Reutilization of disposable rebound tonometer probes: Risk or return?

Purpose: An advantage of rebound tonometry (RT) is its ease of use so that it can also be operated by health care technicians. However, the cost of the disposable measuring probes is high and their reuse carries the risk of infection. Therefore, this study aims to objectify the potential risk of bacterial transmission by RT. Methods: Our experimental setting consisted of two experiments. The first aimed to quantify the number of bacteria on a tonometer probe after immersion in a bacterial suspension in vitro. The experiment was carried out with two different bacteria and compared with results from a Goldmann tonometer probe. The second experiment tested whether bacteria could be transmitted by simulating reuse of a nondisinfected rebound tonometer probe. Results: First experiment: After immersion of the rebound tonometer probe, we measured a bacterial count of 2.43 × 106 Escherichia coli (EC) and 1.12 × 106 Pseudomonas fluorescens. In total, 1.09 × 107 bacteria for EC and 2.61 × 106 for Pseudomonas fluorescens (PF) were measured on the Goldmann tonometer probe. Second experiment: A bacterial transmission could be detected in 36% of cases in which reuse of nondisinfected tonometer probes was simulated. Conclusion: These results show that despite the small surface of the rebound tonometer probe, there is a clear risk of bacterial transmission. Thorough disinfection according to general standards should be mandatory if the tonometer probes are to be reused.

Location and pressure dependent transmission of human and porcine sclera: an anterior to posterior examination.

PURPOSE: For diaphanoscopy or transscleral laser applications, the transmission of the sclera is an essential property. The study aimed to determine the pressure dependent transmission of human sclera from anterior to posterior. METHODS: Pressure dependent transmission measurements were performed by a pressure inducing setup at the range of 60-2058 kPa. The transmissions were measured within spectral range of 350-1100 nm. Specimens of human sclera were taken from corneo-scleral transplants. Those compounds were obtained at pars plicata residual sclera tissue. For an anterior to posterior examination of transmission, samples were taken from halved eye globes, which were formerly fixed in formalin. RESULTS: The pressure dependent transmission increased with rising load at all measured wavelengths for human sclera samples. The highest increase was observed for short wavelengths. With rising pressure, the increase of transmission aimed for a steady state. This behavior was fitted by a limited growing function. With an inducing burden of 2058 kPa, the steady state was already reached and exhibited an increase in transmission factor of 4.1 at 400 nm and 1.8 at 1000 nm. The anterior to posterior measurements of human sclera fixed in formalin were not corresponding to the results of the other human samples. For the porcine samples, the transmission increased from anterior to the equator of the eye globe. Further posterior the transmission decreased and rose again to N. opticus. With rising pressure, the transmission increased at all wavelengths and all locations. Posterior from the equator, with higher pressure the transmission became superior compared to anterior. CONCLUSIONS: The results of human sclera fixed in formalin could be related to formalin-induced cross-linking between the collagen fibers. Because of doubt about the physiological behavior of formalin-fixed samples, formalin-free porcine postmortem eye globes were also probed having a very similar thickness and histological structure as human sclera, so the results could be set in relation to human probes. These results can now be used to create an eye-map to determine maximum possible retina irradiation or illumination durations for transscleral applications in eye surgery.

Transscleral LED illumination pen.

Existing light sources for intraocular illumination are often bulky and expensive and pose a risk for the patient, because light guides are inserted in the eye through incisions and if the tip of these light guides get too close to the retina, the retina can be damaged photochemically within minutes or even seconds. Therefore a new, safe and simple device for intraocular illumination is developed and evaluated for its thermal and photochemical risks to the patient. It consists of a white LED which is integrated into a pen like holder. This device is pressed against the sclera by the physician who seeks for illumination during surgery or for diagnostic purposes. The LED light is transmitted through the sclera without the need for an incision. Considering the relevant standards, the device poses no harm to the patient, and in tests with the authors' own eyes a sufficient intraocular illumination is reached. The proposed device is quite simple but easy to handle and very gentle for the patient.