Effects of intraocular perfusion with two alternating irrigation solutions on the simultaneously recorded electroretinogram of albino rabbits

The direct current electroretinogram (DC-ERG) of 15 unilaterally vitrectomized albino rabbits was studied during continuous intraocular irrigation with a recently developed solution (PHS) produced by Pharmacia Ophthalmics. The mean amplitudes of the b- and c-waves were somewhat lower than corresponding values of previously investigated reference subjects, but not statistically different. In 11 of the 15 rabbits PHS was then replaced by the commonly used balanced salt solution (BSS). The fluids were subsequently repeatedly alternated (PHS, BSS, PHS, BSS, PHS). During irrigation with BSS the average amplitude of the b-wave was reduced to 87% (p < 0.02) and that of the c-wave to 63% (p < 0.001) of the levels obtained during perfusion with PHS. In two rabbits the ERG was studied about one month after vitrectomy, where PHS-irrigation was used both during surgery and for 30 min after its completion. No marked differences were observed between the treated and the untreated eyes as to the b- and c-wave amplitudes at stable stages of the recording. Thus, judged by the ERG, retinal and pigment epithelial functions were influenced unfavorably by BSS, whereas they seemed to be well preserved with PHS. From this point of view PHS appears to be an excellent irrigation solution for vitreoretinal surgery that ought to be clinically tested.     

The c-wave of the electroretinogram and the standing potential of the eye as highly sensitive measures of effects of low doses of trichloroethylene,methylchloroform, and halothane

Low and moderate intravenous doses of trichloroethylene, methylchloroform, and halothane dissolved in a lipid emulsion (Intralipid) were given to cynomolgus monkeys. The DC electroretinogram (ERG) and the standing potential of the eye (SP) were recorded directly with corneal contact lenses, very stable calomel electrodes, and under very constant general anesthesia. Even low doses of the substances (close to the hygienic threshold limit values in Sweden) clearly provoked slow variations with time in the amplitude of the c-wave of the ERG and in the SP level. Both potentials are generated mainly in the pigment epithelium. It is suggested that the effects reflect a direct influence of the chemicals upon the metabolism of the pigment epithelium or on the cell membrane. Thus the method used is a highly sensitive measure of effects of certain halogenated hydrocarbons on structures belonging to the central nervous system.     

Effects of intravitreal perfusion with dopamine in different concentrations on the DC electroretinogram and the standing potential of the albino rabbit eye

The direct current electroretinogram and the standing potential were recorded from both eyes of 23 albino rabbits during intraocular perfusion of one of the eyes, which was vitrectomized, with a physiologic reference solution (PHS). PHS was then replaced by a test solution containing dopamine dissolved in PHS. The fluids were subsequently alternated (PHS-dopamine-PHS). During irrigation with 0.25–0.5 mM dopamine (11 rabbits) the c-wave amplitude was 140% higher (p < 0.001) and during irrigation with 25 mM dopamine (6 rabbits) 85% lower (p < 0.01) than it was during the corresponding initial perfusion with PHS. The simultaneously recorded b-wave amplitude was reduced (0.25–0.5 mM: -22%, p < 0.001; 25 mM: - 69%, p < 0.001) and the SP level increased (0.25–0.5 mM: +2375 V, p < 0.01; 25 mM: +2530 V, p < 0.05) compared with the values obtained during the corresponding preceding irrigation with PHS. Thus the changes in the b- and c-wave amplitudes during perfusion with dopamine were dependent on the concentration of the drug. In the contralateral control eye (23 rabbits) the c-wave amplitude was 21% higher (p < 0.001), the b-wave amplitude 14% higher (p < 0.001) and the standing potential 1007 V higher (p < 0.001) during intravitreal perfusion with dopamine in the other eye than during the preceding irrigation with PHS in that eye, possibly as a result of increasing dark adaptation.     

Effects of low doses of forskolin on the c-wave of the direct current electroretinogram and on the standing potential of the eye

A marked effect of prostaglandins on the b- and c-waves of the direct current electroretinogram was recently reported by our laboratory. The increased b- and c-wave amplitudes in response to prostaglandins may be mediated by cyclic nucleotides acting on fluid and ion transport across the retinal pigment epithelium (RPE). Forskolin is known to increase cyclic adenosine monophosphate in a number of tissues, among them the RPE. To study possible effects of forskolin on the ERG vitrectomy was performed on rabbit eyes, followed by intraocular irrigation with a forskolin solution (10g/ml PHS). Forskolin produced reversible ERG changes with increase in a- (24%, p < 0.001), b- (25%, p < 0.001) and c-wave (53%, p < 0.001) amplitudes and elevation (about 1.0–1.5mV, p < 0.01) of the standing potential of the eye. The increase in c-wave amplitude was significantly greater than that of the a- (p < 0.05) and b- (p < 0.01) wave amplitudes, which seems to imply a primary or at least major effect on the RPE.     

Long-term behavior and intra-individual stability of the direct current electroretinogram and of the standing potential in the albino rabbit eye

The direct current electroretinogram (ERG) and the standing potential (SP) were studied in seven albino rabbits under general anesthesia. Identical experiments were performed on 2 consecutive days. After 30 min of dark adaptation, repeated light stimuli of maximal intensity of the system were presented to the eyes. The interstimulus interval was 70 s, and stimulus duration 10 s. Each experiment lasted for almost 3 h. In the first experiment, the b- and c-wave amplitudes measured in response to the second light stimulus were markedly reduced compared to those recorded in response to the first stimulus. Both amplitudes then recovered. The b-wave attained a peak about 20 min after the start of light stimulation. The peak was followed by a trough about 20 min later, and the amplitude then slowly increased. Following the minimum recorded during the second light stimulus, the c-wave amplitude reached a peak about 14 min after the start of stimulation. A trough in the amplitude occurred 20 min later. The amplitude then slowly increased to the end value, which was higher than the initial level. The a-wave behaved similarly to the b-wave, but the changes in most cases did not attain statistical significance. A minimum in the SP occurring at the second light stimulus was followed by a peak about 13 min after the start of light stimulation, and then by a trough about 17 min later. In the second experiment, performed one day after the first, the development of the a-, b-, and c-wave amplitudes and of the SP was similar to that observed during the first experiment, and no statistically significant differences between the two experiments were found. The reactions of the ERG and the SP were thus very stable between identical experiments performed on two consecutive days.     

The c-wave of the direct-current-recorded electroretinogram and the standing potential of the albino rabbit eye in response to repeated series of light stimuli of different intensities

In 10 experiments on five albino rabbits, the direct-current electroretinogram and the standing potential of the eye were recorded in response to repeated light stimuli (duration, 10 s; interval, 70 s), presented in four series, each consisting of 25 light flashes. Light intensities were, in order of presentation to the eyes, 3, 2, 1 and 0 log rel units (series I, II, III and IV, respectively) below the maximum output of the system. Thirty minutes of dark adaptation preceded each series. At the end of series I, the mean amplitudes of the b- and c-waves were higher and that of the a-wave relatively unchanged compared with the corresponding initial amplitudes. During series II–IV, there was a marked decrease in mean a- and b-wave amplitudes between the first and the following electroretinogram responses, and at the end of the three series, the amplitudes were still significantly reduced compared with the corresponding initial values. The mean c-wave amplitude was also markedly decreased immediately after the first electroretinogram recording, but it later recovered to a large extent. A peak in the c-wave amplitude was discerned about 14–18 minutes after the start of the recordings. A standing potential minimum during the second light stimulus was followed by a peak after about 10–13 minutes. The partially parallel behavior of the c-wave and the standing potential suggests the operation of a pigment epithelial mechanism behind the recovery of the c-wave amplitude. The final amplitudes of the b- and c-waves, and to a large extent also of the a-wave, were about the same irrespective of stimulus intensity. The adaptational processes in the rabbit appear to be more complicated than was previously thought. When electroretinogram amplitudes and standing potential levels are discussed and when one experiment is compared with another one, it is important that adaptational and stimulus conditions, as well as time course, are well controlled and clearly specified.     

Influence of isobutylmethylxanthine on the direct current electroretinogram of albino rabbit eyes

The direct current electroretinogram and the standing potential of the eye were recorded from both eyes of unilaterally vitrectomized albino rabbits. The effect of intraocular irrigation with the nonselective phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) was compared with that of a balanced salt control solution. IBMX (0.5mM) produced a reversible increase in the amplitudes of the a-wave (19%, p < 0.02), b-wave(21%, p < 0.001) and c-wave (12%, p < 0.01) of the electroretinogram. A small elevation of the standing potential was found (0.4 ± 0.2mV), but this increase was not statistically significant (p > 0.05). The results indicate a primary and principal influence of IBMX on the photoreceptors.     

Adrenergic effects on the corneal and intraretinal direct-current electroretinogram and on the standing potential of albino rabbit eyes

This study was undertaken to investigate further the responsiveness of the albino rabbit retinal pigment epithelium and the inner retina to adrenergic agents as reflected in changes of the direct-current electroretinogram and of the standing potential of the eye. After unilateral vitrectomy on albino rabbits, a continuous intraocular perfusion with a reference solution was established. The reference solution was then alternated with the test solution. The direct-current electroretinogram and the standing potential were recorded from both eyes with a scleral contact lens and a reference electrode connected to matched calomel half-cells. Anin vivo experimental technique that allows intraocular perfusion of a test substance and simultaneous intraretinal microelectrode measurements was also used. The-adrenergic agonist phenylephrine (0.04µM, n = 8) produced a reversible increase in c-wave amplitude (48%, p < 0.001) and also a small increase in b-wave amplitude (12%, p < 0.002). There was no significant influence on the a-wave amplitude. The standing potential was elevated at 1694 ± 362µV (mean ± SEM) (p < 0.002). The ₂-adrenergic agonist clonidine caused similar effects on the electroretinogram, although at a higher concentration (40µM, n = 5), with an elevation of the c-wave (25%, p < 0.001) and a small b-wave increase (12% p < 0.002). No significant influence on the a-wave or on the standing potential was found. Intraretinal direct-current electroretinogram-recordings during intraocular perfusion with phenylephrine showed an increase in transepithelial potential (p < 0.004; n = 6), accompanied by a reduction of the slow PIII (p < 0.0035; n = 6). The c-wave increase resulting from-adrenergic stimulation seems to be generated partly across the retinal pigment epithelium, with an increase in transepithelial potential, combined with a reduction of the slow PIII. The elevation of the b-wave amplitude, together with the influence on the slow PIII, suggests-adrenergic effects also on the inner retina. The experimental technique used in this study with intraocular perfusion after vitrectomy and simultaneous intraretinal direct-current recordings seems to be a practicable method for studies of the influence of pharmacologic agents on the retina and the retinal pigment epithelium.Abbreviations DC direct current - RPE retinal pigment epithelium - SP standing potential - TEP transepithelial potential     

Standing potential and c-wave during changes in PO2 and flow in the perfused cat eye

Changing flow rate (F) in arterially perfused cat eyes concomitantly alters the supply of O₂ and greatly affects electrical signals: increasing F increases the standing potential (SP) and decreasing F induces the opposite. Corresponding effects on c-wave are more variable.To separate changes in supply of O₂ from changes in F we performed two types of experiments: (1) changing supply of O₂ while keeping F constant; this was done by switching to a perfusate of different PO₂: and (2) changing F while keeping the supply of O₂ constant; this was done by switching to hypoxic or hyperoxic perfusates and adjusting F to keep the b-wave amplitude constant.Results (1): Decrease in PO₂ left the SP essentially unaffected, but increased the c-wave. Increase in PO₂ tended to increase the SP and to decrease the c-wave. Results (2): Isolated decrease in F did not affect the SP consistently and left the c-wave unchanged. Isolated increase in F often increased the SP, but also left the c-wave unchanged.Covariation between SP and amplitude to the c-wave was absent during hyperoxia.     

A cone-triggered c-wave in the chicken ERG time integration characteristics

The c-waves recorded from the cone-dominant retina of the chicken proved to be cone-triggered. The time course and time integration properties of this retinal potential were compared with those of the rod-triggered c-wave recorded in the frog under scotopic conditions. The results clearly demonstrate theat there is no evidence for time integration in cone-triggered c-waves but that rod-triggered c-waves follow the Bunsen-Roscoe law over more than 2 log units. We propose that these time-related differences may be used in other species as a differentiation criterion between conetriggered and rod-triggered c-waves.     

Effects of quisqualic acid on the corneal and intraretinal direct-current electroretinogram and on the standing potential of the rabbit eye

Quisqualic acid, an excitatory amino acid agonist, has been shown to stimulate inositol phosphate production in the rabbit retina. Inositol trisphosphate serves as a second messenger and increases intracellular calcium. We investigated the influence of quisqualic acid on the direct-current electroretinogram and on the standing potential of the rabbit eye. After unilateral vitrectomy, the corneal direct-current electroretinogram and the standing potential were recorded from both eyes of albino rabbits during simultaneous unilateral intravitreal perfusion with quisqualic acid alternating with control solution. The contralateral eye was used as a control. Intravitreal perfusion with 100-µM and 200-µM quisqualic acid elevated the standing potential significantly. This elevation was accompanied by a significant increase in c-wave amplitude and a significant decrease in b-wave amplitude. Quisqalic acid at 200-µM concentration decreased the a-wave amplitude also.In vivo intraretinal recordings showed that intravitreal perfusion with quisqualic acid at 200-µM concentration significantly increased the retinal pigment epithelial component of the c-wave. We conclude that quisqualic acid influences the direct-current electroretinogram and the standing potential apparently through its action on the retinal pigment epithelium. A possible mode of action is increased production of inositol trisphosphate, followed by an increase in intracellular release of calcium ions and an increase in basal chloride conductance. The decrease in a- and b-wave amplitudes indicates direct effects of quisqualic acid also on the neural retina.Abbreviations EAA excitatory amino acid - IP inositol phosphate - NMDA N-methyl-Daspartate - PPI phosphoinositide - QA quisqualic acid     

The c-wave of the direct-current electroretinogram and the standing potential of the albino rabbit eye in response to repeated series of light stimuli with different interstimulus intervals

The direct-current electroretinogram and the standing potential of the eye of seven albino rabbits were recorded in response to repeated light stimuli, which were presented in four consecutive series. The intervals between the beginning of succeeding stimuli were 8 minutes, 4 minutes, 2 minutes and 70 seconds (series 1, 2, 3 and 4, respectively). Stimulus duration (10 seconds) and light intensity (6.8 × 10⁴ lux) were constant during the experiments. The series lasted for 36–40 minutes, and each was preceded by 30 minutes of dark adaptation. During series 1, the end amplitudes of the a-, b- and c-waves were not significantly changed compared with the initial levels. During series 2, 3 and 4, the a-, b- and c-wave amplitudes were markedly reduced immediately after the first electroretinogram recording. The a- and b-waves then recovered to a limited extent, but the c-wave was more fully restored. A slight peak in the c-wave amplitude could be discerned 16–20 minutes after the start of recording. A decrease in the standing potential was seen 50–54 seconds after the start of light stimulation during all four series, and a peak occurred 12–16 minutes after the start of recording. The similarity in behavior between the c-wave and the standing potential suggests the operation of a pigment epithelial mechanism behind the more complete recovery of the c-wave amplitude. When electroretinogram amplitudes and standing potential levels are discussed, and when one experiment is compared with another one, it is important that adaptational and stimulus conditions, as well as time course, are well controlled and clearly specified.Abbreviations RPE retinal pigment epithelium - SP standing potential     

Photopic c-wave in the chicken ERG: sensitivity to sodium azide,epinephrine, sodium iodate,barbiturates, and other general anesthetics

The c-wave recorded in the chicken electroretinogram proved to be a conetriggered component. The questions arose whether its reactivity to various specific drugs (sodium iodate, sodium azide, epinephrine, or barbiturates) were similar to those described for classic rod-triggered c-waves. We also tested the sensitivity of the chicken c-wave to various general anesthetics. Urethane was found to be the drug that best preserves the c-wave in electrophysiological recordings.     

C-wave versus electrooculogram in diseases of the retinal pigment epithelium

The c-wave and the electrooculogram (EOG) are retinal potentials predominantly generated by the pigment epithelium. In most diseases both parameters show a parallel decrease in amplitude. However, in patients with dominant drusen, and cone dystrophies, and in clinically nonaffected members of families suffering from vitelliform macula degeneration, the EOG is close to normal whereas the c-wave shows a reduced amplitude. These findings suggest a higher sensitivity of the generators of the c-wave compared with those responsible for the EOG. Thus the direct current electroretinogram provides additional diagnostic information.     

Effects of hypoxia and hyperoxia on the human standing potential

We report that the human standing potential, measured by the EOG, rises slowly when oxygen saturation is lowered to near 80% by breathing a controlled oxygen-nitrogen mixture. The standing potential falls abruptly by 20–30% of its amplitude when the oxygen saturation returns to 100%. These changes can be generated reproducibly, with minimal discomfort, under conditions that could be adopted for clinical use. Animal experimental studies by Linsenmeier and Steinberg suggest that this hypoxia-hyperoxia response may be a delayed response to potassium concentration changes in the subretinal space. Since there is no requirement for light and no involvement of the Müller cells, the hypoxia-hyperoxia response may be more specific for pigment epithelial pathology than the c-wave.     

人工泪液对LASIK与LASEK术后干眼症状及泪膜稳定性的影响

目的：探究激光辅助原位角膜磨镶术(LASIK)和激光上皮角膜磨镶术(LASEK)术后配合0.1%玻璃酸钠(HA)治疗对干眼症状及泪膜稳定性的影响。

方法：将2017-02/2017-12纳入的230例460眼近视患者分为LASIK组和LASEK组,然后将每个治疗组随机分为0.1% HA治疗亚组和无HA亚组,两个亚组均在角膜屈光手术后应用0.3%加替沙星和0.5%氯替泼诺。观察各组患者不同时间点干眼症状评分、角膜知觉反应、角膜荧光染色(FL)、基本泪液分泌试验(SⅠt)和泪膜破裂时间(BUT)的变化。

结果：LASIK和LASEK患者术后1wk, 1、3、6mo, 0.1% HA治疗组与无HA组的FL、干眼症状评分和角膜知觉反应均存在显著差异(P<0.05)。各组术后1wk BUT均较术前明显下降。术后其他观察时间点BUT及各时间点术后SⅠt水平虽低于术前水平,但仍在正常范围内。LASEK术后患者的干眼主观症状、泪膜稳定性和角膜表面知觉优于LASIK患者,尤其是在术后1wk, 1、3mo。

结论：两种屈光手术可引起不同程度的干眼症状,LASEK组干眼症状在术后早期较LASIK组轻。早期足量使用不含防腐剂的0.1% HA可有效促进角膜修复,对术后干眼症状有很大帮助。     

SMILE和FS-LASIK术对高度近视患者术后早期角膜高阶像差的影响

目的：研究飞秒激光小切口角膜基质透镜取出术(SMILE)和飞秒激光辅助的准分子激光原位角膜磨镶术(FS-LASIK)对高度近视患者术后早期角膜高阶像差(HOAs)和视觉质量的影响。

方法：以2018-08/2020-08在我院接受角膜屈光手术的高度近视患者102例204眼为研究对象进行前瞻性研究,随机分为SMILE组(51例102眼)和FS-LASIK组(51例102眼),比较两组患者术后视力、角膜HOAs和客观视觉质量,分析角膜HOAs与客观视觉质量的相关性。

结果：术后1mo时,SMILE组和FS-LASIK组患者等效球镜度数均明显降低(P<0.05),且两组患者术后裸眼视力优于术前最佳矫正视力患者占比无差异(95.1% vs 92.2%,P>0.05); 两组患者角膜各高阶像差均明显升高(P<0.05),且SMILE组总球差(SA)、三叶草像差(trefoil)和高阶像差(HOAs)低于FS-LASIK组(均P<0.05); 两组患者客观散射指数(OSI)明显升高,MTF截止频率(MTF_cutoff)、斯特列尔比(SR)、对比度视力(VA100%、VA20%、VA9%)均明显降低(均P<0.05),且SMILE组OSI低于FS-LASIK组,MTF_cutoff和VA9%高于FS-LASIK组(均P<0.05); 高度近视患者术后角膜各高阶像差与MTF_cutoff均呈负相关性,与OSI均呈正相关性(P<0.05)。

结论：SMILE和FS-LASIK术均可有效矫正高度近视,且SMILE术后早期角膜HOAs升高幅度更小,对减轻视觉质量损害具有重要意义。     

三种不同手术对屈光不正患者术后视觉质量及高阶像差的比较

目的：探讨飞秒激光制瓣的准分子激光原位角膜磨镶术(FS-LASIK)、角膜地形图引导LASIK(TG-LASIK)和飞秒激光小切口角膜基质透镜取出术(SMILE)对屈光不正患者术后视觉质量及高阶像差的效果。

方法：纳入2019-12/2020-02本院屈光中心收治的296例586眼单纯近视或近视散光患者。在明确手术适应证的前提下,患者自行选择接受FS-LASIK、TG-LASIK、SMILE手术,其中FS-LASIK组95例189眼,TG-LASIK组104例205眼,SMILE组97例192眼。收集患者术前及术后6、12mo时视力、屈光度、角膜地形图、高阶像差及对比敏感度。

结果：术后6、12mo各组患者裸眼视力、最佳矫正视力及球镜度数、柱镜度数、等效球镜度数均优于术前(P<0.05),组间比较均无差异(P>0.05)。术后6、12mo TG-LASIK组角膜表面规则指数、表面非对称指数均显著低于SMILE组、FS-LASIK组(P<0.05); SMILE组、FS-LASIK组组间比较无差异(P>0.05)。术后6、12mo时FS-LASIK组总高阶像差、彗差、球差及术后6mo时三叶草像差高于TG-LASIK组、SMILE组(P<0.05); 术后6、12mo时SMILE组球差显著低于其他两组(P<0.05)。术后6、12mo时TG-LASIK组在无眩光及有眩光时12.0、18.0c/d频率下对比敏感度显著高于SMILE组、FS-LASIK组(P<0.05)。

结论：FS-LASIK、TG-LASIK、SMILE三种手术均可获得较为满意的治疗效果,但TG-LASIK术后像差增加较小,角膜形态更规则,视觉质量更高。