Electroretinographic changes in eyes of patients with BRCA1 gene mutation

AIM: To assess the retinal function in BRCA1 gene mutation carriers and to evaluate the clinical significance of its potential alterations. PATIENTS AND METHODS: Flash electroretinogram (ERG) was studied in 15 unaffected patients (30 eyes) with constitutional BRCA1 gene mutation. Routine ophthalmological examination was additionally performed in the oldest, unaffected 15 patients and in 15 breast cancer patients being carriers of BRCA1 mutation. RESULTS: In ERGs, in the maximal response, a-wave (p < 0.03) and b-wave (p < 0.05) amplitudes were reduced. In the cone single-flash response, the amplitude of a-wave (p < 0.007) was also reduced. In the oscillatory potentials (OPs), increased amplitude of OP2 (p < 0.03), and increased latencies of OP3 (p < 0.0009) and OP4 (p < 0.03) were obtained. BRCA1 carriers even at old age or after treatment of breast cancer have not presented increased frequency of abnormalities detectable by routine ophthalmological examination. CONCLUSION: It can be hypothesized that dysfunction of rods, cones and inner retinal layers is present in asymptomatic carriers of BRCA1 gene mutation; however, this does not have clinical consequences.     

Retinal function in the von Hippel-Lindau disease

Purpose: To assess the retinal function in patients with von Hippel-Lindau disease (VHL). Patients: Studies were undertaken in 12 patients (17 eyes) with detected VHL gene mutation and 12 normal healthy controls (17 eyes). Methods: Pattern ERG (PERG), standard flash electroretinogram (ERG) recordings were performed in accordance with the International Society for Clinical Electrophysiology of Vision (ISCEV) standards. Results: In VHL patients, electrophysiological statistically significant changes were found. In PERG examination, increased latency of P50 was found in the total VHL group (p<0.02) and in the VHL subgroup with retinal angiomas (p<0.04). In ERG examination, photopic b-wave latency was increased in the total VHL group (p<0.03) and also in the VHL subgroup without retinal angiomas (p<0.05). In OPs, latency increase of OP2, OP3 waves and reduced amplitude of OP3 wave in the total VHL group (OP2 latency, p<0.05; OP3 latency, p<0.01; OP3 amplitude, p<0.03) and in the VHL subgroup with retinal angiomas (OP2 latency, p<0.02; OP3 latency, p<0.008; OP3 amplitude, p<0.02) were obtained. Conclusions: It can be hypothesized that dysfunction of the inner retinal layer is present in individuals with VHL disease even in patients without retinal angiomas.     

Electro-oculographic and electroretinographic studies in HNPCC gene mutation carriers

PURPOSE: To assess retinal function in HNPCC gene mutation carriers. PATIENTS: 19 carriers (38 eyes) of HNPCC genes and controls. METHODS: Electro-oculogram, standard flash electroretinogram and pattern electroretinogram (PERG) recordings were performed. RESULTS: In the total group of HNPCC gene mutation carriers examined by oscillatory potentials, reduced amplitude (p < 0.0004) and increased latency (p < 0.04) of the O3 wave and increased latency (p < 0.02) of the O4 wave were found. In the subgroup of carriers with hMLH1 gene mutation, reduced amplitudes of the O3 (p < 0.0005) and O4 (p < 0.04) waves were identified. In the total group of HNPCC gene mutation carriers examined by PERG, reduced amplitudes of the P50 (p < 0.003), N95 (p < 0.02) and abnormal N95/P50 ratio (p < 0.02) were revealed. In the subgroup of hMLH1 gene mutation carriers, reduced amplitude of the P50 (p < 0.04) and abnormal N95/P50 ratio (p < 0.02) were observed, whereas in the hMSH2 gene mutation carrier subgroup, reduced amplitude (p < 0.03), shortened latency of the P50 wave (p < 0.02) and reduced amplitude of the N95 wave (p < 0.03) were found. CONCLUSION: Constitutional dysfunction of the inner retina appears to be a characteristic feature of HNPCC gene mutation carriers.     

Relationship of oscillatory potential amplitude to A-wave slope over a range of flash luminances in normal subjects

The effect of flash luminance on the relationship of oscillatory potential (OP) amplitude, as a measurement of inner retinal function, to a-wave slope, as a measurement of photoreceptor function, was evaluated in full-field electroretinograms recorded from normal subjects. The ratio of OP amplitude to a-wave slope was found to be independent of flash luminance over a 3000-fold luminance range. This finding raises the possibility that a reduction in the ratio of OP amplitude to a-wave slope in eyes with media opacities may be used as a sign of inner retinal malfunction. Selected cases are presented to illustrate application of this approach.     

Electroretinogram b/a wave ratio improvement in central retinal vein obstruction.

The electroretinogram (ERG), especially the b/a wave ratio, is considered a good indicator of retinal ischaemia in central retinal vein obstruction (CRVO). Seven CRVO patients who showed b/a wave ratio improvement from < 1.0 [negative type (-) ERG] to > or = 1.0 and one from 1.07 to 1.53 were studied. Three mechanisms of change were observed: firstly, the b-wave amplitude increased without an a-wave amplitude decrease (group A, n = 2); secondly, the b-wave amplitude increased with an a-wave amplitude decrease (group B, n = 4); and, thirdly, both decreased, but the a-wave amplitude decreased more markedly (group C, n = 2). In group A, the visual acuities improved markedly. In group B, the visual acuities improved in two cases in which the b-wave amplitude reached the normal range; the visual acuities did not improve in two cases in which the b-wave amplitude did not reach the normal range. In group C, the visual acuities remained poor. The negative (-) ERG or significantly reduced b/a wave ratio is associated with ischaemic CRVO and did not occur because of the filtering effect of the haemorrhage, which may reduce the stimulus light for the ERG. Improvement of the reduced b/a wave ratio with an increased b-wave amplitude was accompanied by improvements in fundus appearance and visual acuity in CRVO. The results suggest that the retinal ischaemia in CRVO, as revealed by the ERG and fluorescein angiogram, may be reversible in some cases.     

Origin of electroretinogram amplitude growth during light adaptation in pigmented rats

We assessed the growth of the rat photopic electroretinogram (ERG) during light adaptation and the mechanisms underlying this process. Full field ERG responses were recorded from anesthetized adult Brown-Norway rats at each minute for 20 min of light adaptation (backgrounds: 1.8, 2.1, 2.4 log scotopic cd m(-2)). The rat photopic b-wave amplitude increased with duration of light adaptation and its width at 33% maximal amplitude narrowed (by approximately 40 ms). These effects peaked 12-15 min after background onset. The narrowing of the b-wave reflected steepening of the b-wave recovery phase, with little change in the rising phase. OP amplitudes grew in proportion to the b-wave. Inhibition of inner retinal responses using TTX resulted in a greater relative growth of b-wave and OP amplitude compared with fellow control eyes, and delayed the change in recovery phase by approximately 5 min. Inhibition of all ionotropic glutamate receptors with CNQX/D-AP7 delayed both rising and recovery phases equally (approximately 12 ms) without altering b-wave width or the time course of adaptation changes. These outcomes suggest that inner retinal light responses are not directly responsible for b-wave amplitude growth, but may contribute to the change in its recovery phase during adaptation. A TTX-sensitive mechanism may help to hasten this process. The cone a-wave was isolated using PDA/L-AP4 or CNQX/L-AP4. A-wave amplitude (35 ms after stimulus onset) also increased with time during light adaptation and reached a maximum (130 +/- 29% above baseline) 12-15 min after background onset. B-wave amplitude growth in fellow control eyes closely followed the course and relative magnitude of cone a-wave amplitude growth. Hence, the increase of the cone response during light adaptation is sufficient to explain b-wave amplitude growth.     

Modulation of the scotopic electroretinogram and oscillatory potentials with systemic hyperoxia and hypercapnia in humans

PURPOSE: Systemic hyperoxia reduces blood flow to the retina while systemic hypercapnia has the opposite effect. However, the effect this modification in blood flow has on neuroretinal function in humans has not been documented yet. The purpose of this study was to evaluate the effect of pure oxygen and carbogen breathing on scotopic electroretinograms (ERGs) and oscillatory potentials (OPs) in humans. METHODS: Thirty-five healthy adults volunteered for this study. The ERGs and OPs were recorded: 1) during room air breathing, 2) after a period of pure oxygen (O(2)) or carbogen breathing, 3) in room air just after the flow of gas was interrupted, and 4) 10 minutes after the end of the gas administration. RESULTS: The amplitude and latency of the a- and b-waves were not altered during systemic hyperoxia. The amplitude of OP3 increased during hyperoxia while the amplitude of the other OPs was not altered. The latency of all OPs remained stable throughout the O(2) session. Ten minutes after the end of pure O(2) breathing, the a- and b-wave latencies were delayed. No change was found in the amplitude of the a-wave during the carbogen session that increased the end-tidal carbon dioxide by 7.1%, whereas the b-wave was reduced ten minutes after the end of carbogen breathing. The amplitude of OP5 was reduced during carbogen breathing, as well as 10 minutes later. The amplitude of all other OPs, as well as the latencies of all ERG and OP components remained stable throughout the carbogen session. CONCLUSIONS: Breathing pure O(2) or carbogen did not compromise retinal function in any major way, likely due to adequate retinal and choroidal regulatory mechanisms. Further investigations are required to better delineate the impact and temporal characteristics of such physiological challenges on retinal function.     

Docosahexaenoic and arachidonic acid influence on preterm baboon retinal composition and function

PURPOSE. Dietary n-3 polyunsaturated fatty acid deficiency and prematurity are both associated with suboptimal visual function in nonhuman primates and in humans. This study reports measurements of retinal long chain polyunsaturate (LCP) concentrations and electroretinogram (ERG) parameters for term and preterm neonatal baboons consuming clinically relevant diets. METHODS. ERGs and retinal fatty acid compositions were obtained from baboon neonates in four groups: term-delivered/breast-fed (B), term/formula-fed (T-), preterm/formula-fed (P-), and preterm/formula (P+) supplemented with long chain polyunsaturates. Initial a-wave slope change (?), a-wave amplitude (a(amp)) and implicit time (a(i)), and b-wave amplitude (b(amp)) and implicit time (b(i)) were determined and correlations to retinal fatty acid concentrations were evaluated. RESULTS. The P+ group ? and b(amp) significantly improved between 0 and 4 weeks' adjusted age, whereas no P- group parameter improved with age. At four weeks, both a(amp) and b(amp) were significantly greater in group B than in all other groups, and ? and a(i) were greater for P+ than for P-. Concentrations of 22:6n-3, 22:5n-3, and Sigman-3 and the 22:5n-6/22:6n-3 ratio correlated positively with improved retinal response parameters, whereas 22:5n-6, 22:4n-6, 20:4n-6, 20:3n-6, 20:2n-9, 20:1n-9, and 18:1n-9 all correlated negatively (P < 0.05); saturates were uncorrelated. The parameters most linearly related to retinal 22:6n-3 were ?, a(i), and a(amp). Retinal 20:4n-6 concentrations were not influenced by prematurity or supplementation. CONCLUSIONS. Breast-feeding optimizes retinal response in 4-week-old baboons. Formula supplemented with 22:6n-3 prevents a decrease in retinal 22:6n-3 and improves preterm ERG parameters compared with unsupplemented formula. Retinal 22:6n-3 status is most closely associated with a-wave parameters.     

Contribution of retinal ganglion cells to the mouse electroretinogram

Purpose

To quantify the direct contribution of retinal ganglion cells (RGCs) on individual components of the mouse electroretinogram (ERG).

Methods

Dark- and light-adapted ERGs from mice 8 to 12 weeks after optic nerve transection (ONTx, n = 14) were analyzed through stimulus response curves for a- and b-waves, oscillatory potentials (OPs), positive and negative scotopic threshold response (p/n STR), and the photopic negative response (PhNR) and compared with unoperated and sham-operated controls, as well as to eyes treated with 6-cyano-7-nitroquinoxaline-2,3-dion (CNQX).

Results

We confirmed in mice that CNQX intravitreal injection reduced the scotopic a-wave amplitude at high flash strength, confirming a post-receptoral contribution to the a-wave. We found that ONTx, which is more specific to RGCs, did not affect the a-wave amplitude and implicit time in either photopic or scotopic conditions while the b-wave was reduced. Both the pSTR and nSTR components were reduced in amplitude, with the balance between the two components resulting in a shortening of the nSTR peak implicit time. On the other hand, amplitude of the PhNR was increased while the OPs were minimally affected.

Conclusion

With an intact a-wave demonstrated following ONTx, we find that the most robust indicators of RGC function in the mouse full-field ERG were the STR components.     

Oscillatory potential analysis and ERGs of normal and diabetic rats

PURPOSE: To identify and characterize the early alterations of the ERG oscillatory potentials (OPs) under conditions of poor glycemic control associated with diabetes in an animal model. To characterize and correlate the a- and b-wave properties of the ERGs of diabetic animals in parallel with the changes in oscillatory potentials. METHODS: Blood sugars, weights, and ERGs were measured for a group of rats each week for 3 weeks to obtain baseline information. A single injection of streptozotocin was given to the experimental animals. Weights, blood sugar, glycosylated hemoglobin, and detailed ERGs were recorded weekly for up to 12 weeks in control and experimental animals. RESULTS: OP kinetics were found to be inherently related to amplitude. Amplitude-matched OPs were delayed in diabetic animals when compared with baseline data from the same animal. The kinetics of OPs in control animals stayed the same or were slightly accelerated relative to their baseline values. For a given recording condition, OP kinetics were very stable over time and this stability was not disturbed in diabetic animals. Diabetic animals showed a small but significant delay in the a-wave, but no change in b-wave timing. The sensitivity of the b-wave was reduced twofold, but that of the a-wave was not changed. CONCLUSIONS: OPs have been used to evaluate retinal function in both diabetic models and patients. The comparison of amplitude-matched OPs is a robust determinant of changes in kinetics. Researchers and clinicians who use OPs may wish to consider the relationship between OP amplitude and kinetics to avoid confounding assessments of abnormalities. The amplitude versus kinetics relationship does not change form in diabetic animals; it is merely shifted (delayed) on the time axis.     

On-response deficit in the electroretinogram of the cone system in X-linked retinoschisis

PURPOSE: The purpose of this study was to evaluate the hypothesis that the reduced b-wave to a-wave ratio of the brief-flash electroretinogram (ERG) of the cone system typically observed in X-linked retinoschisis (XLRS) represents a relatively greater deficit in the ON response (response to light onset) than the OFF response (response to light offset). A second purpose was to investigate the use of sawtooth flicker as a stimulus for eliciting ERG ON and OFF responses. METHODS: Light-adapted, full-field ERGs were recorded in six patients with XLRS and six age-similar control subjects in response to 8-Hz rapid-on and rapid-off sawtooth flicker to emphasize ON and OFF responses, respectively. ERG responses were analyzed in terms of the amplitudes and implicit times of the a-wave, b-wave, and d-wave components. RESULTS: There was no significant difference between the patients with XLRS and the control subjects for either the amplitude of the a-wave of the ON response or the amplitude of the d-wave of the OFF response. However, the amplitude of the b-wave of the ON response was reduced significantly in the patients with XLRS, resulting in a significantly reduced b-wave to d-wave ratio. The patients' implicit times were increased significantly for all waveform components. CONCLUSIONS: The reduced b-wave to d-wave ratio of the ERG of the cone system in these patients with XLRS is consistent with a relative dysfunction of the cone ON bipolar cell pathway in this disorder. The results show further that sawtooth flicker is a promising stimulus for eliciting well-defined ERG waveforms that can provide a quantitative assessment of the properties of ON and OFF responses in retinal disease.     

Topographical alterations of inner retinal activity during systemic hyperoxia–hypercapnia in normal subjects and patients with type 1 diabetes

The purpose of this study was to investigate whether an increase in the circulating oxygen supply can alter inner retinal function, assessed by recordings of multifocal oscillatory potentials. We studied 9 subjects with type 1 diabetes (8 without overt retinopathy, one with 2 microaneurysms) and 10 similar-aged normal subjects. The central 60° of the retina was stimulated by an array of 61 hexagonal elements, and mfOP recordings were obtained while breathing room air or carbogen. First-order kernel analysis of the recordings shows 2 potentials (first-order OP1, OP2), whereas second-order kernel analysis produces 3 potentials (second-order OP1, OP2, OP3). Two methods were used to analyze the results: First, we performed a ring analysis for each subject and measured the amplitudes and latencies of the five potentials. We demonstrate that during carbogen inhalation, the control subjects, but not the patients with diabetes, showed significantly increased second-order OP3 amplitudes, for a retinal ring from around 1.8–13° eccentricity. Secondly, a topographical analysis was performed on the amplitude of the second-order OP3 in all 61 traces (from the average recordings of each subject group), which revealed significant alterations not visible in a ring analysis. A similar topographical analysis of the amplitude of the first-order OP2 revealed a small increase in its amplitude during carbogen inhalation for both subject groups. This study demonstrates that some aspects of inner retinal function are modified by the inhalation of carbogen. The reduced effect of carbogen inhalation on the recordings from the patients with diabetes may be due to compromised vascular perfusion in these subjects.     

The photopic negative response of the flash electroretinogram in retinal vein occlusion

The photopic negative response (PhNR) has recently been shown to be severely affected in central retinal artery occlusion (CRAO), despite relative preservation of the cone b-wave compared to that in the healthy unaffected fellow eye. The aim of this study was to test how the PhNR of the flash electroretinogram (ERG) is affected in human retinal vein occlusion. PhNR was elicited with red stimuli (1 cd s/m², 5 cd s/m², and 7 cd s/m² with 4 ms duration) and blue background (10 cd/m²). Standard Ganzfeld flash ERG was produced according to the ISCEV standard for the clinical electroretinogram (2004). Sixteen patients with central retinal vein occlusion (CRVO), 14 patients with branch retinal vein occlusion (BRVO), and 16 controls were analyzed. The amplitude of the PhNRs was significantly smaller in the CRVO and BRVO eyes than those in the unaffected fellow or control eyes (p = 0.000). There was a significantly greater reduction of PhNR amplitudes than that of other waves including the OPs, rod b-wave, combined a-wave and b-wave, cone a-wave and b-wave, and 30 Hz flicker ERG. Thus, PhNR amplitude in retinal vein occlusion is severely affected. There is a potential role for PhNR in assessing inner retinal damage and evaluating the effect of treatment.     

Reduced response of retinal vessel diameters to flicker stimulation in patients with diabetes.

BACKGROUND/AIM: Stimulation of the retina with flickering light increases retinal arterial and venous diameters in animals and humans, indicating a tight coupling between neural activity and blood flow. The aim of the present study was to investigate whether this response is altered in patients with insulin dependent diabetes mellitus. METHODS: 26 patients with diabetes mellitus with no or mild non-proliferative retinopathy and 26 age and sex matched healthy volunteers were included in the study. Retinal vessel diameters were measured continuously with the Zeiss retinal vessel analyser. During these measurements three episodes of square wave flicker stimulation periods (16, 32, and 64 seconds; 8 Hz) were applied through the illumination pathway of the vessel analyser. RESULTS: In retinal arteries, the response to stimulation with diffuse luminance flicker was significantly diminished in diabetic patients compared to healthy volunteers (ANOVA, p<0.0031). In non-diabetic controls flicker stimulation increased retinal arterial diameters by +1.6% (1.8%) (mean, p<0.001 v baseline), +2.8% (SD 2.2%) (p<0.001) and +2.8% (1.6%) (p<0.001) during 16, 32, and 64 seconds of flicker stimulation, respectively. In diabetic patients flicker had no effect on arterial vessel diameters: +0.1% (3.1%) (16 seconds, p = 0.9), +1.1% (2.7%) (32 seconds, p = 0.07), +1.0% (2.8%) (64 seconds, p = 0.1). In retinal veins, the response to flicker light was not significantly different in both groups. Retinal venous vessel diameters increased by +0.7% (1.6%) (16 seconds, p<0.05), +1.9% (2.3%) (32 seconds, p<0.001) and 1.7% (1.8%) (64 seconds, p<0.001) in controls during flicker stimulation. Again, no increase was observed in the patients group: +0.6% (2.4%), +0.5% (1.5%), and +1.2% (3.1%) (16, 32, and 64 seconds, respectively). CONCLUSION: Flicker responses of retinal arteries and veins are abnormally reduced in patients with IDDM with no or mild non-proliferative retinopathy. Whether this diminished response can be attributed to altered retinal vascular reactivity or to decreased neural activity has yet to be clarified.     

Electroretinographic anomalies in mice with mutations in Myo7a, the gene involved in human Usher syndrome type 1B

PURPOSE. In humans, mutations in the gene encoding myosin VIIa can cause Usher syndrome type 1b (USH1B), a disease characterized by deafness and retinitis pigmentosa. Myosin VIIa is also the gene responsible for the inner ear abnormalities at the shaker1 (sh1) locus in mice. To date, none of the sh1 alleles examined have shown any signs of retinal degeneration. In the present study, electroretinograms (ERGs) were recorded from sh1 mice to determine whether they have any physiological abnormalities. METHODS. ERGs were recorded from mice homozygous for one of nine mutant alleles of Myo7a ranging in age from postnatal day (P)20 to approximately 1 year. All mice were dark adapted for 30 minutes, and all the mutant mice were paired with an appropriately age- and strain-matched control animal. A presumptive null allele of myosin VIIa, Myo7a(4626SB), was used to determine whether mice without myosin VIIa had an increased threshold, as assessed by the light level required to elicit a 15-microV b-wave. RESULTS. At the maximum light intensity used, five of the nine alleles examined had significantly reduced a- and b-wave amplitudes. For example, Myo7a(4626SB) mutant mice had a 20% reduction in a-wave amplitude at the maximum light intensity, and this reduction was the same for mice ranging in age from P20 through 7 months. The b-wave thresholds of the Myo7a(4626SB) mutant mice were not significantly different from those of the control mice. Furthermore, whereas most of the alleles' a-wave implicit times were the same in mutant and control mice, mutant mice with two of the alleles had significantly faster a-wave implicit times. CONCLUSIONS. Mutations in myosin VIIa in mice can lead to decreased ERG amplitudes while threshold remains normal. This is the first report of a physiological anomaly in a mouse model with a mutation in the same gene as involved in USH1B.     

Predominant loss of the photopic negative response in central retinal artery occlusion

PURPOSE: To determine how the photopic negative response (PhNR) is affected in central retinal artery occlusion (CRAO). DESIGN: Observational case series. METHODS: Seven patients with unilateral CRAO were included. Full-field scotopic and photopic electroretinograms (ERGs) including the PhNR were recorded. Each ERG amplitude in the affected eye was expressed as a percentage of amplitude of the corresponding wave in the unaffected eye. RESULTS: Mean of the PhNR amplitude was reduced to 12.3 +/- 11.7% of that of unaffected eyes whereas the cone b-wave amplitude was attenuated to only 73.4 +/- 30.4%. This reduction of the PhNR amplitude was more significant than that of other waves including the rod b-wave, maximum a-wave and b-wave, cone a-wave and b-wave, and 30 Hz flicker ERG (P <.005). CONCLUSIONS: The PhNR was severely affected in CRAO despite relative preservation of the cone b-wave, implicating massive loss of ganglion cells and their axons.     

Selective ganglion cell functional loss in rats with experimental glaucoma

PURPOSE: To characterize retinal functional consequences of elevated intraocular pressure (IOP) in a rat model of experimental glaucoma. METHODS: Unilateral elevation of IOP was produced by hypertonic saline injection into an episcleral vein in 20 adult male Brown-Norway rats. IOP was measured in both eyes of awake animals four to five times per week. After 5 weeks, animals were dark adapted overnight (>12 hours) and full-field electroretinograms (ERGs) were obtained simultaneously from both eyes. Scotopic ERG stimuli were brief white flashes (-6.64-2.72 log cd-s/m(2)). Photopic responses were also obtained (0.97-2.72 log cd-s/m(2)) after 15 minutes of light adaptation (150 cd/m(2)). Eyes were processed the following day for histologic evaluation by light microscopy, including masked determination of optic nerve injury grade (ONIG; 1, normal; 5, severe, diffuse damage). RESULTS: Among experimental eyes, the group average IOP (+/-SD) was 34.5 +/- 4.1 mm Hg, whereas the average for control eyes was 28.1 +/- 0.5 mm Hg (t = 7.1, P < 0.0001). The average ONIG for experimental and control eye groups, respectively, was 3.4 +/- 1.7 and 1.0 +/- 0.02 (t = 6.3, P < 0.0001). The ONIG increased with mean IOP in experimental eyes (r(2) = 0.78, P < 0.0001) and was unrelated to mean IOP in control eyes (r(2) = 0.09, P = 0.18). In experimental eyes with relatively mild IOP elevation (mean IOP < 31 mm Hg) and no structural (histologic) damage to the optic nerve evident by light microscopy (ONIG = 1.1 +/- 0.2, n = 5), there was a selective reduction of the positive scotopic threshold response (pSTR; P < 0.001), whereas other ERG components remained unaltered. In four of the five eyes, pSTR amplitude was reduced by more than 50%, whereas all five had normal scotopic a-wave, b-wave, and OP amplitudes. Eyes with mean IOP of more than 35 mm Hg had reduced a-wave, b-wave, and oscillatory potential (OP) amplitudes. CONCLUSIONS: As demonstrated by prior studies, selective loss of the pSTR is indicative of selective retinal ganglion cell (RGC) injury. In this rat model of experimental glaucoma, selective RGC functional injury occurred before the onset of structural damage, as assessed by light microscopy of optic nerve tissue. The highest IOP levels resulted in nonselective functional loss. Thus, in rodent models of experimental glaucoma, lower levels of chronically elevated IOP may be more relevant to human primary chronic glaucoma.     

显微白内障手术光性视网膜损伤的F—ERG观察

目的　观察现代囊外白内障术中显微镜光照对视网膜功能的影响。方法　应用国际标准化视网膜电流图(F-ERG)记录45例45眼白内障术前及(白内障囊外摘出)术后1moF-ERG最大反应(MCR)(a、b波振幅)。按(WHO)晶状体混浊度分级采用不同术式,A组PHACO术、B组ECCE术。A组术中实际曝光于显微镜下25～40min(31.4min±4.1min),中度光强;B组50～75min(59.8min±8.7min),中高度光强。比较2组中使用不同显微镜光照(时间和光强)对ERG反应的影响,评价其对视网膜功能的损害。结果　白内障术后1moF-ERGa、b波振幅较术前均有不同程度的增大(0.01＜P＜0.05);A组术后F-ERG振幅较术前明显增大(P＜0.01);B组较术前增大,但无显著性差异(0.01＜P＜0.05)。结论　白内障术后ERG反应有不同程度的增强,提示晶状体混浊可减弱ERG反应;显微镜光照下手术时间越长、光照越强,术后1moF-ERG反应增幅越小,提示持续显微镜下手术可致视网膜光毒性损伤。     

Electroretinogram changes after scleral buckling surgery of retinal detachment

Objective To observe changes in visual function after a single scleral buckling surgery for rhegmatogenous retinal detachment (RD) by using ERG (electroretinogram). Methods One eye from 56 patients with rhegmatogenous RD was chosen. Forty-three corresponding normal fellow eyes from these patients were chosen as controls. Single scleral buckling surgery was carried out and a full-field ERG was performed before the surgery, and 1 and 6 months after surgery. Results The mean amplitude of ERG decreased and the latency (except for the a-wave) was delayed in the eye with a retinal detachment, and wavelets of the oscillatory potential decreased or were completely lacking. One month after surgery, the amplitudes of the a and b waves were noticeably improved (except for the 30 Hz flicker responses), but the latency (except for the a-wave) was still delayed. The ratio of b/a (mixed response) increased 1 month after surgery, with no further changes thereafter. The amplitude of the scotopic b wave was 58.1% of the control eyes, while the 30 Hz flicker responses was only 45.8% of controls; the difference between the two responses was significant (P < 0.001). The number of oscillatory potential wavelets increased, but the total amplitude of the oscillatory potentials did not exhibit any obvious changes during the follow-up period (P = 0.20). In the 41 patients whose detachment involved the macula preoperatively, the amplitude of the 30 Hz flicker responses improved significantly after surgery (P = 0.037). Six months after the operation, the wave amplitudes were not significantly different from 1 month after surgery, but there was a tendency toward a decrease in the latency. Conclusions After reattachment of the retina, visual function showed dramatic improvement 1 month after the surgery. The postreceptoral responses recovered more than the a-wave. The rod system recovered more quickly and completely than the cone system during the follow-up period. The incomplete recovery observed by using ERGs indicates that there is irreversible damage that likely occurs following retinal detachment and surgery.     

Electrical responses from the inner retina of rats with streptozotocin-induced early diabetes mellitus

PURPOSE: To evaluate behavior of the scotopic threshold response (STR) and the oscillatory potential (OP) in the electroretinogram (ERG) in streptozotocin (STZ)-induced diabetic rats (DM rats). METHODS: The amplitude of the STR and the OP 3, the implicit time of the STR, and the peak latency of the OP 3 of the DM rats were measured. RESULTS: No significant differences were observed in the mean amplitude or the mean implicit time of the STR between the control and the DM rats. On the other hand, the mean peak latency of OP 3 of the DM rats was significantly prolonged up to 125% of the control rats (p < 0.01), although there were no significant differences between the two groups in the mean OP 3 amplitude. CONCLUSIONS: Although both STR and OP were of inner retinal origin, their behavior was different in DM rats. This result supported some reports describing how dopaminergic amacrine cells generate OP and glycinergic or GABAergic amacrine cells generate STR. In the early stage of diabetic retinopathy, there may be not only minor ischemia but also disorder of neurotransmission of the amacrine cells in the inner retinal layers.