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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thinning of the posterior sclera may imply that stretching and/or weakening of the sclera plays a role in axial elongation of myopic eyes. We investigated the elastic stress-strain properties of sclera from developing tree shrew eyes made myopic by monocular deprivation (MD) of form vision. Five days of MD induced a relative myopia (mean +/- SEM) of -5.6 D +/- 0.6 D (retinoscopy) and a vitreous chamber elongation (deprived minus control) of 106 +/- 14 microns, n = 10 (ultrasonography). Posterior scleral test samples (2 mm wide) cut from myopic eyes were significantly thinner than their contralateral eye controls (149 +/- 4 microns versus 164 +/- 4 microns, n = 10, P < 0.01) when measured with a force-controlled micrometer. However, posterior sclera from control eyes was significantly thicker than that from age-matched normal eyes (164 +/- 4 microns versus 149 +/- 3 microns, n = 10, P < 0.01). Under uniaxial tension, posterior scleral samples from myopic eyes failed at 18% lower load (162 g versus 198 g) and extended approximately 25% more than controls at a load corresponding to 20 mm Hg intraocular pressure. These differences were largely accounted for by the differences in scleral thickness. Finite element modelling of tree shrew eyes using the material properties summarised above, implies that simple elastic stretching of the sclera accounts for less than 20% of the observed difference in axial length between myopic and contralateral control eyes.
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PMID:Form deprivation myopia: elastic properties of sclera. 852 54

To study the optic neuropathy associated with glaucoma, a system for accurate, reliable, and non-invasive monitoring of intraocular pressure (IOP) is required. Of particular interest is the effect of sampling frequency on IOP. To address this issue, ten adult male brown Norway rats (group 1) were acclimatized to a 12-h/12-h light/dark cycle. On 20 days over a 30-day period, rats were anesthetized with short-acting isoflurane (Forane) inhalant anesthesia and IOP for each eye was determined by averaging 15 valid individual readings obtained with a TonoPen 2 tonometer. The last 12 measurement sessions were performed on a daily basis. To determine the minimum tolerable interval between IOP measurement sessions, a second group of 10 animals (group 2) was acclimatized in the same manner as group 1, and IOP was measured every 4 days over a period of 80 days. Next, IOP was measured every 4 days over a period of 28 days, and finally, every 2 days over a period of 19 days. For all group 1 measurements, there was no statistically significant difference between the right and left eye IOP, 14.75 +/- 1.08 (SEM) and 14.90 +/- 1.09 mm Hg, respectively. However, daily measurements produced a steady decrease in IOP and gradual weight loss. For group 2, overall mean right and left eye IOPs were 15.24 +/- 1.28 (SEM) and 15.12 +/- 1.26, respectively and were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Long-term non-invasive measurement of intraocular pressure in the rat eye. 852 7

Using an applanation tonometer, 5 replicate intraocular pressure (IOP) measurements were obtained from each eye of 12 young clinically normal, American alligators. Alligator length ranged from 46 to 117 cm, measured from snout to tail tip. All IOP were recorded by a single observer at an ambient temperature of approximately 25 C, and ranged from 5 to 35 mm of Hg. Observer reliability was excellent (intraclass r = 0.93), and IOP did not change over the ordered sequence of 5 replicate measurements/eye. Replicate IOP) measurements were, therefore, averaged in each eye for comparison between eyes of the same alligator. Left and right eve IOP were highly correlated within individual alligators (r = 0.92), whereas the mean within animal difference between left and right eye IOP was not statistically significant (95% confidence interval [CI] for the left eye-right eye mean difference, - 1.9 to 1.3 min of Hg). Mean IOP determined for 5 confirmed females and 3 confirmed males did not differ significantly between the sexes (95% CI for the male-female difference in means, -2.1 to 3.7 mm of Hg). Mean +/- SEM IOP of 23.7 + 2.1 mm of Hg determined for 4 alligators < -50 cm long was significantly (P = 0.009) greater than mean IOP of 11.6 + 0.5 mm of Hg determined for 8 alligators > 50 cm long (95% CI for the difference in means, 8.5 to 15.7 mm of Hg). In young alligators, the relation between body length and IOP appears to be nonlinear, possibly with a negative exponent.
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PMID:Intraocular pressure variation associated with body length in young American alligators (Alligator mississippiensis). 892 58

The ocular effects of topical prostaglandin F2 alpha (PGF2 alpha) were studied in normotensive human eyes. PGF2 alpha as tromethamine salt, 100 micrograms, was applied to one eye of 23 normotensive subjects, intraocular pressure (IOP) and pupil size were measured, objective and subjective findings recorded during the first 24 h. Tonography was performed in 10 subjects. As compared with the baseline, PGF2 alpha caused a significant IOP reduction between 1 and 24 h (p < 0.001), being maximal (4.9 +/- 0.5 mm Hg, mean +/- SEM, p < 0.001) between 4 and 8 h. As compared with the contralateral control eyes, which received 50 microliters of saline, treated eyes exhibited significant IOP reduction between 1 and 24 h (p < 0.001), being maximal (4.2 +/- 0.4 mm Hg, mean +/- SEM, p < 0.001) at 4 h. PGF2 alpha caused marked conjunctival hyperemia in all eyes. Pupillary diameter was not altered. Aqueous flare and cellular response were not seen. Half of the subjects complained of ocular smarting, mild ocular pain or headache. Total outflow facility did not change (p > 0.05).
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PMID:Effects of topically applied prostaglandin F2 alpha on normotensive human eyes. 903 93

Experimental glaucoma was induced in 1 eye of 6 cynomolgus monkeys by laser treatment of the trabecular meshwork. In 5 of the 6 monkeys the increased intraocular pressure (IOP) caused marked glaucomatous damage in the experimental eye. Ocular blood flow was determined with labeled microspheres 4 years after the laser treatment. IOP was regulated with an external reservoir. With the same perfusion pressure in both eyes no statistically significant difference was observed between the 2 eyes for total ocular blood flow or for blood flow through any of the ocular tissues. Total ocular blood flow was 343.5 +/- 61.4 mg/min (mean +/- SEM) in the control eye and 385.3 +/- 107.7 mg/min in the experimental eye.
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PMID:Ocular blood flow in experimental glaucoma: a study in cynomolgus monkeys. 917 99

This study investigates changes in intraocular pressure (IOP) in rabbits during head-down tilt (HDT), which is commonly used as an experimental model to simulate microgravity. IOP was measured by the needle insertion technique (IOPNEEDLE) and Tono-pen tonometry (IOPTONO-PEN). Although the absolute value of the IOPTONO-PEN was significantly smaller than that of the IOPNEEDLE, a significant correlation (r = 0.99) was observed between them. A linear regression analysis yielded an equation as follows: IOPTONO-PEN = 0. 67 IOPNEEDLE - 0.67. Both the IOPNEEDLE and the IOPTONO-PEN changed depending on the tilt angle. Tilting from horizontal (0 degrees) to 75 degrees head-down increased the IOPNEEDLE and the IOPTONO-PEN by 7.3 +/- 0.8 (mean +/- SEM) mmHg and 4.4 +/- 1.3 mmHg. The IOPNEEDLE elevated from 13.1 +/- 1.3 to 16.9 +/- 1.0 mmHg immediately after the onset of 45 degrees HDT and then gradually declined. The value of the IOPNEEDLE during 8 h of HDT was significantly higher than the value in the control animals, which were kept at the horizontal prone position throughout the experiment. Similar findings were observed in the IOPTONO-PEN. These results suggest that the needle insertion technique and the Tono-pen tonometry are both useful for measuring IOP in rabbits.
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PMID:Measurement of intraocular pressure by both invasive and noninvasive techniques in rabbits exposed to head-down tilt. 953 86

Previously, it had been demonstrated that cataract in diabetic rats can be prevented by systemical administration of the calcium channel blocker verapamil. In addition to that, 0.125% verapamil eye drops were found to significantly reduce the intraocular pressure in ocular hypertensive human subjects. The purpose of this study was to investigate the ocular penetration and elimination of verapamil after topical administration of the drug in rabbits. Two drops of a 0.125% aqueous solution of RS-verapamil hydrochloride (corresponding to a total dose of 125 microg RS-verapamil hydrochloride) were administered into the conjunctival sac. Aqueous humor and blood samples were taken at different times after administration and analysed for drug concentration by combined gas chromatography-mass spectroscopy. Following the instillation of 0.125% verapamil eye drops in a total dose of 125 microg RS-verapamil, mean (+/- SEM) aqueous humor peak levels of 1607 +/- 272 ng/ml were achieved after 20 min. Mean half-life for the elimination from the aqueous humor was 33 min. Topical application of verapamil produced very low serum peak concentrations (10.5 +/- 1.3 ng/ml). The results of our study demonstrate that topically administered verapamil readily penetrates into the anterior chamber leading to aqueous humor drug levels in the microM range without producing serum levels that are high enough to cause cardiovascular side effects.
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PMID:Ocular pharmacokinetics of verapamil in rabbits. 955 Mar 6

The aim of the study was to evaluate whether the Heidelberg retina flowmeter (HRF), a new device for retinal and anterior optic nerve blood flow assessment, can gauge, at least semiquantitatively, a known effect such as an increase in optic nerve blood flow by hypercapnia or a decrease in optic nerve blood flow by hyperoxia or high intraocular pressure (IOP). Measurements with the HRF were obtained at the papilla of three groups of 5 young healthy subjects (1) at baseline and after breathing 5% carbogen, (2) at baseline and after breathing 100% oxygen and (3) at baseline and after increasing IOP to 20 and 50 mm Hg. The changes in the value of the HRF parameter 'flow' were analyzed by means of a paired Student's t test. Breathing 100% oxygen for 7 min resulted in a statistically significant decrease of 34.7+/-2.5% (mean+/-SEM) in HR parameter 'flow' (p < 0.01) at the papilla. Breathing 5% carbogen for 7 min resulted in a statistically significant increase of 18.3+/-2.6% in HRF parameter 'flow' (p = 0.024). Increasing IOP to 20 mm Hg did not result in a statistically significant change in HRF parameter 'flow' (-9.6+/-7.4%; p = 0.13). Increasing IOP from 20 to 50 mm Hg, however, resulted in a statistically significant decrease of 40.1+/-6.6% in HRF parameter 'flow' (p = 0.003). With the applied stimuli, the HRF parameter 'flow' changed in the expected direction, i.e. an increase with hypercapnia and a decrease with hyperoxia or high IOP. The simplicity of use of the HRF instrument suggests that it might be well suited for a non-invasive, at least semiquantitative, assessment of changes in blood flow at the papilla.
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PMID:Effect of carbogen, oxygen and intraocular pressure on Heidelberg retina flowmeter parameter 'flow' measured at the papilla. 956 85

Latanoprost (PhXA41, Xalatan) and isopropyl unoprostone (UF-021, unoprostone, Rescula) two new prostanoid derivatives, have been shown to reduce intraocular pressure (IOP) significantly in patients with glaucoma or ocular hypertension. This study was designed to compare the ocular hypotensive effects of latanoprost and unoprostone in cynomologus monkeys with glaucoma and characterizes the prostanoid's mechanisms of action in normal cynomolgus monkey eyes. Intraocular pressure was measured daily at 0, 0.5, and 1 hour and hourly for 5 additional hours during 1 baseline day, 1 vehicle-treated day, and 5 days of therapy with either 0.005% latanoprost or 0.12% unoprostone applied twice daily, at 9:30 AM and 3:30 PM, to the glaucomatous eye of eight monkeys with unilateral laser-induced glaucoma. Outflow facility was measured in six normal monkeys 3 hours prior to dosing and 1 hour after unilateral dosing with either drug. Aqueous humor flow rates were measured in six normal monkeys hourly for 4 hours on 1 baseline day and on 1 treatment day beginning 1 hour after administration of either drug to one eye. Intraocular pressure was significantly (P < 0.005) reduced after the first application for 4 hours with latanoprost and for 2 hours with unoprostone, up to 5.4 +/- 0.8 mm Hg (mean +/- SEM) (latanoprost) and 3.8 +/- 0.5 mm Hg (unoprostone). Intraocular pressure was significantly (P < 0.005) reduced for at least 18 hours following each PM dose of latanoprost. Intraocular pressure was not reduced (P > .05) 18 hours after each PM dose of unoprostone. An enhancement of the ocular hypotensive effect was observed from day 1 to day 5 with repeated dosing of either drug. Latanoprost produced a greater magnitude of IOP reduction for a longer duration of time than unoprostone after each application. Neither drug altered outflow facility or aqueous humor flow rates. Latanoprost and unoprostone appear to reduce IOP in monkeys by enhancing uveoscleral outflow. Latanoprost appears to be more efficacious and potent than unoprostone in reducing IOP in glaucomatous monkey eyes.
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PMID:A comparative study of latanoprost (Xalatan) and isopropyl unoprostone (Rescula) in normal and glaucomatous monkey eyes. 958 40

The mechanism of the ocular hypotensive effect of bunazosin hydrochloride (an alpha1-adrenergic antagonist) and the possible intermediary role of prostaglandins were studied in New Zealand albino rabbits. Aqueous flow, outflow facility and uveoscleral outflow were determined by fluorophotometry, and intraocular pressure (IOP) was measured by pneumatonometry on the fourth day of twice daily topical treatment with 0.1% bunazosin. Uveoscleral outflow was measured with a tracer infusion technique at 1 to 2 hours after one dose of 0.1% bunazosin. Total outflow facility was measured by a two-level constant-pressure infusion method before and at one hour after one dose of 0.1% bunazosin. The effect of topically applied cyclooxygenase inhibitors, including 0.25% indomethacin and 0.03% flurbiprofen, on the IOP reduction after bunazosin was evaluated. At 3 hours after the seventh consecutive dose given twice-daily, bunazosin significantly (P<0.001) reduced IOP to 13.4+/-0.8 mm Hg (mean +/- SEM) from a baseline of 19.6+/-1.1 mm Hg. Indomethacin significantly inhibited the IOP reduction after one dose of bunazosin, whereas flurbiprofen did not (repeated measures ANOVA). Bunazosin significantly increased uveoscleral outflow (P<0.05) and total outflow facility (P<0.02), but not fluorophotometric outflow facility or aqueous flow. It is concluded that, in rabbits, 0.1% bunazosin reduces IOP predominantly by increasing uveoscleral outflow. The role of prostaglandins in this effect is equivocal.
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PMID:Bunazosin reduces intraocular pressure in rabbits by increasing uveoscleral outflow. 967 29


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