Flow after prostaglandin E1 is mediated by receptor-coupled adenylyl cyclase in human anterior segments.

PURPOSE: To assess the effect of prostaglandin (PG) F2alpha and PGE1 on flow through the trabecular meshwork in organ preserved human anterior segments. METHODS: Isolated human anterior segments were perfused under standard conditions at a constant pressure of 10 mm Hg, while flow was continuously monitored. After a stabilization period, 6 consecutive concentrations of PGs were administered. cAMP levels were determined in the perfusate at baseline conditions and at 10(-6) M PG. RESULTS: Perfusion with concentrations ranging from 10(-10) to 10(-5) M PGE1 resulted in a dose-dependent increase in flow (P < 0.0001), reaching a plateau of a 26% increase at 10(-7) M. Perfusion with PGF2alpha or placebo (Eagle's minimum essential medium) did not influence baseline flow. cAMP produced by human anterior segments increased from 4.8+/-0.6 pmol x 30 min(-1) per anterior segment at baseline to 19.2+/-4.8 pmol x 30 min(-1) per anterior segment after perfusion with 10(-6) M PGE1 (P < 0.005). Perfusion with 10(-6) M PGF2alpha did not influence baseline cAMP production. Perfusion with 10(-5) M GDP-beta-S, an inhibitor of G protein, before and in combination with 10(-6) M PGE1 completely inhibited the increase in flow and cAMP production as observed after PGE1 alone. Perfusion with 10(-5) M GDP-beta-S alone did not affect baseline cAMP production. CONCLUSIONS: In organ preserved perfused human anterior segments, flow and cAMP production in the perfusate are not mediated by receptor-coupled adenylyl cyclase activity at baseline conditions. Perfusion with PGE1 is suggested to increase flow through the trabecular meshwork by stimulation of prostanoid EP2 receptor subtype, EP4 receptor subtype, or both, coupled to G(s) protein, inducing activation of the adenylyl cyclase catalytic unit. The results may indicate a physiological role for EP2 receptor subtype, EP4 receptor subtype, or both in the modulation of flow through the trabecular meshwork after stimulation.

Outflow characteristics of isolated anterior segments of human eyes.

PURPOSE: To evaluate the relationship between intraocular pressure (IOP) and flow through the trabecular meshwork in isolated anterior segments of human eyes. Outflow facility (C) is thought to decrease proportionally with increasing IOP in human eyes in vivo and in vitro. METHODS: Twenty-nine eviscerated human anterior segments were perfused with ascending and descending pressure sequences in a stepwise fashion (range, 4 to 40 mm Hg); 11 of the 29 eyes were treated similarly after 20 hours of perfusion at 12 mm Hg. Pressure-flow sequences of individual eyes were evaluated with a linear (constant C) and a nonlinear regression method (C decreasing with increasing IOP). In addition, in eight intact postmortem eyes, pressure-flow characteristics were determined, followed by perfusion of their isolated anterior segments. RESULTS: Pressure-flow sequences as determined by linear regression had an average correlation coefficient of 0.99. Average C (slope of the plot) was 0.26 +/- 0.03 microliter minute-1 mm Hg-1. There was no influence of direction of pressure sequence or time on C. To test for linearity, the hypothetical outflow obstruction coefficient (Q) was determined for each plot. Median Q of 29 eyes was 0.003 mm Hg-1, and in 45% (13 eyes) Q was negative, suggesting facilitation instead of obstruction. This indicates that the outflow obstruction coefficient is not a physiological parameter in isolated anterior segments. CONCLUSIONS: The relationship between IOP and flow through perfused isolated anterior segments of human eyes is linear between 4 and 40 mm Hg, indicating that within this range outflow facility is constant and does not decrease with increasing IOP.

Electronic monitoring of treatment compliance in patching for amblyopia.

We developed a coinsized occlusion dose monitor (ODM) to measure compliance with patch-wearing during the treatment of amblyopia objectively. It measures the temperature difference between the front and back of the ODM every 2-5 minutes by means of two thermistors. The data is stored in EEPROM memory and read out after recording for a week by connecting it to a PC. The ODM measures 35x23x4 mm and weighs 6 g. The back of the ODM is glued to the front of the amblyopia patch with double-sided Scotch tape. When the patch with the ODM is on the eye, the temperature at the back of the ODM is higher than at the front. Compliance is being studied in children taking part in a large amblyopia cohort study. The parents were instructed during home visits every three months to put the ODM on the patch. After a week, the ODM was collected and read out. Although the parents knew that a recording was being made, compliance was mediocre in many cases. Children were patched infrequently, for 5 minutes only, for long periods on the last days of the recording, at night, etc. Diaries detailing patch time were unreliable.

Autoantibodies to photoreceptor membrane proteins and outer plexiform layer in patients with cancer-associated retinopathy.

Cancer-associated retinopathy (CAR) is a paraneoplastic syndrome that is characterized by degeneration of the retina as a remote effect of cancer outside the eye. The detection of autoantibodies associated with the retinopathy may precede the diagnosis of the underlying cancer. We have examined the sera of two patients with CAR by Western blot analysis. Autoantibodies to a 40kD antigen doublet and a 35 kD antigen were detected. Tissue specificity of the autoantigens was determined by testing several different tissues. The 40 kD antigen doublet was most abundant in retinal extract but was also present in lung and spleen extracts. The 35 kD antigen showed little tissue specificity and was present in all tissues tested. Fractionation of retinal proteins into water-soluble and -insoluble proteins revealed that the 40 kD antigen doublet was highly insoluble and probably represented membrane-associated proteins. Immunohistochemical analysis of the retina showed that the 40 kD antigens locate to the photoreceptors while the 35 kD antigen is located in the outer plexiform layer.