Effects of ethyl alcohol on the directly recorded standing potential of the human eye

Electrophysiology in pigment epithelial changes

The c-wave of the ERG and the slow SP variations reflect mainly the activity of the pigment epithelium. However, both potentials are dependent upon the photoreceptors and/or the inner retina as well. In pigment epithelial abnormalities the c-wave is reduced or abolished, and the slow SP variations, d.c. recorded directly or investigated with the EOG, reduced or abolished as well.

Clinical electro-oculography

Electro-oculography (EOG), a retinal function test, indirectly records slow, light-induced changes in the potential difference between the anterior and posterior poles of the eye. EOG is a valuable clinical tool in diagnosis of tapetoretinal degenerations, vitelliform foveal dystrophy including the carriers of this disease, retinal intoxications and in differential diagnosis of choroidal malignant melanomas. EOG is not an alternative to electroretinography but yields additional information on the function of the retinal pigment epithelium. The main drawback of the present technique is the high inter- and intraindividual variability of the results.

Studies on acute and late stages of experimental central retinal artery occlusion in the Cynomolgus monkey. II. Influence on the cyclic changes in the amplitude of the c-wave of the ERG and in the standing potential of the eye

The slow (2-3/h) oscillations of the c-wave amplitude and of the standing potential of the eye (SP) were studied in the Cynomolgus monkey during the acute and late stages after experimentally induced (laser photocoagulation) occlusion of the central retinal artery (OCRA). Whereas the healthy control eyes showed large cyclic variations in both the c-wave amplitude and the SP, no oscillations in the c-wave amplitude were observed in the OCRA eyes at any stage, and the SP oscillations were barely detectable in these eyes. OCRA causes morphological damage to the inner retina but not to the pigment epithelium-photoreceptor complex, which generates the positive component of the c-wave, and where the SP is also believed to originate. The findings of the present study strongly indicate that the SP and c-wave oscillations are related, and that they are either dependent on an intact inner retina or that the pigment epithelium-photoreceptor complex is functionally affected by OCRA. If not taken into consideration, the marked difference in oscillations between the OCRA eye and the healthy eye may be a major source of error when comparing c-waves from the two eyes, and it seems that some of the conflicting results reported by others can be explained in this way.

Light and alcohol evoked electro-oculograms in cystic fibrosis

Cystic fibrosis (CF) is caused by a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) which is a chloride channel. CFTR is expressed in the retinal pigment epithelium (RPE) where it is believed to be important in generating the fast oscillations (FOs) and potentially contributing to the light-electro-oculogram (EOG). The role of CFTR in the alcohol-EOG is unknown. We recruited six individuals with CF (three homozygotes for Delta508 and three heterozygous for Delta508) and recorded the light- and alcohol-EOGs as well as the FOs and compared them to a control group. The results showed that in the CF group the amplitude of the alcohol- and light-EOGs were normal. However, the time to peak of the light- and alcohol-rises were significantly faster than in the control group. We conclude that CFTR is not primarily responsible for the alcohol- or light-rises but is involved in altering the timing of these responses. The FOs showed differences between the homozygotes, heterozygotes and the controls. The amplitudes were significantly higher and the time to the dark troughs were significantly slower in the heterozygote group compared to both controls and the homozygotes. In contrast, the homozygotes did not differ in either amplitude or the timing of the FOs compared to the controls.

From basic to clinical research: a journey with the retina, the retinal pigment epithelium, the cornea, age-related macular degeneration and hereditary degenerations, as seen in the rear view mirror

PURPOSE

This Acta Ophthalmologica Award and Gold Medal Honorary Lecture (the Lundsgaard Gold Medal Honorary Lecture) reviews some of the work I have carried out with my mentors and many of my wonderful collaborators and research students over more than 40 years, also including related work by other groups. It concentrates on the basic electrophysiology and ultrastructure of the retina and the retinal pigment epithelium (RPE), as well as covering basic and clinical aspects of the cornea, contact lenses, age-related macular degeneration (AMD) and hereditary diseases.

METHODS

The review describes research performed using light and electron microscopy, basic and clinical electrophysiology, genetics and biochemistry in animal experiments and in research on patients. It also outlines clinically used techniques, such as laser and photodynamic treatment and scanning laser ophthalmoscopy.

RESULTS

The paper reports on the following subjects: the mechanisms behind some of the electrical potentials originating in the retina and the RPE and the use of these potentials in hereditary diseases; corneal receptors for lectins and presumably for bacteria; the turnover of the photoreceptor outer segment and the formation of lipofuscin, including the relation of these processes to AMD; certain treatments for AMD, and hereditary degenerations in animal models, such as the RPE65 gene mutation in Briard dogs, which makes them a model of Leber's congenital amaurosis. The dogs are now treated successfully with gene therapy in the USA, and a clinical trial is in preparation.

CONCLUSIONS

During the last 40 years we have had the good fortune to experience a dramatic growth in knowledge and understanding within ophthalmic science of basic mechanisms. Huge progress has been made in diagnostics and clinical ophthalmological treatments, much to the benefit of our patients. Even a small contribution made by my group to these developments has been well worth the effort, particularly as scientific work is not just deeply satisfying: it is also fun!

Alcohol- and light-induced electro-oculographic responses: variability and clinical utility

The alcohol-induced electro-oculographic (EOG) response has been proposed by Arden as an indicator of retinal pigment epithelial (RPE) integrity. We have evaluated the consistency of the alcohol-EOG with respect to clinical applicability and compared this response to the ISCEV-standard EOG. We recorded, in a group of normal subjects (n=29, 14 men with mean age 42+/-11 years and 15 women with mean age 36+/-13 years), the alcohol response to a single oral dose of ethanol at 160 mg/kg (as 40 proof vodka, drunk in 15 s after 12 h of fasting), followed by an ISCEV-standard EOG 90 min after alcohol administration. Blood alcohol levels were monitored at regular intervals with a breath analyzer. We found a wide range of amplitudes in both light and alcohol responses among participants, from minimal to large values. Subjects had a wide range of blood alcohol concentrations from 0.02 to 0.10%; near the time of the response peak, but there was no relationship between alcohol levels and peak/baseline ratios. In addition, there was no relationship between alcohol peak/baseline ratio and the Arden ratio. Neither the alcohol nor the light response parameters showed any relationship with age or gender. Some of the inter-individual variability in the EOG response to alcohol may reflect variable absorption of oral alcohol. The alcohol-induced EOG has too broad a range of responses to be useful clinically for the one-time evaluation of individual patients. We have similar concerns regarding clinical applications of the standard light-induced EOG.

The electro-oculogram

The retinal pigment epithelium (RPE) lying distal to the retina regulates the extracellular environment and provides metabolic support to the outer retina. RPE abnormalities are closely associated with retinal death and it has been claimed several of the most important diseases causing blindness are degenerations of the RPE. Therefore, the study of the RPE is important in Ophthalmology. Although visualisation of the RPE is part of clinical investigations, there are a limited number of methods which have been used to investigate RPE function. One of the most important is a study of the current generated by the RPE. In this it is similar to other secretory epithelia. The RPE current is large and varies as retinal activity alters. It is also affected by drugs and disease. The RPE currents can be studied in cell culture, in animal experimentation but also in clinical situations. The object of this review is to summarise this work, to relate it to the molecular membrane mechanisms of the RPE and to possible mechanisms of disease states.

Two components of the human alcohol electro-oculogram

Light onset or drinking alcohol causes the standing potential of the eye to rise and then fall to a trough (the EOG). After allowing for the time for the alcohol to be absorbed into the blood stream, the changes of current with time are identical for the two agents but each acts through a separate pathway, on the same effector mechanism. We have shown that +ve and -ve processes of the alcohol-EOG may be differentially affected in disease. We have now determined the separate dose-response relationship of the two voltage changes. Alcohol diluted with water was given by mouth to fasting dark-adapted subjects. Recordings continued until both the positive peak and the later negative trough were well-characterised. Doses of alcohol ranged from 3.54 to 450 mg Kg(-1) of body weight. Experiments were carried out on three normal subjects, 4-8th decade. The results are consistent with the hypothesis that each voltage change is determined by the relation: [EtOH] x [R] <--> [EtOH.R], where <--> represents a reversible reaction. For the +ve peak, semi-saturation occurs at approximately 35 mg Kg(-l). For the -ve trough it is smaller, 11 mg Kg(-l). Therefore the result is consistent with there being 2 distinct processes, and the human EOG cannot be a single 'damped oscillation'. During the short period when change of blood alcohol concentration is effective in causing the EOG sequence (using doses which provoke large voltage changes), the computed blood concentration varies from 0.01 to 0.1 mM, i.e. is > 2 orders of magnitude less than the levels required for intoxication.

An automated and modified technique for testing the retinal function (Arden test) by use of the electro-oculogram (EOG) for clinical and research use

The electro-oculogram (EOG) can be recorded by use of skin electrodes positioned near the eye in the horizontal or vertical plane and is dependent on the position of the eye relative to the electrodes and the size of the corneo-retinal potential (CRP). By use of the functional relation between the recorded potential and the eye position - CRP is considered to be constant - the EOG is the eye movement recording method most often used. Changes in CRP dependent on luminance or metabolic influences can be measured, on the other hand, by means of the EOG when eye movements of constant amplitudes are performed. The EOG in this paper is used in the latter sense. The widely used clinical test of rentinal function based on the electro-oculogram firstly described by Arden (Arden index) has been modified to achieve more precise and reliable results by including a gradual dark adaptation procedure and a special data analysis to detect fixation periods. Using modern techniques, the complete procedure has been automated. The efficiency of the procedure and the device is demonstrated in various ways.

Photosensitivity of the isolated pigment epithelium and arachidonic acid metabolism: preliminary results

The administration of 0.1-0.5% of ethanol produces a slow increase in the transepithelial potential (TEP) of about 2 mV in the bovine pigment epithelium (RPE) under ordinary room lighting. However, virtually no response could be observed when ethanol was administered in the dark. Because of this apparent light sensitivity, the ethanol induced response (EIR) was investigated to determine its spectral response characteristics, temporal interaction with light, and the effects of a variety of metabolic inhibitors as well as pertussis and cholera toxins. The spectral response curve peaked at 520 nm with a narrow half width. The EIR was found to be inhibited by pertussis toxin but not cholera toxin. Inhibition of either phospholipase A2 or lipoxygenase/cyclooxygenase resulted in a marked inhibition of the EIR. The incubating solutions of the apical surface of bovine and cultured chick embryo RPE were analyzed by RP-HPLC under conditions of weak white light and darkness. Two peaks in the chromatogram were observed to vary with these conditions and the presence of nordihydroguaiaretic acid simulated the effects of darkness. The RP-HPLC studies did not involve the employment of ethanol. Two different experimental procedures revealed the photosensitivity of the isolated RPE to weak light and suggest that light initiates or promotes arachidonic acid metabolism. A possible regulatory effect of retinoids was also indicated.

Combined effects of DL-alpha-aminoadipic acid with sodium iodate, ethyl alcohol, or light stimulation on the ERG c-wave and on the standing potential of albino rabbit eyes

Albino rabbits were treated with intravitreal injections of DL-alpha-aminoadipic acid (alpha-AAA) into one eye (0.1 ml of a 0.15 M solution) and 0.1 ml of saline into the contralateral eye. Thirteen to fourteen hours later the DC electroretinogram (ERG) and/or the standing potential (SP) were recorded. (1) In eight of nine animals the c-wave amplitude of alpha-AAA injected eyes was increased compared with that of control eyes. Following intravenous injection of Sodium Iodate (40 mg/kg in 2% solution) the c-waves of both eyes were rapidly replaced by negative potentials. In 8 of 9 animals the amplitude reduction was more marked in alpha-AAA-treated eyes than in control eyes, but the final amplitude was higher in the former than in the latter. The SP was reduced with difference in curve form but not significantly in amplitude between the eyes. (2) In nine other rabbits iv.-injected ethyl alcohol (0.4 g/kg in 20% solution) provoked a transient increase of SP level and c-wave amplitude in control eyes and smaller but similar changes in alpha-AAA injected eyes. (3) In another five animals the SP was recorded following a step from darkness to continuous light stimulation. The light peak was less pronounced in alpha-AAA treated eyes than in control eyes.

Changes in the c-wave of the electroretinogram and in the standing potential of the eye after small doses of toluene and styrene

Low and moderate i.v. doses of toluene or styrene dissolved in a lipid emulsion (Intralipid) were given to cynomolgus monkeys. The d.c. ERG and the standing potential (SP) of the eye were recorded directly with corneal contact lenses, very stable calomel electrodes and under very constant general anaesthesia. Even small doses of the solvents, corresponding approximately to the Swedish hygienic threshold limit values for these solvents in air, 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 solvents upon i.a. the cell membrane or the metabolism of the pigment epithelium.

Covariation of the simultaneously recorded c-wave and standing potential of the human eye

The c-wave and the directly recorded standing potential (SP) of the human eye were studied with the aid of a recently developed method including matched temperature stabilized calomel electrodes, d.c. amplifiers and a suction contact lens. This technique, which does not require general anaesthesia, permits simultaneous direct d.c. recordings of the SP and the c-wave in human volunteers during long-term experiments. Upon repetitive light flashes (stimulus duration 1 sec, interval 20 sec and flash intensity 4.5 rel. log units above b-wave threshold) both variables responded with slow amplitude oscillations with a frequency of about 2/hour. The oscillations were similar as to phases and frequencies. Both the potentials are held to be generated mainly in the pigment epithelium. Considering this partly common origin the observed covariation was an interesting finding.