structural changes in the retina. However, it is not known whether this phenotype is age-related or is the consequence of disturbed development. To address this question we investigated the effect of Cfh gene deletion on the retinal phenotype of young and mid-age mice. Cfh −/− mouse eyes exhibited thickening of the retina and reduced nuclear density, but relatively normal scotopic and photopic electroretinograms. At 12 months there was evidence of subtle astroglial activation in the Cfh −/− eyes, and significant elevation of the complement regulator, decay-accelerating factor (DAF) in Müller cells. In the retinal pigment epithelium (RPE) of young control and Cfh −/− animals mitochondria and melanosomes were oriented basally and apically respectively, whereas the apical positioning of melanosomes was significantly perturbed in the mid-age Cfh −/− RPE. We conclude that deletion of Cfh in the mouse leads to defects in the retina that precede any marked loss of visual function, but which become progressively more marked as the animals age. These observations are consistent with a lifelong role for CFH in retinal homeostasis.

Ocular coherence tomography를 이용한 개의 망막변성증 평가

To report retinal image of in a 6-year-old male castrated poodle dog with a 2-month history of nyctalopia using optical coherence tomography (OCT). Ocular reflexes were present in both eyes and slit lamp examination showed anterior subscapular cataract in the right eye. There were fundus abnormalities in both eyes similar to retinal degeneration. Scotopic electroretinograms (ERGs) revealed significantly subabnormal amplitudes and prolonged implicit time, whereas photopic ERGs were better maintained, although far from normal. OCT of affected dogs revealed generalized retinal thinning much more than a normal age-matched dog. Therefore, OCT scanning is considered to be a useful method for retinal evaluation in dogs with retinal degeneration.

Biosynthesis, Characterization, and Efficacy in Retinal Degenerative Diseases of Lens Epithelium-derived Growth Factor Fragment (LEDGF1–326), a Novel Therapeutic Protein

For vision-threatening retinitis pigmentosa and dry age-related macular degeneration, there are no United States Food and Drug Administration (FDA)-approved treatments. We identified, biosynthesized, purified, and characterized lens epithelium-derived growth factor fragment (LEDGF1-326) as a novel protein therapeutic. LEDGF1-326 was produced at about 20 mg/liter of culture when expressed in the Escherichia coli system, with about 95% purity and aggregate-free homogeneous population with a mean hydrodynamic diameter of 9 ± 1 nm. The free energy of unfolding of LEDGF1-326 was 3.3 ± 0.5 kcal mol(-1), and melting temperature was 44.8 ± 0.2 °C. LEDGF1-326 increased human retinal pigment epithelial cell viability from 48.3 ± 5.6 to 119.3 ± 21.1% in the presence of P23H mutant rhodopsin-mediated aggregation stress. LEDGF1-326 also increased retinal pigment epithelial cell FluoSphere uptake to 140 ± 10%. Eight weeks after single intravitreal injection in Royal College of Surgeons (RCS) rats, LEDGF1-326 increased the b-wave amplitude significantly from 9.4 ± 4.6 to 57.6 ± 8.8 μV for scotopic electroretinogram and from 10.9 ± 5.6 to 45.8 ± 15.2 μV for photopic electroretinogram. LEDGF1-326 significantly increased the retinal outer nuclear layer thickness from 6.34 ± 1.6 to 11.7 ± 0.7 μm. LEDGF1-326 is a potential new therapeutic agent for treating retinal degenerative diseases.

Genotype and Phenotype of 101 Dutch Patients with Congenital Stationary Night Blindness

To investigate the relative frequency of the genetic causes of the Schubert-Bornschein type of congenital stationary night blindness (CSNB) and to determine the genotype-phenotype correlations in CSNB1 and CSNB2. Clinic-based, longitudinal, multicenter study. A total of 39 patients with CSNB1 from 29 families and 62 patients with CSNB2 from 43 families. Patients underwent full ophthalmologic and electrophysiologic examinations. On the basis of standard electroretinograms (ERGs), patients were diagnosed with CSNB1 or CSNB2. Molecular analysis was performed by direct Sanger sequencing of the entire coding regions in NYX, TRPM1, GRM6, and GPR179 in patients with CSNB1 and CACNA1F and CABP4 in patients with CSNB2. Data included genetic cause of CSNB, refractive error, visual acuity, nystagmus, strabismus, night blindness, photophobia, color vision, dark adaptation (DA) curve, and standard ERGs. A diagnosis of CSNB1 or CSNB2 was based on standard ERGs. The photopic ERG was the most specific criterion to distinguish between CSNB1 and CSNB2 because it showed a "square-wave" appearance in CSNB1 and a decreased b-wave in CSNB2. Mutations causing CSNB1 were found in NYX (20 patients, 13 families), TRPM1 (10 patients, 9 families), GRM6 (4 patients, 3 families), and GPR179 (2 patients, 1 family). Congenital stationary night blindness 2 was primarily caused by mutations in CACNA1F (55 patients, 37 families). Only 3 patients had causative mutations in CABP4 (2 families). Patients with CSNB1 mainly had rod-related problems, and patients with CSNB2 had rod- and cone-related problems. The visual acuity on average was better in CSNB1 (0.30 logarithm of the minimum angle of resolution [logMAR]) than in CSNB2 (0.52 logMAR). All patients with CSNB1 and only 54% of the patients with CSNB2 reported night blindness. The dark-adapted threshold was on average more elevated in CSNB1 (3.0 log) than in CSNB2 (1.8 log). The 3 patients with CABP4 had a relative low visual acuity, were hyperopic, had severe nonspecific color vision defects, and had only 1.0 log elevated DA threshold. Congenital stationary night blindness 1, despite different causative mutations, shows 1 unique CSNB1 phenotype. Congenital stationary night blindness 2 caused by mutations in CABP4 merely shows cone-related problems and therefore appears to be distinct from CSNB2 caused by mutations in CACNA1F. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Negative impact of melatonin ingestion on the photopic electroretinogram of dogs

Melatonin follows a circadian rhythm entrained by the light/dark cycle and plays a role in promoting light sensitivity at night. It has been suggested that melatonin and dopamine reciprocal inhibition may contribute to the switch between day and night vision. The purpose of this study was to investigate the impact of a high dose of melatonin administration on the photopic and scotopic electroretinogram (ERG) of dogs in the daytime, when it is not thought to be present. Photopic and scotopic ERG luminance response functions were obtained from 7 anaesthetized beagle dogs (3 males and 4 females), once without melatonin (control) and once after oral administration of melatonin (90mg/dog). Vmax (maximal b-wave amplitude achieved) and logK (retinal sensitivity) were calculated from the derived luminance response function. Photopic flicker ERG was also recorded. In photopic condition, a-wave amplitude (control: −126.90μV; with melatonin: −49.64μV; p<0.001) and Vmax (control: 252.50μV; with melatonin: 115.40μV; p<0.001) were decreased. A significant reduction of the photopic flicker ERG amplitude was observed after melatonin ingestion. In scotopic condition, an overall difference was reported before and after melatonin ingestion for the a- and b-wave amplitude, but no change was significant for Vmax. Melatonin ingestion at a high dose during the day decreases the photopic amplitude of a- and b-wave, but has no impact on implicit time. This negative impact of melatonin on photopic system may serve to promote night vision.

Cone survival and preservation of visual acuity in an animal model of retinal degeneration

The prevention of cone loss during retinal degeneration is a major goal of most therapeutic strategies in retinal degenerative diseases. An intriguing issue in the current research in this field is to understand why a genetic mutation that affects rods eventually leads to cone death. The main objective of the present study was to investigate to what extent rescuing rods from degeneration affects the survival of cones and prevents functional impairment of the visual performance. To this purpose, we compared rod and cone viabilities by both ex vivo and in vivo determinations in the rd10 mutant mouse, a validated model of human retinitis pigmentosa. The ex vivo experiments included morphological and biochemical tests, whereas in vivo studies compared the rod-mediated scotopic with the cone-mediated photopic electroretinogram. We also determined the overall visual performance by behaviorally testing the visual acuity (VA). The electroretinogram measurements showed that the kinetics of the photopic response in rd10 mice was slowed down with respect to the age-paired wild-type at a very early stage of the disease, when rods were still present and responsive. We then tested cone viability and function under a pharmacological scheme previously shown to prolong rod survival. The treatment consisted of eye drop administration of myriocin, an inhibitor of the biosynthesis of ceramide, a powerful proapoptotic messenger. The results of biochemical, morphological and functional assays converged to show that, in treated rd10 mice cone photoreceptors, the inner retina and overall visual performance were preserved well after rod death.

Spectral domain optical coherence tomography findings in bilateral peripheral cone dystrophy

To report spectral domain optical coherence (OCT) tomography findings in a case of bilateral peripheral cone dystrophy. A 21-year-old man complained of blurred visual fields on the lateral sides of both eyes. The patient's best-corrected visual acuity was 20/20 in both eyes. Fundus examination revealed mild temporal pallor, while fluorescein angiography did not show any abnormalities. Humphrey's visual field revealed a C-shaped scotoma. Photopic electroretinogram (ERG) and 30-Hz flicker revealed decreased cone function; however, scotopic ERG noted a normal response. Multifocal ERG revealed a relatively well-preserved macular area but with reduced amplitude in the peripheral areas of both eyes. On OCT, the photoreceptor inner and outer segment junction and retinal pigment epithelium (RPE) layers were well preserved in both eyes, except for a slight decrease in outer layer thickness. Moreover, on the macular thickness map obtained from Cirrus HD-OCT, a reduction in internal limiting membrane-RPE thickness that correlated well with visual field defects was revealed in both eyes. On the retinal nerve fiber layer (RNFL) thickness map obtained from Cirrus HD-OCT, the superior quadrant showed decreased RNFL thickness; however, thickness in the temporal quadrant corresponded with thickness in the macular area and was normal in both eyes. The OCT of a patient with peripheral cone dystrophy revealed decreased thickness of the macula with well-preserved retinal structures, which may be one of the distinctive features of this condition.

Inactivation of the microRNA-183/96/182cluster results in syndromic retinal degeneration

The microRNA-183/96/182 cluster is highly expressed in the retina and other sensory organs. To uncover its in vivo functions in the retina, we generated a knockout mouse model, designated "miR-183C(GT/GT)," using a gene-trap embryonic stem cell clone. We provide evidence that inactivation of the cluster results in early-onset and progressive synaptic defects of the photoreceptors, leading to abnormalities of scotopic and photopic electroretinograms with decreased b-wave amplitude as the primary defect and progressive retinal degeneration. In addition, inactivation of the miR-183/96/182 cluster resulted in global changes in retinal gene expression, with enrichment of genes important for synaptogenesis, synaptic transmission, photoreceptor morphogenesis, and phototransduction, suggesting that the miR-183/96/182 cluster plays important roles in postnatal functional differentiation and synaptic connectivity of photoreceptors.

S.P.62 Ocular characteristics of Duchenne Muscular Dystrophy

<h2>Abstract</h2> Electroretinogram (ERG) abnormalities have been described in Duchenne Muscular Dystrophy (DMD). Short isoforms of dystrophin are highly expressed in retina. We sought to expand the retinal phenotypes associated with different DMD genotypes. We studied the ocular characteristics of 16 DMD boys, mean age 9.5years (range 4–15years), glucocorticosteroid (GC) treated, with a range of genotypes: six had mutations at the 5′ end of the gene involving exons 3–13, predicted to affect the full length dystrophin Dp427, seven patients exons 44–57, affecting Dp427 and Dp260, and three patients at the 3′ end, in exon 70, affecting expression of Dp427, Dp260 and Dp71. Visual acuity, colour vision, intra-ocular pressure measures (IOP) and full field ganzfeld flash ISCEV Electroretinograms (ERGs) were assessed. Patients had normal visual acuity, one boy had a red-green colour vision defect, and two had raised IOP due to steroid use. ‘Negative' scotopic ERGs with reduced a:b-wave amplitude ratios were recorded in all patients with mutations involving exons 44–57, one patient with a 8–13 deletion and two patients with the 3′ mutation involving exon 70. The scotopic oscillatory potential (OP2) was reduced in all boys with mutations of exons 44–57, and in one with 8–13. The photopic OP2 was reduced in patients with deletions upstream of exon 30, but preserved in those patients in whom scotopic OP2 was attenuated. Photopic ERG a:b-wave amplitude ratios were reduced across the cohort, including those with 5′ mutations in whom scotopic a:b ratios had been normal. These data show a strong association of mutations downstream of exon 30, the promoter region for Dp260, with abnormal scotopic ERGs. In contrast photopic ERG abnormalities were widespread across all genotypes which may relate to the greater proportion of Dp427, compared with other isoforms, at the synapse of cones to cone on-bipolar cells. Our clinical evaluation also reminds us to monitor IOP during GC treatment.

Recording of the full‐field electroretinogram in minipigs

To test a simple electroretinographic protocol on a representative sample of minipigs. Minipig. Electroretinogram recordings were conducted on 162 healthy minipigs (81 males and 81 females) aged 4-6 months. After a 1.5-h light-adaptation period, the animals were anesthetized with general anesthesia. First, binocular full-field photopic electroretinogram recordings were conducted under photopic conditions. Subsequently, scotopic electroretinogram recordings were conducted during dark-adaptation periods every 4 min for a 20-min period. At the end of this period, the maximal combined rod-cone response was recorded by measuring the retinal response to a single high-intensity flash. We used sclerocorneal clip electrodes as active electrodes and needle electrodes as reference and ground electrodes. The a-wave and b-wave peak times and amplitudes have been measured and statistically analyzed. For each of the statistical comparisons, normality and homogeneity of variances were evaluated. No significant gender differences were observed, with the exception of a higher b-wave amplitude for the photopic ERG recordings observed in females when compared to males (48.14 ± 12.909 μV vs. 42.88 ± 10.666 μV; P = 0.005). The process of dark adaptation was evaluated, and the maximal combined rod-cone response was measured (a- and b-waves amplitude and peak time). We conducted photopic and scotopic electroretinogram recordings from a protocol based on light adaptation followed by dark adaptation using sclerocorneal clip electrodes, which allows quick assembly and examination.

Slowed recovery of human photopic ERG a-wave amplitude following intense bleaches: a slowing of cone pigment regeneration?

We have used the post-bleach recovery of the ERG a-wave to estimate the time-course of regeneration of cone pigment, following bleaching exposures far stronger than in a previous study. We recorded the photopic electroretinogram a-wave from two subjects, in response to dim red flashes delivered following 1-min exposures to intensities ranging from 1.1 × 10(4) to 1.3 × 10(5) photopic cd m(-2). The measured response amplitudes were "linearized" to derive estimates of pigment level. These estimated pigment levels were found to increase at an initially linear rate, consistent with a "rate-limited" model of photopigment regeneration. The extracted time-course was similar to that previously reported in densitometric studies of cone pigment regeneration after similarly intense exposures. On the other hand, the rate of regeneration was slower than measured in the same subjects following less intense bleaches. These results are consistent with the notion that cone pigment regeneration is slowed following very strong bleaching exposures, possibly as a result of depletion of a pool of retinoid.

Transcorneal Electrical Stimulation Promotes Survival of Photoreceptors and Improves Retinal Function in Rhodopsin P347L Transgenic Rabbits

To determine whether transcorneal electrical stimulation (TES) has neuroprotective effects on the photoreceptors, and whether it slows the rate of decrease of the electroretinogram (ERG) in rhodopsin P347L transgenic (Tg) rabbits. Six-week-old Tg rabbits received TES through a contact lens electrode on the left eye weekly for 6 weeks. The right eyes received sham stimulation on the same days. Electroretinograms (ERGs) were recorded before and at 12 weeks after the TES. After the last ERG recordings, the animals were euthanized for morphologic analysis of the retinas. Immunohistochemical (IHC) analysis was performed to detect the immunostaining by peanut agglutinin (PNA) and rhodopsin antibodies in the retinas. The a- and b-wave amplitudes of the photopic ERGs and the b-wave amplitudes of the scotopic ERGs at higher stimulus intensities were significantly larger in the TES eyes than in the sham stimulated eyes (P<0.05, respectively). Morphologic analyses showed that the mean thickness of the outer nuclear layer (ONL) in the visual streak at 12 weeks was significantly thicker in TES eyes than in sham-stimulated eyes (P<0.05). IHC showed that the immunostaining by PNA and rhodopsin antibody in the TES-treated retinas was stronger than that in the sham-stimulated retinas. TES promotes the survival of photoreceptors and preserves the ERGs in Tg rabbits. Although further investigations are necessary before using TES on patients, these findings indicate that TES should be considered for therapeutic treatment for RP patients with a P347L mutation of rhodopsin.

Evaluation of extended release brimonidine intravitreal device in normotensive rabbit eyes

To evaluate the safety profile of a brimonidine extended release intravitreal implant, in normotensive rabbit eyes. Devices were made from hollow poly-l-lactic acid (PLA) tubes and contained hundred micrograms of brimonidine pamoate. Device was injected intravitreally in one eye of 12 New Zealand pigmented rabbits, whereas other eye was injected with a sham implant in masked fashion. Ocular examination was conducted at baseline and months 1, 3 and 6 including dilated fundus examination and electro-retinogram (ERG). Four rabbits were sacrificed at each time-point for retinal histology. ERG data were compared between groups and time-points using anova. No complications were reported from either eye of any rabbits over a 6-month period. Photopic A wave was reduced in the control eye at 1 month compared with baseline (p < 0.01). There was no significant difference in other ERG parameters between the groups at different time-points. Gross retinal histology was normal at all time-points. Extended release intravitreal brimonidine device was found to be safe and in normotensive rabbit eyes.

Age-Related Changes in the Daily Rhythm of Photoreceptor Functioning and Circuitry in a Melatonin-Proficient Mouse Strain

Retinal melatonin is involved in the modulation of many important retinal functions. Our previous studies have shown that the viability of photoreceptors and ganglion cells is reduced during aging in mice that lack melatonin receptor type 1. This demonstrates that melatonin signaling is important for the survival of retinal neurons. In the present study, we investigate the effects of aging on photoreceptor physiology and retinal organization in CH3-f+/+ mice, a melatonin proficient mouse strain. Our data indicate that the amplitude of the a and b waves of the scotopic and photopic electroretinogram decreases with age. Moreover, the daily rhythm in the amplitude of the a- and b- waves is lost during the aging process. Similarly, the scotopic threshold response is significantly affected by aging, but only when it is measured during the night. Interestingly, the changes observed in the ERGs are not paralleled by relevant changes in retinal morphological features, and administration of exogenous melatonin does not affect the ERGs in C3H-f+/+ at 12 months of age. This suggests that the responsiveness of the photoreceptors to exogenous melatonin is reduced during aging.