The Inhibition of the Degrading Enzyme Fatty Acid Amide Hydrolase Alters the Activity of the Cone System in the Vervet Monkey Retina

Recent studies using full-field electroretinography (ffERG) that triggers a non-specific mass response generated by several retinal sources have attributed an important role for cannabinoid receptors in mediating vision in primates. Specific cone-mediated responses evoked through the photopic flicker ERG appear to be a better way to validate the assumption that endogenous cannabinoids modulate the cone pathway, since FAAH is mainly expressed in the vervet monkey cone photoreceptors. The aim of this study is two-fold: (1) to use the photopic flicker ERG to target the cone pathway specifically, and (2) use URB597 as a selective inhibitor of the endocannabinoid degrading enzyme Fatty Acid Amide Hydrolase (FAAH) to enhance the levels of fatty acid amides, particularly anandamide. We recorded ERGs under four different flicker frequencies (15, 20, 25, and 30 Hz) in light-adapted conditions after intravitreal injections of URB597. Our results show that intravitreal injections of URB597, compared to the vehicle DMSO, increased significantly ffERG amplitudes at 30 Hz, a frequency that solely recruits cone activity. However, at 15 Hz, a frequency that activates both rods and cones, no significant difference was found in the ERG response amplitude. Additionally, we found no differences in implicit times after URB597 injections compared to DMSO vehicle. These results support the role of molecules degraded by FAAH in cone-mediated vision in non-human primates.

Clinical and Functional Characteristics of Secondary Geographic Atrophy Against the Background of Exudative Age-Related Macular Degeneration

Background.Studies demonstrate the need for long-term follow-up of patients with wet age-related macular degeneration (AMD) treated with inhibitors of angiogenesis to monitor long-term vision outcomes and assess the safety of antiangiogenic therapy in relation to the risk of secondary geographic atrophy. Aims to determine the characteristic clinical and functional signs of secondary GA that developed against the background of wet AMD. Methods.In 22 patients (25 eyes) with wet AMD and 18 healthy subjects comparable in age and sex standard ophthalmological and instrumental studies were performed and photopic electroretinograms (ERGs) were recorded according to ISCEV standards, flicker-ERGs, multifocal ERGs and electrooculogram. Results.The appearance of the area of secondary atrophy against the background of wet AMD in eyes treated with inhibitors of angiogenesis is clinically indistinguishable from areas of geographic atrophy that developed as an outcome of dry AMD. The ERG-signs of secondary atrophy are described, which are similar to the biomarkers of primary atrophy and specifically differ from them. Secondary atrophy is characterized by the dependence of the increase in the b/a ratio on the atrophic area, reducing of the 8.3 Hz-flicker-ERG amplitude in the absence of 24 Hz-flicker ERG changes. In eyes with secondary atrophy, a significant decrease in the density of the multifocal ERG P1-peak was shown not only in the first hexagon but also in the parafoveal zone. The electrooculography results showed a sharper dark troughs decrease in with an increase in Ardens ratio in patients with secondary atrophya on the background of wet AMD, in contrast to the previously described changes in primary geographic atrophy. Conclusion.Comparison of the change in the b/a ratio with secondary atrophy area in patients with wet AMD may have clinical implications for assessing retinal dysfunction and predicting visual function. Secondary atrophy is associated with a pronounced inhibition of photoreceptor activity with better preservation of cone bipolar cells. The ERG and electrooculography data taking together indicate a more significant dysfunction of the retinal pigment epithelium in GA against the background of wet AMD and the associated deterioration of photoreceptor function than the changes characterizing primary geographic atrophy.

Seizure triggered by flicker electroretinogram in a patient with no history of epilepsy

Purpose It is well known that repetitive flash stimulation may trigger seizures in susceptible individuals. Nevertheless, reports of such incidents occurring during recording of a flash electroretinogram (ERG) are extremely rare. Here, we describe the case of a photic-induced seizure triggered during an ERG recording in the absence of a history of epilepsy or other paroxysmal events. Methods A 14-year-old male patient presented with reduced visual acuity and impaired mesopic vision. Ophthalmological exams confirmed the patient’s complaints but were inconclusive as to the underlying pathophysiology. An ERG recording was performed, during which the 30-Hz flicker stimulus triggered a seizure. Results The ERG was essentially normal, with the exception of a 7-Hz rhythm superimposed onto the flicker ERG response that was recorded when the seizure developed. Conclusions The present case highlights the possibility that the 30-Hz ERG flash stimulus triggers a seizure in patients with no previous paroxysmal events. Literature evidence suggests that the likelihood of such an incident could be reduced by stimulating monocularly.

Comparative Analysis of Functional and Structural Decline in Retinitis Pigmentosas

Retinitis pigmentosa (RP) is a category of inherited retinal dystrophies that is best prognosticated using electroretinography (ERG). In this retrospective cohort study of 25 patients with RP, we evaluated the correlation between 30 Hz flicker ERG and structural parameters in the retina. Internationally standardized 30 Hz flicker ERG recordings, short-wavelength autofluorescence (SW-AF), and spectral domain–optical coherence tomography (SD-OCT) were acquired at two visits at least one year apart. Vertical and horizontal hyperautofluorescent ring diameter measurements with SW-AF, as well as ellipsoid zone (EZ) line width measurements with SD-OCT, were used as structural parameters of disease progression. The 30 Hz flicker ERG amplitude decreased by 2.2 ± 0.8 µV/year (p = 0.011), while implicit times remained unchanged. For SD-OCT, the EZ line decreased by 204.1 ± 34.7 µm/year (p < 0.001). Horizontal and vertical hyperautofluorescent ring diameters decreased by 161.9 ± 25.6 µm/year and 146.9 ± 34.6 µm/year, respectively (p = 0.001), with SW-AF. A correlation was found between the progression rates of the 30 Hz flicker amplitude recorded with Burian–Allen electrodes and both the horizontal ring diameter (p = 0.020) and EZ line (p = 0.044). SW-AF and SD-OCT, two readily available imaging techniques, may be used to prognosticate disease progression because of the reliability of their measurements and correlation with functional outcome.

Retinal defect in children with infantile spasms of varying etiologies

ObjectiveTo determine the prevalence of retinal defect in children with infantile spasms (IS) unrelated to treatment with vigabatrin and clarify if specific primary etiologies for IS are associated with retinal defect more than others.MethodsThis was an observational cohort study including 312 patients (176 male, 136 female) with IS who were vigabatrin-naive. Participants ranged from 1.7 to 34.7 months of age (mean 8.8 months). Electroretinograms (ERGs) were performed according to the International Society for Clinical Electrophysiology of Vision. Retinal defect was identified as abnormal if the 30-Hz flicker ERG amplitude was lower than the age-corrected normal 95% prediction interval. The primary etiology for IS, as determined by the treating pediatric neurologist(s), was obtained from patient health records and classified into 1 of 9 etiologic subgroups: (1) genetic disorders alone, (2) genetic-structural disorders, (3) structural-congenital, (4) structural-acquired (perinatal), (5) structural-acquired (postnatal), (6) metabolic disorders, (7) immunologic disorders, (8) infectious, and (9) unknown causes.ResultsFifty-nine of the 312 vigabatrin-naive children (18.9%) showed retinal defect and the prevalence of retinal defect was highest (24.4%) in the structural-acquired (perinatal) subgroup, which included hypoxic-ischemic defect. Retinal function compared across subgroups showed no significant difference.ConclusionsCare is required in diagnosing retinal toxicity, which would be enhanced by baseline flicker ERG in children with IS prior to starting vigabatrin.