The order Rodentia is the largest order of mammals. It contains 2,020 living species placed in 28 families, which is approximately half of all mammalian species. Despite the large number of rodent species, few are owned as pets. Rodents commonly kept as pets are rats, mice, hamsters, gerbils, guinea pigs, and chinchillas.1 Hamsters are one of the most popular pet species among rodents.2 Approximately 1.1 million hamsters are maintained as pets in approximately 0.87 million homes in the United States.3 Ophthalmic examination is a necessary part of a complete routine health assessment for all domestic animals. Systemic diseases can be associated with ocular lesions in all animal species. Recognition of these ocular signs is useful in the diagnosis and treatment of systemic diseases. The assessment of IOP is a crucial component of a complete ophthalmic examination because assessment of IOP can contribute to the diagnosis of severe ocular diseases (eg, glaucoma or uveitis).4 Assessment of IOP could help clinicians to more accurately diagnose ocular and systemic diseases and to more effectively make treatment decisions.
The IOP can be affected by the tone of extraocular muscles, closure of the eyelids, retraction of the retractor bulbi muscle, external pressure, intraocular changes, drugs, curvature and thickness of the cornea, corneal and scleral rigidity, time of day, head and body position, and tear film viscosity.5–8 It is known that IOP is not constant and varies considerably throughout the day. However, the physiologic role of and mechanisms for daily variation are poorly understood.9
The use of certain drugs, such as anesthetics, may cause alterations in IOP. Ketamine is a dissociative drug that can be used as a sole agent for inducing anesthesia or in combination with other agents for inducing and maintaining anesthesia.10 In clinical practice, ketamine-diazepam and ketamine-xylazine combinations have been used for the induction of anesthesia in hamsters.11
In a previous study12 conducted by our research group, reference values for ophthalmic diagnostic tests (including IOP) in clinically normal Syrian hamsters (Mesocricetus auratus) were reported. The purpose of the study reported here was to assess circadian variation in IOP throughout the day in Syrian hamsters, a nocturnal species. We also assessed effects of anesthetic agents on IOP in clinically normal Syrian hamsters.
PSL portable slit lamp, Reichert Inc, Buffalo, NY.
Binocular indirect ophthalmoscope, Welch Allyn Inc, Skaneateles Falls, NY.
Fluorescein Glostrips Nomax Inc, St Louis, Mo.
Zone-Quick, Menicon America Inc, San Mateo, Calif.
TonoVet, Icare, Tiolat, Helsinki, Finland.
Ketamine 10%, Alfasan, Woerden, The Netherlands.
Xylazine 2%, Alfasan, Woerden, The Netherlands.
Zepadic, Caspian Tamin Pharmaceutical Co, Rasht, Iran.
IBM SPSS 20.0 for Windows, IBM Co, Chicago, Ill.
2. Grzimek B. Hamsters. In: McDade MC, ed. Grzimek's animal life encyclopedia. 2nd ed. Farmington Hills, Mich: Thomson Gale Press, 2008; 239–249.
5. Cunningham AJ, Barry P. Intraocular pressure—physiology and implications for anesthetic management. Can Anaesth Soc J 1986;33: 195–208.
10. Varga M. Anaesthesia and analgesia. In: Harcourt-Brown F, ed. Textbook of rabbit medicine. Oxford: Butterworth-Heinemann Press, 2002; 178–202.
11. Heatley J, Camille Harris M. Hamsters and gerbils. In: Mitchell M, Tully TN Jr, eds. Manual of exotic pet practice. St Louis: Saunders/Elsevier, 2008; 406–432.
12. Rajaei SM, Mood MA, Sadjadi R, et al. Results of selected ophthalmic diagnostic tests for clinically normal Syrian hamsters (Mesocricetus auratus). Am J Vet Res 2016;77: 72–76.
13. Wang X, Dong J, Wu Q. Twenty-four-hour measurement of IOP in rabbits using rebound tonometer. Vet Ophthalmol 2013;16: 423–428.
14. Benozzi J, Nahum LP, Campanelli JL, et al. Effect of hyaluronic acid on intraocular pressure in rats. Invest Ophthalmol Vis Sci 2002;43: 2196–2200.
15. Liu JH, Dacus AC. Endogenous hormonal changes and circadian elevation of intraocular pressure. Invest Ophthalmol Vis Sci 1991;32: 496–500.
16. Willis MA, Anderson DE, Gemensky AJ, et al. Evaluation of intraocular pressure in eyes of clinically normal llamas and alpacas. Am J Vet Res 2000;61: 1542–1544.
17. Wilkie DA, Latimer CA. Effects of topical administration of 2.0% pilocarpine on intraocular pressure and pupil size in cats. Am J Vet Res 1991;52: 441–444.
18. Bito LZ, Merritt SQ, DeRousseau CJ. Intraocular pressure of rhesus monkeys (Macaca mulatta). I. An initial survey of two free-breeding colonies. Invest Ophthalmol Vis Sci 1979;18: 785–793.
19. Chen CL, Gelatt KN, Gum GG. Serum hydrocortisone (cortisol) values in glaucomatous and normotensive Beagles. Am J Vet Res 1980;41: 1516–1518.
22. Hartsfield SM. Advantages and guidelines for using ketamine for induction of anesthesia. Vet Clin North Am Small Anim Pract 1992;22: 266–267.
23. Lin HC. Dissociative anesthetics. In: Thurmon JC, Tranquilli WJ, Benson GJ, eds. Veterinary anaesthesia. 3rd ed. Philadelphia: Williams & Wilkins, 1996; 241–296.
24. Kovalcuka L, Bigele E, Bandere D, et al. The effects of ketamine hydrochloride and diazepam on the intraocular pressure and pupil diameter of the dog's eye. Vet Ophthalmol 2013;16: 29–34.
25. Holve DL, Gum GG, Pritt SL. Effect of sedation with xylazine and ketamine on intraocular pressure in New Zealand White rabbits. J Am Assoc Lab Anim Sci 2013;52: 488–490.
26. Ghaffari MS, Moghaddassi AP. Effects of ketamine-diazepam and ketamine-acepromazine combinations on intraocular pressure in rabbits. Vet Anaesth Analg 2010;37: 269–272.
27. Karabaǧli M, Özer K, Şahin I. The effects of xylazine-ketamine anaesthesia on intraocular pressure in dogs. Istanbul Univ Vet Fak Derg 2014;40: 260–263.
28. Hofmeister EH, Mosunic CB, Torres BT, et al. Effects of ketamine, diazepam, and their combination on intraocular pressures in clinically normal dogs. Am J Vet Res 2006;67: 1136–1139.
30. van der Woerdt A, Gilger B, Wilke D, et al. Effect of auriculopalpebral nerve block and intravenous administration of xylazine on intraocular pressure and corneal thickness in horses. Am J Vet Res 1995;56: 155–158.
33. Blumberg D, Congdon N, Jampel H, et al. The effects of sevoflurane and ketamine on intraocular pressure in children during examination under anesthesia. Am J Ophthalmol 2007;143: 494–499.
34. Johnson TV, Fan S, Toris CB. Rebound tonometry in conscious, conditioned mice avoids the acute and profound effects of anesthesia on intraocular pressure. J Ocul Pharmacol Ther 2008;24: 175–185.
35. Nagdeve NG, Yaddanapudi S, Pandav SS. The effect of different doses of ketamine on intraocular pressure in anesthetized children. J Pediatr Ophthalmol Strabismus 2006;43: 219–223.