The Animal Care Committee of Asahikawa Medical University approved the protocols describing the use of cats and adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Eighty adult cats (2.3–4.5 kg) of either sex were tracheostomized and mechanically ventilated with room air containing 2% sevoflurane. The flow rate of sevoflurane was maintained at 1.5 L/min during the experiment. Catheters were placed in the femoral arteries and vein. The mean arterial BP (MABP) and heart rate were monitored continuously with a transducer (PowerLab; ADInstruments, Inc., Colorado Springs, CO, USA) and recorder (LabChart; ADInstruments, Inc.) in the proximal thoracic descending aorta. Pancuronium bromide (0.1 mg/kg/h) (Daiichi Sankyo Co., Tokyo, Japan) was infused continuously via the femoral vein to maintain skeletal muscle relaxation during the experiment. With the animals prone, the heads were fixed in a stereotaxic instrument. Arterial pH (pH), arterial partial carbon dioxide tension (PaCO2), arterial partial oxygen tension (PaO2), and bicarbonate ion (HCO3−) were measured intermittently with a blood gas analyzer (model ABL5; Radiometer, Copenhagen, Denmark). The rectal temperature was measured and maintained between 37°C and 38°C with a heated blanket. The pupils were dilated with 0.5% tropicamide (Santen Pharmaceutical Co., Osaka, Japan). A 0-diopter contact lens (SEED Co. Ltd., Tokyo, Japan) was placed on the cornea, which was protected by instillation of a drop of sodium hyaluronate (Healon; Abbott Medical Optics, Inc., Abbott Park, IL, USA). A 26-gauge butterfly needle was inserted into the anterior chamber and connected to a pressure transducer and a balanced salt solution (Alcon, Fort Worth, TX, USA) reservoir for monitoring and maintaining the intraocular pressure (IOP) at a constant 10 mm Hg, respectively.