The impact of temperature on Ophthalmic Viscoelastic Devices and clinical implications - a pilot study: Temperature effect on Ophthalmic Viscoelastic Devices.

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.

Benefits to utilising ultrasound in examining the eye.

Ocular ultrasound (US) is not one of ACEMs 'big 5' in terms of US capability that is expected of a trainee or FACEM. Most texts have a small chapter dedicated to ocular US but it is usually at the back or a subsection of a chapter where it is rarely seen or appreciated. However, it is a straightforward scan to perform with many benefits which will be discussed in this article. The eye offers an excellent medium for US beam penetration, making good quality images of the retina easy and quick to acquire. This has the added benefit of being able to share images with an ophthalmologist remotely, improving time to definitive treatment. It can also be used in patients who cannot cooperate with sitting at a slitlamp, for example moribund or trauma patients. The authors propose that ocular US teaching should be incorporated into the ACEM syllabus, being a vital adjunct to a comprehensive eye examination.