Cone A-wave Research Articles

The electroretinography to identify biomarkers of idiopathic hypersomnia and narcolepsy type 1.

Hypersomnia spectrum disorders are underdiagnosed and poorly treated due to their heterogeneity and absence of biomarkers. The electroretinography has been proposed as a proxy of central dysfunction and has proved to be valuable to differentiate certain psychiatric disorders. Hypersomnolence is a shared core feature in central hypersomnia and psychiatric disorders. We therefore aimed to identify biomarkers by studying the electroretinography profile in patients with narcolepsy type 1, idiopathic hypersomnia and in controls. Cone, rod and retinal ganglion cells electrical activity were recorded with flash-electroretinography in non-dilated eye of 31 patients with idiopathic hypersomnia (women 84%, 26.6 ± 5.9 years), 19 patients with narcolepsy type 1 (women 63%, 36.6 ± 12.7 years) and 43 controls (women 58%, 30.6 ± 9.3 years). Reduced cone a-wave amplitude (p = 0.039) and prolonged cone (p = 0.022) and rod b-wave (p = 0.009) latencies were observed in patients with narcolepsy type 1 as compared with controls, while prolonged photopic negative response-wave latency (retinal ganglion cells activity) was observed in patients with idiopathic hypersomnia as compared with controls (p = 0.033). The rod and cone b-wave latency clearly distinguished narcolepsy type 1 from idiopathic hypersomnia and controls (area under the curve > 0.70), and the photopic negative response-wave latency distinguished idiopathic hypersomnia and narcolepsy type 1 from controls with an area under the curve > 0.68. This first original study shows electroretinography anomalies observed in patients with hypersomnia. Narcolepsy type 1 is associated with impaired cone and rod responses, whereas idiopathic hypersomnia is associated with impaired retinal ganglion cells response, suggesting different phototransduction alterations in both hypersomnias. Although these results need to be confirmed with a larger sample size, the electroretinography may be a promising tool for clinicians to differentiate hypersomnia subtypes.

Rituximab Monotherapy versus Rituximab and Bortezomib Combination Therapy for Treatment of Non-paraneoplastic Autoimmune Retinopathy.

To study whether rituximab and bortezomib combination therapy is more effective than rituximab monotherapy in the treatment of non-paraneoplastic autoimmune retinopathy (npAIR). Retrospective case series involving six patients with npAIR, taking either rituximab and bortezomib combination therapy (three cases) or rituximab monotherapy (one case and two historical patients). Patients on both treatment regimens showed stability in most of the visual function parameters during the one year of follow-up. Combination therapy resulted in improvement of scotopic combined rod and cone a-wave and b-wave amplitudes in all eyes where they were available (four eyes); however, rituximab monotherapy resulted in only two eyes with stable scotopic combined rod and cone a-wave and b-wave amplitudes, while four eyes showed a decrease in both a- and b-wave amplitudes. The average improvement in b-wave amplitude (50.7% 29.4% [range, 25-90%]) was higher than the average improvement in a-wave amplitude (35.7% 9.74 [range, 25-63%]). No severe adverse effects were reported. Rituximab and bortezomib combination therapy may not be more effective than rituximab monotherapy in npAIR patients for most of the visual function parameters; however, this combination therapy may be more effective in improving scotopic combined rod and cone a- and b-wave amplitudes. This may indicate the higher efficacy of combination therapy when there is involvement of the inner retina.

ERG assessment of altered retinal function in canine models of retinitis pigmentosa and monitoring of response to translatable gene augmentation therapy.

To analyze ERG responses from two dog models of retinitis pigmentosa, one due to a PDE6A mutation and the other a CNGB1 mutation, both to assess the effect of these mutations on retinal function and the ability of gene augmentation therapy to restore normal function. Scotopic and photopic ERGs from young affected and normal control dogs and affected dogs following AAV-mediated gene augmentation therapy were analyzed. Parameters reflecting rod and cone function were collected by modeling the descending slope of the a-wave to measure receptor response and sensitivity. Rod-driven responses were further assessed by Naka-Rushton fitting of the first limb of the scotopic b-wave luminance-response plot. PDE6A-/- dogs showed a dramatic decrease in rod-driven responses with very reduced rod maximal responses and sensitivity. There was a minor reduction in the amplitude of maximal cone responses. In contrast, CNGB1-/- dogs had some residual rod responses with reduced amplitude and sensitivity and normal cone responses. Following gene augmentation therapy, rod parameters were substantially improved in both models with restoration of sensitivity parameters log S and log K and a large increase in log Rmax in keeping with rescue of normal rod phototransduction in the treated retinal regions. Modeling of rod and cone a-waves and the luminance-response function of the scotopic b-wave characterized the loss of rod photoreceptor function in two dog models of retinitis pigmentosa and showed the effectiveness of gene augmentation therapy in restoring normal functional parameters.

Using the RETeval Device in Healthy Children to Establish Normative Electroretinogram Values.

To provide normative data of full-field electro-retinogram (ERG) responses in the pediatric population using the RETeval ERG device (LKC Technologies, Inc) in healthy children without evidence of retinal disease. This was a single-site cross-sectional study of healthy pediatric patients with normal dilated fundus examinations and no known retinal diseases. Participants were recruited to undergo dilated full-field ERG using the handheld RETeval device. The International Society for Clinical Electrophysiology of Vision 5-step protocol was used. Photopic and dark-adapted scotopic responses were recorded using skin electrodes. Main outcome measures were normative RETeval ERG values and correlation of age with measured ERG parameters. Thirty-eight eyes of 20 healthy patients (aged 4 to 17 years) were included in the study. Of the 20 normal patients, 9 were male and 11 were female. Normative mean, median, and range values were recorded for the measured full-field ERG parameters. Pearson correlation was moderately positive between age and oscillatory potential and scotopic dim flash amplitude (r = 0.59, P = .006 for both). A positive correlation was also found between age and cone a-wave implicit time (r = 0.67, P = .001). The handheld RETeval system is a useful tool for obtaining full-field ERGs in children without anesthesia. Moderate positive correlations were observed between age and oscillatory potential and scotopic dim flash amplitude. A strong correlation was found between age and cone a-wave implicit time. The current study provides a baseline of normative full-field ERG values in children. [J Pediatr Ophthalmol Strabismus. 2021;58(1):17-22.].

Electrophysiological function in eyes with reticular pseudodrusen according to fundus distribution.

Reticular pseudodrusen (RPD) could be present not only in the posterior pole but extramacular area also as a confluent morphological pattern. Thus RPD can be classified by the fundus distribution for the assessment of visual prognosis. The electrophysiological function in eyes with reticular pseudodrusen (RPD), showing various fundus distribution were evaluated using full-field electroretinogram (ERG). Retinal distribution of RPD was divided into three types (localized, intermediate, and diffuse) according to the extent of involvement of retinal areas by fundus photograph montages. RPD were present with the diffuse type in 21 eyes (25.6%), with the intermediate type in 30 eyes (36.6%), and with the localized type in 31 eyes (37.8%). The average age was 74.76 ± 4.52 (range, 65–81) years in the diffuse type, 72.47 ± 9.13 (range, 55–91) years in the intermediate type, and 70.26 ± 7.77 (range, 61–89) years in the localized type. The mean amplitudes of the scotopic rod response, scotopic maximal combined response, oscillatory potentials (OP), photopic cone response, and 30Hz cone flicker response were more decreased in the diffuse, intermediate, and localized types in order, except for the photopic cone a-wave response. The diffuse type showed reduced amplitudes of ERG responses than the normal control group under all testing conditions except for the photopic a-wave response, and differences were statistically significant with the age restriction and adjustment methods (Bonferroni-corrected P < 0.05). The mean implicit times of ERG responses were significantly delayed in the diffuse type in the photopic b-wave. (Bonferroni-corrected P < 0.05). Extensive retinal involvement of RPD correlates with severely reduced electrophysiological retinal function. This acquired form of decreased electrophysiological function should be regarded as different from those of hereditary retinal degeneration.

N-Methyl-N-Nitrosourea-Induced Acute Alteration of Retinal Function and Morphology in Monkeys.

The purpose of this study was to investigate both functional and morphologic alteration of the retina acutely induced by N-methyl-N-nitrosourea (MNU) in monkeys. The MNU was administered intravenously at a single dose of 40 mg/kg to six cynomolgus monkeys, and standard full-field electroretinograms (ERGs) were recorded 1, 3, and 7 days after dosing. In addition, the rod and cone a-waves in response to high-intensity flashes were analyzed by the a-wave fitting model (a-wave analysis). The photopic negative response (PhNR) was also recorded at the same time points. Furthermore, the retinas of two animals each were examined histopathologically 1, 3, or 7 days after dosing. The MNU attenuated all the standard full-field ERGs including the rod-driven and cone-driven responses; in the combined rod-cone response, the b-wave was more affected than the a-wave. In the a-wave analysis, the sensitivity parameters (S) of the rod and cone a-waves had decreased on the day after dosing and remained unchanged thereafter. The maximum response parameter (Rmax) of the rod a-wave gradually decreased. On the other hand, the Rmax in the cone a-wave transiently increased on the day after dosing and decreased thereafter; the PhNR amplitude showed a similar time course change. Histopathologically, the retinal lesion on the day after dosing mainly consisted of pyknosis and karyorrhexis in the photoreceptor nucleus. Depletion of some photoreceptor nuclei, and shortening and disorientation of the photoreceptor segments became prominent at 3 and 7 days after dosing. Localization of degenerated photoreceptors was consistent with that of rhodopsin-positive photoreceptors, resulting in a well-preserved central fovea. Our results indicated that MNU acutely induced rod-dominant photoreceptor degeneration in monkey retinas, but the photoreceptor function was impaired in both the rods and cones. Functional involvement of the postreceptoral components was also indicated.

Sildenafil-induced reversible impairment of rod and cone phototransduction in monkeys.

To investigate functional alteration of the retina induced by sildenafil in monkeys. Sildenafil was administered intravenously to cynomolgus monkeys at dose levels of 0, 1, 3, and 10 mg/kg, and standard full-field electroretinograms (ERGs) were recorded. The rod and cone a-waves in response to high-intensity flashes were also analyzed by the a-wave fitting model (a-wave analysis). Additionally, the photopic negative responses were recorded. Sildenafil at 3 mg/kg or more induced the following alterations in the standard full-field ERGs immediately after dosing: delayed b-wave in the rod response; delayed a-wave in the combined rod-cone response; and attenuated b-waves in the single-flash cone response and in the 30 Hz flicker. Additionally, the following changes were observed in the 10 mg/kg group: attenuated b-wave in the rod response; attenuated a-wave and delayed b-wave in the combined rod-cone response; delayed oscillatory potentials; and attenuated and delayed a-wave in the single-flash cone response. In the a-wave analysis immediately after dosing, sildenafil selectively decreased the sensitivity parameter (S) in the cone a-wave at 3 mg/kg, and in both the rod and cone a-waves at 10 mg/kg. The S value was highly correlated with plasma sildenafil concentration. The above changes fully recovered 24 hours after dosing. Sildenafil produced reversible impairment of the rod and cone phototransduction in monkeys. Meanwhile, involvement of the postreceptoral retinal components was suggested. These findings contribute to the clarification of sildenafil-induced visual disturbances. It is suggested that the photoreceptors are predominantly, but not exclusively, affected in the retina of humans with sildenafil-induced visual disturbances.

Photopic negative response in branch retinal vein occlusion with macular edema.

In patients with branch retinal vein occlusion (BRVO) and macular edema, the relations among full-field electroretinogram (ffERG) parameters and parameters of retinal function or morphology remain uncertain. The objective of this study was to investigate the correlations between parameters of the ffERG, including the photopic negative response (PhNR), and retinal functional or morphological parameters in these patients. In 62 consecutive BRVO patients (mean age: 68.5 ± 10.6 years; 32 women and 30 men), the amplitude and implicit time of the a-wave cone, b-wave cone, 30 Hz flicker, and PhNR were calculated from the ffERG. Microperimetry was employed to measure the macular sensitivity within the central 4°, 10°, and 20° fields, while macular thickness and volume within these fields were measured by optical coherence tomography. Best-corrected visual acuity (BCVA) was determined on the logarithm of the minimum angle of resolution scale. The cone b-wave, 30 Hz flicker, and PhNR amplitudes showed a significant correlation with BCVA. In addition, the cone a-wave, cone b-wave, 30 Hz flicker, and PhNR amplitudes all showed a significant correlation with macular sensitivity within the central 4°, 10°, and 20° fields. Only the 30 Hz flicker amplitude showed a significant correlation with the macular thickness and volume within the 4°, 10°, and 20° fields, while the other ERG parameters did not. These findings suggest that PhNR may be a useful ERG parameter for evaluating inner retinal function in BRVO patients.

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.

Association of electroretinogram and morphological findings in central retinal vein occlusion with macular edema

The objective of this study was to evaluate the relations among electroretinogram (ERG) parameters (cone a-wave, cone b-wave, and 30 Hz flicker), retinal thickness, and retinal volume in 16 patients with central retinal vein occlusion and macular edema. The amplitude and implicit time of the ERG parameters were extracted from the ERG traces. Retinal thickness and volume were measured by optical coherence tomography in nine macular subfields. Then the correlations among ERG parameters and morphological parameters were analyzed. The cone b-wave and 30 Hz flicker implicit time were correlated with retinal thickness and volume in seven out of nine subfields, excluding the temporal subfields. In addition, the amplitude of the cone b-wave was correlated with retinal thickness and volume in the nasal inner and nasal outer subfields. These findings suggest that retinal thickness and volume may be associated with outer and inner retinal function in central retinal vein occlusion patients.

Cone-Rod Dysfunction Is a Sign of Early-Onset High Myopia

High myopia (HM) is one of the leading causes of irreversible blindness because of its associated complications. Early-onset HM (eoHM) that presents before primary school age may be genetically determined, whereas late-onset HM (loHM) is affected by genetic and environmental factors. Identification of signs that differentiate eoHM from loHM may provide valuable clues toward understanding the molecular basis of HM. In this study, 42 subjects with HM were recruited, including 32 eoHM (onset age, ≤5 years) and 10 loHM (onset age, 12.4 ± 2.5 years). Clinical data from these two groups were compared, including best visual acuity, refraction, axial length, and electroretinography. The mean amplitudes of rod b-wave, maximum a-wave, maximum b-wave, cone a-wave, and cone b-wave of patients with eoHM were 179 ± 72 μv, -158 ± 63 μv, 345 ± 105 μv, -20 ± 11 μv, and 42 ± 21 μv, respectively, whereas those of patients with loHM were 252 ± 77 μv, -235 ± 60 μv, 464 ± 65 μv, -36 ± 9 μv, and 104 ± 26 μv, respectively (p < 0.001). Patients with eoHM had significantly reduced responses of cones and rods, especially cones, as compared with patients with loHM. The cone-rod responses in patients with loHM were within normal range. The findings suggest that cone-rod dysfunction may be a sign for eoHM compared with loHM.

Glycogen Synthase Kinase-3 Overexpression Replicates Electroretinogram Anomalies of Offspring at High Genetic Risk for Schizophrenia and Bipolar Disorder

Electroretinogram (ERG) anomalies occur in patients with psychiatric disorders and represent potential biomarkers for diagnosis. For instance, decreased rod ERG (b-wave amplitude at Vmax) is a biological endophenotype in young offspring at high genetic risk (HR) for schizophrenia (SZ) and bipolar disorder (BD). Also, a decrease in cone a-wave and rod a- and b- wave was observed in SZ patients. However, the biological underpinning of these anomalies remains unknown. Several genetic variants associated with enhanced risk for SZ and/or BD can activate glycogen synthase kinase-3 isozymes (GSK3α and β). Here we examined the potential contribution of GSK3α and β in the modulation of the ERG. Cone and rod ERGs were recorded in mice having increased (prpGSK3β mice) or reduced (GSK3β(+/-) mice) GSK3β expression and in GSK3α knockout (KO) mice. In prpGSK3β mice, we observed a decrease in rod b-wave amplitude at Vmax, whereas enhanced b-wave amplitude at Vmax was found in GSK3β(+/-) mice. An increase in cone a- and b-wave amplitude at Vmax and in rod b-wave amplitude at Vmax was observed in GSK3α-KO mice. GSK3 expression modulates some ERG parameters. The phenotype observed in prpGSK3β mice is consistent with observations made in HRs. ERG anomalies observed in GSK3β(+/-) and GSK3α-KO mice confirm an association between the rod and cone b-wave amplitude and the expression of GSK3 isozymes. Changes in GSK3 expression or activity may explain some ERG anomalies in HRs and patients, thus supporting the biological validity of ERG measurements as a valuable biomarker for psychiatric research.

Association of electroretinogram and morphological findings in branch retinal vein occlusion with macular edema

The objective of this study is to evaluate the relations among electroretinogram parameters (cone a-wave, cone b-wave, and 30-Hz flicker), retinal thickness, and retinal volume in patients with branch retinal vein occlusion (BRVO) and macular edema. We prospectively examined 33 patients (33 eyes) with BRVO and macular edema. The amplitude and implicit time of the a-wave cone, b-wave cone, and 30-Hz flicker were calculated automatically from the ERG. Retinal thickness and volume were measured by optical coherence tomography (OCT) in nine macular subfields. Then, correlations between the ERG parameters and morphological parameters were analyzed. The 30-Hz flicker amplitude was significantly smaller in the eyes with BRVO and macular edema than in the unaffected contralateral eyes. Thirty-hertz flicker and cone b-wave implicit times were significantly longer in the eyes with macular edema than in the unaffected eyes. The implicit time of the cone b-wave was correlated with both retinal thickness and retinal volume in the temporal subfields. Thirty-hertz flicker amplitude was correlated with both retinal thickness and volume in the temporal and superior outer (site of occlusion) subfields, while 30-Hz flicker implicit time was correlated with retinal thickness and volume in the outer temporal subfield. Multiple regression analysis demonstrated that the retinal thickness and volume of the temporal subfields were significant "determinants" of the implicit time for the cone b-wave and 30-Hz flicker, as well as the 30-Hz flicker amplitude. These findings suggest that OCT parameters of the temporal region may reflect postreceptoral cone pathway function in BRVO patients with macular edema.

Significant Correlation between Electroretinogram Parameters and Ocular Vascular Endothelial Growth Factor Concentration in Central Retinal Vein Occlusion Eyes

Central retinal vein occlusion (CRVO) leads to retinal ischemia, which then induces an upregulation of vascular endothelial growth factor (VEGF). The aim of this study was to determine whether a significant correlation exists between the ocular VEGF levels and the amplitudes and implicit times of different components of the electroretinogram (ERG) in eyes with a CRVO. The medical records of the 20 consecutive patients who had macular edema secondary to CRVO and were examined at the Nagoya University Hospital from November 2008 to February 2010 were reviewed. Because all the patients were scheduled to receive an intravitreal injection of bevacizumab (IVB), it was possible to collect samples of the aqueous humor before the IVB. The correlation between the different components of the ERGs and the VEGF concentration in the aqueous was determined. The mean VEGF concentration of the aqueous humor was 416 pg/mL with a range of 100-1260 pg/mL. The b/a ratio of the single flash ERGs (P = 0.049; ρ = -0.45), implicit times of the cone a-wave (P = 0.028; ρ = 0.50), cone b-wave (P = 0.0059; ρ = 0.63), and 30 Hz flicker ERGs (P = 0.0058; ρ = 0.63) were significantly correlated with the VEGF concentration in the aqueous. The significant correlations between the different components of the ERGs and the aqueous VEGF concentration indicate that full-field ERGs can be used to detect the CRVO patients at a high risk of developing neovascularization of the iris.

Endogenous nitric oxide enhances the light-response of cones during light-adaptation in the rat retina

The electroretinogram (ERG) is a non-invasive indicator of retinal function. Light flashes evoke a cornea-negative a-wave followed by a cornea-positive b-wave. Light-adaptation is known to increase the amplitude of cone-dependent b-waves. To identify the underlying mechanism, we recorded rat cone photoresponses in situ, using intravitreally-injected glutamate to block synaptic transmission and intense paired-flash stimuli to isolate cone a-waves. Steady adapting illumination caused a progressive increase in cone a-wave amplitude, which was suppressed in a dose-dependent manner by intravitreal CPTIO, a nitric oxide scavenger. We conclude that light-adaptation causes release of nitric oxide, which enhances the cone photoresponse.

Contribution of post-receporal cells to the cone a-wave of the human electroretinogram in congenital stationary night blindness and autoimmune-like retinopathy

In normal subjects the later part of the cone a-wave to a brief flash increases in amplitude after 50–100ms darkness due to a contribution from secondary hyperpolarising cells. We recorded these responses along with clinical ON and OFF ERGs in patients with inner retinal dysfunction to see if this part of the a-wave is affected. Patients with autoimmune-like retinopathy and CSNB2 had abnormal ON and OFF responses but the a-wave increased in amplitude in the dark as in normals. Conversely, the OFF-response was normal in CSNB1 but the a-wave did not increase in the dark. Contrary to expectation these results show some hyperpolarising cell function in autoimmune-like disease and CSNB2 and some OFF-pathway abnormality in CSNB1. The a- and d-wave are needed to assess OFF-pathway function.

Age-Related Decline in Rod Phototransduction Sensitivity in Rhesus Monkeys Fed an n-3 Fatty Acid–Deficient Diet

Docosahexaenoic acid (DHA), an n-3 fatty acid, is the major polyunsaturate in rod outer segments. The effect of long-term n-3 fatty acid deficiency on rod and cone phototransduction was investigated in the rhesus monkey. From birth to approximately = 9 years rhesus monkeys were fed an n-3-deficient diet (n = 9) known to reduce retinal DHA by 80%. Monkeys in the control group (n = 12) received either 8% alpha-linolenic acid (ALA) or 0.6% DHA, both of which support normal retinal DHA levels. None of the diets contained carotenoids. Photoactivation kinetics were assessed from the rate of increase and a P3 model fit of the ERG a-wave. Maximal cone amplitude and sensitivity were measured from the cone a-wave at 4 ms. The rod photoresponse and rod recovery were derived by using a paired flash Rod sensitivity was reduced by 40% in the n-3-deficient monkeys at 9 but not 4.5 years. The onset of the rising phase of the photoresponse was significantly delayed (P < 0.004) at 9 years. Rod recovery was delayed by 20% in n-3-deficient monkeys at both ages, but only for bright saturating flashes. Cone phototransduction was not altered by n-3 deficiency. Long-term dietary n-3 deficiency in the rhesus monkey was associated with two changes in retinal function. First, there was a delay in rod recovery that has remained relatively constant throughout life. Second, there was an age-dependent loss in rod phototransduction sensitivity; the lack of dietary carotenoids may have contributed to this decline.

Contribution of post-receptoral cells to the a-wave of the human photopic electroretinogram

ERGs were recorded to red flashes (0.01–50 ph cd s m 2) presented against a steady background (2000 sc td) or 0–300 ms after its suppression. The cone a-wave was altered in form and increased in amplitude in the dark. Peak amplitudes were doubled when the dark period was 50–100 ms and also when it was 150–200 ms. Measurement of the a-wave at fixed times showed that amplitude increase occurred at times later than 6–8 ms. The a-wave receives a significant negative-signal contribution from two post-receptoral mechanisms. These are adapted by weak backgrounds and recover their sensitivity extremely rapidly in the dark. The cone photocurrent alone contributes 40–70% of peak amplitude depending on stimulus intensity.

Utility in clinical practice of standard vs. high-intensity ERG a-waves

Standard ERG a-waves represent contributions from both photoreceptor and inner retinal cells, while the leading edge of the high-intensity a-wave is produced only by photoreceptors. This has raised questions about the value of the a-wave as an indicator of photoreceptor disease, and has led to suggestions for standardizing higher-intensity stimuli. Our objective was to compare the behavior of standard and high-intensity a-waves in clinical practice. Standard ISCEV (International Society for Clinical Electrophysiology of Vision) a-waves and high-intensity a-wave responses were recorded under scotopic and photopic conditions from normal subjects and from patients with photoreceptor dystrophies and other diseases. The standard scotopic a-wave amplitude followed the high-intensity a-wave closely among patients with different diagnoses, and the results did not change significantly when cone a-waves were subtracted to isolate rod signals. The only exception was one patient with the enhanced S cone syndrome (ESCS) whose dark-adapted responses were cone-driven. Initial peak times clustered in a small range for both standard and high-intensity responses, and were not very sensitive to disease. High-intensity a-waves can show photoreceptor characteristics directly, and may help analyze some rare disorders. However, in our study the amplitude of conventional scotopic a-waves mirrored that of the high-intensity responses quite closely over a wide range of patients. This suggests that for practical purposes even if it is not perfect, the standard ERG is an excellent indicator of photoreceptor disease.

Mutations in CABP4, the Gene Encoding the Ca 2+-Binding Protein 4, Cause Autosomal Recessive Night Blindness

Mutations in genes encoding either components of the phototransduction cascade or proteins presumably involved in signaling from photoreceptors to adjacent second-order neurons have been shown to cause congenital stationary night blindness (CSNB). Sequence alterations in CACNA1F lead to the incomplete type of CSNB (CSNB2), which can be distinguished by standard electroretinography (ERG). CSNB2 is associated with a reduced rod b-wave, a substantially reduced cone a-wave, and a reduced 30-Hz flicker ERG response. CACNA1F encodes the alpha 1-subunit of an L-type Ca2+ channel (Cav1.4 alpha ), which is specific to photoreceptors and is present at high density in the synaptic terminals. Ten of our patients with CSNB2 showed no mutation in CACNA1F. To identify the disease-causing mutations, we used a candidate-gene approach. CABP4, a member of the calcium-binding protein (CABP) family, is located in photoreceptor synaptic terminals and is directly associated with the C-terminal domain of the Cav1.4 alpha . Mice lacking either Cabp4 or Cav1.4 alpha display a CSNB2-like phenotype. Here, we report for the first time that mutations in CABP4 lead to autosomal recessive CSNB. Our studies revealed homozygous and compound heterozygous mutations in two families. We also show that these mutations reduce the transcript levels to 30%-40% of those in controls. This suggests that the reduced amount of CABP4 is the reason for the signaling defect in these patients.