How to Measure the Whole Ocular Rigidity?

Pitchon, Elie M.

doi:10.1016/j.ajo.2006.06.010

Cited by 3 publications

(5 citation statements)

References 3 publications

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“…The value of K, however, is not always constant or well-behaved, and has been shown by subsequent research to vary considerably from species to species, giving rise to numerous other empirical expressions of ocular rigidity [7]. Although ocular rigidity is influenced by the viscoelastic properties of the corneoscleral tissues, no clear relation exists between ocular rigidity and the intrinsic material properties of the tissues involved [8, 17, 18]. An attempt to determine the average elasticity of the whole eye by eliminating the confounding influence of geometry on pressure-volume data [7] represents a worthy advance, but one that continues to suffer from the limited ability of pressure-volume data to provide information about the specific tissues of the eye.…”

Section: Introductionmentioning

confidence: 99%

MR elastography of the ex vivo bovine globe

Litwiller

Lee

Kolipaka

et al. 2010

Magnetic Resonance Imaging

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Purpose: To evaluate the feasibility of using MR elastography (MRE) to assess the mechanical properties of the eye. Materials and Methods:The elastic properties of the corneoscleral shell of an intact, enucleated bovine globe specimen were estimated using MRE and finite element modeling (FEM), assuming linear, isotropic behavior. The two-dimensional (2D), axisymetric model geometry was derived from a segmented 2D MR image, and estimations of the Young's modulus in both the cornea and sclera were made at various intraocular pressures using an iterative flexural wave speed matching algorithm.Results: Estimated values of the Young's moduli of the cornea and sclera varied from 40 to 185 kPa and 1 to 7 MPa, respectively, over an intraocular pressure range of 0.85 to 9.05 mmHg (1.2 to 12.3 cmH 2 O). They also varied exponentially as functions of both wave speed and intraocular dP/dV, an empirical measure of ''ocular rigidity.'' Conclusion: These results show that it is possible to estimate the intrinsic elastic properties of the corneoscleral shell in an ex vivo bovine globe, suggesting that MRE may provide a useful means to assess the mechanical properties of the eye and its anatomy. Further development of the technique and modeling process will enhance its potential, and further investigations are needed to determine its clinical potential.

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Section: Introductionmentioning

confidence: 99%

MR elastography of the ex vivo bovine globe

Litwiller

Lee

Kolipaka

et al. 2010

Magnetic Resonance Imaging

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“…Furthermore, concerns have been raised regarding accuracy of this method because of the valve effect of the iris-lens diaphragm. 14,15 The intraocular volume and its changes are not directly measurable by simple means. However, axial length certainly contributes to the overall size of the eye and may even be the determining factor.…”

Section: à3mentioning

confidence: 99%

Non-invasive biometric assessment of ocular rigidity in glaucoma patients and controls

Ebneter

Wagels

Zinkernagel

2008

Eye

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Purpose To determine in vivo whether a pharmacologically induced change in intraocular pressure (IOP) leads to measurable changes in axial eye length and whether there is a difference between glaucoma patients and control subjects. Methods 42 subjects (19 patients with primary open angle glaucoma and 23 control patients matched for age and gender) underwent axial eye length measurement using partial coherence laser interferometry and measurement of IOP using dynamic contour tonometry before and 2 h after oral intake of 500 mg acetazolamide. Student's t-test was used to compare differences in the means. Results An identical drop in IOP was induced in both the glaucoma (mean ± SEM: 2.90 ± 0.44 mmHg, n ¼ 19) and the control group (mean±SEM: 3.17±0.32 mmHg, n ¼ 23). The change in axial eye length was significantly smaller (P ¼ 0.026) in the glaucoma group (mean±SEM: À14.2±3.2 lm, n ¼ 19) compared with the control group (mean ± SEM: À23.0 ± 2.98 lm, n ¼ 23). Conclusions Our results strongly suggest that the ocular rigidity is increased in patients with established glaucoma in comparison to control subjects. Ocular rigidity could play a role in the pathogenesis and pathophysiology of glaucoma. Determination of ocular rigidity could be helpful in detection of glaucoma.

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“…Furthermore, it has been criticized for potentially measuring rigidity at the anterior chamber, rather than at the whole eye, because the anatomic relationship between the iris and lens surface has a valve effect, 20 preventing flow from the anterior chamber to the posterior chamber (unless the iris anatomy is modified, e.g. by an iridotomy) 21 . Accordingly, it has been suggested that the same methodology can be applied to eyes with and without an iridotomy, to examine the effect of the potential iris valve mechanism may have on OR measurements 21 .…”

Section: Alternative Methods Of or Measurementmentioning

confidence: 99%

“…by an iridotomy) 21 . Accordingly, it has been suggested that the same methodology can be applied to eyes with and without an iridotomy, to examine the effect of the potential iris valve mechanism may have on OR measurements 21 . However, the fact that all measurements were performed with dilated pupils implies that results, may, in reality, reflect total OR, rather than anterior chamber rigidity.…”

Section: Alternative Methods Of or Measurementmentioning

confidence: 99%

“…21 Accordingly, it has been suggested that the same methodology can be applied to eyes with and without an iridotomy, to examine the effect of the potential iris valve mechanism may have on OR measurements. 21 However, the fact that all Figure 1. Rigidity curves derived from manometric anterior chamber measurements, with 4 mL infusions and 400 Hz readings every 2 s until the intraocular pressure (IOP) reaches 40 mmHg.…”

Section: Alternative Methods Of or Measurement Intraoperative Anteriomentioning

confidence: 99%

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Ocular rigidity: biomechanical role, in vivo measurements and clinical significance

Detorakis

Pallikaris

2012

Clinical Exper Ophthalmology

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Ocular rigidity (OR) refers to the relationship between pressure and volume changes in the eyeball. Since the description of the differential tonometry method for the calculation of an OR coefficient by Friedenwald, several other methodologies have been proposed to measure OR, including the anterior chamber manometry, axial length (AL) changes, measurement of pulse amplitude and fundus pulse, ultrasound elastography and evaluation of corneal hysteresis. However, most of these methodologies suffer from deficiencies, such as invasive nature, poor accuracy or reproducibility or technical complexity. Nevertheless, it is possible that OR affects the pathogenesis and clinical course of a variety of ocular conditions, including glaucoma, age-related macular degeneration, presbyopia, corneal changes following refractive surgery as well as the accuracy of IOP measurements by many tonometers. Thus, the future development of non-invasive and easy-to-use methodologies for the accurate measurement of OR in the every-day practice would be clinically important.

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How to Measure the Whole Ocular Rigidity?

Cited by 3 publications

References 3 publications

MR elastography of the ex vivo bovine globe

MR elastography of the ex vivo bovine globe

Non-invasive biometric assessment of ocular rigidity in glaucoma patients and controls

Ocular rigidity: biomechanical role, in vivo measurements and clinical significance

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