RESUMO
PURPOSE: To evaluate how temperature impacts the rheology of common Ophthalmic Viscoelastic Devices (OVDs) and clinical implications. SETTING: Tennent Institute of Ophthalmology, Glasgow, with Department of Mechanical and Aerospace Engineering, and Advanced Materials Research Laboratory, University of Strathclyde, Glasgow, UK. DESIGN: Laboratory pilot study. METHODS: The viscous and elastic responses of three OVDs (Eyefill-SC/Eyefill-C/Eyefill-HD; Bausch & Lomb) were measured using rotational and extensional rheometers at clinically relevant temperatures (5°C, 25°C, 37°C). Thermal properties were evaluated using differential scanning calorimetry and laser-flash analysis. RESULTS: The OVDs tested exhibited viscoelastic properties and shear-thinning behaviour. Apparent viscosities and relaxation time were higher at lower temperatures. The Eyefill-C and Eyefill-SC exhibited predominantly viscous character at low frequencies with a transition to predominantly elastic behaviour at high frequencies. An increase in temperature led to a decrease in relaxation time under shear and extension. At low frequencies, Eyefill-C and Eyefill-SC moduli increase with decreasing temperatures. Eyefill-HD at 25°C and 37°C displays two cross-over points, with the storage modulus dominating at low and high frequencies indicating a predominantly elastic behaviour. Thermal property analysis revealed Eyefill-C had the lowest thermal conductivity. CONCLUSIONS: This pilot study confirms our clinical experience that OVD properties are affected by low temperatures, with increased viscosities at low shear rates and higher relaxation times.Cold OVD can cause greater resistance to initiation of IOL injection system forces (compared to warmer OVD). Excessively forced injection using cold OVD could contribute to inadvertent cannula detachment if incorrectly assembled, or uncontrolled IOL release leading to avoidable injury.