Changes in intraocular pressure and aqueous humor dynamics of normal human eyes after topical application of bunazosin hydrochloride

The effects of topically applied bunazosin hydrochloride, a recently developed highly selective alpha 1-adrenergic antagonist, on intraocular pressure, pupillary diameter, aqueous protein concentration, anterior chamber volume, aqueous flow rate and tonographic outflow facility were investigated in eight normal human volunteers. A single application of 0.1% bunazosin hydrochloride caused a significant unilateral reduction in the intraocular pressure from 30 minutes through 4 hours after the application, with a maximum decrease of 2.0 +/- 0.5mmHg (mean +/- SEM) below the contralateral control eyes at 2 hours post-application. Neither pupillary diameter, anterior chamber volume nor outflow facility was affected by the drug application. Both aqueous protein concentration measured with a flare-cell meter and aqueous flow rate determined by fluorophotometry were unaltered. The mechanism of intraocular pressure reduction appears to be an increase in uveoscleral outflow and/or a decrease in episcleral venous pressure.     

Topical vanadate lowers intraocular pressure in rabbits

In unanesthetized rabbits the topical application of vanadate lowered intraocular pressure. Tonographic outflow facility and episcleral venous pressure were unaltered by topical vanadate. As estimated from the tonographic data, aqueous humor flow was reduced by approximately 30%. Posterior chamber aqueous humor ascorbate increased in the eye receiving topical vanadate, and this was compatible with a decreased rate of aqueous humor flow. Topical vanadate did not alter anterior chamber aqueous humor protein or cyclic AMP. In five monkeys intraocular pressure was also significantly reduced by topical vanadate.     

The canine eye: in vitro dissolution of the barriers to aqueous outflow.

Facility of aqueous outflow and time-dependent changes in its hyaluronidase-sensitive and hyaluronidase-resistant components were evaluated in freshly excised canine eyes by constant pressure quantitative aqueous perfusion. Mean baseline facility of outflow was 0.24 microliter/min/mm Hg. With prolonged perfusion at constant intraocular pressure, facility of outflow was observed to increase almost linearly for at least 3 hr and continued to increase for up to 10 hr, reaching a maximum several times the initially measured facility. Perfusion with pooled dog aqueous humor did not prevent the time-dependent increase in measured facility. Rapid exchange of anterior chamber contents with perfusion solution alone produced an immediate threefold increase in facility, again followed by a gradual time-dependent facility increase. Rapid exchange of anterior chamber contents with hyaluronidase produced an immediate fivefold increase in facility with stabilization of measured facility over 3 hr and subsequent perfusion. The time-dependent changes in measured facility of outflow or "washout phenomenon" appeared to result from the gradual dissolution of the hyaluronidase-sensitive component of the barriers to aqueous outflow in the canine eye.     

Studies on the mechanism of action of timolol and on the effects of suppression and redirection of aqueous flow on outflow facility

Long-term use of drugs that suppress aqueous humor formation, such as timolol and dorzolamide, or that redirect aqueous humor outflow from the trabecular meshwork, such as prostaglandin F2alpha analogues, could cause underperfusion of the trabecular meshwork and a secondary decrease in outflow facility. We investigated the mechanism of suppression of aqueous humor formation by timolol in monkey eyes by measuring aqueous humor ascorbate levels. We also determined whether suppression of aqueous humor formation with and without redirection of aqueous humor away from the trabecular meshwork could lead to a subsequent reduction in outflow facility, and whether this reduction was correlated with increased fibronectin levels in anterior chamber aqueous humor. In cynomolgus monkeys, unilateral dose/aqueous humor formation response curves were generated for timolol, dorzolamide, and a combination of timolol + dorzolamide. Aqueous humor formation and/or outflow facility were measured in both eyes after approximately four days, four weeks and seven weeks of twice daily treatment with 3.5 microg timolol + 1.0 mg dorzolamide to one eye and 30% DMSO to the other. In some monkeys, 5 microg prostaglandin F2alpha-isopropyl ester (PG) was added to timolol + dorzolamide for 4-week treatments. Intraocular pressure and corneal endothelial transfer coefficients (k(a)) were also measured at four weeks. Aqueous humor fibronectin levels were determined in four monkeys after approximately 9.5 weeks of timolol + dorzolamide treatment. Aqueous humor formation, intraocular pressure, and aqueous humor ascorbate levels were also determined in rhesus monkeys at baseline and after a single unilateral topical administration of 25 microg timolol. Compared to baseline for the same eye, aqueous humor formation was significantly decreased in treated eyes at all doses of timolol and at 1.8 and 4 mg dorzolamide. Compared to the opposite control eye, aqueous humor formation was lower in treated eyes after 3.5 and 5 microg timolol and after all doses of dorzolamide. Aqueous humor formation after treatment with 3.5 microg timolol + 1.0 mg dorzolamide was decreased in treated vs. control eyes, after four days and was suppressed in both treated and control eyes after four weeks of treatment, but not when PG was added. There was no difference in k(a) values with or without the addition of PG. Intraocular pressure was significantly lower in both treated and control eyes vs. baseline after approximately 6.5 weeks treatment with timolol + dorzolamide when taken 2 hr after the last dose and after approximately 3.5 weeks treatment with timolol + dorzolamide + PG when measured 6 hr after the last dose. Outflow facility after treatment with timolol + dorzolamide was unchanged after four days, tended to be lower in the treated vs. control eyes after four and seven weeks, and was significantly lower in treated vs. control eyes after four weeks treatment with timolol + dorzolamide + PG (0.352 +/- 0.052 vs. 0.515 +/- 0.096 microl min(-1) mmHg(-1), p < or = 0.02). Both treated vs. control eye aqueous humor fibronectin levels were below the level of detection for our assay (0.01 microg ml(-1)). The 25 microg timolol dose decreased ipsilateral, but not contralateral intraocular pressure (12.6 +/- 1.7 vs. 15.2 +/- 0.9; p < 0.05) and aqueous humor formation (1.40 +/- 0.08 vs. 2.03 +/- 0.09 microg ml(-1), p < or = 0.01). There was no difference in anterior chamber ascorbate levels in treated vs. control eyes or compared to their respective baselines. Our findings indicate that timolol affects neither ciliary epithelial transport of ascorbate nor aqueous fibronectin levels. Our data also indicate that decreasing aqueous humor formation over a period of time can lead to reduction in outflow facility, particularly when combined with therapy that redirects aqueous from the trabecular meshwork. Future intraocular pressure-lowering therapies for glaucoma may better be directed at enhancing flow through the trabecular pathway as opposed to decreasing aqueous humor formation or rerouting aqueous humor away from the trabecular meshwork.     

Effects of topical epinephrine on aqueous humor dynamics in the cat

The purpose of this study was to investigate, in cats, the effects of topical epinephrine on aqueous humor dynamics as measured by the non-invasive method of fluorophotometry and by other methods. Measurements were carried out on 12 cats before and after one week of twice daily treatment with 2% epinephrine hydrochloride to one eye. Aqueous flow and outflow facility were determined using fluorophotometry. Uveoscleral outflow was calculated from these results and was evaluated with anterior chamber perfusion of FITC-dextran. Outflow facility also was measured by tonography. Epinephrine-treated eyes, compared with their baseline values, showed a 31% reduction in intraocular pressure (P<0.001), a 23% reduction in aqueous flow (P<0.05), a 60% increase in fluorophotometric outflow facility (P<0.05), and a 43% increase in tonographic outflow facility (P<0.05). Treated eyes, compared with contralateral control eyes, showed a 27% reduction in IOP (P<0.005), a 25% reduction in aqueous flow (P<0.005), a 38% increase in fluorophotometric outflow facility (P<0.05), and a 34% increase in tonographic outflow facility. When evaluated by both fluorophotometry and FITC-dextran tracer methods, epinephrine had no significant effect on uveoscleral outflow. It was concluded that, in cats treated with topical epinephrine twice daily for a week, a reduction in intraocular pressure is induced by an increase in outflow facility and decrease in aqueous flow.     

The effect of intraocular pressure on resistance to outflow

As intraocular pressure is increased, facility of aqueous outflow decreases. For many years this fact was obscured by the often used procedure of experimental perfusion into the anterior chamber. Anterior chamber perfusion deepens the anterior chamber; retrodisplacement of the iris-lens diaphragm tenses the trabecular mesh with resulting facility increase and obscuration of the facility-reducing effect of pressure. The probable mechanism of facility reduction under experimental conditions is apposition of the inner wall of Schlemm's canal to the outer wall. Since facility of aqueous outflow is not constant at different intraocular pressures, application of Poiseuille's law to the eye must be restricted to each pressure investigated.     

Prostaglandin F2 alpha increases uveoscleral outflow in the cynomolgus monkey

Cynomolgus monkeys were treated topically in one eye twice daily with prostaglandin F2 alpha-l-isopropylester (PGF2 alpha-IE) for nine doses. On treatment day 4, 3 hr after the seventh dose, intraocular pressure (IOP) in the treated eye was reduced by 65% compared to the controls, to less than 5 mmHg. On treatment day 5, 3 hr after the ninth dose, total outflow facility was determined by two-level constant pressure perfusion of the anterior chamber. Immediately thereafter, uveoscleral outflow was determined by intracamerally infusing [125I]- or [131I]-albumin and fluoresceinated dextran, and calculating the volume of anterior chamber fluid required to have deposited the quantity of tracer recovered from the various ocular and periocular tissues. Simultaneously, trabecular outflow was determined by calculating the volume of anterior chamber fluid required to have deposited the quantity of tracer recovered from the general circulation. Total facility was approximately 50% higher in treated than in control eyes, but the effect was variable, of marginal statistical significance, and perhaps due to increased pseudofacility or uveoscleral facility. Uveoscleral outflow was approximately two to three-and-a-half times higher in treated than in control eyes, the magnitude of the effect being dependent upon the timing and pressure at which the perfusion was conducted. Trabecular outflow was reduced by approximately 75% in the treated eyes relative to control so that the proportion of total outflow comprised by trabecular outflow in the treated eyes was only one third that in the controls. Total aqueous flow was slightly (approximately 20%) but not significantly reduced in the treated eyes. The IOP lowering effect of PGF2 alpha in the cynomolgus monkey is due largely if not exclusively to an increase in uveoscleral outflow of aqueous humor, with aqueous outflow being redirected from the trabecular to the uveoscleral route.     

Effectiveness of trabeculectomy in glaucoma.

A follow-up study of 90 eyes in 60 patients subjected to trabeculectomy between 1967 and 1972 showed that intraocular pressure was controlled at the onset in 84% of the eyes, and eventually controlled in over 97%. Only 11% of the eyes required further medication and 5.5% further surgery. Subconjunctival drainage was established by means of a bleb in 91%. Trabeculectomy produced a high significant fall in intraocular pressure (P less than .001) and a parallel rise in aqueous outflow facility. The absolute fall in intraocular pressure was constant whether the preoperative pressure was high or low and whether or not the postoperative pressure remained above 20 mm Hg. This method was virtually free of major operative and postoperative complications when used appropriately; and it can be modified during the operation to deal with peripheral anterior synechiae. The anterior chamber remained formed or, if lost, was speedily re-formed. The anterior chamber rarely flattened postoperatively.     

Increased intraocular pressure following topical azide or nitroprusside.

In rabbits the topical administration of sodium azide (NaNs) or sodium nitroprusside (SNP) increased intraocular pressure in a dose-response manner. These agents, which activate guanylate cyclase, elevated cyclic GMP in the aqueous humor. Systemic blood pressure and pulse were not altered. Tonographic outflow facility was unchanged, suggesting an increase in aqueous humor flow as the mechanism for the elevation of intraocular pressure. Posterior chamber aqueous humor ascorbate concentration was decreased in the eye receiving the NaN3 or SNP. Systemic pretreatment with phenoxybenzamine, an alpha-adrenergic blocking agent, prevented the elevation of intraocular pressure observed following NaN3 and SNP. Pretreatment with systemic indomethacin, propranolol, or acetazolamide or the topical application of atropine or epinephrine failed to alter the elevation of intraocular pressure by either NaN3 or SNP.     

Serum obstruction of aqueous outflow in enucleated eyes

We perfused enucleated human eyes via the anterior chamber by the constant pressure technique. Infusion of human serum into the anterior chamber of enucleated human eyes for 30 minutes at 23 mm Hg pressure induced a 42% decrease in facility of outflow, which was not relieved by irrigation of the anterior chamber with balanced salt solution or alpha-chymotrypsin. Diluted serum also reduced the facility of outflow. Measured in a glass viscometer, diluted serum had less viscosity than undiluted, but interfered with outflow from the eye more than anticipated on the basis of viscosity alone. When we used lens depression to induce tension on the iridocorneal angle to simulate the effects of contraction of the ciliary muscle, outflow facility increased in control eyes that had not been exposed to serum and in serum-perfused eyes. However, the partial obstruction to outflow that had been induced by serum persisted. Normal serum components may become adsorbed or entrapped in the aqueous outflow system so as to obstruct outflow, and this may result in secondary glaucoma in eyes with chronic uveitis.     

Effects of systemic desmopressin on aqueous humor dynamics in rabbits

Intravenous desmopressin, a synthetic antidiuretic hormone, resulted in a dose-dependent increase in intraocular pressure (IOP) in rabbits. IOP was increased 3.6 +/- 0.8 mm Hg 6 hr following injection of desmopressin 200 mUnits/kg with the increase lasting over 10 hr. IOP returned to baseline 24 hr after the injection. Systemic blood pressure, plasma osmolarity and arterial blood gases were not altered by desmopressin. The increased IOP was not associated with alterations in measured outflow facility or episcleral venous pressure. Five hours after desmopressin injection, calculated aqueous humor flow was increased approximately 57%. Aqueous humor ascorbate measurements for calculation of flow to diffusion ratios and anterior chamber fluorophotometry also were consistent with an increased rate of aqueous humor formation as the mechanism for the IOP elevation. Desmopressin administration did not increase aqueous humor protein or aqueous humor cyclic AMP concentration. Systemic pretreatment with indomethacin only partially blocked the IOP increase. Systemic pretreatment with demeclocycline completely blocked the desmopressin-induced increase in IOP.     

The canine eye: in vitro studies of the intraocular pressure and facility of aqueous outflow

Possible interdependence of facility of aqueous outflow and intraocular pressure was examined by quantitative aqueous perfusion at four levels of intraocular pressure in 69 canine eyes, freshly excised post-mortem. Statistically similar, time-dependent increases in facility of outflow occurred over steps of increasing and decreasing, and at constant intraocular pressue. Pretreatment with intracameral hyaluronidase diminished the rate of facility increase, reducing it to 20% or less in one third of the eyes so perfused. Observed increases in canine facility of outflow with changing intraocular pressure appeared to result primarily from "washout" of the hyaluronidase-sensitive component of the barriers to aqueous outflow and not from direct effects of the intraocular pressure.     

Adenosine 3',5'-monophosphate increases the outflow of aqueous humor from the rabbit eye.

Direct administration of cyclic-AMP into the anterior chamber increases the outflow facility of the eye for aqueous humor. This is consistent with the hypothesis that catecholamines lower the intraocular pressure of the rabbit eye, at least in part, by a cyclic-AMP-mediated mechanism. This mechanism is active in the outflow channels and increases the rate at which aqueous humor leaves the anterior chamber.     

Effects of topical PGF2 alpha on aqueous humor dynamics in cynomolgus monkeys

Single topical applications of prostaglandin F2 alpha (PGF2 alpha) tromethamine salt to living cynomolgus monkey eyes reduced intraocular pressure (IOP). Twice daily topical application was far more effective, so that after the 7th 50 micrograms or 100 micrograms dose on day 4, IOP fell 40-50%, to 8-10 mm Hg. Following twice daily application of 50 or 100 micrograms for greater than 3 days: (1) no increase in total outflow facility could be demonstrated by 2-level constant pressure perfusion or Schiotz tonography; (2) no decrease in aqueous humor formation rate could be demonstrated by fluorophotometry--rather, aqueous flow may have increased; (3) anterior chamber aqueous humor protein concentration was unaltered, but entry of intravenously injected fluorescein into the cornea and anterior chamber tended to increase; (4) there was a weak but sometimes statistically significant miosis of up to approximately 0.5 mm. We conclude that in the cynomolgus monkey: (1) PGF2 alpha is a potent ocular hypotensive agent with only very weak miotic and blood-aqueous barrier-disrupting effects; (2) the ocular hypotensive action of PGF2 alpha is definitely not due to increased conventional outflow facility or decreased aqueous production, but probably to increased uveoscleral drainage of aqueous humor.     

负压吸引眼压效应的实验研究

目的 探讨负压吸引对实验动物眼压的影响及机理。方法 新西兰大白兔18只,右眼进行负压吸引,左眼作对照。观察眼压、房水动力学及房角组织病理结构改变。结果 负压吸引可以降低眼压,相应持续30d。负压吸引组的房水外流速度增加,组织病理学结构显示负压吸引后房水静脉扩张、Fantan间隙变宽,巩膜和小梁网出现间隙。结论 负压吸引可以降低眼压,该效应与房水外流速度增加有关。     

Uveoscleral outflow using different-sized fluorescent tracers in normal and inflamed eyes

Sodium fluorescein and fluorescinated dextrans (FD) of selected molecular weights were combined and perfused into the anterior chamber of normal and inflamed eyes of cynomolgus monkeys. The eyes were dissected into iris, anterior and posterior uvea, anterior and posterior sclera, retina and intraocular fluids (excluding aqueous). Each tissue was homogenized and centrifuged and the supernatant was run through a gel-filtration column to separate the fluorescent tracers. Each of the resultant peaks was quantitated and facility of uveoscleral outflow was determined. In control eyes the calculated facility of uveoscleral outflow was very similar with all tracers (from 0.047-to 0.052 microliter min-1 mmHg-1) and each tracer was found in highest concentration in the anterior sclera and anterior uvea. In inflamed eyes the calculated facility of uveoscleral outflow increased two- to five-fold with each tracer (0.12-; 0.17-; 0.29-; and 0.24 microliter min-1 mmHg-1 with fluorescein, and the fluorescinated dextrans of MWs 4000, 40,000 and 150,000, respectively). Each tracer was found in the anterior sclera and uvea in inflamed eyes whereas the posterior sclera and uvea contained predominantly the higher molecular-weight tracers (MWs 40,000 and 150,000). It is concluded that iridocyclitis causes an increase in uveoscleral outflow by increasing the permeability of the anterior uvea to all tracers and fluid. Small tracers may then diffuse into uveal blood vessels or across the sclera, yielding lower values for uveoscleral outflow. Of the four tracers studied, the optimal tracer size for studying uveoscleral outflow in either normal or inflamed eyes is MW 40,000.     

Uveoscleral aqueous outflow in the rhesus monkey: importance of uveal reabsorption.

The uveal absorption of aqueous humor at two different intraocular pressures was measured in rhesus monkeys by sampling vortex vein blood during anterior chamber perfusion of Ringer's solution containing both fluorescein and 125I albumin. At 20 mm. Hg, an excess of fluorescein equivalent in amount to 0.45 microliter/min. of anterior chamber perfusate and an excess of 125I albumin equivalent to 0.18 microliter/min. of perfusate was found in the vortex vein blood compared to systemic blood. At 32 mm. Hg, an excess of 0.86 microliter/min. of fluorescein and 0.26 microliter/min. of 125I albumin was measured. The increase in fluorescein absorption at the higher intraocular pressure was significant (0.025 less than p less than 0.05), with a uveal outflow facility of 0.034 microliter/min./mm. Hg. At an intraocular pressure of 20 mm. Hg, uveal aqueous outflow is less than 10% of total aqueous outflow. The pressure dependence of the uveal uptake of fluorescein implies an aqueous reabsorption into the uveal vessels by ultrafiltration. Uveoscleral aqueous "outflow" appears to consist of intraocular uveal reabsorption of water and small molecules from the aqueous, with only larger molecules like albumin actually leaving the eye through posterior scleral vessel perforations. This reabsorption plays a minor role in intraocular pressure regulation under normal conditions.     

The effect of colchicine on the rate of formation of aqueous humour and the gross outflow facility in the albino rabbit

Colchicine, a naturally occurring plant alkaloid which prevents the polymerisation of cytoplasmic microtubules, lowers the intraocular pressure after topical administration or intravitreal injection. In this study wer have examined the effect of topically administered colchicine on the rate of formation of aqueous humour and the gross outflow facility in the albino rabbit eye. The disappearance of [¹⁴C]inulin from the anterior chamber was measured to calculate the rate of aqueous humour formation and in a separate group of animals the gross outflow facility determined using a constant pressure perfusion technique.Topically administered colchicine (10, 20 and 40 μg/eye) inhibited the rate of aqueous humour formation dose-dependently. The mean rate of formation in control eyes was 3·68 ± 0·09 μl/min (n = 16) decreasing to 1·8 μl/min (n = 9) in eyes treated with 40 μg colchicine. Furthermore, the gross outflow facility of colchicine treated (10 μg/eye) eyes (0·49 ± 0·03 μl/min/mmHg) was significantly greater (P < 0·05) than that of contralateral control eyes (0·39 ± 0·03 μl/min/mmHg).The pharmacological evidence available indicates that colchicine is acting via mechanisms of microtubule disruption to produce an ocular hypotensive response, suggesting that microtubules may be involved in the formation of aqueous humour and possibly the maintainance of cell shape and form in the outflow vessels of the anterior chamber.     

The effect of topical PGF2 alpha on uveoscleral outflow and outflow facility in the rabbit eye.

Prostaglandin F2 alpha (PGF2 alpha) is a powerful ocular hypotensive agent in rabbit, cat, dog, monkey and human. In cynomolgus monkeys, the intraocular pressure (IOP) lowering is due to increased uveoscleral outflow (Fu). Because the anatomy of the rabbit outflow apparatus differs significantly from that of the primate, we sought to determine whether the mechanism of the PGF2 alpha-induced IOP fall was the same. PGF2 alpha tromethamine salt (PGF2 alpha-TS) (50 micrograms) applied to one eye of 14 conscious rabbits produced a significant IOP fall of 7.4 +/- 0.9 mmHg (P less than 0.001). In untreated control eyes, Fu determined from the quantity of intracamerally perfused [125I]albumin found in the ocular and periocular tissues accounted for 5-8% of total aqueous outflow. In 15 unilaterally PGF2 alpha-treated rabbits, after 4-6 hr dosing Fu was 49 +/- 14% higher in the treated than in the contralateral control eyes. Total outflow facility of outflow from the anterior chamber to the general circulation were measured concurrently in 11 rabbits using a two-level constant pressure perfusion and isotope accumulation technique. Both facilities tended to be higher in the treated eyes than in the controls, with a strong correlation between drug-induced changes in total facility and changes in facility of flow to blood (r = 0.85, P less than 0.001). In eight rabbits treated unilaterally with 50 micrograms PGF2 alpha-TS, the fluorophotometrically determined aqueous formation rate was probably not decreased relative to control eyes. Protein levels in the aqueous humor were approximately eight-fold higher in PG-treated vs. control eyes, suggesting a drug-induced compromise of the blood-aqueous barrier.(ABSTRACT TRUNCATED AT 250 WORDS)     

The immediate response in applanation pressure to intravenous acetazolamide in primary glaucomas and glaucoma suspects.

The decays in the applanation pressures of both eyes, after a reduction of the aqueous secretion by means of intravenous acetazolamide, are studied with respect to shape and steepness by comparison with reference curves calculated from different values of the facility of aqueous outflow. The pressure decays in three out of four eyes with narrow-angle glaucoma exhibited "breaks" possibly resulting from a stepwise reopening of the chamber angle during the decompression. Twenty patients with intraocular hypertension and open angles could be divided into two groups according to the facility of aqueous outflow (in mul mmHg-1 min-1), estimated from approximately matching reference curves: Nine patients with facilities above 0.15 had normal visual fields and nearly indentical pressure curves of the two eyes. Out of 11 patients with facilities below 0.15, seven patients had glaucomatous visual field defects and excavated optic discs. The pressure curves of eye pairs in this low facility group showed asymmetry, and breaks were seen in approximately half of the curves. These might be caused by changes in the outflow facility due to a decompression of collapsed outflow channels. However, the morphological basis for such an interpretation is not as well founded as in the case of narrow-angle glaucoma.