Effect of Bottle Height and Vacuum Level on Fluid Dynamics during Phacoemulsification in Normal Canine Eyes Ex Vivo

Abstract

The purpose of the present study was to evaluate the effects of phacoemulsification with different fluidic parameters on the intraocular tissues and intraocular pressure (IOP) in dogs. Phacoemulsification is the most commonly performed cataract surgery. Fluid dynamics and phacodynamics have been reported as one of the important contributing factors to postoperative complications following phacoemulsification. Fluidic parameters consist of bottle height (BH), ultrasound energy, vacuum, and aspiration and irrigation flow rate. To improve the success rate of phacoemulsification, the surgeon must understand these parameters which maintain anterior chamber stability during phacoemulsification by the balance between the influx of irrigating fluid and both the efflux of aspirating fluid and incisional fluid loss. Advances in phacoemulsification technology and fluidics have enabled the operator to control these parameters, making the procedure safer and more effective. This study was performed to evaluate the effects of phacoemulsification using different BHs and vacuum levels on fluid dynamics inducing IOP and intraocular structural changes in normal canine eyes ex vivo. This study consists of two chapters. Chapter I demonstrated the effects of phacoemulsification with different fluidic parameters on the intraocular tissues using contrast-enhanced magnetic resonance imaging (CE-MRI). Phacoemulsification with the BH / the vacuum pressure set at 50 cm / 80 mmHg for one eye and at 120 cm / 150 mmHg for the opposite eye was performed on 10 pairs of enucleated canine eyes using irrigation fluid containing diluted MRI contrast agent. CE-MRI was carried out immediately after phacoemulsification. Low fluidic parameters led to decreased fluid passage through the zonules, reducing fluid passage into the vitreous. These also resulted in decreased amount of irrigation solution used during phacoemulsification in the dog. Chapter II optimized fluid dynamics to define the fluidic parameters for preventing surge and IOP elevation through measuring IOP in a venturi phacoemulsification machine in dogs. Flow and IOP were measured using a pressure transducer at various settings of BH and vacuum and with two different sized clear corneal incisions (CCI). Flow was directly proportional to the BH and vacuum, whereas IOP was directly proportional to the BH and inversely to the vacuum. Flow with an irrigation/aspiration (I/A) handpiece was significantly less than with a phaco handpiece, explaining why IOP with an I/A handpiece was significantly higher than with a phaco handpiece. With the I/A handpiece, vacuum parameters less than 450 mmHg did not result in surge. Although phacoemulsification with a 3.2 mm CCI could induce lower IOP, a 3.0 mm CCI might lessen the irrigation flow stress on the eye. Based on the results of the present studies, low fluidic parameters led to reduced surgical stress on the intraocular tissues by decreasing the amount of irrigation solution used and by decreasing IOP during phacoemulsification in the dog. In particular, BH during the I/A stage should be reduced to avoid unnecessary stress on the canine eye when using a venturi system.