Ola Textorius

Studies on acute and late stages of experimental central retinal artery occlusion in the Cynomolgus monkey. I. Intensity-amplitude relations of the D.C. recorded ERG with special reference to the c-wave.

The main positive component of the c‐wave of the ERG is generated by the pigment epithelium — receptor complex, which is supplied from the choroidal circulation. Occlusion of the central retinal artery (OCRA) causes serious morphological damage only to the inner retina. An effect on the c‐wave is therefore not primarily to be expected. In this study on five Cynomolgus monkeys with unilateral, laser‐induced OCRA the c‐wave was decreased, slightly in the early stage and markedly in the late stage. A hypothetical explanation of the reduced c‐wave amplitude, involving changes in potassium ion concentration, is discussed. The conflicting results in other reports may be explained by uncontrolled influence of slow c‐wave amplitude oscillations, by differences between acute and late stages, and by possible surgical damage to the choroidal circulation in some cases.

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.

EFFECTS OF ETHYL ALCOHOL ON THE DIRECTLY RECORDED STANDING POTENTIAL OF THE HUMAN EYE

The effects of ethanol on the human standing potential (SP) were studied with a recently developed method, which allows direct SP recordings by means of a suction contact lens, temperature stabilized calomel electrodes and d.c. amplification. It is well known that the human SP oscillates with a frequency of about 2/hour in response to a sudden change in illumination. In the present paper marked cyclic variations of the SP, resembling damped oscillations, were provoked by a small oral dose of ethyl alcohol. A first maximum was reached after about 10 min. The difference in amplitude between the peak and the trough of the first oscillation was of the order of 4 mV. The oscillatory frequency was about 2/hour. The length of a cycle varied between 25 and 34 min in different volunteers, being fairly constant in the same subject on different occasions. The SP response to ethanol was similar both under scotopic and photopic conditions. The results correlate well with earlier findings of 2/hour oscillations in c‐wave amplitude in response to ethanol, as may be expected considering the partly common origin of the c‐wave and the SP.

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.

Effects of intraocular irrigation with melatonin on the c-wave of the direct current electroretinogram and on the standing potential of the eye in albino rabbits

The direct current electroretinogram (ERG) and the standing potential (SP) were recorded from both eyes of 14 albino rabbits during intraocular perfusion of one of the eyes, which was vitrectomized, with a recently developed eye irrigation solution (PHS) produced by Pharmacia Ophthalmics. PHS was then replaced by a test solution containing melatonin dissolved in PHS (0.002 μM-200 μM). The fluids were subsequently alternated (PHS - melatonin - PHS). During uniocular irrigation with melatonin the mean c-wave amplitude and SP level of the intact control eye were increased (c-wave + 24%, p < 0.01; SP + 0.65 mV, p < 0.05) compared with the values during the initial perfusion with PHS. In contrast, the c-wave amplitude of the irrigated eye was markedly decreased in many rabbits during perfusion with melatonin compared with the initial PHS, but the mean reduction was small and not statistically significant. The mean SP level was reduced (-1.54 mV, p < 0.001). This difference between the eyes probably depends on the route by which melatonin reaches the retinal pigment ephithelium and thus whether it primarily affects the apical (as in the irrigated eye) or the basal (as in the control eye) pigment epithelial membrane. A peak in the e-wave amplitude was observed in both eyes during uniocular irrigation with melatonin when compared with the amplitude measured during the initial perfusion with PHS (irrigated eye: + 27%, p < 0.001; control eye + 18%, p < 0.002).

Combined effects of DL-α-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-α-aminoadipic acid (α-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 α-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 α-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 α-AAA injected eyes. (3) In another five animals the SP was recorded following a step from darkness to continous light stimulation. The light peak was less pronounced in α-AAA treated eyes than in control eyes.

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 μV, p < 0.01; 25 mM: +2530 μV, 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 μV 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.

EARLY EFFECTS OF SODIUM IODATE ON THE DIRECTLY RECORDED STANDING POTENTIAL OF THE EYE AND ON THE c‐WAVE OF THE DC REGISTERED ELECTRORETINOGRAM IN ALBINO RABBITS

The early effects of intravenously administered sodium iodate (NaIO3) on the directly recorded standing potential (SP) of the eye and on the c‐ and b‐waves of the DC registered ERG were studied in 8 anaesthetized albino rabbits. In 5 of 6 animals obtaining 40 mg NaIO3/kg bwt. the SP decreased immediately following the injection, and had attained a level 3.5–4 mV below the original one after 1 h. The c‐wave declined rapidly and 6 min after the injection it was replaced by a large cornea‐negative potential. The b‐wave was relatively unchanged except in one animal. In 2 rabbits treated with 30 mg NaIO3/kg bwt. and in the 6th animal obtaining 40 mg NaIO3/kg bwt. an SP increase instead of a decrease was seen, and the c‐wave was more slowly (about 22 min after the injection) replaced by the cornea‐negative potential. The b‐wave was somewhat increased. These results demonstrate the dose‐related and interindividual variability in the SP reaction to NaIO3 and are in good agreement with the well‐known ultrastructural pigment epithelial injury and c‐wave changes produced by this substance.

The c-wave of the human electroretinogram in central retinal artery occlusion.

The pigment epithelium‐receptor complex, which is supplied from the choroidal circulation, is the main source of the c‐wave of the ERG. Occlusion of the central retinal artery (OCRA), which causes serious damage to the inner retinal layers, should therefore not primarily be expected to affect the c‐wave amplitude. Nevertheless, conflicting reports of increased, decreased and unchanged c‐waves have appeared in the literature. In the present study on four patients with OCRA the affected eyes showed diminished b‐ and c‐waves. On the other hand, both the a‐wave and the trough between the b‐ and c‐waves were accentuated in the diseased eyes. Experiments in progress on Cynomolgus monkeys with experimentally induced unilateral OCRA show similar results.

Pneumatic retinopexy in 50 patients

Abstract Pneumatic retinopexy was introduced in our clinic in 1986. This paper reports the results from the first 50 cases. Detachments with multiple breaks within 3 clock hours and proliferative vitreoretinopathy up to grade C1 were included. This technique compares favorably to buckling procedures in selected cases. The primary success rate was 83%, and the overall success rate was 90% (penumatic retinopexy ± scleral buckling ± vitrectomy).