Effects of photocoagulation on intraretinal PO2 in cat

PURPOSE: To test the hypothesis that intraretinal Po(2) increases after photocoagulation. METHODS: Anesthetized cats underwent retinal argon laser photocoagulation. At least 4 weeks after treatment, Po(2)-sensitive microelectrodes were used to record intraretinal Po(2) profiles from healed photocoagulation lesions in anesthetized cats breathing air. Histopathologic examination of the retinas was used to confirm that the photoreceptors were destroyed and that the inner retinal layers were preserved, though somewhat disorganized, as in human panretinal photocoagulation (PRP). RESULTS: The retina and tapetum were thinner in the lesioned retina than in the nonphotocoagulated retina. Average Po(2) across the inner 50% of the retina was higher (22 +/- 10 mm Hg) in photocoagulated retina than in untreated retina (14 +/- 7 mm Hg; P < 0.01; n = 13 cats). The minimum Po(2) was also significantly higher, whereas choroidal Po(2) was significantly lower in the photocoagulated retina than in untreated retina. No significant difference was found in the preretinal vitreous. After lesions, inner retinal Po(2) could also be maintained above zero, even in the absence of retinal circulation. CONCLUSIONS: Previous measurements showed increased Po(2) in the preretinal vitreous of rabbits and pigs (but not cats) after photocoagulation of the outer retina. These intraretinal measurements in cats provide further evidence for a chronic increase in inner retinal Po(2) in lesioned areas during air breathing.     

Quantification of in vivo anaerobic metabolism in the normal cat retina through intraretinal pH measurements

We examined intraretinal [H+] in the intact retina of anesthetized cats using H+-sensitive microelectrodes to obtain spatial profiles of extracellular [H+]. One H+ is produced when an anaerobically generated ATP is utilized. We theorized that H+ production directly reflects anaerobic glucose consumption. From the choroid (pH approximately 7.40), [H+]o steadily increased to a maximum concentration in the proximal portion of the outer nuclear layer (pH approximately 7.20). The shape of the profile was always concave down, indicating that a net production of H+ occurred across the avascular outer retina. A three-layer diffusion model of the outer retina was developed and fitted to the data to quantify photoreceptor H+ extrusion into the extracellular space (Q(OR-H+)). It was determined that the outer segment (OS) layer had negligible H+ extrusion. The data were then refitted to a special three-layer model in which the OS layer Q(H+) was set equal to zero, but in which the inner segments and outer nuclear layer produced H+. The resulting Q(OR-H+) was several orders of magnitude lower than previous measurements of Q(OR-lactate), which were based on choroidal mass balances of lactate. Stoichiometrically, one H+ is produced for each lactate produced, so we concluded that Q(OR-H+) is a measure of net rather than total H+ production. Because retinal acid production is so high, the retina must contain efficient H+ clearance and/or neutralization mechanisms that prevent severe acidosis. The effect of light on retinal extracellular [H+] and Q(OR-H+) was also examined. As expected, light adaptation caused a retinal alkalinization that resulted from a 52% reduction in Q(OR-H+). This is in agreement with previous studies that have shown that both oxidative (e.g. Haugh et al., 1990) and glycolytic metabolism (Wang et al., 1997a,c) in the photoreceptor are decreased by a factor of 2 during light adaptation. Although we could not obtain absolute values for outer retinal glycolysis, changes in Q(OR-H+) appear to directly reflect changes in glycolytic metabolism.     

Anatomical correlations between soma size, axon diameter, and intraretinal length for the alpha ganglion cells of the cat retina

Retinal ganglion cells within the same region of the retina may have different lengths of axon before reaching the optic disc depending on the route they take with respect to the temporal raphe. We have investigated whether there is a correlation between soma and intraretinal axon diameter and how these parameters relate to intraretinal axon length on both sides of the cat temporal raphe. Retinas were wholemounted and alpha-cell somata and fibers stained with a modified neurofibrillar method. Moving peripherally from the area centralis along the raphe there was a progressively increasing difference between the intraretinal axon lengths for nearly adjacent cells across the raphe, which reached a maximum of 4-5 mm at the retinal periphery. Cells on the nasal aspect of the raphe had shorter axons than did adjacent cells on the temporal aspect of the raphe. Comparison of soma diameter samples across the raphe showed there was no clear trend between soma diameter and intraretinal length. Replotting the raphe and sample areas on a cell density map indicated that differences in soma diameter could be attributed to ganglion-cell density differences between the sampled areas. Examination of the stained cells revealed that within the initial length of the axon there was a region showing a reduction of axon diameter (diameter less than 1 micron), which varied in length from cell to cell. The axon was, therefore, divided into three segments: the portion of axon prior to thinning (A), the thin segment itself (B), and the part of the axon after the thin segment (C). The diameter of each segment (A,B,C) and the lengths of the first and second segments (A,B) were significantly correlated with soma diameter (P less than 0.001). From measurements of the axon diameter of segment C, it was concluded that alpha-cell axons continue to increase in diameter along their path towards the optic disc. The present report indicates that alpha-cell soma size, when going from the area centralis to the periphery along the raphe, reaches a plateau and then declines within more peripheral retinal locations in spite of increasing intraretinal axon length. Thus, there is no positive correlation between soma or axon diameter and intraretinal axon length. The anatomical findings are discussed in relation to previous reports of retinal development and complementary conduction times within intraretinal and extraretinal visual pathways.     

Contribution from proximal retina to intraretinal pattern ERG: the M-wave

Intraretinal electroretinographic (ERG) responses were recorded from cat to spatial square wave gratings that were reversed in contrast (pattern ERG, PERG). Maximum 8 Hz PERG amplitudes occurred in proximal retina. Intraretinal ERGs to circular spots (photopic) also were maximal in proximal retina and resembled the M-waves of cold-blooded retinas. The temporal transforms of M-wave responses to 8 Hz flicker (to simulate contrast reversal conditions) imitated the 8 Hz PERG, suggesting that the M-wave may contribute significantly to the PERG.     

A versatile system for studying mammalian intraretinal metabolism and function in situ.

Microelectrodes can be introduced into the intact mammalian eye after the preparation has been stabilized with an animal head-holder and an ocular fixation ring. A versatile system for introduction and manipulation of the electrode consists generally of three coaxially orientated tube-like structures which interadapt in a telescopic fashion: an illuminator is threaded into the main body of a micromanipulator, the electrode, in turn, is threaded into the illuminator. The whole central axis therefore moves in unison as the micromanipulator is positioned or advanced by a remotely controlled hydraulic motion operating system. Two drive jacks, angularly attached to the main body, can move the central axis within a 38° conical plane around the vertical axis. Intravitreal and transretinal vertical movements (down to 2 μm) can be executed by coarse and fine controls respectively. The illuminator is used for intravitreal, fundic and electrode illumination as well as photo-stimulation (for electroretinography). PO₂ and pH microelectrodes have been successfully used in this system. Local electroretinograms can be made using the PO₂ electrode as the sensor. Simultaneous transretinal PO₂ measurements and electroretinography are theoretically possible using a single PO₂ electrode. Microelectrode measurements are generally made in a specially designed Faraday cage.     

Nonlinear-linear transition in the frog intraretinal electroretinogram

The electroretinographic system is stimulated with sinusoidal light signals at various frequencies. Such steady state responses indicate that the system contains two frequency ranges a low frequency nonlinear range and a higher frequency essentially linear range. The transitional frequency range is from about 3–5 c/s. Reduction of stimulus amplitude at low frequency does not indicate any significant linearization.     

结核性脉络膜结节联合视网膜结节1例

眼结核的表现形式多样,有时会被误诊漏诊。本病例为一年轻男性,以右眼视力突发下降为主诉就诊,眼部表现可见黄斑区脉络膜占位病灶及视网膜内小病灶,经γ-干扰素释放试验、胸部CT等检查,确诊为血型播散性肺结核,眼部诊断为结核性脉络膜结节联合视网膜结节,全身接受抗结核治疗后,眼部病灶消退。     

A technique for recording the electroretinogram (ERG) from chronically implanted electrodes in animals

A technique is described for recording the electroretinogram in monkeys from electrodes surgically implanted in the supraorbital bone. Recordings from these electrodes evidenced response wave-forms which had a high correlation with those recorded simultaneously from a corneal-wick electrode. The technique described should prove to be more convenient than the corneal wick for prolonged recording sessions or repeated measurements from the same animal and also permits recordings to be obtained in an unanesthetized preparation.     

Morphology of intraretinal new vessels in the PETH rat

The mature stages of retinal dystrophy in PETH rats are characterised by loss of the photoreceptor layer and invasion of the retinal pigment epithelium by new capillaries derived from the retinal vessels. The new capillaries are fenestrated where they are adjacent to the basement membrane of the retinal pigment epithelium and are surrounded by cells of the disrupted pigment epithelium, which follow the course of the capillaries into the inner retina. Abnormal basement membrane deposits are common within the retinal pigment epithelium.     

Normal EOG values in intraretinal metastasis from cutaneous melanoma: a case report

Purpose: The electro-oculogram (EOG) is a powerful test to diagnose primary and metastatic choroidal tumors. While in benign tumors light-peak to dark-trough ratio values are in the range of normal subjects, these values appear highly altered in eyes affected by malignant choroidal tumors. Here we report a clinical case of a patient with intraretinal metastasis from cutaneous melanoma; notwithstanding the malignancy of the tumor, the EOG doesn't present alterations. Methods and results: Standard electro-oculographic recordings were performed before and after local excision of the tumor; recordings from the normal eye were taken as control. The EOG values were always normal in both eyes. Histological sections showed no evident change in the cell population of the retinal pigment epithelium (RPE) and Bruch's membrane. Conclusion: Our results suggest that the presence of an intact RPE is a crucial requirement to obtain a normal EOG. This revised version was published online in July 2006 with corrections to the Cover Date.     

A method for DC-ERG recording of alert humans

Summary We developed a technique for DC-coupled ERG recording of the alert human. The equipment consists of three units: a new cornea suction glass, a separate electrode, and a vacuum control device. We get stable recordings of more than one-half hour.By comparison with the EOG the identity of the EOG on-peak and ERG c-wave is assured. A fine structure of DC-ERG recording of 100 V amplitude is closely correlated to the variation of the blood pressure in the ophthalmic artery. It may either be caused by the variable electric conductivity of the eyeball due to the blood pressure or it may reflect a variation of the retinal potential itself.

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Zusammenfassung Es wurde eine Technik zur gleichspannungsgekoppelten ERG-Ableitung vom wachen Menschen entwickelt. Die Apparatur besteht aus einem neu entwickelten Cornea-Haftglas, einer getrennten Elektrode und einer Vakuum-Konstanthaltung. Mit dieser Technik wurden stabile Ableitungen über eine halbe Stunde und länger möglich.Durch einen Vergleich mit dem EOG konnte der on-peak des EOG als C-Welle des ERG identifiziert werden. Die DC-ERG-Ableitungen zeigen eine Feinstruktur mit einer Amplitude von 100 (V, die eng mit den Blutdruckschwankungen in der Arteria ophthalmica korreliert ist. Da das ERG unter Einbeziehung des variablen Volumenleiters des Augapfels abgeleitet wird, kann diese Feinstruktur entweder durch eine pulssynchrone elektrische Widerstandsänderung oder durch eine Änderung des retinalen Potentials selbst bedingt sein.

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Supported by the Deutsche Forschungsgemeinschaft SFB 70.