Tonometry – Past, Present and Future

Kirstein, Elliot M.; Elsheikh, Ahmed; Gunvant, Pinakin

doi:10.5772/37393

Cited by 10 publications

(4 citation statements)

References 59 publications

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“…It is known that the corneal thickness increases (due to edema) at a higher altitude (3, 13, 38) and thicker corneas reveal an improperly higher IOP reading (39). McNamara (40) and Wang (41) consequently determined that 1 h and longer corneal hypoxia causes an increase in the corneal thickness.…”

Section: Discussionmentioning

confidence: 99%

Intraocular Pressure Response to Short-Term Extreme Normobaric Hypoxia Exposure

et al. 2019

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Purpose: The purpose of the study was to determine the intraocular pressure response to normobaric hypoxia and the consequent recovery under additional well-controlled ambient conditions. Second, the study attempted to determine if the intraocular pressure changes were dependent on its baseline, initial heart rate, sex and arterial oxygen saturation.Methods: Thirty-eight visually healthy volunteers (23 women and 15 men) of an average age 25.2 ± 3.8 years from 49 recruited participants met the inclusion criteria and performed the complete test. Initial intraocular pressure (baseline), heart rate, and arterial oxygen saturation were measured after 7 min of rest under normal ambient conditions at an altitude 250 m above sea level. Each subject then underwent a 10 min normobaric hypoxic exposure and a subsequent 7 min recovery under normoxic conditions. Within hypoxic period, subjects were challenged to breathe hypoxic gas mixture with fraction of inspired oxygen of 9.6% (~6.200 m above sea level). Intraocular pressure and arterial oxygen saturation were re-measured at 4 and 10 min during the hypoxia and at 7 min after hypoxia termination.Results: Intraocular pressure increased in 1.2 mmHg ± 1.9 mmHg and 0.9 mmHg ± 2.3 mmHg at 4 and 10 min during the hypoxic period and returned approximately to the baseline at 7 min of recovery. The influence of sex was not statistically significant. The arterial oxygen saturation decreased in 14.9 ± 4.2% at min 4 and 18.4 ± 5.8% at min 10 during hypoxia and returned to the resting value at 7 min of recovery. The decrease was slightly higher in the case of women if compared with men. The hypoxia induced changes in intraocular pressure were significantly correlated with the arterial oxygen saturation changes, whereas the relationship with intraocular pressure baseline and initial heart rate were insignificant.Conclusion: There was a significant increase in intraocular pressure as a response to short-term normobaric hypoxia, which returned to the baseline in 7 min after hypoxia. The increase was dependent on the induced oxygen desaturation.

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Section: Discussionmentioning

confidence: 99%

Intraocular Pressure Response to Short-Term Extreme Normobaric Hypoxia Exposure

et al. 2019

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“…In fact, no statistically significant influence of anterior segment parameters on DCT-assessed IOP has been detected. Moreover, DCT measurements have shown a good concordance with anterior chamber manometry, in contrast to GAT-determined IOP values [1,2,8,26]. Several studies have examined the differences between DCT and GAT according to corneal morphology [7,22,25].…”

Section: Dct Versus Gatmentioning

confidence: 99%

“…For example, IOP measurement with a Goldmann applanation tonometer (GAT) is significantly influenced by the central corneal thickness (CCT), whereas when using a DCT - and thus avoiding applanation - the CCT would play a lesser role in IOP assessment [1,7]. Other, non-CCT-related factors, such as the IOP level, scleral thickness, ocular elasticity, axial length (AL), and lens status, could influence OPA measurements [7,8,9]. As the characteristics and the pathophysiological variability of OPA remain partially unclear, several researchers are attempting to answer these open questions and find clinically useful applications.…”

Section: Introductionmentioning

confidence: 99%

Review on Dynamic Contour Tonometry and Ocular Pulse Amplitude

et al. 2015

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Intraocular pressure (IOP) measurement is the cornerstone of the management of glaucoma patients. The gold standard for assessing IOP is Goldmann applanation tonometry (GAT). Recently, the dynamic contour tonometer (DCT) has become available. While both devices provide reliable IOP measurements, the results are not interchangeable. DCT has the advantage of measuring an additional parameter: ocular pulse amplitude (OPA). OPA is defined as the difference between systolic and diastolic IOP and represents the pulsatile wave front produced by the varying amount of blood in the eye during the cardiac cycle. It has been shown to vary with ocular structural parameters, such as axial length, corneal thickness, and ocular rigidity, as well as with systemic variables like heart rate, blood pressure, and left ventricular ejection fraction. Although the existence of some of these associations is still controversial, the clinical relevance of OPA has been consistently suggested, especially in glaucoma. Further research on this intriguing parameter could not only provide insight into glaucoma pathophysiology but also help integrate this variable into clinical practice.

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“…The main objective of this study is to investigate the influence of considering the fluid-structure interaction between the air puff and the cornea on the reliability of methods to estimate the biomechanically-corrected IOP and the corneal material behavior. IOP is interlinked with material stiffness in a complex loop as the measurement of IOP in tonometry is commonly influenced by corneal stiffness, while the tangent modulus (a measure of stiffness) is known to increase with the level of IOP (Kirstein et al, 2011;Eliasy et al, 2019). The challenge to provide estimations of IOP and corneal stiffness that are independent of each other was dealt with in the present study using numerical modeling and employing the results to build algorithms to estimate fIOP and corneal material index fSSI.…”

Section: Discussionmentioning

confidence: 99%

Fluid-Structure Interaction Based Algorithms for IOP and Corneal Material Behavior

Maklad

Eliasy

Chen

et al. 2020

Front. Bioeng. Biotechnol.

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Purpose: This paper presents and clinically validates two algorithms for estimating intraocular pressure (IOP) and corneal material behavior using numerical models that consider the fluid-structure interaction between the cornea and the air-puff used in non-contact tonometry. Methods: A novel multi-physics fluid-structure interaction model of the air-puff test was employed in a parametric numerical study simulating human eyes under air-puff pressure with a wide range of central corneal thickness (CCT = 445-645 µm), curvature (R = 7.4-8.4 mm), material stiffness and IOP (10-25 mmHg). Models were internally loaded with IOP using a fluid cavity, then externally with air-puff loading simulated using a turbulent computational fluid dynamics model. Corneal dynamic response parameters were extracted and used in development of two algorithms for IOP and corneal material behavior; fIOP and fSSI, respectively. The two algorithms were validated against clinical corneal dynamic response parameters for 476 healthy participants. The predictions of IOP and corneal material behavior were tested on how they varied with CCT, R, and age. Results: The present study produced a biomechanically corrected estimation of intraocular pressure (fIOP) and a corneal material stiffness parameter or Stress-Strain Index (fSSI), both of which showed no significant correlation with R (p > 0.05) and CCT (p > 0.05). Further, fIOP had no significant correlation with age (p > 0.05), while fSSI was significantly correlated with age (p = 0.001), which was found earlier to be strongly correlated with material stiffness. Conclusion: The present study introduced two novel algorithms for estimating IOP and biomechanical material behavior of healthy corneas in-vivo. Consideration of the fluid structure interaction between the cornea and the air puff of non-contact tonometry in developing these algorithms led to improvements in performance compared with bIOP and SSI.

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Tonometry – Past, Present and Future

Cited by 10 publications

References 59 publications

Intraocular Pressure Response to Short-Term Extreme Normobaric Hypoxia Exposure

Intraocular Pressure Response to Short-Term Extreme Normobaric Hypoxia Exposure

Review on Dynamic Contour Tonometry and Ocular Pulse Amplitude

Fluid-Structure Interaction Based Algorithms for IOP and Corneal Material Behavior

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