Scotopic Flash Research Articles

Retinal On-Pathway Deficit in Congenital Disorder of Glycosylation Due to Phosphomannomutase Deficiency

To describe novel electroretinographic (ERG) findings associated with congenital disorder of glycosylation due to phosphomannomutase deficiency (PMM2-CDG) (previously known as congenital disorder of glycosylation type 1a). Two male siblings with genetically confirmed PMM2-CDG underwent full-field ERG to a range of scotopic and photopic flash luminances that extended the International Society for Clinical Electrophysiology of Vision standard protocol and included scotopic 15-Hz flicker and photopic prolonged on-off stimulation. Photopic prolonged ERGs were profoundly electronegative with absent b-waves but preserved oscillatory potentials. Prolonged off-responses and off-oscillatory potentials were preserved. Transient full-field photopic ERGs revealed a broad a-wave and narrow b-wave, and the photopic 30-Hz flicker ERG had a sawtooth waveform. The scotopic b-waves of both cases were attenuated to the fifth percentile, whereas scotopic a-wave amplitudes were at the 50th to 75th percentile, giving a reduced a:b ratio. The scotopic a-wave waveform was well defined to bright flash luminance. The number of scotopic oscillatory potentials was preserved, although amplitudes were smaller than average. Scotopic 15-Hz flicker ERGs were evident to a range of flash luminances and showed an expected phase cancellation between -1.5 and -1.0 log scotopic td (troland) • s, but phase increased only for the fast rod pathway. We find, for the first time to our knowledge, an association of PMM2-CDG with a selective on-pathway dysfunction in the retina. This ERG phenotype localizes the site of retinal dysfunction to the on-bipolar synapse with photoreceptors. Modeling the unusual combination of ERG findings helps our understanding of the role of N -glycosylation at this synapse and provides a focus for future studies of potential intervention.

‘Cone dystrophy with supranormal rod response’ in children

AimTo describe the initial clinical presentation of children with ‘cone dystrophy with supranormal rod response,’ a distinct retinal disorder from recessive KCNV2 mutations.MethodsRetrospective case series.ResultsNine children (seven families) initially examined...

Influence of Glutathione on the Electroretinogram in Diabetic and Non-diabetic Rats

Aims: The purpose of this study was to investigate the influence of glutathione on the electroretinogram (ERG) in diabetic and non-diabetic rats.Materials and Methods: Streptozotocin (STZ: 60 mg/kg) was injected into male RCC Wistar rats to induce hyperglycemia, with buffer instead of STZ injected into age-matched non-diabetic controls. After 8 weeks, ERG measurements were obtained at seven different scotopic flash intensities on the two groups of anesthetized, dark-adapted rats (controls, STZ). Following ERG measurements, eyes were enucleated for measurements of retinal/vitreous GSH and glutathione disulfide (GSSG).Results: Diabetic rats produced delayed b-wave ERG signals (increased implicit times), but had normal a-wave and b-wave amplitudes, a-wave implicit times, and oscillatory potentials. No differences were observed in retinal GSH or GSSG between controls and diabetics; however, correlations between GSH and all ERG parameters (with the exception of b-wave implicit times) were noted, and were not significantly altered by the presence of hyperglycemia.Conclusions: GSH is likely to play an important role in retinal function as assessed by the ERG, with this role not substantially altered in rats diabetic for 8 weeks.

Decreasing dietary linoleic acid promotes long chain omega-3 fatty acid incorporation into rat retina and modifies gene expression

Age-related macular degeneration (AMD) may be partially prevented by dietary habits privileging the consumption of ω3 long chain polyunsaturated fatty acids (ω3s) while lowering linoleic acid (LA) intake. The present study aimed to document whether following these epidemiological guidelines would enrich the neurosensory retina and RPE with ω3s and modulate gene expression in the neurosensory retina. Rat progenitors and pups were fed with diets containing low or high LA, and low or high ω3s. After scotopic single flash and 8-Hz-Flicker electroretinography, rat pups were euthanized at adulthood. The fatty acid profile of the neurosensory retina, RPE, liver, adipose tissue and plasma was analyzed using gas chromatography. Gene expression was analyzed with real-time PCR in the neurosensory retina. Diets rich in ω3s efficiently improved the incorporation of ω3s into the organs and tissues. This raising effect was magnified by lowering LA intake. Compared to a diet with high LA and low ω3s, low LA diets significantly upregulated LDL-receptor gene expression. Similar but not significant upregulation of CD36, ABCA1, ALOX5 and ALOX12 gene expression was observed in rats fed with low LA. No effect was observed on retinal function. Increasing the intake in ω3s and lowering LA improved the enrichment with ω3s of the tissues, including the neurosensory retina and RPE, and upregulated genes involved in lipid trafficking in the neurosensory retina. Those results consistently reinforced the beneficial role of ω3s in the prevention of AMD, especially when the diet contained low levels of LA, as suggested from epidemiological data.

Congenital stationary night blindness is associated with the leopard complex in the miniature horse

To determine if congenital stationary night blindness (CSNB) exists in the Miniature Horse in association with leopard complex spotting patterns (LP), and to investigate if CSNB in the Miniature Horse is associated with three single nucleotide polymorphisms (SNPs) in the region of TRPM1 that are highly associated with CSNB and LP in Appaloosas. Three groups of Miniature Horses were studied based on coat patterns suggestive of LP/LP (n=3), LP/lp (n=4), and lp/lp genotype (n=4). Horses were categorized based on phenotype as well as pedigree analysis as LP/LP, LP/lp, and lp/lp. Neurophthalmic examination, slit-lamp biomicroscopy, indirect ophthalmoscopy, and scotopic flash electroretinography were performed on all horses. Hair samples were processed for DNA analysis. Three SNPs identified and associated with LP and CSNB in the Appaloosa were investigated for association with LP and CSNB in these Miniature Horses. All horses in the LP/LP group were affected by CSNB, while none in the LP/lp or lp/lp groups were affected. All three SNPs were completely associated with LP genotype (χ(2) = 22, P << 0.0005) and CSNB status (χ(2) =11, P<0.0005). The Miniature Horse breed is affected by CSNB and it appears to be associated with LP as in the Appaloosa breed. The SNPs tested could be used as a DNA test for CSNB until the causative mutation is determined.

Effect of Chondroitin Sulfate on Intraocular Pressure in Rats

To study the effect of intracameral injections of chondroitin sulfate (CS) on intraocular pressure (IOP), retinal function, and histology in rats. Acute or chronic injections of CS were performed unilaterally in the rat anterior chamber, whereas the contralateral eye was injected with vehicle. IOP was daily or weekly assessed by a tonometer. Retinal function was assessed by scotopic electroretinography (ERG) and the visual pathway by flash visual evoked potentials (VEPs), whereas the retinal and optic nerve head structure were examined by histologic analysis. A single injection of 8 mg (but not 2 or 4 mg) CS induced a significant increase of IOP. The increase of IOP induced by a single injection of 8 mg CS lasted for 7 days, whereas chronic (weekly) administration during 10 weeks induced a significant and sustained increase in IOP compared with eyes injected with vehicle. A significant decrease of scotopic ERG a- and b- wave amplitude was observed after 6 and 10 weeks of CS administration. Moreover, a significant decrease in scotopic flash VEP N2-P2 component amplitude was observed in eyes treated with CS for 6 and 10 weeks. A significant loss of ganglion cell layer cells and optic nerve axons was observed in eyes receiving CS for 10 weeks. These results suggest that exogenous CS simulates the accumulation of CS in primary open-angle glaucoma and that increased amounts of CS could play a key role in the IOP dysregulation characteristic of glaucoma.

Hyper‐response of OP3 to systemic hyperoxia in the dark‐adapted retina

We have demonstrated that the third wavelet (OP3) of the scotopic flash oscillatory potential (OP) complex shows a hyper-response during experimentally-induced systemic hyperoxia. The objective of the present study was to further evaluate and detail the time course of this enhanced retinal response. Twenty healthy adults volunteered for this study. The OPs were recorded with a DTL-type electrode following pupillary dilation and retinal dark adaptation. Stimuli consisted of white flashes. The OPs were recorded at 8 points in time before, during and after breathing pure oxygen (O2). The arterial blood O2 saturation (SaO2), end-tidal CO2 (EtCO2), respiratory rate (RR), pulse rate (PR) and blood pressure (BP) were monitored throughout the experiment. The amplitude of the OPs did not vary significantly across test conditions except for OP3, which increased with systemic hyperoxia and was still elevated by the end of the experiment. The SaO2 and RR increased, the EtCO2 and PR decreased, whereas the BP was not altered during O2 breathing. This study provides further evidence indicating that the neural generators of OP3 display a unique hyper-reactivity to increased systemic O2 levels in the young healthy adult. Further studies looking at OP3 are still needed to determine if this unique behavior could serve as an index of altered oxygen level and retinal function in health or disease.

Electrophysiological deficits in the retina of the DBA/2J mouse

The DBA/2J (D2J) is a genetic mouse model for glaucomatous neurodegeneration because the animals develop anatomical and functional retinal deficits that partially can be correlated with elevated intraocular pressure (IOP). The IOP starts to increase at an age of about 6 months as a result of morphological changes within the anterior eye segment, e.g., pigment dispersion and iris synechiae. The purpose of the present study was to investigate how ERG responses change in individuals at different ages in D2J mice and to compare these changes with normal aging effects in pigmented C57/B6 (B6) mice. IOP was measured in awake, non-sedated D2J and B6 mice with a rebound tonometer. At ages between 2-3 and 10 months, scotopic flash ERGs were measured five times with about 2 months' intervals. In addition, light adapted flicker ERGs were recorded. Our data show that the D2J shows lower flicker ERG responses than the B6 mice already at an age of 2-3 months. Dark adapted flash ERG responses are not decreased at this age. In both mouse strains the ERG responses decrease as a function of age, but there is a stronger decrease in the D2J mice. The data of flicker ERGs suggest the presence of early functional deficits in the D2J retina that possibly have a post-receptoral origin. The scotopic flash ERG reveals a functional deficit that occurs at a later stage and that possibly is IOP dependent. But, the deficits appear at an age at which the IOP is still lower than in the B6 mouse, indicating that other factors play an additional role.

Microwave = Thermal Balloon Endometrial Ablation

The electroretinogram (ERG) is an electrical response of the retina to photic stimulation. A flash of light or bright appearance of a pattern elicits a biphasic negative/positive waveform. The a-wave originating in the receptor level of rods and cones is the initial large negative wave. The b-wave originating in the midretina is the following large positive component. Protocols include full-field and multifocal ERGs. Full-field ERGs are recorded if one is most interested in the global health of the retina, such as in retinitis pigmentosa. A limitation of the full-field ERG is that the recording is a massed potential from the whole retina. Multifocal ERGs can map small scotomas in the central 40 + degrees of visual field. Abbreviated methods are used with infants and in the operating room as part of an exam under anesthesia. The effects of toxic medications can be detected and quantified using ERGs. The ERG is useful to assess cases of retinal foreign bodies and trauma to estimate the extent of retinal dysfunction. Foreign bodies affect retinal function depending on the extent of trauma to the retina and the location and composition of the object. Systemic metabolic disorders usually reduce ERG b-wave amplitudes, particularly the scotopic dim flash ERGs.

ERGs in children with pancreatic enzyme insufficient and pancreatic enzyme sufficient cystic fibrosis

We recorded scotopic and photopic flash electroretinograms (ERGs) in pediatric subjects with cystic fibrosis, aged 4 to 18 years, who were either pancreatic insufficient (PI) or pancreatic sufficient (PS). The aim of the study was to determine whether vitamin supplementation in the PI group allowed comparable retinal function in these two groups. ERGs were recorded from a mixed-gender group of 41 children and adolescents (4 to 17 years of age) with cystic fibrosis. The subjects were grouped according to pancreatic function into PI (n = 29) and PS (n = 12). Full-field flash ERGs were recorded from one eye using a DTL fiber. The pupil was dilated prior to recording using two drops of 0.5% tropicamide. ISCEV photopic and scotopic stimuli and recording conditions were used. Serum levels of vitamin A, beta carotene and retinol binding protein (RBP) were measured on the day of ERG recording. There was no significant difference in ERG amplitudes or implicit times between PI and PS groups. Vitamin A, beta carotene, and RBP levels were not significantly different across the two groups and were not correlated with implicit times or amplitudes of any of the ERG types recorded here. Similarity of ERGs across the PI and PS cystic fibrosis patient populations tested here suggests that the supplementation protocol applied to these populations allows similar levels of retinal function (as indicated by flash ERG parameters) in the two groups.

Diagnosis in a patient with fundus albipunctatus and atypical fundus changes

We report a case of an 11-year old Caucasian female with nyctalopia since early childhood with an atypical clinical presentation of fundus albipunctatus (FA), and a novel mutation in the RDH5 gene. In addition to white spots in the fundus, patchy areas of hypopigmentation were noted, which were reminiscent for an early stage of retinitis punctata albescens (RPA). Electroretinographic testing (ERG) showed a non-detectable, dark adapted, isolated rod response and a markedly decreased combined rod and cone response to an achromatic stimulus. After patching one eye overnight, both the isolated rod response and combined rod and cone scotopic white flash response were normal. A Goldmann-Weekers dark adapted final threshold response was also within the normal range. The patient showed a previously reported heterozygous mutation for Gly238Trp, and a novel Arg157Gln mutation. Genetic testing and extended ERG and psychophysical testing may be necessary to diagnose FA from early stages of progressive RPA.

Selective inner retinal dysfunction precedes ganglion cell loss in a mouse glaucoma model

Background/aims:To correlate ganglion cell function with defined parameters of the elevated intraocular pressure profile (IOP) in a mouse glaucoma model and to determine the temporal relationship of these functional changes...

Amax to scotopic Imax diagnoses feline hereditary rod cone degeneration more efficiently than any other combination of long protocol electroretinogram parameters

To evaluate two recent methods for detecting feline hereditary rod cone degeneration with maximum efficiency from a long full-field flash ERG protocol. One combines 12 of these measures in an equation that is derived from iterative principal components factor analysis. The other uses the amplitude of the a-wave to the brightest available flash alone. We tested the original 12-parameter equation, by applying it to 50 new ERG series in 23 backcrossed cats. They were necessarily either heterozygous or homozygous for hereditary rod cone degeneration. A masked observer compared the ERG score and fundus examinations. We reanalyzed the old, new and combined data sets. Data sets with only one session per animal were analysed to avoid problems from non-random sampling. A two factor linear model of the a-wave was evaluated. The prior equation, applied to the new data, discriminated the groups as well as it had initially. In the reanalysis, group separation continued to increase with even fewer measures compared to the previously reported study. Eventually, one measure, the amplitude of the a-wave (amax) to the brightest scotopic flash (Imax) discriminated the groups better than any other measure or combination of measures in all analyses, including data sets using only one session for each animal and in a two factor linear model of the a-wave. Amax to Imax alone proved to be the best diagnostic criterion in all analyses. No linear model is likely to discriminate affected from unaffected animals more effectively because additional variables increased variance more rapidly than they increased discrimination. Amax to Imax may detect other rod and rod/cone dystrophies equally efficiently.

Rod and Cone a-Waves in Central Retinal Vein Occlusion

To evaluate rod and cone a-waves in cases with unilateral central retinal vein occlusion (CRVO). Scotopic and photopic flash electroretinograms (ERGs) were recorded in seven patients aged 54-84 with unilateral hemorrhagic CRVO. Rod and cone a-waves were analyzed using photoreceptor models, and Rm(p3) (maximum a-wave amplitude) and S (sensitivity) were calculated. Decreased rod log S was found in all seven cases, and decreased cone log S was found in five cases. In only one case, rod log S in the fellow eye was decreased. The alterations in rod and cone log Rm(p3) were smaller than those in rod and cone log S. Of three cases in which ERGs could be recorded again after a certain follow-up period, rod log S and cone logS became larger in two cases and smaller in one case. The change in the phototransduction cascade was confirmed not only in rods but also in cones in five of our seven cases of CRVO. The ERG findings might reflect the functional change in the photoreceptor layer after the onset of CRVO.

Experimentally Reduced Perfusion of One Eye Impairs Retinal Function in Both Eyes

The oscillatory potential index of scotopic white flash electroretinograms is reversibly enhanced in the contralateral eye when the ocular perfusion pressure (OPP) to the test eye is transiently reduced. A transient increase in the intraocular pressure (IOP) and decrease in the OPP in the test eye induced quantifiable vascular changes in the optic nerve head of the contralateral eye. We explored this contralateral phenomenon looking at ganglion cell function in both eyes during elevated IOP and decreased OPP in the test eye only. Our specific objective was to characterize the effects that transient hypoperfusion had on the neural generators of the pattern-reversal electroretinograms (pERGs), the ganglion cells, and preganglion neurons. A transient elevation in the IOP was sustained in 10 healthy subjects by scleral suction to reduce the baseline OPP by 15, 30, 45, and 60% for 2-min intervals. For each level of OPP, pERGs were evoked by a checkerboard with 75 minarc high-contrast black-white checks reversing at 5 Hz and recorded bilaterally using DTL fiber electrodes. The pERGs were also recorded immediately after removal of scleral suction and at 2-min intervals thereafter for an 8-min recovery interval. The unilateral decrease in OPP differentially reduced the pERG in the test and contralateral eyes. The pERG for the test eye returned to baseline amplitude within 2 min of removing the suction cup. In contrast, the pERG in the contralateral eye remained below baseline throughout the entire 8-min recovery interval. The observation of a bilateral decrease in the pERGs while the OPP was decreased in the test eye only suggested that these neuronal changes were modified at more central visual centers for retinal function to be compromised bilaterally. This latter effect may have been mediated by the transiently altered OPP or yet unknown neurohormonal mechanisms.

Characterization of retinal damage in the episcleral vein cauterization rat glaucoma model

Episcleral vein cauterization (EVC) is used in rats to generate a glaucoma model with high intraocular pressure (IOP). The long-term retinal damage in this glaucoma model, however, has not been accurately quantified. We report the location and amount of retinal ganglion cell (RGC) damage caused by (EVC) induced IOP elevation in two rat strains. IOP was raised in one eye of Wistar ( N=5) and Brown-Norway(B-N)( N=7) rats by EVC and monitored monthly until IOP in contralateral eyes equalized at 5 months post-surgery. Animals were maintained for 3.5–4.5 additional months. B–N rats ( N=7) that had no EVC served as controls for this strain. Scotopic flash ERGs were recorded at baseline and just prior to euthanasia. Automated counts of all retrogradely labeled RGCs in retinal flat-mounts were determined and compared between contralateral eyes. RGC density maps were constructed and RGC size distribution was determined. Oscillatory potentials in the group of eyes which had elevated IOP were decreased at the time of euthanasia, when IOP had returned to normal. The group of normal B–N rats had similar RGC counts between contralateral eyes. In the experimental group the mean number of RGCs was not significantly different between control and experimental eyes, but 1 of 5 Wistar and 2 of 7 B–N experimental eyes had at least 30% fewer RGCs than contralateral control eyes. Total retinal area in B–N experimental eyes was higher compared to contralateral eyes. Cumulative IOP exposure of the experimental eyes was modestly correlated with RGC loss while oscillatory potentials appeared to be inversely related to RGC loss. In retinas with extensive (>30% RGC loss) but not complete damage, smaller cells were preserved better than larger ones. The above results indicate that RGC loss in both Wistar and B–N strains is variable after a prolonged elevation of IOP via EVC. Such variability despite equivalent IOP levels and ERG abnormalities, suggests unknown factors that can protect IOP-stressed RGCs. Identification and enhancement of such factors could prove useful for glaucoma therapy.

Amax is the Best a-wave Measure for Classifying Abyssinian Cat Rod/Cone Dystrophy

To see if any a-wave measure segregated normal cats from those affected by a recessively inherited Abyssinian rod/cone dystrophy more efficiently than a(max) to scotopic I(max). A-waves to electroretinograms (ERGs) evoked by a 4 cd x s/m(2) scotopic flash were extracted from 241 ERG sessions using 108 cats. They were either wild type or from an affected Abyssinian stock. Fourty four were bred by back-crossing to have a 50% probability of being affected. Most were diagnosed by retinal appearance or by the pattern of loss in a long protocol ERG. Eight were still unclassified. The diagnostic efficiency of amplitudes at 7, 8, 9, and 10 ms and a(max), of a(max) peak time, age at testing, and the main components of principal components factor analysis were compared by scaling their ability to segregate affected and normal cats. Variance and overlap between the groups both decreased as time along the a-wave increased. The loading of each animal on the largest factor also gave considerable overlap. There was a small absolute separation between groups when a(max) itself was used. Age and peak time were uncorrelated with disease. The light intensity used could be calculated to be equivalent to one sufficient for about 75% of full saturation in man. A(max) is a simple measure that is already in routine clinical use. When the flash is very bright and the animal fully dark adapted, this single measure is the most efficient sign of this rod/cone degeneration and possibly of all degenerations involving rods.

Visual Defects Associated with Vigabatrin: A Study of Epileptic Argentine Patients

The aim of the present study was to assess visual alterations in a population of Argentine patients treated with the antiepileptic drug vigabatrin. Twenty patients receiving vigabatrin and 15 patients receiving carbamazepine were examined with automated perimetry using a Humphrey 120-point full screening strategy. In addition, scotopic flash electroretinograms were performed. Of 20 patients treated with vigabatrin, two were unable to cooperate with testing. Of the remaining 18 patients, all but two showed at least one non-detected point inside the central 40 degrees of the visual field of each eye. Of the 15 carbamazepine-treated patients, three were unable to perform the study. None of the remaining 12 patients showed visual field defects. Both a- and b-wave amplitudes of the scotopic electroretinogram were significantly reduced in 12 patients receiving vigabatrin. Visual field defects among patients on vigabatrin therapy may occur with a higher frequency than previously recognized. The Humphrey 120-points full field screening test and electroretinography are useful tools to assess the visual dysfunction associated with vigabatrin.

Consequences of an increase in the ocular perfusion pressure on the pulsatile ocular blood flow.

In previous studies we have demonstrated that physical exertion constricted the major retinal arteries, increased the redness of the optic nerve head, and attenuated scotopic white flash oscillatory potentials. These anatomic and functional changes in the human retina suggested that blood flow to the innermost retinal layers was modified in some way to cause these changes. The objective of this study was to determine whether physical exertion also affected blood flow in the choroid, the exclusive source of blood to the outermost layers of the retina. Eighteen healthy adults volunteered for this study. An OBF Tonograph system (OBF Laboratories UK Ltd., Malmesbury, Wiltshire, U.K.) was used to derive the pulsatile ocular blood flow, which reflects the pulsatile component of blood flow in the choroid, at rest and 20 minutes after biking at a heart rate of 140 beats/min. At the systemic level, biking increased the blood pressure and the heart rate. At the ocular level, the duration of the systolic and diastolic phases of the intraocular pulse was shortened, and the pulse amplitude and volume were reduced. Despite the attenuation of the intraocular pulse parameters, the pulsatile ocular blood flow increased by some 18% after exercise largely because of the much larger increase in heart rate. The ocular perfusion pressure increased, whereas the intraocular pressure decreased. Physical exertion in the form of aerobic exercise increased the pulsatile component of blood flow in the choroid. Because the choroid is the sole blood supply to the outer retina, it was concluded that the degree of perfusion of the photoreceptors necessary for vision is increased by physical exertion. This increased choroidal blood flow is presumably to sustain vision as blood is directed to the large muscle groups involved in the physical activity.

ERG rod a-wave in Oguchi disease

We analyzed the change in the ERG rod a-wave waveform during the course of dark adaptation in two patients with Oguchi disease. Two Japanese patients showed a homozygous arrestin 1147delA mutation. Scotopic flash ERGs were recorded after different periods of dark adaptation. ERG rod a-waves were obtained after subtraction of the cone ERG contribution. The rod a-waves were fitted with a model of the rod receptor signal. The parameters, Rm p3 ( maximum a-wave amplitude) and S ( sensitivity) were calculated. Longer periods in the dark produced larger rod a-wave but only to the first flash presented. The amplitude of the response to subsequent flashes was essentially independent of the period of dark adaptation. Rm p3 increased with advance of dark adaptation. However, S was nearly constant. Our results suggest that the cause of delayed dark adaptation is not to be sought in the activation of phototransduction process or the regeneration of rhodopsin per se but rather in the deactivation process of the phototransduction cascade.