Agreement of rebound and applanation tonometry intraocular pressure measurements during atmospheric pressure change

This study investigated the agreement of intraocular pressure measurements using rebound tonometry and applanation tonometry in response to atmospheric changes in a hyperbaric chamber. Twelve eyes of 12 healthy subjects were included in this prospective, comparative, single-masked study. Intraocular pressure measurements were performed by rebound tonometry followed by applanation tonometry in a multiplace hyperbaric chamber at 1 Bar, followed by 2, 3 and 4 Bar during compression and again at 3 and 2 Bar during decompression. Mean differences between rebound and applanation intraocular pressure measurements were 1.6, 1.7, and 2.1 mmHg at 2, 3, and 4 Bar respectively during compression and 2.6 and 2.2 mmHg at 3 and 2 Bar during decompression. Lower limits of agreement ranged from -3.7 to -5.9 mmHg and upper limits ranged from -0.3 to 1.9 mmHg. Multivariate analysis showed that the differences between rebound and applanation intraocular pressure measurements were independent of atmospheric pressure changes (p = 0.79). Intraocular pressure measured by rebound tonometry shows a systematic difference compared to intraocular measured by applanation tonometry, but this difference is not influenced by changes of atmospheric pressure up to 4 Bar in a hyperbaric chamber. Agreement in magnitude of change between devices suggests rebound tonometry is viable for assessing intraocular pressure during atmospheric changes. Future studies should be designed in consideration of expected differences in IOP values provided by the two devices.

Comparison of Intraocular Pressure before and after Laser in Situ Keratomileusis Measured with Applanation Tonometry, Non Contact Tonometry and Rebound Tonometry

Background Measurement of intraocular pressure (IOP) plays a central role throughout ophthalmology. It is part of routine ophthalmologic examinations and important in the management and follow-up of patients with glaucoma. While elevated IOP remains the most important risk factor for development and progression of open angle glaucoma, at least half of the population diagnosed with open angle glaucoma is asymptomatic. Objectives The aim of our study is to compare the accuracy of intraocular pressure measurement before and after Laser in situ keratomeulsis (LASIK) surgery using three different types of Tonometers: Goldmann Applanation tonometry (GAT), Non contact tonometry (NCT) and Rebound tonometry (I care), considering the change in the central corneal thickness (CCT). Patients and Methods In this study Eighty eyes of 40 patients with mean age of 27.00±6.00 years were scheduled for LASIK..Central corneal thickness before and after surgery was obtained by Ultrasound (US) pachymetry.IOP values were measured before and after surgery using three different types of Tonometers: Goldmann Applanation tonometry, Non contact tonometry and Rebound tonometry. Results The results revealed that lower post-operative IOP measurements using all techniques. The least affected technique was Non –contact with IOP change 16%, followed by GAT with IOP change 18%, and finally Rebound with IOP change 19 %, respectively. The percentage of change in CCT between pre- and post- LASIK surgery measured with the Ultrasound pachymetry was statistically highly significant. There was a clinical significant correlation between Percentage of tissue ablation (PTA) and IOP change for GAT, NCT and rebound tonometry. Also, there was a significant correlation between Residual stromal bed (RSB) and IOP change for GAT and NCT. There was no clinical significant correlation between Ablation depth (AD) and percentage of change of IOP measurements pre and post LASIK, except for IOP measured with GAT when AD < 40.00 µm. Conclusion Refractive surgery causes significant lowering of IOP as measured using Goldmann applanation tonometry, non contact tonometry and rebound tonometry. The least affected tonometry post LASIK is non contact tonometry. The reduction was correlated to the percentage of tissue ablated. The ideal method to measure IOP in post-LASIK patients would be a device that is free of corneal factors.

The Basic Values of Intraocular Pressure Measured by Rebound Tonometry in Guinea Pig

Elevated intraocular pressure (IOP) is the most important risk factor associated with the progression of glaucoma and the research on animal models is constantly evolving. Rebound tonometry has been shown to be useful for the evaluation of IOP, not only for the human patient but also for the animal patient. The aim of the paper is to assess intraocular pressure in guinea pigs in order to establish reference values. IOP was measured for three days, at different time intervals, in 40 guinea pigs, using the iCare Tonovet TV01 tonometer. The mean values obtained in coloured guinea pigs were 13.82 mmHg ± 1.64 mmHg in the right eye, 14.11 mmHg ± 1.68 mmHg in the left eye, and in white guinea pigs 12.56 mmHg ± 0.95 mmHg in the right eye, 13.02 mmHg ± 1.29 mmHg for the left eye. The values obtained from this study it can be concluded that the strain of coloured, records the highest values in the morning, which remain linear during the day, and decrease in the evening compared to the white strain which has a constant evolution during the day, and in the evening increases.