Contamination of disposable tonometer prisms during tonometry

Goldmann Applanation Tonometry: Comparison of Intraocular Pressure Values Obtained with Disposable Tip and Conventional Applanation Prism in the Population without Clinical Signs of Glaucoma

Aim

Comparing intraocular pressure (IOP) measurements using Goldmann applanation prism and TonoSafe® in the population without signs of glaucoma.

Material and methods

Patients with no ocular pathologies, except ametropia (until ± 4 D) or IOP of <30 mm Hg without signs of glaucoma by optic disc structural analysis by fundus biomicroscopy. The IOP was measured sequentially using the traditional cone and the TonoSafe®, according to a randomization list to determine which device would be used first. The measurements from the right and left eyes were compared separately. Since there was no statistical difference, both eyes were considered in this study.

Results

A total of 385 eyes of 194 patients with a mean age of 66.4 ± 11.2 years old were included. The mean IOP with conventional prism was 14.2 ± 3.6 and 14.3 ± 3.6 mm Hg with TonoSafe®. Differences were not statistically significant by the Wilcoxon test (p = 0.3). The median was 14.0 mm Hg for both groups. The mean difference between measurements was 0.04 mm Hg, with the median equal to zero. There was no statistical difference in IOP readings according to which device was the first measurement.

Conclusion

No statistical difference was found in IOP was measured with conventional prism or TonoSafe® in the population without signs of glaucoma.

Clinical significance

The data provided by our study support the efficacy and safety of the disposable tonometer compared to the Goldman tonometer in measuring IOP in patients without glaucoma.

How to cite this article

Soares PHA, Santos RDO, Filho CRADM, et al. Goldmann Applanation Tonometry: Comparison of Intraocular Pressure Values Obtained with Disposable Tip and Conventional Applanation Prism in the Population without Clinical Signs of Glaucoma. J Curr Glaucoma Pract 2023;17(2):75-78.

Economic and Environmental Impact of Single-use Plastics at a Large Ophthalmology Outpatient Service

PRéCIS:: The use of disposable tonometer prisms and gonioscopy lenses at a large ophthalmology outpatient service incurs significant financial and environmental waste that may not be justified given the limited data surrounding arguments for their use.

PURPOSE

To quantify the economic and environmental burden of single-use plastics from an ophthalmology outpatient service at a large tertiary hospital and describe the relative value and evidence for the safety of disposable versus nondisposable tonometer prisms and gonioscopy lenses.

METHODS

The total number of single-use applanation tonometer prisms and gonioscopy lenses used per year at Boston Medical Center (BMC) was estimated, and the average dollars spent and plastic waste generated in kilograms per year were then determined. These values were compared with the total spending and waste that would be produced if the clinic were to use nondisposable tonometer prisms and gonioscopy lenses exclusively.

RESULTS

Single-use tonometer prisms cost an average of $70,282 per year and produce ~100.8 kg of plastic waste per year at BMC. Single-use gonioscopy lenses cost ~$9,040 per year and produce 8.8 kg of plastic waste per year at BMC. An excess of $65,185 and 109.6 kg of plastic waste could be avoided each year by only using nondisposable tonometer prisms and gonioscopy lenses at the BMC ophthalmology outpatient service.

CONCLUSIONS

Single-use plastics in ophthalmology outpatient services generate significant environmental waste and financial cost compared with nondisposable instruments. This cost may outweigh the benefits of these instruments given the limited data surrounding arguments for their use.

Disposable versus non-disposable tonometer prisms: a UK national survey

Purpose

To determine the prevalence of disposable tonometer versus non-disposable tonometer use in the UK and to determine methods of decontamination and frequency of replacement of prisms.

A total of 137 ophthalmology departments were interviewed by telephone using a structured questionnaire. The main outcome measured were:

types of tonometer prisms used in clinic (disposable, non-disposable and/or other)

average disposable prisms used per clinic session

average lifespan of non-disposable prisms

prism preference by glaucoma and other teams within department.

A cost and benefit analysis was then performed on the data acquired.

Results

One hundred and fifty-five departments were identified for the survey. Of these, 137 (88.3%) responded. Eighty-one departments (59.1%) used Tonosafe prisms alone, whereas 22 departments (16.1%) used Goldmann non-disposable prisms exclusively. Thirty-five departments (64%) on average have a change rate of 26.5% per year (range: 0–100, median: 20) attributed to damage, loss or theft. Sixteen departments (29%) reported that prisms were used until damaged or lost. Four departments (7%) were uncertain of their prism usage and could not provide further information.

Conclusions

Majority of eye departments in the UK opt for disposable prisms. This survey shows the perceived cost-effectiveness of disposable prisms is overestimated when the true cost of disinfection and damage is taken into account. Significant cost savings coupled with the low risk of infectivity (if decontaminated properly) should prompt clinicians and ophthalmic departments worldwide to reconsider the use of non-disposable prisms.

A systematic review and cost-effectiveness analysis of tonometer disinfection methods

OBJECTIVE

The Goldmann applanation tonometer presents the problem of being one of the most widely used pieces of equipment in the ophthalmic clinic and a known risk factor for the transmission of epidemic keratoconjunctivitis (EKC). The purpose of this review is to assess the effectiveness of 3 methods of disinfection: alcohol swabs, immersion in peroxide, and the use of disposable prisms. An economic evaluation is undertaken to assess the cost-effectiveness of the 3 alternatives. In doing so, we contribute an evidence-based overview of the issue at an opportune time, because several jurisdictions are developing protocols regarding tonometer tip disinfection.

DESIGN

Systematic review and cost-effectiveness analysis.

METHODS

A comprehensive literature review was undertaken with a librarian, comprising searches of 6 electronic databases and hand searches of the grey literature. A 3-level screening process was undertaken by 2 reviewers according to prespecified inclusion and exclusion criteria. Values from included papers were used to inform a cost-effectiveness analysis undertaken using a decision tree model implemented in TreeAge. The analysis was undertaken from the hospital perspective and included all equipment and labour costs.

RESULTS

Synthesis of in vitro data indicates that all 3 methods are plausible methods of disinfection with a 64% reduction in log growth of EKC when peroxide is used compared with alcohol swabs. The incremental cost-effective ratios from the cost-effectiveness analysis were $12,000/case averted using peroxide and $61,000/case averted with Tonosafe as compared with alcohol.

CONCLUSIONS

Assuming clinical infection rates match in vitro disinfection data, the cost of bleach is high and the cost of Tonosafe is unacceptably high to reduce 1 potential case of adenoviral keratoconjunctivitis.

Comparison of IOPen rebound tonometer with Goldmann applanation tonometer at different IOP levels

AIM

To compare the accuracy of IOPen rebound tonometer with Goldmann applanation tonometer (GAT) in individuals with low, normal and high intraocular pressure (IOP) and to evaluate the effect of central corneal thickness (CCT) on IOP measurements.

METHODS

This cross-sectional study consisted of 159 participants. IOP of one eye of each subject was measured consecutively with IOPen and GAT. Then CCT was measured using an ultrasonic pachymeter. Based on GAT IOP readings, participants were divided into low, normal and high IOP groups. Correlation between tonometers and CCT was calculated by spearman's correlation coefficient. Agreement between tonometers was evaluated using Bland-Altman method.

RESULTS

Non-significant underestimation of IOP by IOPen was observed in low IOP group (Mean difference: 0.20mmHg; P=0.454) and also in normal IOP group (Mean difference: 0.56mmHg; P=0.065). However, IOPen significantly overestimated IOP in high IOP group (Mean difference: 1.06mmHg; P=0.038). The 95% limits of agreement (LoA) width between IOPen and GAT IOPs were 7.84, 8.57 and 14.27mmHg in low, normal and high IOP groups, respectively. Low IOP group had thinner corneas compared to high IOP group (P=0.034). IOP measurements taken by IOPen were not influenced by CCT (P=0.099) while poor correlation between CCT and GAT was found (R=0.17, P=0.032). Using receiver operating characteristic (ROC) curve, cutoff value of 18.75mmHg was determined for IOPen with sensitivity of 98.1 and specificity of 97.2%.

CONCLUSION

Accuracy of IOPen is comparable to GAT in patients with low or normal IOP but IOPen overestimates IOP at high IOP levels. CCT does not affect IOP readings with IOPen.

Minimal cross-infection risk through Icare rebound tonometer probes: a useful tool for IOP-screenings in developing countries

AIMS

Recently, a new rebound tonometer has been introduced into the market, which might be useful for glaucoma screenings in developing countries. Disposable probes, that are potentially reusable, are recommended by the manufacturer. Our study aimed to address the question of microbial transmission risks if the probes are reused.

METHODS

IOP measurements were obtained from 100 healthy eyes. The used probes were inoculated on broth and culture media. In addition, 10 probes were analyzed using environmental scanning electron microscopy in saturated hydrogen-steam atmosphere after usage and wipe disinfection technique with Sekusept 4% solution or Isopropanol 70%.

RESULTS

No bacterial or fungal growth could be detected in any of the inoculated agar plates or broth tubes. No microorganisms, clumps of cells, or single intact epithelium cells were detected in any of the probes using environmental scanning electron microscopy. Cell debris was detected on seven probes; three probes were completely free of any residual cell elements.

CONCLUSION

Transmission of possibly infective material through reused probes is significantly less than for reusable Goldmann probes if the same sterilization protocols are applied. Re-usage of the probes appears safe and is helpful in avoiding unnecessary costs.

Prion stability and infectivity in the environment

The biology of normal prion protein and the property of infectivity observed in abnormal folding conformations remain thinly characterized. However, enough is known to understand that prion proteins stretch traditional views of proteins in biological systems. Numerous investigators are resolving details of the novel mechanism of infectivity, which appears to feature a protein-only, homologous replication of misfolded isoforms. Many other features of prion biology are equally extraordinary. This review focuses on the status of infectious prions in various natural and man-made environments. The picture that emerges is that prion proteins are durable under extreme conditions of environmental exposure that are uncommon in biological phenomena, and this durability offers the potential for environmental reservoirs of persistent infectivity lasting for years. A recurrent theme in prion research is a propensity for these proteins to bind to mineral and metal surfaces, and several investigators have provided evidence that the normal cellular functions of prion protein may include metalloprotein interactions. This structural propensity for binding to mineral and metal ions offers the hypothesis that prion polypeptides are intrinsically predisposed to non-physiological folding conformations that would account for their environmental durability and persistent infectivity. Similarly, the avidity of binding and potency of prion infectivity from environmental sources also offers a recent hypothesis that prion polypeptides bound to soil minerals are actually more infectious than studies with purified polypeptides would predict. Since certain of the prion diseases have a history of epidemics in economically important animal species and have the potential to transmit to humans, urgency is attached to understanding the environmental transmission of prion diseases and the development of protocols for their containment and inactivation.

Comparison of the rebound tonometer with the Goldmann applanation tonometer in glaucoma patients

PURPOSE

To determine the agreement between the measurement of intraocular pressure (IOP) by the rebound tonometer (RBT) and by the Goldmann applanation tonometer (GAT) and to find out the effect of central corneal thickness (CCT) values on IOP measurements in glaucoma patients.

METHODS

IOP was measured with the RBT and GAT, respectively, in 61 eyes of 61 glaucoma patients. CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. The mean IOP measurement by the RBT was compared with the measurement by the GAT, by Student's t-test. Bland-Altman analysis was performed to assess the clinical agreement between the two methods. The effect of CCT on measured IOP was explored by linear regression analysis.

RESULTS

The mean patient age was 56.7+/-21.1 years (range: 30-80 years). There were 32 (52.46%) women and 29 (47.54%) men in the study group. The mean IOP readings were 18.70+/-4.76 mmHg using the RBT, and 18.27+/-3.49 mmHg using the GAT. The difference was not statistically significant (mean difference 0.43+/-2.55, P=0.2). A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <2.3 mmHg between the RBT and GAT. There was a strong correlation between the RBT and GAT readings (r=0.852, P<0.0001). The IOP measurements with the two methods were correlated with CCT (r=0.40, P=0.02 for the RBT and r=0.48, P<0.0001 for the GAT). The IOP increased 1.1 mmHg and 8 mmHg for every 100-microm increase in CCT for the GAT and RBT, respectively.

CONCLUSION

The RBT slightly overestimated the IOP value by 0.43 mmHg on average when compared with the GAT. Nevertheless, the RBT readings appeared to be more affected by the various thicknesses of different corneas when compared with those obtained using the GAT.

Tonometer disinfection practice in the United Kingdom: A national survey

PURPOSE

To assess current tonometer disinfection practice in the UK, and compare with published recommendations.

METHODS

Every ophthalmology unit with training recognition in the UK was contacted (n=155). A senior nurse at each institution completed a telephone questionnaire regarding local tonometer disinfection practice.

RESULTS

The response rate was 100%. Thirty-five units (23%) reported exclusive use of disposable tonometer heads and were excluded from further analysis. One hundred and twenty units (77%) used either reusable or a combination of reusable and disposable tonometer heads. Where reusable heads were used, 80 units (67%) immersed them in a chlorine-based solution such as sodium hypochlorite or sodium dichloroisocyanurate. Others used isopropyl alcohol (18 units), hydrogen peroxide (12 units), chloramine (5 units), chlorhexidine (4 units) and peracetic acid (1 unit). Where a chlorine-based agent was used, the concentration of available chlorine ranged from 125 to 30 000 p.p.m., with 50 units (63%) using a concentration of less than 5 000 p.p.m. (i.e., inadequate based on published recommendations). Where the tonometer head was immersed in disinfectant between patients (n=101), 29 units (29%) provided just one tonometer head per practitioner, making adequate soak time between patients unlikely. Every unit replenished the disinfectant at least daily, deemed sufficient for most agents. However, hydrogen peroxide solutions should be replenished twice daily, which did not take place in nine units.

CONCLUSION

This survey reveals disparity between current tonometer disinfection practice and published international recommendations, with some institutions using practices that may render patients susceptible to transmissible infection.

Are Disposable Prisms an Adequate Alternative to Standard Goldmann Tonometry Prisms in Glaucoma Patients?

PURPOSE

To evaluate the accuracy and reliability of 2 single-use tonometry devices (Tonosafe and Tonojet) as an alternative to standard Goldmann prisms in patients attending dedicated glaucoma clinics.

DESIGN

Prospective experimental study with human subjects.

PARTICIPANTS

Two hundred forty glaucoma patients who attended 2 glaucoma clinics at the Stepping Hill Hospital between January and February 2005.

METHODS

During each examination, intraocular pressure (IOP) was measured 3 times, using the standard Goldmann prism, Tonosafe, and Tonojet, respectively. The prism sequence was predetermined at random using a computer, and the measurements were taken at 5-minute intervals. Data were analyzed using the Bland-Altman method of differences.

MAIN OUTCOME MEASURE

Intraocular pressure.

RESULTS

Intraocular pressure ranged from 6 to 68 mmHg. Linear regression analysis indicated that there was a proportional bias between Goldmann and Tonosafe (r2 = 0.368, P<.001), especially for values higher than 25 mmHg. On the other hand, there was no statistically significant proportional bias between Goldmann and Tonojet (r2 = 0.006, P = 0.14).

CONCLUSIONS

Caution should be exercised when using Tonosafe prisms in the presence of IOP higher than 25 mmHg. On the other hand, Tonojet is an adequate and useful alternative to the Goldman tonometer for glaucoma patients.