Outflow facility studies in the perfused human ocular anterior segment

Erickson-Lamy, Kristine; Rohen, Johannes W.; Grant, W. Morton

doi:10.1016/0014-4835(91)90024-9

Cited by 52 publications

(35 citation statements)

References 8 publications

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“…25 The aqueous outflow decreased in a linear fashion with increased perfusion pressure. 11,12 Grant and colleagues 25 proposed that the apposition of SC inner wall and outer wall contributed to the increasing resistance as well as abnormal resistance in glaucoma. Extensive SC wall apposition began to develop at relatively low pressures (20-25 mm Hg) in the living eye.…”

Section: Discussionmentioning

confidence: 99%

“…10 Reduced SC size may be associated with elevated IOP because the dimension of SC is closely related to trabecular outflow. [10][11][12] Past observations of reduced SC size and its correlation with outflow facility were obtained in cadaveric eyes. Therefore, characterization of the in vivo morphologic effects of PGF2a analogs on the pressure sensitive outflow pathway, especially SCs, may help us elucidate the ocular hypotensive mechanism of these drugs.…”

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confidence: 99%

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Expansion of Schlemm's Canal by Travoprost in Healthy Subjects Determined by Fourier-Domain Optical Coherence Tomography

Chen¹,

Huang²,

Zhang³

et al. 2013

Invest. Ophthalmol. Vis. Sci.

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PURPOSE.To determine the effect of travoprost 0.004% on Schlemm's canal (SC) in healthy human eyes using Fourierdomain optical coherence tomography (FD-OCT).METHODS. Twelve healthy volunteers were recruited for a double-blind, placebo-controlled, randomized, and paired comparison study. Right eyes of subjects were randomly assigned to receive either travoprost 0.004% or placebo; the contralateral eye received the other treatment. FD-OCT imaging of SC and measurements of IOP were carried out before and at 1, 2, 4,6,8,12,24,36, 48, 60, 72, and 84 hours after eye drop instillation.RESULTS. After instillation of travoprost eye drops, IOP gradually reduced, and the SC lumens expanded, while those values remained unchanged in placebo treated eyes. At 8 hours after the travoprost administration, the mean SC area increased 90.30% and 90.20%, respectively, in the nasal and temporal quadrant of the treated eyes as compared with the placebo group. The SC area and IOP showed a similar pattern of changes at most time points examined. In travoprost-treated eyes, a statistically significant correlation between SC area and IOP is observed (r ¼ À0.2817; P ¼ 0.0004). Measurements of the SC area showed sufficient repeatability and reproducibility.CONCLUSIONS. SC can be noninvasively imaged and quantitatively assessed in the living healthy human eye by FD-OCT. Travoprost treatment leads to SC lumen expansion accompanied by a drop of IOP in the healthy eye, likely as a result of the enhancement of pressure sensitive trabecular meshwork outflow induced by travoprost. (Invest Ophthalmol Vis Sci.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Expansion of Schlemm's Canal by Travoprost in Healthy Subjects Determined by Fourier-Domain Optical Coherence Tomography

Chen¹,

Huang²,

Zhang³

et al. 2013

Invest. Ophthalmol. Vis. Sci.

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“…Bárány (1964) initially developed the 2-level constant pressure perfusion technique for living monkey eyes to avoid possible influences of changes in eye parameters (e.g., P e , spontaneous IOP [P 0 ] or aqueous humor formation [AHF]) on C measurements. However, since these eye parameters do not exist in cultured anterior segments, 1-level constant pressure perfusion (Erickson-Lamy et al, 1991) and constant flow rate perfusion (Johnson and Tschumper, 1987) are typically used to determine C in organ culture. Based on different perfusion techniques, two basic formulas derived from the Goldmann equation are used to calculate C: (A) C=(F 2 -F 1 )/(P 2 -P 1 ), which is usually used in 2-level constant pressure perfusion either in living animals or in cultured anterior segments (F 1 or F 2 represents F at P 1 [lower perfusion pressure] or P 2 [higher perfusion pressure]); (B) C=F/P, which is usually used in 1-level constant pressure perfusion or constant flow rate perfusion in cultured anterior segments (P, perfusion pressure; P e is ignored in this formula because it is assumed to be zero in the cultured anterior segments).…”

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confidence: 99%

Factors affecting outflow facility calculations

Tian

Gabelt

et al. 2006

Experimental Eye Research

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Outflow facility (C), a ratio of outflow rate (F) to relevant pressure, is an important indication of outflow resistance in the ocular drainage pathway. The higher the C, the lower the outflow resistance. According to the classic Goldmann equation, C=F/(IOP-P e )(IOP, intraocular pressure; P e , episcleral venous pressure). Since anterior chamber (AC) perfusions directly measure outflow and are less affected by scleral creep and rigidity or changes in uveal blood content than repeated tonography in living eyes, they are widely used to determine C in living animals or cultured anterior segments from enucleated eyes. Bárány (1964) initially developed the 2-level constant pressure perfusion technique for living monkey eyes to avoid possible influences of changes in eye parameters (e.g., P e , spontaneous IOP [P 0 ] or aqueous humor formation [AHF]) on C measurements. However, since these eye parameters do not exist in cultured anterior segments, 1-level constant pressure perfusion (Erickson-Lamy et al., 1991) and constant flow rate perfusion (Johnson and Tschumper, 1987) are typically used to determine C in organ culture. Based on different perfusion techniques, two basic formulas derived from the Goldmann equation are used to calculate C: (A) C=(F 2 -F 1 )/(P 2 -P 1 ), which is usually used in 2-level constant pressure perfusion either in living animals or in cultured anterior segments (F 1 or F 2 represents F at P 1 [lower perfusion pressure] or P 2 [higher perfusion pressure]); (B) C=F/P, which is usually used in 1-level constant pressure perfusion or constant flow rate perfusion in cultured anterior segments (P, perfusion pressure; P e is ignored in this formula because it is assumed to be zero in the cultured anterior segments). A comparison of C values calculated using Formula B and the data obtained during 2-level constant pressure perfusion in vivo or in vitro requires the following modifications: C=F 1 /(P 1 -P 0 ) or C=F 2 /(P 2 -P 0 ) where F 1 or F 2 is due to the change in pressure from P 0 to P 1 or P 2 (P 0 is assumed to be stable during short-term perfusions in vivo and is zero in vitro). C values from the same eye and the same perfusion are often quite different when calculated by the two formulas, since Formula A calculates C for the change in pressure from P 1 to P 2 , whereas Formula B calculates C either for the change in pressure from P 0 to P 1 or P 2 in living eyes or for a given pressure (P 1 or P 2 ) in cultured segments. However, the difference has not been clearly stated in previous studies, so that confusion might occur when comparing C values obtained by the two formulas. Additionally, C at different pressures may also be affected by factors physiologically unrelated to the formulas. To determine factors that may affect C values and to evaluate the significance of these factors in aqueous humor dynamics research, we compared C values calculated by Formulas A and B based on some previous perfusion experiments.

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“…The isolated, perfused anterior segment of primate and bovine eyes is an established method for studying aqueous humor outflow [28, 92, 95, 96, 97]. Perfusion of the anterior segment of bovine eyes with detached iris, ciliary body and ciliary muscle at a pressure of 8.8 mm Hg yielded a constant outflow rate of 6–8 µl/min with an outflow facility of 0.87 µl·mm Hg/min and an outflow resistance of 1.15 mm Hg·min/µl.…”

Section: The Perfused Anterior Segmentmentioning

confidence: 99%

Regulation of Trabecular Meshwork Contractility

Stumpff

Wiederholt²

2000

Ophthalmologica

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Ample evidence supports the theory that trabecular meshwork possesses smooth-muscle-like properties. Trabecular meshwork cells express a large number of transporters, channels and receptors, many of which are known to regulate smooth-muscle contractility. It has been shown that trabecular meshwork can be induced to contract and relax in response to pharmacological agents. In the model of the bovine eye, confirmed in some cases by experiments on primates, agents that contract trabecular meshwork reduce outflow. On the cellular level, this is coupled with depolarization and a rise in intracellular calcium. Relaxation of trabecular meshwork, on the other hand, appears to be coupled to a stimulation of the maxi-K channel, inducing hyperpolarization and a closure of L-type calcium channels. No significant differences between cells from a human and a bovine source emerged, either in classical measurements of membrane voltage, in measurements of intracellular calcium or patch-clamp experiments. Thus, pharmacological agents that relax trabecular meshwork seem promising candidates for further research – the ultimate goal being an improvement of glaucoma therapy in humans.

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Outflow facility studies in the perfused human ocular anterior segment

Cited by 52 publications

References 8 publications

Expansion of Schlemm's Canal by Travoprost in Healthy Subjects Determined by Fourier-Domain Optical Coherence Tomography

Expansion of Schlemm's Canal by Travoprost in Healthy Subjects Determined by Fourier-Domain Optical Coherence Tomography

Factors affecting outflow facility calculations

Regulation of Trabecular Meshwork Contractility

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