 Autonomic Innervation and Microcirculation in the Eye -Implication for Glaucoma Pathophysiology Preliminary Program
February 26-27, 1999 in Erlangen, Germany Supported by Sonderforschungsbereich 539 "Glaukome, einschließlich PEX" of the "Deutsche Forschungsgemeinschaft" (DFG-German Research Foundation) February 27, 1999 Session I: Uvea and Episclera: Structure and Function Chair: E.Lütjen-Drecoll 9.00h -12.00h
Session II: Instrinsic Factors Influencing Ocular Circulation: Neurotransmitter Chair: W. Neuhuber 14.00h - 15.00h
Chair: G.Michelson 15.30h - 18.00h
MECHANISMS UNDERLYING THE CHOROIDAL BLOOD FLOW RESPONSE TO ACUTE CHANGES IN PERFUSION PRESSURE. KIEL, J.W.Department of Ophthalmology, University of Texas Health Science Center at San Antonioe-mail contribution for discussion Purpose: to determine the mechanism(s) responsible for the choroidal blood flow response to acute changes in mean arterial pressure (MAP). Methods: Pentobarbital anesthetized rabbits were artificially ventilated and instrumented with occluders on the aorta and inferior vena cava to control MAP, an ear artery cannula to measure MAP, and a vitreal cannula to measure IOP. Choroidal blood flow was measured by laser Doppler flowmetry using a fiber optic probe placed in the vitreous near the retina over the posterior pole. The standard protocol entailed brief (2-3 min) ramp increases and decreases in MAP before and after pharmacologic inhibition of potential neural, humoral and local mechanisms. Results: Under control conditions, choroidal blood flow was relatively unchanged at perfusion pressures (PP) between 70 - 40 mmHg, and linearly related to PP between 40 - 10 mmHg. Ganglionic blockade shifted the choroidal pressure-flow (P-F) relation downward at PP < 50 mmHg indicating a loss of an unknown source of neural vasodilatory tone. Atropine failed to elicit a similar response, indicating little neural cholinergic involvement. By contrast, nitric oxide (NO) synthase inhibition with L-NAME caused a downward shift in the P-F relation greater than seen with ganglionic blockade, implicating nitridergic nerves as a possible source of vasodilatory tone in combination with local endothelial NO. The vasoconstrictor tone unmasked by L-NAME was inhibited by calcium channel blockade and the non-selective endothelin antagonist, A-182086, but was unaffected by ganglionic blockade, alpha adrenergic blockade, angiotensin II blockade, or vasopressin blockade. Conclusions: These results indicate that the choroidal blood flow response to acute changes in MAP in the anesthetized rabbit is mediated in part by a neural vasodilator system and by a dynamic interaction between locally generated NO and endothelin. In the conscious state or under pathologic conditions, these mechanisms are likely modulated by additional local and neurohumoral mechanisms. Support: NEI Grant EY09702; an unrestricted departmental grant from RPB; and a gift of A-182086 from Abbott Laboratories INNERVATION OF CILIARY MUSCLE TIP, SCLERAL SPUR AND TRABECULAR MESHWORK IN PRIMATE EYESSELBACH JM, WITTMANN, M, LÜTJEN-DRECOLL E Anatomisches Institut LS II der Universität Erlangen-Nürnberg e-mail contribution for discussion Purpose: Morphological and physiological studies show contractility of scleral spur and trabecular meshwork (TM) indicating modulation of aqueous outflow independent of ciliary muscle contraction. We have investigated the innervation of the ciliary muscle tips, the scleral spur and the different layers of the TM. Methods: Serial sagittal and tangential sections of the anterior segments of 6 cynomolgus monkey eyes and 6 human eyes (age 58-94 years) were investigated immunohistochemically using antibodies against neurofilament, SP, CGRP, vesicular acetylcholine transporter (VACHT), VIP, NOS, NPY, TH and SMA. In addition, ultrathin sections were performed at the level of the posterior scleral spur. Results: In both species, abundant VACHT-IR but only single CGRP- and SP-IR nerve fibers were found in the ciliary muscle tip. In the scleral spur numerous nerve terminals stained for SP, CGRP, VIP, NOS and TH and in human but not in monkey eyes numerous fibers also stained for VACHT. In the posterior scleral spur of monkey eyes, structures similar to the mechanoreceptor-like terminals described in human eyes were found. In both species, staining for SP, CGRP, NOS and VACHT was present in all parts of the TM, but the nerve fibers were less numerous than in the scleral spur. In the TM no staining for TH and NPY was observed. Conclusions: Differences in innervation between ciliary muscle and outflow tissues might be involved in outflow modulation independent from ciliary muscle contraction. On the other hand innervation of the elongated human scleral spur and human and monkey TM by VACHT fibers could allow simultaneous contraction of both outflow tissues and ciliary muscle thereby preventing disruption of these tissues during strong muscle contraction. ANGIOARCHITECTURE AND INNERVATION OF THE PRIMATE ANTERIOR EPISCLERASELBACH JM, ROHEN JW, LÜTJEN-DRECOLL E Anatomisches Institut LS II der Universität Erlangen-Nürnberg e-mail contribution for discussion Purpose: To investigate the episcleral vasculature and its innervation, which could play an important role in aqueous humour outflow regulation. Methods: Serial tangential sections of the anterior sclera and episclera of 6 cynomolgus monkey eyes and 10 human eyes were investigated enzyme- and immunohistochemically using antibodies against neurofilament, synaptophysin, SP, CGRP, vesicular acetylcholine transporter (VACHT), VIP, NPY, TH, smooth-muscle a-actin (SMA) as well as the NADPHdiaphorase reaction. Results: In the most anterior portion, the episclera contains a dense venous plexus which mainly drains aqueous humor. All episcleral vessels including collector channels showed staining for SMA indicating lack of capillaries. The vascular pattern could easily be examined as all vascular endothelial cells stained for NADPHd. Branches of the anterior ciliary arteries form the episcleral arterial circle. Branches of these arteries anastomose with the episcleral veins. In the monkey episclera 4-6/mm2 arteriovenous anastomoses (AVA) are found, in the human episclera only 0,5-1/mm2. These AVA are characterized by a narrow arteriolar segment and by a wider funnel-shaped venous segment. Numerous nerve endings staining for NADPHd and TH are found at the arteries and veins as well as at the venules of the episcleral plexus. Besides, nerve fibers staining for NPY, VIP, VACHT, CGRP and SP are found at the arteries and, however less numerous, at the veins. This innervation pattern is very similar at the AVA. In the episclera anterior to the vascular circle numerous free nerve endings staining for SP and CGRP are found. Conclusions: The AVA between branches of the anterior ciliary arteries and the aqueous draining episcleral veins, the extended episcleral venous plexus and their dense innervation probably allow a subtle modulation of blood flow and presumably of aqueous humor outflow. A CHOROIDAL FOCUSING MECHANISM: WHAT HAS BEEN LEARNT FROM THE CHICK? WILDSOET, CF.New England College of Optometry, Boston e-mail contribution for discussion Purpose: The choroid is traditionally thought of as a vascular tissue subserving the needs of inner ocular tissues in relation to thermoregulation and nutrition. However, recent research has uncovered a novel role for the choroid, that of refractive modulation.1,2 The purpose of this presentation is to provide some insight into the processes underlying this choroidal focusing (accommodation) mechanism. Method: The basic phenomenon of ³choroidal accommodation² will be described for the chick about which most is known. Observations from the various laboratories that have contributed to our current understanding of this phenomenon will also be reviewed. Results: In brief, eyes exposed to hyperopic defocus show choroidal thinning and those exposed to myopic defocus show choroidal thickening; in both cases, these changes serve to at least partly compensate for the defocus experienced by moving the retina toward the plane of focus of the eye. These changes can be detected by high frequency ultrasonography in a matter of hours, earlier than the scleral growth changes that generally follow. The capacity of the chick choroid to thin is limited by the capacity of this relatively thin tissue (approx. 200-250 um) to reduce its thickness further; its capacity to thicken is much greater, with increases of 3-fold or more possible. Thickened choroids show expanded lacunae (lymphatic-like spaces) as well as increases in glycoaminoglycan synthesis, protein and water content. Choroidal blood flow is also increased although the latter appears to be short-lived relative to the thickness changes. The choroid is richly innervated and contains a variety of different neurotransmitters including nitric oxide, and it also contains nonvascular smooth muscle elements; recent observations in relation to these players and their likely significance for choroidal accommodation will be discussed. Conclusion: Taken together, these data suggests that both vascular and nonvascular (muscular and/or osmotic) mechanisms may contribute to choroidal accommodation which plays an important role in emmetropization. EFFECT OF DARK ADAPTATION ON LDF BLOOD FLOW IN THE PRELAMINAR REGION OF THE OPTIC NERVE HEAD.Riva C.E.1,2 Logean, E.1 Petrig B.L.1 and Falsini B.3. Institut de Recherche en Ophtalmologie, Sion1; University of Lausanne2, Switzerland; Università Cattolica del S. Cuore, Rome, Italy3. e-mail contribution for discussion Purpose. Laser Doppler measurements performed immediately after the transition from dark adaptation (DA) to light led to the hypothesis that retinal blood flow is increased during DA, but the use of visible lasers has prevented measurements during DA. The aim of this work was to test this hypothesis. Methods. We quasi-continuously measured the flux of red blood cells in superficial vessels of the prelaminar region of the optic nerve head (the region fed by branches of the central retinal artery) during and after DA using a laser Doppler flowmeter (LDF) in the near-infrared (810 nm). Measurements were performed in 5 normal subjects (age 27 to 60 years) during light (baseline), various periods of DA (2 to 16 min) and again during light. Results. Average RBC flux did not change significantly (-0.2 ± 6%, 95% cim, p > 0.05) during the various periods of DA, as determined from linear regressions of the flux versus time. Following the transition from DA to light, the flux increased momentarily by as much as 50%. The value at the peak of this increase occurred approximately 30 sec after the light was turned on. Measurements in one subject after 2, 4, 8 and 16 min of DA showed that this value depended upon DA. It increased during the first 4 min of DA and then remained constant. Conclusions. Our study does not support the hypothesis that retinal blood flow in normal volunteers increases during DA. Furthermore, the results show that the increase in flow observed after DA is a transient process induced by the dark/light transition. Supported by the Swiss National Science Foundation Grant #3200-053785 and the Italian CNR 95.01715.CT04. Effect of Dark Exposure on Choroidal Blood Flow in the Fovea Centralis.Longo A.1, Geiser M.2 and Riva C.E.2. 1Istituto di Oftalmologia, Università di Catania, Italy and 2Institut de Recherche en Ophtalmologie, Sion, Switzerland. e-mail contribution for discussion Purpose. To study the effect of dark exposure on choroidal blood flow in the foveal area. Methods. In 8 healthy volunteers (age 25-60 years), the choroidal blood flow parameters (ChBVel, ChBVol and ChBF) have been measured by a confocal laser doppler flowmeter with a probing laser at 785 nm, 80 (µW at the cornea). Blood pressure and IOP were measured to determine the ocular perfusion pressure. Measurements were performed at environmental light level for 20 minutes (Exp. 1). In Exp. 2, after a baseline measurement at environmental light, the subjects were measured in darkness during 20 minutes and then at environmental light again for10 minutes. Results. In both experiments, no change of perfusion pressure was detected. While in Exp. 1, there was no change in the flow parameters, in Exp. 2, however ChBVol and ChBF decreased significantly (p < 0.01) by approximately 11% and 15%, respectively. After 6 min of light following darkness, the blood flow parameters were not statistically different from baseline values. Additional experiments showed no effect of the probing beam on the flow parameters, although the fundus irradiance provided by the laser was far above that of the environmental illumination. Conclusion. The transition from light to darkness decreases choroidal blood flow in the foveal region of the human fundus. Our data suggest that this effect is the result of a neural or metabolic process rather than a change in local choroidal temperature. Supported by grants #3200-053785 from the Swiss National Science Foundation, #491 from the Priority Program Optics II, Loterie Romande, Lausanne, Switzerland and Annual Grant of Società Oftalmologica Siciliana. Ocular Cold Pressor Test -A New Test in the Diagnostics of Low Tension GlaucomaMichelson G, Harazny J, Welzenbach J. Dept. of Ophthalmology and Eye Hospital, University of Erlangen-Nürnberg, Germany e-mail contribution for discussion Background: The optic nerve atrophy in Low Tension Glaucoma (LTG) may be caused by a disorder of the autonomic nervous system producing vasospastic reactions in ocular vessels. The detection of ocular vasospasm in patients with LTG may help for the diagnose of LTG and may support a rational therapy with Ca++-antagonists. Purpose: To detect vasospastic reactions in ocular vessels during cold provocation. Methods: By the „ocular cold pressor test" the velocity pulse curve in the ophthalmic artery and the arterial blood pressure was continuously measured and stored before, during, and after cold provocation. The cold provocation was performed by immersion of a hand in cold water (4°C) for 3min. Off-line the pulse curves of the ophthalmic artery was analysed by Fast Fourier Transformation in respect to the 1th to 5th harmonic. The spectral index of the pulse curve may serve an index for the elasticity of the vessel wall of the ophthalmic artery. 48 patients with LTG and 55 normal persons were evaluated. Results: Patients with LTG showed in 46% a significant decrease in elasticity of the ophthalmic artery during cold provocation. Conclusion: The „Ocular Cold Pressor Test" may be a new tool in the diagnostic approach in patients with Low Tension Glaucoma. Supported by Deutsche Forschungsgemeinschaft DFG Mi320/2-3, DFG-Sonderforschungsbereich 539 (Glaukome, einschließlich PEX) MORPHOLOGIC FINDINGS IN CHRONIC HIGH-PRESSURE EXPERIMENTAL GLAUCOMA IN RHESUS MONKEYS AND THEIR IMPLICATIONS FOR OCULAR PERFUSIONJONAS JB (1), HAYREH SS (2) (1)Department of Ophthalmology and Eye Hospital, Friedrich-Alexander-University Erlangen-Nürnberg in Erlangen, Schwabachanlage 6, 91054 Erlangen, Germany, and (2) Department of Ophthalmology and Visual Sciences, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA. e-mail contribution for discussion Purpose. To evaluate parapapillary chorioretinal atrophy in chronic high-pressure glaucoma in rhesus monkeys, and effects of age and atherosclerosis and chronic arterial hypertension, in a prospective, planned study. Methods. The study comprised 76 eyes of 38 monkeys. First, experimental atherosclerosis and chronic arterial hypertension were produced in 24 animals. Then experimental high-pressure glaucoma was produced by laser photocoagulation of the anterior chamber angle in 38 eyes of the 38 animals. Intraocular pressure measurements and fundus photography were serially performed. The photographs were morphometrically analyzed. Results. In the glaucomatous eyes, area and frequency of beta zone of parapapillary atrophy were significantly larger (p<0.0001) at end of the study than at baseline. Area of beta zone was significantly (p<0.0001) and negatively correlated with neuroretinal rim area. In an intraindividual inter-eye comparison, beta zone was significantly (p<0.0001) larger in the glaucomatous than in contralateral non-glaucomatous eyes. Increase of beta zone and loss of neuroretinal rim were statistically independent of presence and size of beta zone at start of study. Beta zone was significantly (p=0.036) greater in older than younger monkeys; however, atherosclerosis-arterial hypertension showed no significant influence on frequency and size of beta zone. Area and frequency of alpha zone showed no significant change between baseline values and those at the end of study. Conclusions. In experimental chronic high-pressure glaucoma in monkeys, beta zone of parapapillary atrophy is positively correlated with glaucomatous optic nerve damage. This confirms previous biomorphometric and histomorphometric studies on patients with glaucoma. In chronic experimental high-pressure glaucoma, neuroretinal rim loss and increase of beta zone may be independent of pre-existing parapapillary atrophy. Increase of beta zone may be independent of concomitant atherosclerosis-arterial hypertension. OCULAR PERFUSION IMPLICATIONS OF MORPHOLOGICAL DIFFERENCES BETWEEN HIGH-PRESSURE GLAUCOMA AND NORMAL-PRESSURE GLAUCOMAJonas JB, Budde WM Department of Ophthalmalogy and Eye Hospital, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany e-mail contribution for discussion Purpose. To get hints for the possibly vasogenic pathogenesis of glaucomatous optic neuropathy, we evaluated the appearance of the optic nerve head in chronic high-pressure glaucoma and normal-pressure glaucoma. Methods. The study included 52 eyes with focal normal-pressure glaucoma and 28 eyes with juvenile-onset primary open-angle glaucoma which served as model for chronic high-pressure glaucoma. Color stereo optic disc photographs and wide-angle retinal nerve fiber layer photographs were morphometrically examined. Results. Both study groups did not vary significantly in count of localized retinal nerve fiber layer defects, size of parapapillary atrophy, optic cup depth, steepness of disc cupping, rim-to-disc area ratio, diameter of retinal arterioles, and frequency and degree of focal retinal arteriole narrowing. In normal-pressure glaucoma versus juvenile open-angle glaucoma, localized retinal nerve fiber layer defects were significantly broader, disc hemorrhages were found significantly more often and were larger, and neuroretinal rim notches were present more frequently and were deeper. Conclusions. Chronic high-pressure glaucoma and normal-pressure glaucoma show morphologic similarities in the appearance of the optic nerve head. The lower frequencies of detected disc hemorrhages and rim notches in high-pressure glaucoma may be due to a smaller size of disc bleedings and localized retinal nerve fiber layer defects in high-pressure glaucoma. Both glaucoma types have morphologic features in common suggesting that they possibly belong to the spectrum of the same pathologic process. This may have implications for the discussion of the vasogenic theory of glaucomatous optic neuropathy. DUCKS ARE VERY HUMAN: COMPARATIVE ANATOMY OF CHOROIDAL GANGLION CELLSNEUHUBER, W. L. and SCHRÖDL, F. Anatomy Institute, University of Erlangen-Nürnberg, Erlangen, Germany e-mail contribution for discussion Purpose: The choroid of the human eye harbours up to 2000 intrinsic ganglion cells. Their targets, neuronal connectivity and transmitters are almost unexplored, as is their function. However, they probably play an important role in regulation of ocular perfusion and intraocular pressure. The aim of this study was to establish an animal model to investigate the functional anatomy of choroidal ganglion cells using experimental morphological techniques. Data obtained in this model species should provide a basis for further elucidation of the intrinsic innervation of the human choroid. Methods: Duck eyes were obtained from animals decapitated for commercial purposes at a local farm. Human eyes were obtained from surgical enucleation. After fixation in buffered aldehydes or Zamboni's fixative, wholemounts or flat frozen sections of the choroid were immunocytochemically stained for nNOS/NADPH-diaphorase, VIP, galanin, tyrosine hydroxilase, CGRP, neurofilaments, PGP 9.5 and smooth muscle actin. DiI was applied on the ciliary nerve of fixed eyes for bulk labeling of the extrinsic innervation and to test the possibility of choroido-fugal projections of intrinsic neurons. Specimens were investigated using conventional light and confocal laser scanning microscopy. Other choroids were processed for ultrastructural immunocytochemistry. Results: The duck eye harbours about 1500 to 3500 intrinsic neurons. They are embedded into the smooth muscular meshwork forming a "lymphatic sponge". They stain positively for nNOS/NADPH-d, VIP and galanin although the coexistence of these markers is not 100%. They not only innervate choroidal arteries but also smooth muscle fibers of the "lymphatic sponge". On the other hand, they establish close contacts to non-vascular smooth muscle fibers, sometimes of the macula adherens type. Intrinsic neurons receive synaptic input from tyrosine hydroxilase immunoreactive sympathetic, and CGRP positive trigeminal afferent fibers. There is also suggestive evidence for intrinsic synaptic input. Intrinsic neurons of the human choroid resemble duck neurons in their chemical coding (nNOS/VIP/GAL) and their innervation by sympathetic fibers. Conclusions: Intrinsic choroidal neurons innervate, besides choroidal blood vessels, non-vascular smooth muscle, are mechanically coupled to non-vascular smooth muscle fibers, and receive synaptic input from sympathetic, trigeminal afferent and probably also other intrinsic neurons. Available data suggest close similarities to intrinsic neurons in the human choroid. Choroidal neurons may function as motor to vascular and non-vascular smooth muscle, mechanosensors and integrators of synaptic input from various sources. The duck eye may provide a valuable model for the study of the functional role of choroidal ganglion cells, and for getting insights in their possible involvement in glaucoma pathogenesis. (Supported by DFG/SFB 539, B.II.3) MUSCARINIC AND NITRERGIC REGULATION OF CHOROIDAL BLOOD FLOW BY THE CILIARY GANGLION IN BIRDS.FITZGERALD, M.E.C.1, ZAGVAZDIN, Y.2, CUTHBERTSON, S.2, KIMBLE, T.2, LAMOREAUX, W.3, and REINER, A.2. 1Dept. of Biol, CBU; 2Dept. of Anat. & Neurobiol., UT, Memphis, TN; 3Dept. Biol., CUNY, Staten Island, NY USA e-mail contribution for discussion Purpose: Both cholinergic and nitrergic mechanisms have been implicated in parasympathetic control of blood flow. Our goal in the present study was to use the anatomical, biochemical, physiological and pharmacological methods to elucidate the relative contributions of these two mechanisms to control of choroidal blood flow (ChBF) by the ciliary ganglion (CG) in birds. Methods: NADPHd histochemistry and immunohistochemistry were used to characterize the cholinergic and nitrergic organization of the preganglionic input to pigeon CG and its output to choroid. Western blots were used to assess levels of endothelial NOS (eNOS) in choroid. ChBf regulation was studied using transcleral laser Doppler flowmetry and pharmacological inhibition of nitrergic or cholinergic transmission in pigeon. Results: While preganglionic endings from the nucleous of Edinger-Westphal (EW) on choroidal neurons of the CG contained nNOS, few if any choroidal neurons or their postganglionic fibers to choroid contained nNOS. Western blots demonstrated eNOS in pigeon choroid. Inhibition of NO formation by L-NAME or blockade of M3-type muscarinic receptors by the selective antagonist 4DAMP resulted in near complete or complete blockade of the increase in ChBF yielded by EW microstimulation. Conclusions: Choroidal vasodilation in response to CG activation in bird is likely to occur via M3-mediated cholinergic stimulation of endothelial NO formation. NO released by preganglionic endings on choroidal neurons also may contribute to the choroidal response to EW activation. Supported by NIH-EY-05298 (AR) and NIH-AG-10538 (MECF) REDUCED PERIPAPILLARY HEMODYNAMICS IN NORMAL TENSION GLAUCOMAK.-G. Schmidt1, V. Klingmüller2, A. v. Rückmann1, R. Becker1, and L.E. Pillunat3 Depts. of Ophthalmology1 & Diagnostic Radiology2, U. of Giessen; and Dept. of Ophthalmology, U. of Hamburg3, Germany e-mail contribution for discussion Purpose: The optic nerve head, the area of primary damage in the glaucomas, is directly supplied by the peripapillary choroid and the short posterior ciliary arteries (SPCAs). This study was designed to evaluate for choroidal and SPCA hemodynamics in high tension (HTG), normal tension (NTG) primary open angle glaucoma patients, and healthy controls (CTL). Methods. 20 HTG, 12 NTG, and 59 CTL without clinically relevant extracranial stenosis (<50% reduction in vessel diameter) as excluded by sonography of common and internal carotid arteries, were evaluated for SPCA peak systolic flow, enddiastolic flow, pulsatility and resistance indexes using 9 MHz linear and phased array scanners (Elegra Advanced System, Siemens, Germany) with transmission energy being reduced to 40% (B-, C-, & triplex-modes), three temporal SPCAs being the vessels investigated, ocular pulse amplitude (OPA; OBF-System, OBF Labs, UK), intraocular pressure (IOP) and systemic perfusion parameters. Results (Mean + SEM). In CTL SPCA peak systolic flow (cm/s) was 10.90 + 0.23, enddiastolic flow (cm/s) was 3.26 + 0.10, pulsatility index was 1.30 + 0.05, resistance index was 0.69 + 0.01 OPA (mmHg) was 2.2 + 0.1, IOP (mmHg) was 14.4 + 0.33, RR syst./diast. (mmHg) was 131.1. + 1.4/76.4 + 0.8, and HR (min. -1) was 62.4 + 1.0. When compared to CTL matched for age, sex, and refraction, OPA was significantly (sig., p< 0.05) reduced in NTG, color and spectral sonography showed a sig. (p< 0.05) reduction in diastolic flow patterns and a sig. (p< 0.05) increase in pulsatility index, whereas parameters investigated were not sig. (p< 0.05) altered in HTG. Systemic perfusion parameters were not sig. (p< 0.05) different in any group. Conclusion. These data suggest reduced hemodynamics in the choroid and in SPCAs of NTG patients, which may contribute to progression of this optic neuropathy in this subgroup of patients with normal intraocular pressures. CARBONIC ANHYDRASE INHIBITION AND OPTIC NERVE OXYGEN TENSIONEinar Stefansson MD PhD, Peter Koch Jensen MD, Thor Eysteinsson, PhD, Kurt Bang, Jens F. Kiilgaard MD; JeNs Dollerup PhD, Erik Scherfig MD, Morten LaCour MD, Anne Vienke University of Iceland, Landspitalinn, 101, Reykjavik, Iceland e-mail contribution for discussion Purpose: To study how the oxygen tension of the optic nerve (ONPO2) is affected by the administration of the carbonic anhydrase inhibitors dorzolamide and acetozolamide. Methods: Polarographic oxygen electrodes were placed in the vitreous cavity over the optic disc in anaestethized pigs. Blood gasses and cardiovascular physiology were monitored while ONPO2 was recorded continuously with varying breathing gasses and intravenous application of drugs. Results: The mean ONPO2 was found to be 24.1 + 11.6 mmHG when breathing room air. In response to breathing 5,19% CO2 the ONPO2 changed from 20,8 +5,6 mmHg to 28,9 + 3,6 mmHg (n=4, p<0,001). Intravenous injections of 500 mg dorzolamide raised the ONPO2 from 16,4 + 6,1 mmHg to 26,9 + 12,2 mmHg, or 52,5% + 21,2% (n=5; p=0,017) and this effect was dose dependent. Intravenous injections of 500 mg acetazolamide raised the ONPO2 from 23,6 +9,5 mmHg to 30,9 + 10,0 mm Hg (n=6, p<0,001). Conclusion: Carbonic anhydrase inhibition by dorzolamide and acetazolamide raises ONPO2 and this effect was dose dependent. These data demonstrate a direct effect by carbonic anhydrase inhibitors on the oxygen tension of the optic nerve. LYMPHATIC VESSELS IN THE AVIAN CHORIDM.E. de Stefano* and E. Mugnanini# *Dip. Biologia Cellulare e dello Svilupo, Università "La Sapienza", Roma, Italy. #Northwestern University, Institute for Neuroscience, Chicago, IL, USA. e-mail contribution for discussion The avian choroid contains a large system of thin-walled lacunae similar in their fine structure to lymphatic vessels. While terminating blindly among the blood vessels of the choriocapillaris facing the Bruch's membrane, in the suprachoroidea the lymphatic capillaries merge to form larger lacuanae, extending toward the posterior portion of the bulb. Numerous small- and medium-sized lacunae aggregate in correspondence of the large vortex veins that leave the eye bulb, and small branches are seen entering the sclera and abutting the muscular wall of the large scleral veins. Characteristic cellular plugs protrude as villi in the veins' lumina and are penetrated by the small branches of the lymphatic lacunae, suggesting these structures represent sites of communication between lymphatics and scleral veins. Experiments showing engorgement of the lymphatic lacunae with blood cells after lowering the intraocular pressure (IOP) by paracentesis of the anterior eye chamber further support this hypothesis. Although lacking a muscular tunica, the thin endothelial lining of the large lacunae is often abutted by short appendages of stromal smooth muscle cells, which are richly innervated and may control the patency of the lymphatic vessels and contribute to pump the lymph into the scleral veins. We propose that lymphatic lacunae in the avian choroid represent a true lymphatic system involved in removing transretinal and local fluids, in draining part of the ciliary processes-born aqueous humor, and in controlling IOP. Moreover, thickening of the suprachoroidea during recovery from experimental myopia in chicks, a mechanism that moves the retina forward and compensates for the defocus, suggest a choroidal role in controlling normal and abnormal eye growth. Despite reports of the presence of lymphatic capillaries in monkey and human choroid, no such extensive system of lymphatic vessels occupying large part of the choroid and connecting to the scleral veins has been described, suggesting important differences in the functional involvement of the choroid in pathologies concerning ocular fluids imbalance as glaucoma. Supported by funds from Istituto Pasteur-Fondazione Cenci Bolognetti and NIH grant NS 09904. FUNCTIONAL MORPHOLOGY OF THE PRIMATE CHOROIDLÜTJEN-DRECOLL E, MAY CA, WAGNER C Institute of Anatomy, University Erlangen-Nürnberg e-mail contribution for discussion The vasculature of the primate choroid consists mainly of branches of the short ciliary arteries which in the suprachoroid run in parallel to the scleral surface and pass nearly perpendicularly through the choroid proper to supply the lobularly arranged choriocapillaris. The arteries are connected to an elastic network extending in the anterior-posterior direction between the ciliary muscle and the elastic fibers surrounding the optic nerve head and, in the radial direction between Bruch's membrane and the suprachoroid. An elaborated choroidal nerve fiber plexus innervates the choroidal vasculature. Within this plexus especially in the suprachoroidal layer numerous ganglion cells are found. Innervated smooth muscle cells connect the vessels with the elastic network. Numerous lymphatic-like spaces are present int he choroid proper surrounded by different kinds of mast cells and other kinds of free cells. Within the spaces Koganei-cells are found, which often are squeezing through the sclera into the orbit. PARAPAPILLARY ATROPHY IN THE CHRONIC OPEN-ANGLE GLAUCOMAS AND THEIR RELATION TO INTRAOCULAR PRESSUREBUDDE WM, JONAS JB, LANG P Dept. Ophthalmology, Friedrich-Alexander Universität Erlangen-Nürnberg e-mail contribution for discussion PURPOSE. To evaluate whether parapapillary atrophy varies among chronic open-angle glaucomas with different intraocular pressure levels. METHODS. The study included 631 Caucasian patients with primary open-angle glaucoma (POAG), 123 patients with secondary open-angle glaucoma (pseudoexfoliative glaucoma; n=86; pigmentary glaucoma; n=37), and 481 normal subjects. POAG was differentiated into highly myopic POAG (n=32), juvenile POAG (n=33), focal normal-pressure glaucoma (n=52), "sclerotic POAG" with marked fundus tesselation (n=89), and "ordinary POAG" comprising the remaining POAG eyes (n=425). Color stereo optic disc photographs were morphometrically evaluated. The IOP was measured in day and night profiles. RESULTS. Beta zone of parapapillary atrophy was significantly (P<0.0001) larger in highly myopic POAG (4.11 ± 3.42 mm2) than in sclerotic POAG (1.00 ± 1.37 mm2). In sclerotic POAG, beta zone was significantly larger than in pseudoexfoliative glaucoma (0.65 ± 0.93 mm2; P=0.02), pigmentary glaucoma (0.42 ± 0.58 mm2; P<0.001), and ordinary POAG (0.66 ± 1.06 mm2; P<0.001). In ordinary POAG, beta zone was significantly larger than in focal normal-pressure glaucoma (0.29 ± 0.38 mm2; P=0.02) and juvenile POAG (0.33 ± 0.72 mm2; P<0.01). The two latter groups did not vary significantly (P=0.27) in beta zone. Compared with all glaucoma groups, beta zone was significantly the smallest in the normal eyes (0.18 ± 0.57 mm2). Taken all glaucoma groups except the focal normal-pressure group, the size of parapapillary atrophy increased significantly with decreasing level of intraocular pressure. CONCLUSIONS. Beta zone of parapapillary atrophy varies by a factor of more than 3 to 1 between the various types of chronic primary and secondary open-angle glaucomas. With exception of the focal normal-pressure glaucoma, it is inversely related with the level of the intraocular pressure. |