Die fixation des menschlichen auges

Zusammenfassung Während der Fixation wird ein Fixationsfeld beansprucht im Ausmaße von 100 , d.i. das Bereich der dünnsten und höchsten Zapfen, von 1 Durchmesser. In diesem Fixationsfeld ist der Fixationspunkt der Willkür entzogen. Während der strengen Fixation macht das Auge bekanntlich dreierlei Bewegungen, von denen die schnellen ebenfalls in einem Feld von 100 Durchmesser liegen. Das maculopapilläre Bündel führt die Erregungen aus dem auch in Bezug auf das Ableitungssystem ausgezeichneten Fixationsfeld ab. Die Sehschärfe unterschreitet weit die Grenze von 1 , was auf die Synapsenfunktionen der Retina, des Corpus geniculatum laterale und auf die cortikalen Bezirke zurückgeführt wird.

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Summary During fixation a fixation-field of 100 diameter is required, corresponding to the area of the thinnest and longest cones of 1 diameter. Within this fixation-field the position of the fixation point is involuntary and at random. The fast component of the three eye movements during fixation also covers a field of 100 diameter. Impulses from this field are conducted via the maculo-papillary bundle. The visual acuity is far below the limit of 1 ; this is attributed to the synaptic function of the retina, the lateral geniculate body and the cortical areas.

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Résumé Pendant la fixation un champ de 100 se trouve occupé, c'est-à-dire la région des cônes les plus hauts et les plus minces, qui ont pour diamètre 1 . Dans le champ de fixation le point de fixation n'est plus soumis à la volonté. Pendant la fixation précise l'oeil fait trois sortes de mouvements; les plus rapides d'entre eux intéressent aussi un champ d'un diamètre de 100 . Le faisceau papillo-maculaire conduit les influx nerveux hors du champ de fixation. L'acuité visuelle descend bien en-dessous de 1 . Ce fait est attribué aux fonctions synaptiques de la rétine, du corps genouillé externe et des régions corticales.

     

Lamellar excimer laser keratoplasty: Reproducible photoablation of corneal tissue

We examined the depth of ablation of the recipient bed with different counts of oscillations of excimer laser beam, to determine the correlation between planned and real depth. The ablation rate per oscillation was tested preoperatively by blackened photographic paper of defined thickness and thus was calculated to be 5 m. Forty pig eyes were used for the first study. Each eight eyes were ablated in the planned depth 100 m, 200 m, 300 m, 400 m and 500 m. The corneal thickness was measured with an ultrasonic pachymeter before and after the procedure. The depth measured after the photoablation was 99.4 ± 36.4 m for 100 m planned depth, 186.7 ± 55.3 m for 200 m, 298.4 ± 68.5 m for 300 m, 373.9 ± 65.7 m for 400 m and 480.1 ± 59.3 m for 500 m. Comparing the depth measured after the photoablation to planned depth, there was a significant correlation (correlation coefficient: R = 0.93; p < 0.0001). Five other corneas trephinated from pig cadaver eyes were ablated from the endothelial side to the desired thickness (100 to 500 m) of lamellar graft. In a second step a donor mask was placed onto the cornea and a laser light spot was led until perforating on all sides. The lamellar keratoplasty was completed by suturing the corneal graft into the bed. Macroscopic and microscopic examination of sutured eyes after fixation showed a good fit of wound margins and stromal interface. These results indicate that excimer laser is useful for reproducible corneal photoablation in lamellar keratoplasty.     

Cytotoxic effects of antiproliferative agents on human retinal glial cells in vitro

Purpose: Proliferative vitreoretinopathy (PVR) is characterizedby the formation of cellular membranes on the detached retina and also in the vitreous. Glial cellscan be found in epiretinal and subretinal membranes from eyes with PVR, proliferative diabeticretinopathy (PDR), idiopathic macular pucker, uveitis and other diseases affecting theretina. Proliferation and contraction of glial cells appears to play a role in the pathogenesisof PVR. This study is designed to inspect the effectiveness of harringtonine, as well as colchicine,daunomycin and fluorouracil, against cellular proliferation of cultured human retinal glial cellsthat might be involved in the retinal and/or vitreous proliferation. Methods: Cultures of human retinal glial cells were preparedusing the enzyme digesting method. Cells that had been in culture for 2–5 passages were usedin this study. Harringtonine (0.063 g/ml 2.0 g/ml), colchicines(0.5 g/ml 16.0 g/ml), daunomycin (0.1 g/ml 3.2 g/ml) and 5-fluorouracil(0.5 g/ml 16.0 g/ml) were added to cultures of human retinal glial cellsand the proliferation rates of the cells were measured by the MTT method. Results: Harringtonine at the dosage of 0.063 g/mlinduced suppression of cellular growth, but the changes were not statistically significant (p > 0.05).At a dosage ranging from 0.125 g/ml to 2.0 g/ml, harringtonine significantly suppressedcellular growth according to the test (p < 0.01). Likewise, other antiproliferativeagents inhibited cellular growth significantly at a dosage from 1.0 g/ml to 16.0 g/ml(colchicine), 0.2 g/ml to 3.2 g/ml (daunomycin) and 1.0 g/ml to 16.0 g/ml(5-fluorouracil), but not at 0.5 g/ml (colchicine), 0.1 g/ml (daunomycin) and0.5 g/ml (5-fluorouracil). The ID₅₀ were 0.33 g/ml (harringtonine), 3.11 g/ml (colchicine), 0.79 g/ml (daunomycin) and 5.23 g/ml (5-fluorouracil), respectively.Conclusions: Harringtonine was extremely effective ininhibiting human retinal glial cell proliferation, like other antiproliferative drugs such as colchicine,daunomycin and 5-fluorouracil. Harringtonine, therefore, may be a candidate for further studies regardingthe treatment of experimental PVR.     

Argon-Laser Coagulation der Kanincheniris

Zusammenfassung Beim Chinchilla-Kaninchen wurde das kammerwinkelnahe Drittel der Iris nach Ermittlung der Schwellenwerte mit Argon-Laser-Energien von 0,02–4,8 J und einem Brennfleckdurchmesser von 50 m coaguliert. Irisschädigungen, die mit einer Energie von 1,2 J erzielt werden konnten, untersuchten wir 30 min post coagulationem sowie 72 Std, 10 und 28 Tage nach der Exposition spaltlampen-, stereo- und rasterelektronenmikroskopisch. Nach 30 min findet sich ein zentraler Substanzdefekt von 50–80 m Durchmesser, der von einer intermediären Zone 30–60 m Breite stärkerer Zelldestruktion umgeben ist. Daran schließt sich eine periphere Zone abnehmender Zellstörung bis zu 200 m Breite an. Nach 72 Std lassen sich am Rand des zentralen Defektes entzündliche Zeichen nachweisen. Nach 10 bzw. 28 Tagen bleibt der zentrale Defekt erhalten, die oben genannten angrenzenden Zonen sind jedoch nicht mehr eindeutig abgrenzbar.

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Argon-laser coagulation in the rabbit irisDetermination of threshold dosis and respective scanning electron microscopic findings

Summary The lateral third of the iris near the chamber angle was photocoagulated after determination of the threshold dose with argon-laser energy of 0.02–4.8 J and spot diameters of 50 m. Iris lesions produced with energy levels of 1.2 J, were examined with slitlamp, dissecting microscope, and scanning electron microscope. After 30 minutes the following findings were recorded: central stromal defect 50–80 m in diameter, surrounded by an intermediary zone of 30–60 m with severe cell destruction; a peripheral zone up to 200 m in breadth with less cell fragmentation adjacent to the intermediary zone. After 72 hours the margin of the central defect showed inflammatory changes. After 10–28 days the central defect remained stable; the bordering zones described previously were no longer discernible.

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Auszugsweise vorgetragen auf der 45. Versammlung der Vereinigung Rhein-Mainischer Augenärzte am 14. und 15. Oktober 1972 in Mainz.

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Die Untersuchungen wurden in dankenswerter Weise unterstützt durch die Jung-Stiftung für Wissenschaft und Forschung und die Stiftung Volkswagen-Werk.     

Intraocularer Druck und Kammerwasserzirkulations-Untersuchungen an Kaninchenaugen nach intravenöser Verabreichung von Propranolol (Inderal®)

Zusammenfassung Der intraoculare Druck der mit Urethan anaesthesierten Kaninchen betrug 20,8 mm Hg. I.v. verabreichtes Propranolol (Inderal, 0,3 mg/kg Körpergewicht) verringerte diesen Druck auf 18,8±1,3 mm Hg. Die totale Leichtigkeit des Kammerwasserabflusses an den Kontrollaugen betrug 0,309±0,090 l/mm Hg/min, während sich nach Verabreichung von Propranolol dieser Wert auf 0,237 ±0,083 l/mm Hg/min veränderte. Die Kammerwasserproduktion in den Kontrollaugen betrug 2,16±0,78 l/min. Nach Verabreichung von Propranolol ging sie auf 1,15±0,64 l/min zurück. Die Differenzen erwiesen sich als statistisch signifikant. Die Abnahme der Abflußleichtigkeit erscheint den Daten nach geringer als die Abnahme der Kammerwasserproduktion. Dadurch erklärt sich die Verringerung des intraocularen Druckes. Aufgrund des Vergleiches der verschiedenen und von einander abweichenden Literaturangaben vermuten die Verfasser, daß das Propranolol außer der tonusverringernden Wirkung auf die -adrenergen Receptoren auch noch einen anderen Wirkungsmechanismus entfalten kann.

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Intraocular pressure and circulation of aqueous humour in rabbit eyes following intravenous administration of propranolol (Inderal^®)

Summary The intraocular pressure of rabbits under urethan anaesthesia was found to be 20.8±2.4 mm Hg. 0.3 mg/kg body weight propranolol given intravenously lowered intraocular pressure to 18.8±1.3 mm Hg. The total facility of outflow from control eyes examined at constant pressures of perfusion was 0.309 ±0.09 l/mm Hg/min, which was reduced to 0.237±0.08 l/mm Hg/min by propranolol given systemically. The formation of aqueous humor in the control eyes was 2.16±0.78 l/min, which was diminished to 1.15±0.64 l/min by propranolol. The differences are statistically significant. The decrease in facility of outflow is smaller than the decrease in formation of aqueous humour, which accounts for the lower intraocular pressure. On the basis of the various and gently differing data in the literature it is assumed that propranolol may have some other mode of action in addition to its -adrenolytic effect on receptors.

     

In-vivo-Messungen der Breite des Schlemmschen Kanals beim Hydrophthalmus

Zusammenfassung In-vivo-Messungen der Breite des Schlemmschen Kanals ergaben bei 9 Hydrophthalmusaugen einen Mittelwert von 678 m. Die Extremwerte lagen bei 600 m und 800 m. Damit unterscheiden sich diese Werte signifikant von denen, die bei Glaucoma-simplex-Augen in vivo ermittelt worden waren (Mittelwert ¯x: 542 m, Extremwerte 425 m und 625 m).Die Kanalbreite bei Hydrophthalmusaugen nimmt sowohl mit dem Hornhautdurchmesser als auch mit der Höhe des Augeninnendrucks zu.Die Erfolgsaussichten einer Trabekulotomie bei Hydrophthalmusaugen sind offenbar besser, wenn die Kanalbreite unter 650 m liegt. Die Trabekulotomie sollte deshalb so früh wie möglich ausgeführt werden.

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In vivo-measurements of the latitude of Schlemm's canal in buphthalmos

Summary In 9 cases of buphthalmos in vivo-measurements of the latitude of Schlemm's canal gave us a mean value of 678 m. The extreme values ranged between 600 m and 800 m. Therefore these values differ significantly from those measured in vivo in chronic simple glaucoma (¯x: 542 m, extreme values 425 m and 625 m). The latitude of Schlemm's canal correlates with the diameter of cornea and the rise of intra-oculare pressure.In cases of buphthalmos the success of trabeculotomy seems to be better, if the latitude of Schlemm's canal is less than 650 m. Trabeculotomy should therefore be performed as soon as possible.

     

„Aberrante“ Ganglienzellen in der Wurzel des Nervus oculomotorius des Menschen

Zusammenfassung 56 Nn. oculomotorii von 37 Erwachsenen (mittleres Alter 66 Jahre) wurden untersucht. In 25 der 56 Nerven (44,6%) bzw. bei 19 der 37 Erwachsenen (51%) wurden insgesamt 243 Ganglienzellen in der Nervenwurzel gefunden. Der mittlere Durchmesser von 100 Zellen betrug 43.7 (range: 26,8–69,8 ; größte Frequenz bei 35–45 ). Histologisch ähneln sie den sensiblen Zellen eines Spinalganglions. Es wird die Frage aufgeworfen, ob es sich um aberrante Ganglienzellen oder ein Zellsystem handelt.Der Befund eines sensiblen Ganglion mit 46 Ganglienzellen im Verlauf des N. trochlearis wird erwähnt.

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Aberrant ganglion cells in the human ocullomotor nerve

Summary 56 oculomotor nerves of 37 adult men (mean age 66 years) were examined. A total amount of 243 nerve cells were counted in 25 nerves (44.6%) that is to say in 19 men (51%). The mean diameter of 100 cells was 43.7 (range: 26.8–69.8 ,). The diameter of most of the cells fell between 35 to 45 . Histologically they look like sensory cells of a spinal ganglion. The question arises, whether these neurones represent aberrant cells or an independent neuronal grouping.The finding of a sensory ganglion in the course of the trochlear nerve with 46 nerve cells in it is mentioned.

     

Die Stereo-Ultrastruktur der Cornealoberfläche bei der Ratte

Zusammenfassung Die dreidimensionale Beschaffenheit der Cornealoberfläche der Ratte wurde mittels des Scanning Electron Microscope und anhand konventioneller elektronenmikroskopischer Schnittpräparate untersucht. Dabei konnte das Vorhandensein von Mikrovilli (0,15 breit, bis 1,0 hoch) und von Mikroplicae (0,1–0,2 breit, 0,3–0,4 hoch, 1–3 lang) nachgewiesen werden. Bei diesen Strukturen dürfte es sich um während der Desquamation entstandene Ausstülpungen der Epithelzellmembran im Bereiche der Desmosomen handeln.

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The stereo ultrastructure of the corneal surface in rat

Summary Combined morphological examination of the corneal surface of rat both with the scanning and the transmission electron microscope reveals two kinds of protrusions covering the polygonal, regularly arranged epithelial cells: Mikrovilli and Mikroplicae; the former being approximatively 0.15 large and up to 1.0 high, the latter being 0.1–0.2 large, 0.3–0.4 high and 1–3 long. These formations are with high probability the remnants of desmosomes having been formed during desquamation.

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Diese Untersuchungen wurden mit Unterstützung des Fonds National suisse de la recherche scientifique (Nr. 5322.3) durchgeführt.     

Retinal toxicity and ocular kinetics of 1-β-D-arabinofuranosyl-E-5-(2-bromovinyl)uracil in rabbits

The intraocular penetration of 1--d-arabinofuranosyl-E-5-(2-bromovinyl)uracil (BV-araU), a new antiviral drug, after oral administration, the effects of non-toxic intravitreal doses of BV-araU, and the intraocular kinetics of BV-araU after intraocular injection were studied in rabbits. The intravitreal penetration of BV-araU after oral administration was very poor: 0.11 ± 0.13 g/ml and 0.20 ±0.02 g/ml respectively in albino and pigmented rabbits 2 h after 30 mg/kg. An intravitreal injection of 200 g BV-araU caused transient electroretinographic (ERG) changes, whereas a 100-g injection and intravitreal irrigation with 20 g/ml BV-araU caused no ERG and histologic changes over the 4-week follow-up period. The half-life of the intravitreal concentration of BV-araU after an intravitreal injection was short (2.4 h). The results suggest that an intravitreal injection of 100 g BV-araU or an intravitreal irrigating solution containing 20 g/ml BV-araU is nontoxic to the retina and may be used for treatment of retinitis caused by varicella-zoster virus or herpes simplex virus type 1.     

Increased release of tenascin in tear fluid after photorefractive keratectomy

Background: Extracellular matrix protein tenascin (TN) is expressed in the anterior stroma during corneal wound healing. In this study we analysed TN release in tear fluid after photorefractive keratectomy (PRK). Methods: Tear fluid TN concentrations of ten PRK patients were measured with an immunoassay. Tear fluids were collected preoperatively and 1, 2 and 7 days after PRK. The tear fluid collection time and the volume of tears collected were registered. Because tear fluid flow was greatly increased postoperatively, tear fluid flow-corrected release (TN flux) was calculated. Results: The tear fluid flow was 4.50±0.94 l/min (mean±SEM) preoperatively, 55.48±16.70 l/min (P<0.01) on the 1st, 33.91±7.91 l/min (P<0.01) on the 2nd, and 13.79±5.49 l/min (P>0.05) on the 7th postoperative day. The preoperative TN concentration was 0.85±0.20 g/ml. On the 1st postoperative day it decreased to 0.37±0.17 g/ml (P>0.05), most likely due to the dilution effect caused by hypersecretion after PRK. The TN concentration was 0.67±0.12 g/ml (P>0.05) on the 2nd and 0.78±0.15 g/ml (P>0.05) on the 7th postoperative day. The preoperative TN flux was 5.23±1.88 ng/min. On the 1st and 2nd postoperative days the TN flux was 14.40±4.99 ng/min (P<0.05) and 22.66±6.I2 ng/min (P<0.05), respectively. On the 7th postoperative day a tendency towards decreased flux (14.00±6.02 ng/min, P>0.05) was observed. Conclusion: Although there is a minor decrease in TN concentration after PRK due to increased tear fluid flow, a significant increase in TN flux was observed. Complete reepithelialization of the ablated area was observed in all eyes at the follow-up visit on postoperative day 7.     

Evaluation of toxicity and efficacy of a combination of antineoplastic agents in the prevention of PVR

The retinal toxicity of a combination of antineoplastic drugs in free and liposome-encapsulated form was determined in the rabbit eye. Bleomycin sulfate and 5-fluorouridine were evaluated by clinical observation, electroretinogram, and histological study. Forty-five eyes were injected with combinations of various doses of bleomycin and 5-FUR in free and encapsulated form; 10 eyes served as controls. The nontoxic free dose was found to be 3.5g bleomycin and 150g 5-FUR. Liposome encapsulation increased the nontoxic dose to 4.7g bleomycin and 200g 5-FUR. Four groups of rabbits in which proliferative vitreoretinopathy had been induced were used for the efficacy study; the control group received an injection of PBS; the second group was injected with a combination of 3.5g bleomycin and 150g 5-FUR in free form; the third group was injected with the identical doses in liposome-encapsulated form; and the fourth group received encapsulated bleomycin (4.7g) and 5-FUR (200g). The dose used in Group 4 was significantly more effective (P<0.01) in preventing tractional retinal detachment and marginally more effective (P=0.054) in preventing neovascularization.Supported in part by U.S. Public Health Service grants EY07541 and EY02377 from the National Eye Institute, the National Institutes of Health Services, Bethesda, MD     

Effect of Prostaglandin E2 on aqueous humor flow in the rabbit eye

Summary The examinations were carried out in albino rabbits under urethane anaestesia. After intracameral injection of 0.5 g Prostaglandin E₂, dissolved in 10 l 10% ethanol, intraocular pressure increased by 20.5±4.9 mm Hg. Aqueous humor protein concentration in the uninjected control eyes was 0.176±0.03 g%. Thirty minutes after intracameral injection of 10 l 10% ethanol solution the concentration rose to 0.38±0.19 g-%, and after of 0.5 g Prostaglandin E₂ to 1.85 ±0.41 g% These interventions were not followed by significant changes in aqueous humor osmolarity (normal value 313.7±17.9 mOsm, after ethanol 330 5±18. 0, and after prostaglandin E₂ 329.3±6.9).In a special series of experiments the rate of aqueous humor production was determined. In the uninjected control eyes a value of 1.57±0.61 l/min was found, but after intracameral injection of 0.5 g prostaglandin E₂, 5.45±1.99 l/min.The authors draw the conclusion that prostaglandin E₂ increases intraocular tension not by enhancing aqueous humor production but by disrupting the bloodaqueous humor barrier.

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Zusammenfassung Die Untersuchungen wurden an Albinokaninchen in Urethannarkose durchgeführt. Nach Injektion von 0,5 g Prostaglandin E₂ (in 10 l10%iger Äthanollösung) in die Vorderkammer stieg der Augenbinnendruck um 20,5±-4,9 mm Hg an. Der Gesamteiweißgehalt im Kammerwasser der intakten Kontrollaugen betrug 0,176±0,03 g-%. 30 min nach Einspritzung von 10 l 10%iger Äthanollösung in die Vorderkammer erhöhte sich der Gesamteiweißgehalt auf 0,38±0,19 g-%. Diese Einwirkungen hatten keine signifikante Änderung der Kammerwasser-Osmolarität zur Folge (Normalwert 313,7±17,9 mOsm, nach Äthanol 330,5±18,1 und nach Prostaglandin E₂ 329,3±6,9).In einer besonderen Versuchsreihe wurde die Kammerwasserproduktion bestimmt. In den intakten Kontrollaugen ergab sich hierbei ein Wert von 1,57±0,61 (l/m, nach Gabe von 0,5 g Prostaglandin E₂ aber 5,45±1,99 l/min.Die Autoren ziehen den Schluß, daß Prostaglandin E₂ den Augenbinnendruck nicht durch Steigerung der Kammerwasserproduktion, sondern durch Schädigung der Blut-Kammerwasserschranke erhöht.

     

Über das Vorkommen lichtempfindlicher,fluorescierender Substanzen in verschiedenen Geweben von Rinderaugen

Zusammenfassung und Ergebnisse Papierchromatographisch wurde aus Hornhäuten, Linsen und Netzhäuten von Rindern eine nach denR _f -Werten und UV-Spektren gleiche Substanz isoliert. Sie fluorescierte im alkalischem Medium leuchtend grün, im sauren leuchtend blau. Die Absorptionsmaxima lagen in n/10 Natronlauge bei 258–260 m und bei 400 m und in n/10 Salzsäure bei 258–260 m und bei 360 m. Auffallend war die starke Lichtempfindlichkeit dieser Verbindung. Eine Identifizierung der fluorescierenden Substanz gelang nicht. Auf Grund der gefundenen UV-Spektren und derR _f -Werte in Pteridinlaufmitteln kann vermutet werden, daß es sich um ein Pteridin handeln könnte.Mit 5 Textabbildungen     

Toxicity of 1-(β-d-arabinofuranosyl)cytosine after intravitreal injection in the rabbit eye

The retinal toxicity of intravitreally injected 1-(-d-arabinofuranosyl)cytosine (cytarabine) was examined in 7 chinchilla rabbits to determine if cytarabine can be used as local therapy for vitreoretinal non-Hodgkin's lymphoma. Fractionated dose of 600 g, 1500 g, and 2700 g cytarabine in stabilized saline were given intravitreally in one eye (2 × 300 g, 5 × 300 g, and 3 × 900 g, respectively, with an interval time of 24 h) and stabilized saline in the other eye as control. Toxic effects were evaluated with biomicroscopy, direct ophthalmoscopy, fluorophotometry, electroretinography, light, and electron microscopy. Toxic effects were found with the 1500 g and 2700 g doses only. They consisted of a temporary impairment of the blood retina barrier function for fluorescein as measured by fluorophotometry and an irreversible change of the b-wave in the electroretinograms. No histopathologic changes were seen under the light microscope. Electron microscopic examination showed aberrations in the synaptic pedicles of the photoreceptor cells at a dose of 1500 g cytarabine. The results suggest that the cytarabine dose that is expected to be therapeutic for vitreoretinal non-Hodgkin's lymphoma (about 90 g given in three doses of 30 g) is non-toxic for ocular structures.Correspondence to: J.A. van Best     

The effect of the water-drinking test on aqueous humor dynamics in healthy volunteers

In 19 healthy volunteers (9 men, 10 women) we studied the effect of drinking 1000 ml of water within 10 min on aqueous humor dynamics. Fluorescein was applied topically five times, 6 h before measurements. All readings were taken during the afternoon. The Wilcoxon signed-rank test was used to evaluate the statistical relevance of the data. Aqueous humor flow was measured 60 min before (F1) and 10 min (F2), 30 min (F3), 60 min (F4) and 90 min (F5) after drinking 11 of water. Flow (mean ± SD) changed as follows: F1, 2.25 ± 1.2 ll/min ; F2, –3.29 ± 3.4 /min (P < 0.0000); F3, 1.69 ± 1.0 gml/min (P=0.007); F4, 2.39±0.9 l/min (P=0.25); F5, 2.64±0.9 l/min (P=0.02). Three to four days later the identical procedure was performed in each individual: F1, 2.06 ± 1.0 l/min F2, –3.12 ± 2.4 l/min (P < 0.0000); F3, 1.09 ± 0.6 l/min (P < 0.0001); F4, 1.76 ± 0.6 l/min (P=0.15); F5, 2.54±0.8 l/min (P=0.01). The correlation coefficient for the left and night eyes (F1–F5, both days) was r=0.85. The mean flow in the 19 healthy volunteers during the afternoon hours was 2.25 ± 1.0 l/min. Water load consistently led to a reflux of unbound fluorescein into the eye about 10 min later. This is documented as a negative flow. Ninety minutes after drinking 1000 ml of water there is a significant increase in flow, which is in contrast to the normal diurnal curve of aqueous humor dynamics. Water load causes hydremia and an increase in episcleral venous pressure. Fluorophotometry together with water load may be useful to study the aqueous humor dynamics in healthy and glaucomatous eyes and eyes with ocular hypertension.     

Contact diode laser: High power application through fiberoptic cutting tips

Diode laser energy has been applied through a fiberoptic probe using a power setting of 2.5 watts (W) in the continuous mode. In this study we employed high-power diode laser energy (4 to 12 W, continuous wave) to incise ocular tissue through a fiberoptic probe using 100m and 300m tips. The retina was photocoagulated with a 300m orb tip. No bleeding occurred at the incision sites. Histologic evaluation revealed coagulation into the healthy tissue ranging from 10 to 50m.     

Effect of oxygen on relaxation of retinal pericytes by sodium nitroprusside

Background: This study addresses whether oxygen modulates the relaxation induced in retinal pericytes by sodium nitroprusside (SNP), a nitric oxide (NO) donor that stimulates the NO/guanylate cyclase pathway. Methods:Bovine retinal pericytes were cultured on silicone. On the silicone surface, basal pericyte contractile tone induces wrinkles. Drug-induced changes in pericyte contractile tone were assessed by changes in the number of wrinkles. The effects of 100% nitrogen (hypoxia) and 100% oxygen (hyperoxia) were studied on: (a) the basal tone of quiescent pericytes, (b) the relaxation to 3 and 10 M SNP or 1 M forskolin, and (c) the recontraction that followed the washout of 3 M SNP or 1 M forskolin. Results: Neither hypoxia nor hyperoxia had any apparent influence on pericyte basal tone, on forskolin-induced relaxation, or on pericyte recontraction after a forskolin-induced relaxation. In hypoxia, relaxations to SNP 3 M (P<0.05) and 10 M (P<0.01) were significantly more pronounced than in hyperoxia. Hypoxia also reduced the recontraction after an SNP-induced relaxation (P<0.001). Conclusion: Oxygen modulates the relaxation of bovine retinal pericytes evoked by SNP (guanylate cyclase-mediated), but not the relaxation induced by forskolin (adenylate cyclase-mediated). These results suggest that in the retinal capillary circulation an interaction between oxygen and the NO/guanylate cyclase pathway modulates pericyte tone, and thus potentially blood flow.     

Experimental evaluation of online optical coherence pachymetry for corneal refractive surgery

Purpose Online optical coherence pachymetry (OCP) allows to monitor central changes of the corneal cross section intraoperatively. In this experimental evaluation the validity of the optical measurements for corneal refractive surgery was assessed.Methods Online OCP based on low-coherence interferometry with a wavelength of 1310 nm and a measurement frequency of 74 Hz was directly integrated in a clinical excimer laser. In 16 patients the central corneal thickness was measured with online OCP and ultrasound pachymetry (US). Furthermore, the ablation characteristics were assessed in corneoscleral discs unsuitable for transplantation (n=12) and PMMA samples (n=18).Results Online OCP was possible in all patients and materials studied. The mean central corneal thickness was 537±31 m (OCP) and 546±33 m (US). The corneal reproducibility was ±4.3 m (coefficient of variation [CV] 0.8%) with online OCP and ±3.7 m (CV 0.68%) with US. The reproducibility in PMMA samples was ±1.0 m (CV 0.16%). There was a significant correlation between online OCP and US measurements (r=0.93, P<0.001). The mean difference was 9.1 m or 1.69% (P=0.01), and the limits of agreement (95% CI) ranged from –15 m to 33 m. There was a significant linear relationship (r=0,95; P<0.001) between the calculated and the optically determined ablation depth with online OCP. Also ablation depth measurements in PMMA correlated positively with spectrophotometric values (r=0.98; P<0.001).Conclusion In this experimental evaluation, online OCP revealed to be a precise and reproducible method to assess the central corneal thickness and its changes intraoperatively. This could be important to monitor incisional and excimer laser-based corneal refractive procedures, such as PRK or LASIK.The authors have no commercial, proprietary or financial interest in any research or devices described in the presented study     

Die Latenzzeit (retino-thalamo-cortical) beim Kaninchen bei Reizung mit energiegleichem verschiedenfarbigem Licht

Zusammenfassung Bei Reizung des Kaninchenauges mit energiegleichen Lichtern verschiedener Spektralbereiche zeigte sich, daß nur mit Rotlicht _max 641 m kein Elektroretinogramm und keine spezifischen Aktionspotentiale des Corpus geniculatum laterale und der Sehrinde abzuleiten sind.Gleiche Latenzzeiten der Augen- und Gehirnaktionspotentiale ergeben sich bei Anwendung von Lichtreizen gleicher Energie, 1,7·10^–2 W, im kurzwelligeren Spektralbereich (_max 479 m blau, 538 m grün, 585 m gelb).Die Feststellung, daß kurze Einzellichtreize eines Spektralbereiches über 600 m gleicher Energie am Auge und Gehirn keine Aktionspotentiale erstehen lassen, legt nahe, daß Rotlicht beim Kaninchen keinen Seheindruck hinterläßt.Mit 7 TextabildungenDie Untersuchungen wurden mit freundlicher Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

The resistance of the trabecular meshwork to aqueous humor outflow

A theoretical model is presented that is able to explain for the first time the pressure drop across the trabecular meshwork. The ramified flow paths in the subendothelial region of the trabecular meshwork can be interpretated as a filter bed. Data from transmission electron microscope (TEM) photographs are the starting point of the theoretical consideration. Taking shrinkage of the sections into account, the pressure gradient across the subendothelial region amounts to 0.05 mm Hg. As these canaliculi are coated by a film of glycosaminoglycans (GAGs), the pressure drop is presumably a function of the film thickness. Only film thicknesses of 0.35 m lead to pressure gradients in the experimentally verified magnitude. As the whole filter bed probably does not contribute to the filtration but only about 10%, the pressure drop specified is reached when the GAG coating is 0.25 m. As these values seem to be fairly realistic, it can be concluded that the subendothelial region of the juxtacanalicular meshwork (about 2 m thickness) can be regarded as the locus generis of aqueous humor outflow resistance.