Posterior optic buttonholing prevents intraocular pressure peaks after cataract surgery with primary posterior capsulorhexis.

BACKGROUND: The performance of a primary posterior capsulorhexis (PPC) with and without posterior optic buttonholing (POBH) may significantly influence the intraocular pressure (IOP) after cataract surgery in age-related cataract patients. METHODS: The prospective randomized clinical study was performed at the department of Ophthalmology, Medical University of Vienna, Austria. Thirty consecutive cataract patients with bilateral same-day cataract surgery (60 eyes) under topical anesthesia were enrolled. In randomized order, cataract surgery with combined PPC/POBH was performed in one eye; in the other eye, cataract surgery was performed with PPC and in-the-bag implantation of the intraocular lens (IOL). Standardized IOP measurements by Goldmann applanation tonometry were performed preoperatively, 1, 2, 4, 6, 8 and 24 hours postoperatively, as well as 1 week and 1 month postoperatively. RESULTS: During the first 24 hours after surgery, all IOP measurements were significantly lower in eyes with combined PPC/POBH when compared to eyes with solitary PPC (p < 0.001). No IOP peaks of more than 27 mmHg were observed with combined PPC/POBH. In contrast, in eyes with PPC and in-the-bag IOL implantation, seven patients had an IOP peak of more than 27 mmHg and four IOP peaks of more than 30 mmHg. One week and 1 month postoperatively, IOP measurements were statistically comparable, and no significant differences could be observed between the two groups (p > 0.05). CONCLUSION: Postoperative IOP peaks after cataract surgery with sole PPC can be effectively prevented by the buttonholing of the IOL through the posterior capsulorhexis.

Effects of vitamin C on hyperoxia-induced reduction of retinal blood flow.

OBJECTIVE: Breathing of 100% oxygen causes vasoconstriction in retinal vessels paralleled by a decrease in blood flow. The mechanism underlying this effect is still unclear, but may be related to the increased generation of reactive oxygen species during hyperoxia. Thus, the purpose of the present study was to investigate whether vitamin C, an agent with strong antioxidative properties, modifies the retinal vasoconstrictor response to hyperoxia. METHODS: A randomized, double-masked, placebo controlled, two-way crossover study was performed in 12 healthy young volunteers. 100% oxygen was administered via a breathing mask for 12 min. Retinal blood flow was measured before and during oxygen breathing in the presence of either ascorbic acid (3 g) or placebo on two different study days. Retinal blood flow was determined based on measurement of retinal vessel diameters and red blood cell velocity. RESULTS: Breathing of 100% oxygen induced a pronounced reduction of retinal arterial (-7.6%+/-6.5%) and venous diameters (-12%+/-6%). Hyperoxia induced vasoconstriction was not altered by co-administration of vitamin C (-8.6%+/-4.8% in arteries and -15%+/-7% in veins). Likewise, RBV and retinal blood flow decreased in response to oxygen by -24%+/-53% and -38%+/-42%. Again, the reduction of retinal hemodynamic parameters was not altered by co-administration of vitamin C. CONCLUSIONS: Oxygen induced blood flow response in the human retina is not altered by a single dose of vitamin C in healthy, young subjects. Whether this indicates that ROS are not involved in hyperoxia induced vasoconstriction of retinal vessels or is related to other factors has yet to be determined.

Acute effects of intravenously administered ethanol on retinal vessel diameters and flicker induced vasodilatation in healthy volunteers.

There is evidence from several vascular beds that acute alcohol consumption causes ocular hypotension and peripheral vasodilatation. The current study investigated the effects of intravenously administered ethanol on retinal vessel diameters and on flicker induced retinal vasodilatation. For this purpose, ethanol (0.35 g/kg) or placebo (physiologic saline solution) was administered intravenously for 40 min in a randomized, double masked, two way cross-over design to 12 healthy male volunteers. Retinal vessel diameters and flicker induced vasodilatation were measured before administration of ethanol as well as 30, 50, 90 and 130 min after the start of infusion with a retinal vessel analyzer. Intraocular pressure, systemic blood pressure and blood ethanol concentration were determined at the same time points. Intravenous administration of ethanol increased blood ethanol concentration from 0.0 g/l to 0.56+/-0.10 g/l. Ethanol reduced IOP, but did not change ocular perfusion pressure. After cessation of the infusion blood ethanol concentration started to drop reaching a blood ethanol concentration of 0.22+/-0.06 g/l 130 min after the start of infusion. Retinal arterial diameters increased significantly after administration of ethanol by a maximum of +4.2+/-4.0%, whereas no change was observed in retinal veins. Neither arterial nor venous diameters were influenced by administration of placebo. Flicker stimulation induced a significant dilatation in both arterial and venous diameters. Ethanol did not change flicker responses in arteries or in retinal veins. In conclusion, intravenous administration of ethanol increases retinal arterial diameters, whereas venous diameters remained unchanged. Whether this is related to a direct vasodilator effect or to a hitherto unidentified mechanism remains to be clarified.

Strategies for reducing variance in laser Doppler flowmetry measurements.

BACKGROUND: Scattering of blood flow data as assessed with laser Doppler flowmetry (LDF) in humans is a problem in many studies using this technique. We set out to reduce variability in LDF data by eliminating the effect of the total returning light level (DC) on LDF parameters in the choroid through partial regression analysis. METHODS: In 20 healthy subjects, choroidal blood flow parameters were measured at different DC values using a portable confocal LDF device. We used two different strategies to reduce scattering of data eliminating the effect of yield, which is defined as DC/gain. On the one hand, we used a previously described method based on a third-order polynomial fit, which combines all obtained data. On the other hand, we applied a new method based on a linear fit for each individual subject. RESULTS: Variability of data during changes in DC is higher for LDF parameters volume and flow than for velocity. Both methods were successful in reducing scattering of LDF parameters with varying DC. CONCLUSIONS: The present study indicates that both methods to correct for changes in yield were successful in reducing the variability of LDF measurements. When systematic changes in DC occur after an intervention, one needs to be careful in interpreting the obtained data and it remains to be shown if either of the two techniques is capable of correcting for this effect. The approach presented here may, however, represent an effective, easily applicable and valid approach to reduce scattering of data from using LDF to assess blood flow in the posterior pole of the human eye.

Macular morphology after cataract surgery with primary posterior capsulorhexis and posterior optic buttonholing.

PURPOSE: To evaluate possible changes in macular morphology after cataract surgery with combined primary posterior capsulorhexis and posterior optic buttonholing in comparison to conventional in-the-bag intraocular lens (IOL) implantation. DESIGN: Prospective randomized study. METHODS: Fifty consecutive age-related cataract patients with normal macular morphology and function waiting for bilateral cataract surgery were enrolled. Cataract surgery with combined primary posterior capsulorhexis and posterior optic buttonholing was performed in one eye; in the fellow eye cataract surgery was performed with in-the-bag IOL implantation, leaving the posterior lens capsule untouched. Optical coherence tomography measurements were performed one week and one month postoperatively. RESULTS: During follow-up, no statistically significant changes of macular morphology could be observed in any of the tested patients. Mean central retinal thickness, minimum and maximum retinal thickness, and central retinal volume were all statistically comparable between the eyes with combined primary posterior capsulorhexis and posterior optic buttonholing and the control eyes (P > .05). Best-corrected visual acuity was full in all patients (Snellen 20/25 and better). No cases of subclinical macular edema were observed. CONCLUSION: Cataract surgery with combined primary posterior capsulorhexis and posterior optic buttonholing apparently does not increase the risk for postoperative macular edema in patients with a normal macula, since no cases of biomicroscopically noticeable macular edema with visual loss were observed in the first 1,000 eyes with primary posterior capsulorhexis/posterior optic buttonholing cataract surgery and no case of subclinical macular edema was found in this prospective randomized study.

Comparison of the effect of Viscoat and DuoVisc on postoperative intraocular pressure after small-incision cataract surgery.

PURPOSE: To evaluate the effect of Viscoat (sodium chondroitin sulfate 4%-sodium hyaluronate 3%) and DuoVisc (Viscoat and Provisc [sodium hyaluronate 1%]) on postoperative intraocular pressure (IOP) after bilateral small-incision cataract surgery. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This prospective randomized study comprised 60 eyes of 30 consecutive patients with age-related cataract in both eyes. Each patient's eyes were randomly assigned to receive Viscoat or DuoVisc during cataract surgery. DuoVisc is a packet containing 2 ophthalmic viscosurgical devices (OVDs): the dispersive Viscoat, which was used for intraocular lens (IOL) implantation. In the Viscoat group, the Viscoat was used during the entire surgery. The intraocular pressure (IOP) was measured preoperatively as well as 1, 6, and 20 to 24 hours postoperatively. RESULTS: One and 6 hours postoperatively, the mean IOP was significantly higher in the Viscoat group than in the DuoVisc group (25.8 mm Hg and 20.5 mm Hg, respectively, at 1 hour and 24.7 mm Hg and 21.1 mm Hg, respectively, at 6 hours) (P<.05). At 20 to 24 hours, the mean IOP was not statistically significantly different between the 2 groups. Intraocular pressure spikes to 30 mm Hg or higher occurred in 4 eyes in the DuoVisc group and 11 eyes in the Viscoat group (P<.05). CONCLUSIONS: Viscoat caused significantly higher IOP increases and significantly more IOP spikes than DuoVisc in the early postoperative period. Therefore, if Viscoat is used during cataract surgery, an additional cohesive OVD should be used for IOL implantation.

Anterior chamber depth and change in axial intraocular lens position after cataract surgery with primary posterior capsulorhexis and posterior optic buttonholing.

PURPOSE: To compare axial position changes of the intraocular lens (IOL) by measuring anterior chamber depth (ACD) after small-incision cataract surgery with primary posterior continuous curvilinear capsulorhexis (PPCCC) and posterior optic buttonholing (POBH) of the IOL and after conventional cataract surgery with phacoemulsification and in-the-bag IOL implantation. SETTING: Department of Ophthalmology, Medical University of Vienna, Austria. METHODS: This prospective comparative study comprised 23 patients (46 eyes) with age-related cataract who had bilateral cataract surgery and implantation of an acrylic IOL (YA-60BB, Hoya). In randomized order, cataract surgery with PPCCC and POBH of the IOL was performed in 1 eye of each patient. In the fellow eyes, conventional phacoemulsification cataract surgery with in-the-bag IOL implantation was performed. The ACD was measured 1 to 2, 6, and 24 hours as well as 7 and 30 days postoperatively using high-resolution partial coherence laser interferometry. A baseline measurement was taken preoperatively in all patients. RESULTS: Ten patients completed 10 to 12 months of follow-up. Postoperatively, the axial IOL position was stable in eyes with PPCCC-POBH (P>.05). In contrast, a significant axial shift of the IOL in the anterior direction was observed in control eyes with in-the-bag IOL implantation (P<.001). The resulting refractive shift was significantly higher in control eyes than in eyes with PPCCC-POBH (P<.001). CONCLUSION: Combined PPCCC and POBH for cataract surgery significantly reduced postoperative anterior movement of the IOL.

Altered nitric oxide system in patients with open-angle glaucoma.

OBJECTIVE: To investigate the ocular blood flow response to systemic nitric oxide synthase inhibition in patients with primary open-angle glaucoma. METHODS: In 12 patients with glaucoma and 12 age-matched control subjects, subfoveal choroidal blood flow, optic nerve head blood flow, ocular fundus pulsation amplitude, intraocular pressure, and systemic hemodynamic parameters were measured at baseline and after inhibition of nitric oxide synthase by intravenous administration of NG-monomethyl-L-arginine. RESULTS: The increase in blood pressure in response to NG-monomethyl-L-arginine was comparable between the 2 study cohorts. In patients with glaucoma, the decrease of optic nerve head blood flow (P = .03) and fundus pulsation amplitude (P<.001) during nitric oxide synthase inhibition was significantly less pronounced than in healthy control subjects. A tendency toward a reduced response in choroidal blood flow was seen (P = .051 between groups) in patients with glaucoma. CONCLUSIONS: This is the first in vivo study providing evidence for an altered ocular L-arginine/nitric oxide system in patients with glaucoma. Normalization of the ocular nitric oxide production may be beneficial in terms of normalization of ocular blood flow and neuroprotection of retinal ganglion cells.

Intravenous administration of clonidine reduces intraocular pressure and alters ocular blood flow.

AIM: To evaluate the effect of intravenously administered clonidine on ocular blood flow in healthy volunteers. METHODS: A randomised, double-masked, placebo-controlled, two-way crossover study was performed in 12 healthy young volunteers. Clonidine (0.2 microg/kg/min) or placebo was administered intravenously over 10 minutes. The effects of clonidine were studied at baseline and up to 150 minutes after infusion. Ocular haemodynamics were measured using laser Doppler flowmetry, laser Doppler velocimetry and a retinal vessel analyser. RESULTS: Clonidine significantly decreased mean arterial pressure (MAP) and intraocular pressure (IOP). Calculated ocular perfusion pressure decreased significantly by -8.7+/-8.7% after infusion of clonidine (p<0.01 vs placebo). Retinal arterial diameters increased by +4.4+/-2.7% (p = 0.012 vs placebo), whereas no significant change was observed in retinal veins. Red blood cell velocity decreased by -16+/-14% (p<0.01 vs placebo) after infusion of clonidine. Hence, calculated retinal blood flow decreased by -14+/-12% (p = 0.033 vs placebo). Choroidal blood flow increased by +18+/-19% (p<0.01 vs placebo) and optic nerve head blood flow increased by +16+/-23% (p = 0.046 vs placebo) 30 minutes after administration of clonidine but both returned to baseline thereafter. CONCLUSION: The short-time increase in choroidal and optic nerve head blood flow indicates a transient vasodilatory effect of clonidine due to an unknown mechanism. The decrease in retinal blood flow indicates clonidine-induced vasoconstriction in the retinal microvasculature.

Postoperative course of intraocular pressure after cataract surgery with combined primary posterior capsulorhexis and posterior optic buttonholing.

PURPOSE: To evaluate the natural course of intraocular pressure (IOP) after cataract surgery with combined primary posterior continuous curvilinear capsulorhexis (PPCCC) and posterior optic buttonholing (POBH) of the intraocular lens (IOL) in adult patients. SETTING: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. METHODS: Fifty consecutive patients with age-related cataract awaiting cataract surgery under topical anesthesia in both eyes were enrolled prospectively. In randomized order, cataract surgery with combined PPCCC and POBH was performed in 1 eye. In the fellow eye, cataract surgery was performed conventionally with in-the-bag IOL implantation and the posterior lens capsule kept intact. Standardized IOP measurements by Goldmann applanation tonometry were performed 1, 2, 4, 6, 8, and 24 hours postoperatively. Follow-up IOP measurements were taken at 1 week and 1 month. Twenty-five patients received 1-time IOP-lowering medication immediately after cataract surgery; the other 25 did not receive IOP-lowering drops. RESULTS: During the first 24 hours postoperatively, no significant differences in IOP were observed between the PPCCC-POBH group and the conventional surgery group (P>.05). No IOP peaks greater than 27 mm Hg were observed in any eye. One week and 1 month postoperatively, no significant differences in IOP were found between groups (P>.05). The use of IOP-lowering drops significantly reduced postoperative IOP. However, no IOP spikes >27 mm Hg were found with and without the use of IOP-lowering drops. CONCLUSION: The course of IOP after cataract surgery with combined PPCCC and POBH showed the technique to be as safe as conventional cataract surgery with in-the-bag IOL implantation.

Influence of infusion volume on the ocular hemodynamic effects of peribulbar anesthesia.

PURPOSE: To test the hypothesis that ocular blood-flow response to peribulbar anesthesia can be reduced by using a smaller volume of anesthetic mixture. SETTING: Departments of Ophthalmology and Clinical Pharmacology, Medical University of Vienna, Vienna, Austria. METHODS: Twenty patients scheduled for bilateral age-related cataract surgery were enrolled in a prospective randomized balanced observer-masked crossover study. Two study days with a 2 mL injection volume or 5 mL injection volume used for peribulbar anesthesia were scheduled. On 1 study day, patients received the 1-dose regimen and on the other study day, when the contralateral eye had surgery, patients received the other injection volume. On both study days, the anesthetic mixture consisted of an equal amount of lidocaine, bupivacaine, and hyaluronidase independently of the injection volume. Intraocular pressure (IOP), blood pressure, and pulse rate were measured noninvasively. Ocular fundus pulsation amplitude (FPA) and peak systolic and end diastolic flow velocities in the central retinal artery were measured with laser interferometry and color Doppler imaging, respectively. The results were recorded as means +/- SD. RESULTS: Peribulbar anesthesia increased IOP and reduced FPA and flow velocities in the central retinal artery. The effects on IOP (5 mL, 35.1% +/- 16.0%; 2 mL, 14.1% +/- 14.1%; P<.001) and ocular hemodynamic parameters (FPA: 5 mL, -17.5% +/- 7.8%/2 mL, -7.3% +/- 7.2%, P<.001; peak systolic velocity: 5 mL, -19.5% +/- 10.7%/2 mL, -10.6% +/- 9.8%, P = .013; end diastolic velocity: 5 mL, -16.7% +/- 6.2%/2 mL, -8.4% +/- 7.3%, P = .005) were more pronounced with the 5 mL injection volume than with the 2 mL injection volume. CONCLUSIONS: An injection volume of 2 mL instead of 5 mL reduced the ocular blood-flow response to peribulbar anesthesia. This procedure may be used in patients with ocular vascular disease to reduce the incidence of anesthesia-induced ischemia and loss of vision.

Effects of moderate changes in intraocular pressure on ocular hemodynamics in patients with primary open-angle glaucoma and healthy controls.

PURPOSE: There is some indirect evidence for altered autoregulation in patients with glaucoma, but only a few studies have measured ocular blood flow directly during changes in ocular perfusion pressure. The present study was designed to compare pulsatile choroidal blood flow and optic nerve head (ONH) blood flow during moderate increases in intraocular pressure (IOP) in patients with primary open-angle glaucoma (POAG) and normal controls. DESIGN: Two nonrandomized studies comparing blood flow responses in glaucoma patients and controls in an open design. PARTICIPANTS AND CONTROLS: Sixteen patients with POAG glaucoma and 16 healthy gender-matched and age-matched controls were included in the choroidal blood flow experiments. The ONH blood flow experiment was performed in 14 POAG patients and 14 healthy gender-matched and age-matched controls. METHODS: In the first study, pulsatile choroidal blood flow was assessed by laser interferometric measurement of fundus pulsation amplitude (FPA). In the second study, ONH blood flow was measured using laser Doppler flowmetry. In both cohorts, the IOP was increased stepwise by 10 and 20 mmHg using a suction cup. MAIN OUTCOME MEASURES: Fundus pulsation amplitude and ONH blood flow. RESULTS: The baseline values of FPA and ONH blood flow were lower in glaucoma patients as compared with age-matched and gender-matched healthy controls. In patients with POAG, FPA decreased by -4.5+/-5.8% and -11.3+/-4.9% during elevation of IOP of 10 and 20 mmHg, respectively. These results were not different from the results in healthy controls, where FPA decreased by -5.1+/-3.4% and -12.2+/-4.9% at the 2 pressure levels (P = 0.23 between groups). Optic nerve head blood flow showed no changes during the increase of IOP of 10 and 20 mmHg in either of the 2 groups (glaucoma patients, +2.1+/-14.7% and -0.8+/-15.2%; healthy controls, +4.3+/-12.0% and +0.2+/-14.2%; P = 0.83 between groups). CONCLUSIONS: The present study does not provide evidence for altered autoregulation in patients with POAG during a moderate increase in IOP. However, these results do not necessarily contradict the concept of vascular dysregulation in glaucoma.

Effects of adenosine on intraocular pressure, optic nerve head blood flow, and choroidal blood flow in healthy humans.

PURPOSE: There is evidence from a variety of animal studies that the adenosine system plays a role in the control of intraocular pressure (IOP) and ocular blood flow. However, human data on the effect of adenosine on IOP and choroidal and optic nerve blood flow are not available. METHODS: The effect of stepwise increases in doses of adenosine (10, 20, and 40 micro g/kg per minute, 30 minutes per infusion step) on optic nerve head blood flow, choroidal blood flow, and IOP was determined in a placebo-controlled double-masked clinical trial in 12 healthy male volunteers. Blood flow in the optic nerve head and choroid was measured with laser Doppler flowmetry. In addition, fundus pulsation amplitude in the macula (FPAM) and the optic nerve head (FPAO) were assessed with laser interferometry. RESULTS: Adenosine induced a small but significant decrease in IOP (at 40 microg/kg per minute: 12% +/- 13%), which was significant versus placebo (P = 0.046). In addition, adenosine induced a significant increase in choroidal blood flow (P < 0.001) and optic nerve head blood flow (P = 0.037), and FPAM (P = 0.0014) and tended to increase FPAO (P = 0.057). At the highest administered dose, the effect on choroidal hemodynamic parameters between 14% and 17%, whereas the effect on optic nerve hemodynamic parameters was between 3% and 11%. CONCLUSIONS: These data are consistent with adenosine inducing choroidal and optic nerve head vasodilatation and reducing IOP in healthy humans. Considering the neuroprotective properties of adenosine described in previous animal experiments the adenosine system is an attractive target system for therapeutic approaches in glaucoma.

Role of endothelin-1 in choroidal blood flow regulation during isometric exercise in healthy humans.

PURPOSE: There is evidence that the choroid has some autoregulatory capacity in response to changes in ocular perfusion pressure (OPP). The mediators of this response are hitherto unidentified. The hypothesis for the current study was that endothelin (ET)-1 and/or angiotensin (ANF)-II may be involved in choroidal vasoconstriction during an increase in OPP. METHODS: To test this hypothesis a randomized, double-masked, placebo-controlled, three way crossover study was performed in 12 healthy male volunteers. Subjects received on different study days intravenous infusions of the specific ET(A) receptor antagonist BQ-123, the angiotensin converting enzyme inhibitor enalapril or placebo. During these infusion periods subjects were asked to squat for 6 minutes. Choroidal blood flow was measured using a confocal laser Doppler flowmeter and ocular perfusion pressure (OPP) was calculated from mean arterial pressure and intraocular pressure. RESULTS: BQ-123 and enalapril had no effect on basal blood pressure, pulse rate, intraocular pressure, or choroidal blood flow. During isometric exercise, a pronounced increase in mean arterial pressure paralleled by an increase in OPP was observed. Although choroidal blood flow slightly increased during squatting, the increase was much less pronounced than the increase in OPP, indicating some regulatory potential of the choroid. Enalapril did not alter the choroidal pressure-flow relationship during isometric exercise, but BQ-123 induced a significant leftward shift of the pressure-flow curve (P < 0.001). CONCLUSIONS: The present data indicate that ET-1, but not ANG II, plays a role in choroidal blood flow regulation during isometric exercise in healthy humans. Hence, impaired choroidal autoregulation in patients with ocular vascular diseases may arise from an altered endothelin system. Further studies in such patients are warranted to verify this hypothesis.

Role of NO in choroidal blood flow regulation during isometric exercise in healthy humans.

PURPOSE: Nitric oxide (NO) is an important regulator of basal choroidal blood flow. Animal experiments indicate that NO is also involved in choroidal blood flow regulation during changes in ocular perfusion pressure and inhibition of NO synthase (NOS) has been reported to shift choroidal pressure-flow curves to the right. The hypothesis for the study was that inhibition of NOS may influence choroidal blood flow during isometric exercise. METHODS: To test this hypothesis, a randomized, double-masked, placebo-controlled, three-way crossover study was performed in 12 healthy male volunteers. Subjects received on different study days intravenous infusions of N(G)-monomethyl-L-arginine (L-NMMA), phenylephrine, or placebo. During these infusion periods, subjects were asked to squat for 6 minutes. Choroidal blood flow was assessed with laser Doppler flowmetry, and ocular perfusion pressure (OPP) was calculated from mean arterial pressure and intraocular pressure. RESULTS: L-NMMA and phenylephrine increased resting OPP by 10% and 13%, respectively, but only L-NMMA reduced resting choroidal blood flow (-17%, P < 0.001). The relative increase in OPP during isometric exercise was comparable with all drugs administered. Isometric exercise increased choroidal blood flow during administration of placebo and phenylephrine, but not during administration of L-NMMA (P < 0.001 vs. placebo). CONCLUSIONS: These data indicate that NO plays an important role in the regulation of choroidal blood flow during isometric exercise.

Partial antagonism of endothelin 1-induced vasoconstriction in the human choroid by topical unoprostone isopropyl.

BACKGROUND: There is increasing evidence that reduced ocular blood flow plays a role in the pathogenesis of glaucoma. In patients with normal-tension glaucoma, ocular blood flow abnormalities may be associated with dysfunction of the endothelin 1 (ET-1) regulation system. OBJECTIVE: To test the hypothesis that unoprostone, a topical docosanoid, may affect ET-1--induced vasoconstriction in the human choroid. METHODS: In a placebo-controlled, randomized, double-masked, 2-way crossover design, ET-1 (2.5 ng/kg per minute for 150 minutes) was administered intravenously to 24 healthy individuals. Thirty minutes after the start of ET-1 infusion, 1 drop of unoprostone or placebo was instilled into the right eye. After another 30 minutes, 2 drops of unoprostone or placebo was topically administered. This procedure was continued and the dose was increased further until 4 drops of unoprostone or placebo was reached. Subfoveal and pulsatile choroidal blood flow were assessed using laser Doppler flowmetry and laser interferometric measurement of fundus pulsation amplitude, respectively. RESULTS: Administration of exogenous ET-1 decreased choroidal blood flow (mean +/- SEM, 17% +/- 2%; P<.001) and fundus pulsation amplitude (mean +/- SEM, 19% +/- 2%; P<.001). This effect was significantly blunted when topical unoprostone was coadministered (mean +/- SEM decrease in choroidal blood flow, 7% +/- 2%; P =.04 vs. placebo; mean +/- SEM decrease in fundus pulsation amplitude, 12% +/- 2%; P<.001 vs. placebo). CONCLUSION: There is a functional antagonism between ET-1 and topical unoprostone in the choroidal vasculature. CLINICAL RELEVANCE: Our findings of a functional antagonism between ET-1 and topical unoprostone in the choroidal vasculature may be important in vascular eye diseases associated with increased ET-1.

Effect of laser photocoagulation on the retinal vessel diameter in branch and macular vein occlusion.

OBJECTIVE: To investigate the response of retinal vessel diameters to photocoagulation treatment and their role for the success of laser treatment in patients with retinal vein occlusion. METHODS: The study included 14 patients with branch vein occlusion or macular vein occlusion. The ophthalmologic examination included best-corrected visual acuity, biomicroscopy, fundus photography, and fluorescein angiography. Retinal vessel diameters were quantified before and after laser photocoagulation using a retinal vessel analyzer. MAIN OUTCOME MEASURE: Retinal vessel diameters. RESULTS: In cases manifesting macular vein occlusions, no significant change of the vessel diameter in any vessel was observed during the follow-up period. In the group with branch vein occlusion, all vessels tended to constrict after the laser photocoagulation. The effect of laser treatment on retinal vessel diameters was significant for superotemporal (P =.045, analysis of variance [ANOVA]) and inferotemporal branch veins (P =.03, ANOVA). Vasoconstriction was more pronounced in the occluded branch veins (P =.009, ANOVA) compared with the nonaffected veins (P =.12; ANOVA). The change of visual acuity after 3 months was correlated with the change of vessel diameter 3 months after laser treatment for occluded venular branches (r = 0.78, P =.02, linear regression). There was no correlation between the number of laser burns and the change of vessel diameters in the affected veins in this period (r = 0.12, P =.75, linear regression). CONCLUSIONS: Our results show that retinal photocoagulation in patients with branch vein occlusion has a vasoconstrictive effect on occluded veins. The correlation between the change in visual acuity and the change in vessel diameter indicates that branch vein constriction after photocoagulation may be an early indicator of the success of laser treatment.

Comparison of ultrasound pachymetry and partial coherence interferometry in the measurement of central corneal thickness.

PURPOSE: To compare central corneal thickness (CCT) measurements obtained with 3 ultrasound pachymeters and with partial coherence interferometry (PCI) and evaluate the effect of repeated contact by a pachymetry probe on corneal thickness. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: Central corneal thickness was measured in 20 eyes of 20 healthy volunteers with 3 different ultrasound pachymeters (DGH 500, DGH Technology Inc.; SP 2000, Tomey Inc.; Paxis, Biovision Inc.) and with PCI. In each eye, 5 measurements with PCI were followed by 5 measurements with each ultrasound pachymetry device and another 5 measurements with PCI. RESULTS: The mean CCT measured with the DGH 500, SP 2000, and Paxis was 541.0 microm, 539.2 microm, and 545.1 microm, respectively. Although the differences among the 3 ultrasound pachymetry devices were within 6.0 microm, they were statistically significant (P<.05). The PCI measurements were significantly smaller (P <.05) than the ultrasound measurements: 518.8 microm before and 517.5 microm after repeated contact with the ultrasound pachymetry probe (P <.05). The mean precision (standard deviation) was 0.77 microm for PCI and between 2.40 microm and 3.58 microm for ultrasound pachymetry measurements. The correlation coefficients for the intraobserver variability were 0.999 for PCI and between 0.987 and 0.995 for ultrasound pachymetry measurements. CONCLUSIONS: Partial coherence interferometry was the more precise method of measuring CCT and had better intraobserver variability. Repeated contact by a pachymetry probe reduced corneal thickness by 1.3 microm. However, the reason for the smaller measurements with PCI than with ultrasound pachymetry remains unclear.

Measurements in the peripheral retina using LDF and laser interferometry are mainly influenced by the choroidal circulation.

PURPOSE: Two laser based methods for the assessment of ocular hemodynamics in humans have been investigated: laser Doppler flowmetry (LDF) and laser interferometric measurement of fundus pulsation amplitude (FPA). When the laser with either of the two methods is focused onto the fovea it is obvious that only choroidal blood flow contributes to the signals. When the laser is, however, directed to other parts of the retina the situation is more complex. Whereas the retina shows a pronounced vasoconstrictor response to systemic hyperoxia the effect in the choroid is small. We therefore investigated the effect of 100% O2 breathing on results as obtained with the above mentioned techniques at different fundus locations. METHODS: Twelve healthy subjects were included. Four 15-minutes 100% O2 breathing periods were scheduled for each subject. During two of these breathing periods LDF was performed at the fovea (ChBFf) and at a fundus location approximately 7.5 degrees nasally to the fovea (ChBFp), respectively. During the other two periods FPA was assessed at the same fundus locations (FPAf, FPAp). RESULTS: ChBFf tended to decrease during 100% oxygen breathing (6 +/- 4%), but this effect was not significant. The decrease in ChBFp (10 +/- 4%), was comparable. FPAf (10 +/- 2%; P < 0.001) and FPAp (13 +/- 2%; P < 0.001) decreased significantly during systemic hyperoxia, but again there was no difference in the response obtained at the two fundus locations. CONCLUSION: When LDF and FPA are applied at the peripheral retina the obtained signal is mainly influenced by the choroidal circulation.

Effect of NO synthase inhibition on retinal vessel reaction to isometric exercise in healthy humans.

PURPOSE: It has been shown that retinal blood flow is autoregulated, meaning that flow is independent of perfusion pressure within a certain range. We tested the hypothesis that nitric oxide (NO) synthase inhibition alters the response of retinal arterial and venous vessels during isometric exercise. METHODS: In this study, nine healthy subjects were included. Each subject received the NO synthase inhibitor Ng-monomethyl-l-Arginine (l-NMMA, the α-receptor agonist phenylephrine or placebo intravenously on three study days. Retinal vessel diameter was assessed with the retinal vessel analyser (RVA), at baseline and during a squatting period of 6-7 min in absence or presence of l-NMMA, phenylephrine or placebo. RESULTS: Mean arterial pressure (MAP) and pulse rate (PR) increased significantly during all pretreatment squatting periods (p < 0.001) Retinal venous and arterial diameters showed a continuous decrease during squatting (p < 0.001). Phenylephrine increased MAP and PR but did not alter the retinal vessel diameter response to squatting. Administration of l-NMMA lead to a significant decrease in venous diameter before isometric exercise (p = 0.004). In addition, the retinal venous diameter response during administration of the NO synthase inhibitor was less pronounced than during phenylephrine or placebo (p < 0.001). CONCLUSION: Our study confirms that NO plays an important role in the control of retinal vascular tone at rest. In addition, the present data indicate a role of NO in retinal autoregulation, because the response of retinal venous diameters was altered after NO synthase inhibition. The nature of involvement, however, appears to be complex and requires further studies.