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Commentary: Tonometry probes – Is sterilization mandatory with every reutilization?

2023; Medknow; Volume: 71; Issue: 5 Linguagem: Inglês

10.4103/ijo.ijo_238_23

1998-3689

Shaina Saroya, Kirandeep Kaur, Arnav Singh Saroya, Bharat Gurnani, Arvind Kumar Morya,

Ocular Surface and Contact Lens

Glaucoma is the leading cause of irreversible blindness in the world, with a reported prevalence varying from 2.1 to 2.6%.[1] Childhood glaucoma alone is known to affect >3,00,000 children worldwide, causing significant years of vision loss.[2] Thus, it is essential to correctly estimate the intraocular pressure (IOP) as this is a disease affecting all age groups. Glaucoma has been often referred to as a silent thief of vision, as the visual defect is often not perceived until advanced damage has happened. There are different methods of IOP measurement, including direct methods–manometry and indirect methods–tonometry. Goldmann tonometry, an applanation procedure, is the gold standard for IOP measurement. Rebound tonometry (RT) is used for estimating IOP based on deceleration and rebound time from the corneal surface. Different models include iCare TA01i, iCare PRO, iCare HOME, and iCare ic100. iCare, a rebound tonometer, is an Food and Drug Administration (FDA)-approved handheld battery-based device that bounces a small and is a light-weighted disposable probe. This is specifically useful for children and patients with corneal opacity. Other recent advances include Tono-Pen, the ICare tonometer, dynamic contour tonometry, TGDc-01 tonometry, and the ocular response analyzer. Multiple innovations from time to time have been attempted to minimize measurement errors. However, still, significant concerns lie regarding the cost of disposable tonometry probes and disinfection techniques. Many different techniques have been proposed and tested for the disinfection of tonometry probes. Some of these include dry heat, mechanical cleaning with a disposable wipe/sterile gauze, cleaning with gauze soaked in alcohol or chemicals such as hydrogen peroxide and merthiolate, soaking in chemicals such as 70% isopropyl alcohol, 1:1000 merthiolate, 3% hydrogen peroxide, and 1:10 diluted household bleach (sodium hypochlorite), ultraviolet rays, and gas sterilization. However, all these techniques are unreliable, time-consuming, or might damage the tonometry probes.[3] Schmitz et al.[4] described the use of ultraviolet radiations for activation of herpes simplex virus type 1 and adenovirus type 2. In developing countries, glaucoma is becoming like a two-edged sword. The increasing burden of the disease impels the need for cost-effective screening technologies. Another challenge is to decrease the cost of glaucoma management among diagnosed cases. The idea for disinfection of tonometry probes is a simple way of cutting down the cost of glaucoma screening. Komatsu et al.,[5] in their study, proved the transmission of hepatitis B through tears. Results from a study by Amin et al.[6] confirmed the transmission of proteinaceous material through contact tonometry. They also found that this transmission could be reduced if the tonometer tips were rinsed in water. Britt et al.,[7] in their study, tested the dispersion of HIV transmission risk during air puff tonometry and confirmed the scatter of eye droplets when the puff was blown for IOP estimation. A safe and innovative way of three-step disinfection was described by Hu et al.,[8] including wiping of tonometer probes with swabs soaked with 75% ethyl alcohol, ofloxacin eye drops, and 75% ethyl alcohol for at least 5 s. Atkins et al.,[9] in their review article, studied different tonometry procedures and found that all tonometers contribute to the transmission of infections in vitro. They also reported variability among different sterilization techniques. Thus, there is no clear-cut evidence of how much different tonometers predispose quantitatively toward the risk of infection transmission. In the present study, a comparison has been made between the Goldmann applanation (GAT) and the RT, and the potential risk of bacterial transmission using Escherichia coli (E. coli) and Pseudomonas fluorescens (P. fluorescens) has been suggested.[10] The bacterial load on both the tonometry probes was compared, and they found that a high number of bacteria could adhere to RT (1.7 mm diameter, 4.5 mm² surface area) compared to GAT (6 mm diameter, 28 mm² surface area) despite its smaller surface area. This indicated that the risk of transmission is not directly dependent on the size of the probes but also on the texture, which leads to higher pathogens per surface unit, making it less favorable compared to GAT in this trial. The second in vivo trial was conducted to test if bacteria get transferred when a non-disinfected RT probe was reused. The results showed bacterial growth on the agar plates in nearly one-third of the cases, showing a raised risk of pathogen transfer via non-disinfected or insufficiently disinfected tonometer probes. Even though the small number of participants in this study is one of its limitations. Despite that, through the in vitro and in vivo trials, the present study solidly demonstrates the possible transmission of a bacterial pathogen through non-disinfected RT tonometer probes. The study results have a very important clinical implication showing the high risk of bacterial contamination of tonometry probes. Thus, it is important to disinfect the probes even though the risk of clinically relevant infection is less. Thus, regardless of the type of tonometry, it is important to disinfect them thoroughly if these are to be re-utilized.