848 Reports Investigative Ophthalmology October 1976

in our opinion, it should be used with some reser­ The effect of miotics on the intraocular vation as a prognostic test for the later appearance pressure of conscious owl monkeys. J. W. of glaucomatous visual field defects since the indi­ LAMBLE AND A. P. LAMBLE. vidual pressure vulnerability of the optical nerve head may vary—in this respect, even if more in­ The intraocular pressure of conscious, unsedated formative, it shares the fate of other tests for owl monkeys (Aotus trivirgatus) was measured aqueous humor dynamics. witli an applanation tonometer. Untreated eyes of the conscious animals were found to have higher From the Departments of Ophthalmology, Rigs- values than those reported for owl monkeys anes­ hospitalet and Gentofte Hospital, Copenhagen, thetized with pentobarbitone.* Locally applied Denmark. Supported by grants from the Commit­ tee for the Prevention of Blindness and artist Hjal- pilocarpine, carbachol, and oxotremorine gave con­ mar Westerdahl's Fund. Submitted for publication centration-related reductions in pressure, oxo­ March 22, 1976. Reprint requests: Ole I. Nissen, tremorine being the most potent and having Department of Ophthalmology, Rigshospitalet, longer duration of effect than the other com­ Blegdamsvej, DK 2100 Copenhagen 0, Denmark. pounds. Slight reductions were also observed with aceclidine and R.S. 86. These results are discussed Key words: acetazolamide test, facility of aqueous in relation to the effects of niiotics in man. outflow, glaucoma test, intraocular hypertension, pathological and apathological aqueous circula­ In studies on monkeys anesthetized with pento­ tion, weight tonography. barbitone, it was reported that locally adminis­ tered pilocarpine increased the outflow facility.1' 2 REFERENCES However, no significant reduction in intraocular pressure was induced by pilocarpine, but it is 1. Nissen, O. I., and Hoppe, R.: The facility of aqueous outflow calculated from the rate of notable that under the anesthetic, the basal pres­ fall in applanation pressure after intravenous sure was low even in untreated eyes. Possibly the acetazolamide in man, Acta Ophthalmol. 52: observation of Cevario and Macri:i that pento­ 390, 1974. barbitone apparently reduces aqueous inflow in 2. Nissen, O. I.: The immediate response in ap­ rhesus monkeys is significant, since pilocarpine planation pressure to intravenous acetazol­ might be unable to induce further reductions if amide in primary glaucomas and glaucoma the intraocular pressure is approaching that of the suspects, Acta Ophthalmol. 53: 537, 1975. recipient veins. 3. Grant, W. M.: Tonographic method for mea­ suring the facility and rate of aqueous flow in The present study reports the effects of several human eyes, Arch. Ophthalmol. 44: 204, parasympathomimetic drugs on the eyes of fully 1950. conscious owl monkeys, and it has been shown 4. Brubaker, R. F.: The effect of intraocular that consistent reductions in intraocular pressure pressure on conventional outflow resistance can be obtained under appropriate experimental in the enucleated human eye, INVEST. OPH­ conditions. THALMOL. 14: 286, 1975. Methods. Male owl monkeys (Aotus trivirgatus) 5. Moses, R. A.: Constant pressure applanation weighing 0.8 to 1.5 kilograms were used in groups tonography. III. The relationship of tono- of five to seven. During tonometry each animal metric pressure to rate of loss of ocular vol­ ume. Arch. Ophthalmol. 77: 181, 1967. was loosely restrained in a cloth bag which en­ 6. Thorburn, W.: Recordings of applanating veloped the trunk and limbs. After thorough train­ force at constant intraocular pressure. V. In­ ing, the animals accepted the experimental proce­ traocular volume changes due to changes in dures without apparent anxiety. The pneumatic the content of aqueous humour, Acta Oph­ tonometer using a Digilab, Inc. (Cambridge, thalmol. 51: 390, 1973. Mass.) floating probe was constructed in this 7. Levene, R., and Hyman, B.: The effect of in­ laboratory. Oxygen was admitted to the probe at a traocular pressure on the facility of outflow, pressure of 34.5 kPa. (5 p.s.i.) and the recordings Exp. Eye Res. 8: 116, 1969. were made using a Bell & Howell (Pasadena, 8. Ellingsen, B., and Grant, W. M.: The rela­ tionship of pressure and aqueous outflow in Calif.) transducer (4-421-001) and transducer in­ enucleated human eyes, INVEST. OPH­ dicator (1-176) and an Omniscribe pen recorder THALMOL. 10: 430, 1971. (Houston Instrument Div., Bausch & Lomb, Inc., 9. Johnstone, M. A., and Grant, W. M.: Pres­ Bellaire, Texas). Open-stopcock manometric cali­ sure-dependent changes in structures of the bration was carried out on five eyes of anes­ aqueous outflow system of human and mon­ thetized owl monkeys. key eyes, Am. J. Ophthalmol. 75: 365, 1973. The parasympathomimetic drugs were dissolved 10. Grierson, I., and Lee, W. R.: Changes in the in sterile physiological saline, and 10 or 20 /d of monkey outflow apparatus at graded levels of intraocular pressure: a qualitative analysis by a given solution was administered topically to each light microscopy and scanning electron mi­ croscopy, Exp. Eye Res. 19: 21, 1974. * Pentobarbitone = pentobarbital. Downloaded from iovs.arvojournals.org on 09/28/2021 Volume 15 Reports 849 Number 10

Z 4-0h

001 CONCENTRATION Fig. 1. The concentration-effect curves for oxotremorine (H), pilocarpine (•) and carbachol (A). Responses are expressed as the mean (- S.E.M.) of the greatest differences in intraocular pressure between the treated eyes and the untreated eyes observed after drug treatment. The number of animals receiving each treatment is shown.

eye with an Eppendorf micropipette. Local anes­ prevent confusion of any physiological variation thesia for tonometry was induced by instillation in pressure with the drug effects. of 0.02 ml. of an 0.5 per cent oxybuprocaine hy­ Pilocarpine hydrochloride 0.25 to 2.0 per cent, drochloride solution prepared in sterile saline. carbachol (carbamyl choline chloride) 0.25 to Pressure values are given as the mean ± stan­ 4.0 per cent, and oxotremorine 0.005 to 0.5 per dard error. Comparisons have been made using cent all gave concentration-related decreases in two-sample or paired-difference t tests. intraocular pressure. Their effects are illustrated Results. In a preliminary experiment on owl in Fig. 1 in which the drug concentrations are monkeys treated only with local anesthetic for given in molar terms. Results are expressed as the tonometry, it was found that the mean intraocular mean of the greatest differences in tension ob­ pressure ± S.E.M. was 25.95 ± 1.09 mm. Hg served between treated and untreated eyes after at 1000 hours Greenwich Mean Time. Observed drug administration. It can be seen that oxotrem­ at hourly intervals for 6 hours, the individual orine is more potent than the other agents. With eyes showed physiological variation of up to 4.27 0.5 per cent oxotremorine, systemic parasympatho­ mm. Hg. However, the opposite eyes of the ani­ mimetic effects were apparent, i.e. salivation and mals varied similarly and at no time was a signifi­ diarrhea, in three of the seven animals tested and, cant difference detected, with the paired t test, therefore, higher concentrations were not tested. between the right eye and the left eye values of The time courses of responses to approximately the group. Therefore, in experiments to show equipotent submaximal concentrations of the three drug effects, only one eye of each monkey was drugs are illustrated in Fig. 2 and it is seen that treated, and the responses have been expressed the duration of effect varies in this order: oxo­ as the difference in pressure between the treated tremorine > carbachol > pilocarpine. eye and the control opposite eye, in order to Two other agents were also investigated: (-)- Downloaded from iovs.arvojournals.org on 09/28/2021 850 Reports Investigative Ophthalmology October 1976

oh

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TIME (hr) Fig. 2. The time course of responses to submaximal concentrations of • oxotremorine (0.025 per cent), • pilocarpine (0.5 per cent) and A carbachol (0.5 per cent) on groups of six or seven owl monkeys. Responses are expressed as the mean difference in intraocular pressure between the treated eyes and the untreated eyes (± S.E.M. where relevant).

aceclidine hydrochloride and R.S. 86 (spiro-(N'- Discussion. The owl monkey is of the class methyl-piperidyl-4'-) -N-ethyl succinimide hydro- Simiae and has a trabecular plexus similar to that bromide, Sandoz). One hour after administration of man.4 Its eyes are large and this allows tonom­ of 0.5 per cent aceclidine a significant (p <0.02) etry to be performed easily. However, one pos­ increase of 2.29 ± 0.75 mm. Hg in the mean in­ sibly relevant structural difference compared with traocular pressure of the treated eyes over con­ man is that the vitreous is a viscous liquid. trol eyes was observed, although the values re­ The intraocular pressure of owl monkeys under turned to control levels after 2 hours. A small but pentobarbitone anesthesia has been measured by significant (p. <0.01) reduction of 2.24 ± 0.68 several workers. Mims and Holland4 obtained mm. Hg was observed 1 hour after administration values of 15.7 mm. Hg by Schi0tz tonometry, of 1.0 per cent aceclydine, but pressures were 13.2 mm. Hg by applanation tonometry, and 14.1 again at control levels after 2 hours. R.S. 86, 0.5 mm. Hg by manometry. Swietliczko and David5 per cent, gave no significant effect on intraocular obtained a mean value of 14.6 mm. Hg by manom­ pressure, although a 1.0 per cent solution caused etry, with a range of 10.2 to 18.9 mm. Hg. a reduction of 3.61 ± 1.12 mm. Hg after 1 hour Similar values have been obtained manometrically which was significant (p <0.01). There was no and tonometrically in owl monkeys anesthetized significant effect after 2 hours. However, a 2.0 with pentobarbitone, in this laboratory (unpub­ per cent solution of R.S. 86 gave a reduction lished results). which was significant after 1 hour and 2 hours, There have also been reports of low intraocular but was of similar magnitude at 1 hour (3.73 pressure in other primate species under pentobar­ ± 0.31 mm. Hg) to that seen with 1.0 per cent bitone anesthesia1' 2 and it is interesting that R.S. 86. Barany1 found a value of 8.9 mm. Hg in Cer- Downloaded from iovs.arvojournals.org on 09/28/2021 Volume 15 Reports 851 Number 10

copithecus ethiops under pentobarbitone anes­ REFERENCES thesia, whereas a value of 20 mm. Hg was found 1. Barany, E. H.: The mode of action of pilo­ in the same species under light ether anesthesia. carpine on outflow resistance on the eye of {! Kitazawa and Langham have reported values of a primate (Cercopithecus ethiops), INVEST. 18-20 mm. Hg in Macaca mulatta sedated with OPHTHALMOL. 1: 712, 1962. phencyclidine. Thus, in view of the finding of 2. Edwards, J., Hallman, V. L., and Perkins, E. Cevario and Macri3 that pentobarbitone appar­ S.: Perfusion studies on the monkey eye, ently reduces aqueous inflow, it is not considered Exp. Eye Res. 6: 326, 1967. surprising that the intraocular pressure has been 3. Cevario, J., and Macri, F. J.: The inhibitory effect of pentobarbital Na on aqueous humor found to be higher in conscious owl monkeys formation, INVEST. OPHTHALMOL. 13: 384, than in those anesthetized with pentobarbitone. 1974. This study has demonstrated that the intra­ 4. Mims, J. L., and Holland, M. C: Applanation ocular pressure of owl monkeys is reduced in a and Schi0tz tonometer standardizations for dose-related manner by several parasympathomi­ the owl monkey eye with a new technique for metic agents. Oxotremorine was the most potent measuring episcleral venous pressure, INVEST. compound tested and its effects were prolonged OPHTHALMOL. 10: 190, 1971. compared with the other drugs. It has been dem­ 5. Swietliczko, I., and David, N. J.: Fluorescein onstrated7 to have a higher heptane: water parti­ angiography in experimental ocular hyper­ tension, Am. J. Ophthalmol. 70: 351, 1970. tion coefficient than either pilocarpine (71 times) 6. Kitazawa, Y., and Langham, M. E.: The in­ or R.S. 86 (12 times), and this suggests that it fluence of adrenergic potentiators on the would penetrate membranes more easily, which ocular response to catecholamines in primates might contribute to its greater potency. and man, Nature 219: 1376, 1968. Pilocarpine gives maximal reductions in intra­ 7. Herz, A., Holzhauser, H., and Teschemacher, ocular pressure in many glaucoma patients at a H.: Central nicotine- and muscarine-like prop­ concentration of 2.0 per cent,8 and it has been erties of cholinomimetic drugs with regard shown to have similar potency in the owl monkey. to their lipid solubilities, Ann. N. Y. Acad. Sci. 142: 21, 1967. However, the duration of its effects in human 8 8. Drance, S. M., and Nash, P. A.: The dose beings has been reported to be greater than that response of human intraocular pressure to which was observed in the monkeys. Carbachol pilocarpine, Can. J. Ophthalmol. 6: 9, 1971. has been shown to have slightly greater potency 9. Morrison, W. H.: Stability of aqueous solu­ and duration of effects than pilocarpine in man, tions commonly employed in the treatment provided that a surfactant is incorporated in the of glaucoma. 1. The pharmacology of miotics, solution.9 In the owl monkey slightly lower Am. J. Ophthalmol. 37: 391, 1954. potency was found compared to pilocarpine, al­ 10. Romano, J. H.: Double-blind cross-over com­ though there was no surfactant in the solution. parison of aceclidine and pilocarpine in open- A slightly greater duration of effect was observed, angle glaucoma, Br. J. Ophthalmol. 54: 510, 1970. however. Aceclidine has been reported to have similar potency to pilocarpine in man,10 but it was markedly less potent in the owl monkey. In conclusion, it may be said that the fully The effect of cation ionophores on intra­ conscious owl monkey responds to locally applied ocular pressure. STEVEN M. PODOS. parasympathomimetic drugs with a pattern of changes in intraocular pressure which is not dis­ The ionophores A23187 and X537A, which in­ similar to that seen in human beings. The species crease the permeability of cell membranes to cal­ would, therefore, possibly represent a valuable cium and other divalent cations, produced sig­ predictive model for the investigation of new nificant elevation of intraocular pressure in rabbits. parasympathomimetic glaucoma treatments. Topical instillation of these ionophores in concen­ trations of 1.0 and 0.1 per cent were effective. We thank Mr. E. J. McQuade of Digilab, Inc., Aqueous humor protein and facility of outflow for the gift of the floating probe and Dr. M. were similar in ionophore-treated and control eyes. Taeschler of Sandoz for supplying the R.S. 86. Pretreatment with indomethacin did not block the We are also grateful to Mrs. J. Barrett for tech­ nical assistance. intraocular pressure rise induced by A23187. Alterations of intracellular calcium might control Submitted for publication April 26, 1976. cellular processes within the eye as in many Reprint requests: J. W. Lamble, Ph.D., Smith & other biological systems. Nephew Research Ltd., Gilston Park, Harlow, CM20 2RQ, Essex, England. The secondary messenger system of cyclic Key Words: owl monkey, Aotus trivirgatus, nucleotides is involved in the control of aqueous tonometry, intraocular pressure, parasympatho­ humor dynamics. Changes in the cyclic adenosine mimetics, pilocarpine. 3',5'-monophosphate (cyclic AMP) level in aque- Downloaded from iovs.arvojournals.org on 09/28/2021