Julie A. Kiland

Effects of serotonergic compounds on aqueous humor dynamics in monkeys

Purpose. The effects of several serotonergic agonists on aqueous humor formation (AHF), total outflow facility (OF) and intraocular pressure (IOP) were investigated in living cynomolgus monkeys. Methods. We determined the effect of a single topical unilateral 300 µg or 3 mg dose of the 5-HT agonists serotonin, 5-carboxamidotryptamine (5-CT), sumatripan, gepirone, and 8-hydroxy-2(di-n-propylaminotetralin) (8-OH-DPAT) and a 450 µg dose of flesinoxan on IOP (Goldmann applanation tonometry), AHF (scanning ocular fluorophotometry) and total OF (8-OH-DPAT only, topically and intracamerally). Results. Serotonin, 5-CT, sumatripan or gepirone had no significant effect on IOP or AHF. 8-OH-DPAT caused an AHF increase of ~70% over 6 hr in both ipsilateral drug- and contralateral vehicle-treated eyes, but no significant change in IOP compared with baseline measured on a separate occasion in the same animals. 8-OH-DPAT did not increase protein levels or rate of entry of systemically administered fluorescein in the anterior chamber aqueous humor compared to historic controls, and no difference was seen between ipsilateral and contralateral eyes. Flesinoxan had no effect on IOP and produced an insignificant 25% increase in flow in treated eyes compared to baseline. Conclusion. The results for 8-OH-DPAT and possibly flexinoxan indicate the presence of a secretion-stimulating 5-HT1A receptor in monkey ciliary epithelium that has little effect on IOP. OF was unchanged following 8-OH-DPAT administered topically or following intracameral exchange.

Benzalkonium Chloride and Glaucoma

Glaucoma patients routinely take multiple medications, with multiple daily doses, for years or even decades. Benzalkonium chloride (BAK) is the most common preservative in glaucoma medications. BAK has been detected in the trabecular meshwork (TM), corneal endothelium, lens, and retina after topical drop installation and may accumulate in those tissues. There is evidence that BAK causes corneal and conjunctival toxicity, including cell loss, disruption of tight junctions, apoptosis and preapoptosis, cytoskeleton changes, and immunoinflammatory reactions. These same effects have been reported in cultured human TM cells exposed to concentrations of BAK found in common glaucoma drugs and in the TM of primary open-angle glaucoma donor eyes. It is possible that a relationship exists between chronic exposure to BAK and glaucoma. The hypothesis that BAK causes/worsens glaucoma is being tested experimentally in an animal model that closely reflects human physiology.

1α,25-Dihydroxyvitamin D3 and its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D3 (2MD), suppress intraocular pressure in non-human primates

Ocular hypertension is the greatest known risk factor for glaucoma that affects an estimated 70 million people worldwide. Lowering intraocular pressure (IOP) remains the mainstay of therapy in the management of glaucoma. By means of microarray analysis, we have discovered that 1α,25-dihydroxyvitamin D(3) (1α,25-(OH)(2)D(3)) regulates genes that are known to be involved in the determination of intraocular pressure (IOP). Topical administration of 1α,25-(OH)(2)D(3) or its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), markedly reduces IOP in non-human primates. The reduction in IOP is not the result of reduced aqueous humor formation, while a 35% increase in aqueous humor drainage by 1α,25-(OH)(2)D(3) was found but this increase did not achieve significance. Nevertheless, our results suggest that 1α,25-(OH)(2)D(3), or an analog thereof, may present a new approach to the treatment of glaucoma.

Effect of H-7 and Lat-B on Retinal Physiology

Purpose: To investigate the effects of H-7 and Latrunculin B (Lat-B) on retinal vascular permeability and electrophysiology at concentrations that increase outflow facility in monkeys. Methods: One eye of 1 rhesus and 22 cynomolgus monkeys received an intravitreal bolus injection of H-7 or Lat-B; the opposite eye received vehicle. Multifocal electroretinograms (mfERGs), and photopic and scotopic full-field electroretinograms (ffERGs, sERGs) were recorded in subsets of monkeys at baseline and at multiple time-points post-H-7 or Lat-B. Vitreous fluorophotometry (VF) and fluorescein angiography (FA) were also performed. Results: No differences between the H-7 or Lat-B treated and control eyes were found in ffERGs, mfERGs, sERGs, or in FAs in any monkey. No significant difference was found in vitreous fluorescein levels between H-7 treated or Lat-B treated vs. control eyes. Conclusions: No effect on retinal vascular permeability or retinal electrophysiology was apparent after intravitreal administration of H-7 or Lat-B at doses that increase outflow facility and lower IOP when given intracamerally.

Comparison of Goldmann Tonometry Measurements Using Creamer vs Fluorescein in Cynomolgus Monkeys

Fluorescein cannot be used to measure intraocular pressure (IOP) repeatedly at short intervals, or during fluorophotometric determination of aqueous flow. Therefore, we compared minified Goldmann tonometer measurements of IOP obtained using commercial fluorescein vs dairy or non-dairy creamer to highlight the mires. In ocular normotensive monkeys, measurements using fluorescein averaged 1.94±0.49 mmHg higher than with creamer (p<0.001), and fluorescein- vs creamer- measured IOP ratios averaged 1.17±0.05 (p<0.005). However, when IOP was manometrically controlled from 15-60 mmHg, the mean difference between fluorescein and creamer readings was only 0.49 ± 0.94 mmHg and the fluorescein/creamer IOP ratio averaged 1.01 ± 0.032. This essential identity held from 15-60 mmHg IOP, the difference increasing by only 0.013±0.055 mmHg/ mmHg manometric pressure. Coffee creamer is an alternative to fluorescein to measure IOP.

Application of canaloplasty in glaucoma gene therapy: where are we?

PURPOSE Schlemms canal (SC) inner wall is adjacent to the juxtacanalicular trabecular meshwork (TM) over their entire circumference. We seek to transfer reporter and therapeutic genes to these outflow-modulating tissues via canaloplasty surgery in live monkeys. METHODS A standard canaloplasty surgical approach was performed in cynomolgus monkeys using flexible canaloplasty catheters, modified for monkey eyes with a 175-μm outer diameter and an LED-lighted tip. A 6-0 prolene suture was used for the exact localization of SC. Trypan blue was injected during catheter withdrawal to document catheter placement within SC and to determine ease of injecting fluid into SC. Before, during, and after the injection, the position of the catheter and the anatomic details were video-captured with an externally positioned noncontact endoscopic imaging system and 50 mHz ultrasound biomicroscopy (UBM). RESULTS A 360° catheterization and injection of dye into SC was achieved. Suture, catheter, and trypan blue were imaged with the endoscope camera system and the catheter was also visualized with UBM. Trypan blue was seen in the SC over 5 clock hours after a 1 clock-hour insertion of the catheter. CONCLUSIONS A modified canaloplasty catheter device might be used for gene delivery to the SC/TM area without circumferential catheterization. Further studies comparing different delivery methods of the vector/transgene into the SC using canaloplasty are needed.

Effects of topical corticosteroid administration on intraocular pressure in normal and glaucomatous cats

OBJECTIVE The objective of this study was to determine the effect of topical corticosteroid (CCS) therapy on intraocular pressure (IOP) in normal cats and cats with primary feline congenital glaucoma (FCG). ANIMALS STUDIED Five normal and 11 FCG cats were studied in two cohorts. PROCEDURES IOP was measured by a single, masked observer, once daily, 3-5 days/week throughout the course of CCS treatment and for up to 11 days after treatment discontinuation. One eye per cat was randomly assigned for treatment twice daily with CCS; balanced salt solution (BSS) applied to the contralateral eye served as a control. Differences between eyes and between weeks of the study period were calculated for each cat. A positive response to CCS was defined as a consistent >15% or >25% higher IOP in the treated relative to control eye in normal and FCG cats, respectively. RESULTS A total of 8 of 11 FCG cats responded to topical CCS after 1-5 weeks of treatment with an increase in IOP relative to the untreated eye (maximum IOP discrepancy of 56 mmHg). Two of five normal cats responded to topical CCS with an appreciable, but clinically unimportant increase in IOP in the treated eye (maximum IOP discrepancy of 6.4 mmHg). CONCLUSIONS Our data indicate that the incidence of steroid-induced IOP elevation in cats is lower than that of previously published feline studies. Cats with preexisting compromise in aqueous humor outflow may show a greater, clinically relevant response to topical CCS than normal cats.

Relationship of aqueous outflow resistance to age and total volume perfused in rhesus and cynomolgus monkeys.

PURPOSE The effect of total volume perfused on outflow resistance (the reciprocal of outflow facility) and the effect of age on the rate of change in resistance as a function of total volume were determined in rhesus and cynomolgus monkeys. METHODS Outflow facility was measured under general anesthesia by two-level constant pressure perfusion in one eye of 22 rhesus and 17 cynomolgus monkeys (ranging in age, respectively, from 4 to 25 and from 3 to 12 years). Total volume perfused was calculated from data obtained during the perfusion. RESULTS Resistance decreased in both cynomolgus and rhesus monkeys as total volume perfused increased (-0.085 ± 0.021 and -0.022 ± 0.011 mm Hg/μL/min/μL(tot); P = 0.001 and P = 0.047, respectively). Rate of change in resistance significantly increased in cynomolgus monkeys as total volume perfused increased (0.0018 ± 0.0.0007 mm Hg/μL/min/μL(tot), P = 0.033); however, this was not the case in rhesus monkeys. After accounting for total volume perfused, the rate of change in resistance significantly decreased with increasing age in rhesus monkeys (-0.0068 ± 0.0026 [mm Hg/μL/min]/μL(tot)/y, P = 0.017). There was no significant difference in rate of change in resistance with age, after accounting for total volume, in the cynomolgus monkeys. CONCLUSIONS The present study supports previous findings indicating that total washout is largely dependent on perfusion volume. However, in populations with old/elderly animals, such as our rhesus group, we found that age does play a significant role in rate of change in resistance, and may be an even more important factor to consider in the rate of resistance change than volume perfused in aged animals.

Effect of timolol maleate gel-forming solution on intraocular pressure, pupil diameter, and heart rate in normal and glaucomatous cats.

OBJECTIVE To determine the effects of once-daily topical treatment with timolol maleate gel-forming solution (GFS) on intraocular pressure (IOP), pupil diameter (PD), and heart rate (HR) in normal cats and cats with feline primary congenital glaucoma (FCG). ANIMALS STUDIED AND PROCEDURES A single drop of timolol maleate 0.5% GFS was administered topically to one randomly assigned eye of 18 adult cats (8 normal, 10 FCG) at 8 am for 8 days; the opposite eye served as the untreated control. IOP was measured in both eyes (OU) every 2 h (PD and HR were measured every 4 h), for 14 h total, 1 day prior to and on days 1 and 8 of treatment. In a second treatment phase, a single drop of timolol was administered at 8 pm for 3 nights and IOP, PD, and HR were measured, as above, beginning at 8 am on day 4. Slit-lamp examinations were conducted prior to and after treatment phases. Comparisons of mean IOP, PD, and HR were made at each time point and between treated and untreated eyes by repeated-measures ANOVA and Tukey-Kramer post hoc test, with P < 0.05 considered significant. RESULTS Timolol maleate 0.5% GFS had an inconsistent effect on IOP, with maximum IOP-lowering effect (mean = 5.6 mmHg, 17.4%) observed 6 h post-treatment in FCG. The drug caused significant miosis (from 4 to 8 h post-treatment), but had no effect on HR. CONCLUSION Once-daily application of timolol maleate 0.5% GFS may be of limited clinical benefit in the management of feline congenital glaucoma.