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Introduction

Outbreaks of epidemic ocular infections have occurred in ophthalmology clinics in medical centres around the world in the past several years,1–3 with insufficient disinfection of Goldmann tonometer prisms being implicated as a potential source of transmission.4 Epidemiological and clinical studies of epidemic keratoconjunctivitis outbreaks in ophthalmology clinics have demonstrated that tonometer tips, contaminated eye drops, and contact with infected healthcare workers are vehicles for transmission of adenovirus serotypes.3,5,6 Adenovirus can survive for
7–14 days at room temperature on a dry surface and is resistant to 70% isopropyl alcohol,7 which is often used in busy clinic settings.8 Improper sterilization techniques also increase the risk of corneal injury and burn secondary to residual cleansing solution on reusable Goldmann prisms.9

Therefore, in 2009, the Veterans Affairs Boston Healthcare System (VABHS) introduced single-use Tonosafe disposable tonometer prisms (Clement Clarke, Columbus, OH, USA) as an alternative to Goldmann tonometer prisms for measuring intraocular pressure (IOP) across all general and specialty eye clinics. The Tonosafe tonometer head, which consists of a precision- molded plastic holder and an acrylic disposable optical doubling applanating prism,10 has similar properties to the Goldmann tonometer. The Tonosafe holder and prism combined mass is equivalent to that of the Goldmann, 1.65±0.05 g, and has an identical applanating surface area.11 The Goldmann applanation tonometry method has inherent errors in IOP measurement accuracy, due to the variability in corneal thickness and rigidity, as well as the tear film surface tension. These are impacted by adhesion properties and the prism material, which exert a pressure that offsets the effect of corneal resistance.12 The acrylic Tonosafe tip may affect the adhesion properties of the tear film, leading to measurement errors as well.
Previous smaller studies have investigated the accuracy of the Tonosafe disposable tonometer prism compared with the Goldmann tonometer prism, with majority of IOP measurements being in the normal range,13 thereby lacking generalizability at higher pressures. This large-scale quality assurance study was conducted to assess the reliability of IOP measurements of the Tonosafe disposable compared with Goldmann tonometer prisms, particularly at the extremes of intraocular pressure, and to assess the suitability of the Tonosafe disposable tonometer prisms for clinic-wide implementation in an academic tertiary referral setting, as an acceptable substitute for GAT to measure IOP in ophthalmology clinics.

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Contact: Liz Vogel at 513-947-1444, ext. 18 or lizv@ideopia.com