transducer were smaller. Langham and Edwards10 evaluated 20 eyes of 12 rabbits under open and closed stopcock conditions and found that the pneumatono-.
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4. Pomerantz RJ, Kuritzkes DR, de la Monte SM, et al. Infection of the retina by human immunodeficiency virus type 1. NewEnglJMed. 1987;317:1643-1647. 5. Faber DW, Wiley CA, Lynn GB, Gross JG, Freeman WR. Role of HIV and CMV in the pathogenesis of retinitis and retinal vasculopathy in AIDS patients. Invest Ophthalmol Vis Sri. 1992;33:2345-2353. 6. Qavi HB, Green MT, SeGall GK, Lewis DE, Hollinger FB. Transcriptional activity of HIV-1 and HHV-6 in retinal lesions from AIDS patients. Invest Ophthalmol Vis Sri. 1992;33:2759-2767. 7. Gao E-K, Yu X-H, Lin C-P, Zhang H, Kaplan HJ. Intraocular viral replication after systemic murine cytomegalovirus infection requires immunosuppression. Invest Ophthalmol Vis Sri. 1995;36:2322-2327. 8. Stoddart CA, Cardin RD, Boname JM, Manning WC, Abenes GB, Mocarski ES. Peripheral blood mononuclear phagocytes mediate dissemination of murine cytomegalovirus. J Virol. 1994; 68:6243-6253. 9. Atherton SS, Newell CK, Kanter MY, Cousins SW. Retinitis in euthymic mice following inoculation of murine cytomegalovirus (MCMV) via the supraciliary route. CurrEyeRes. 1991; 10:667-677.
Comparison of Three Tonometers for Measuring Intraocular Pressure in Rabbits Lisa S. Abrams, Susan Vitale, and Henry D. Jampel Purpose. Rabbits are used commonly for the evaluation of drugs and surgery to lower intraocular pressure (IOP). The authors compared the accuracy and variability of three tonometers for measuring IOP in rabbits. Methods. The anterior chamber of adult rabbits was cannulated with a 25-gauge needle connected to an elevated bottle of balanced salt solution. The bottle was raised and lowered to control IOP. A fluid-filled pressure transducer also was placed in the anterior chamber. Intraocular pressure was decreased in increments of 5 to 10 cm H2O from 50 to 0 mm Hg and was recorded with each of these instruments: the hand-held applanation tonometer, the Tono-pen XL, and the pneumatonometer. From the Wilmer Ophlhalmological Institute, Johns Hopkins University, Baltimore, Maryland. Presented in part al the annual meeting of the Association for Research in Vision and Ophthahnology, Sarasota, Florida, May 1994. Supported by National Glaucoma Research, American Health Assistance Foundation, Rockville, Maryland. Submitted for publication July 5, 1995; revised November 3, 1995; accepted December 13, 1995. Proprietary interest category: N. Reprint requests: Lisa S. Abrams, Wilmer Ophthalmological Institute, Johns Hopkins University, 600 North Wolfe Street, Baltimore, MD 21287-9205.
10. Bale JFJr, O'Neil ME, Lyon B, Perlman S. The pathogenesis of murine cytomegalovirus ocular infection: Anterior chamber inoculation. Invest Ophthalmol Vis Sri. 1990;31:1575-1581. 11. Holland GN, Fang EN, Glasgow BJ, et al. Necrotizing retinopathy after intraocular inoculation of murine cytomegalovirus in immunosuppressed adult mice. Invest Ophthalmol Vis Sri. 1990; 31:2326-2334. 12. Bale JFJr, O'Neil ME. Detection of murine cytomegalovirus DNA in circulating leukocytes harvested during acute infection of mice. / Virol. 1989; 63:26672673. 13. Grefte A, Harmsen MC, van der Giessen M, Knollema S, van Son WJ, The TH. Presence of human cytomegalovirus (HCMV) immediate early mRNA but no ppUL83 (lower matrix protein pp65) mRNA in polymorphonuclear and mononuclear leukocytes during active HCMV infection. / Gen Virol. 1994; 75:19891998. 14. Duan Y, Ji Z, Atherton SS. Dissemination and replication of MCMV after supraciliary inoculation in immunosuppressed BALB/c mice. Invest Ophthalmol Vis Sri. 1994; 35:1124-1131.
Results. The Tono-pen XL and the hand-held applanation tonometer underestimated the IOP, whereas the pneumatonometer slighdy overestimated IOP. Under closed stopcock conditions, at IOPs between 3 and 30 mm Hg, the Tono-pen XL was as accurate as the pneumatonometer but had a smaller variance; the hand-held applanation tonometer had lower accuracy and higher variability. Conclusions. The Tono-pen XL is the tonometer of choice for measuring IOP in rabbits within the range of IOP 3 to 30 mm Hg. All tonometers were less accurate when the IOP was elevated markedly. Invest Ophthalmol Vis Sci. 1996; 37:940-944. Jvabbits often are used in the evaluation of new medications and surgical procedures for glaucoma. Although the measurement of intraocular pressure (IOP) in rabbits has been extensively studied,1"4 the optimal method has not been established. The pneumatonometer is frequently used, but it has the theoretical disadvantage of being a high displacement tonometer. The hand-held applanation tonometer has only occasionally been used. The Tono-pen XL (Mentor, Norwell, MA), a miniaturized Mackay-Marg tonometer, has recently come into use as a convenient, portable, accurate instrument for the measurement of IOP in humans,5'6 and it might be a good choice for measuring IOP in rabbits. In the current study, we sought to compare the usefulness of the pneumatonometer,
Reports
the hand-held applanation tonometer, and the Tonopen XL for the measurement of IOP in rabbits. METHODS. Four eyes of four New Zealand white rabbits were studied. All studies were approved by the institutional Animal Care and Use Committee and were in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. The rabbits were sedated with an intramuscular injection of a 1:1 mixture of ketamine hydrochloride and xylazine. At the start of each experiment, baseline IOP was measured after sedation, before any intraocular manipulation. Intraocular pressure was measured with a pneumatonometer (Biorad, Santa Ana, CA), a handheld applanation tonometer (Kowa Optimed, Torrance, CA), and the Tono-pen XL (Mentor, Norwell, MA). Each tonometer was first calibrated according to the manufacturer's instructions. Measurements by the Tono-pen XL were repeated until the coefficient of variation was displayed as
