Corneal hysteresis and its relevance to glaucoma

Deol, Madhvi; Taylor, David A.; Radcliffe, Nathan M.

doi:10.1097/icu.0000000000000130

Cited by 108 publications

(93 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…cornea and lamina thickness) (Jonas and Holbach, 2005), or with susceptibility to disease (cornea thickness and hysteresis vs. glaucoma progression) (Deol et al, 2015; Medeiros et al, 2013). We have demonstrated that we can detect not only the front and back of the eye simultaneously, but the side as well.…”

Section: Discussionmentioning

confidence: 99%

Whole-globe biomechanics using high-field MRI

Voorhees

Jan

et al. 2017

Experimental Eye Research

View full text Add to dashboard Cite

The eye is a complex structure composed of several interconnected tissues acting together, across the whole globe, to resist deformation due to intraocular pressure (IOP). However, most work in the ocular biomechanics field only examines the response to IOP over smaller regions of the eye. We used high-field MRI to measure IOP induced ocular displacements and deformations over the whole globe. Seven sheep eyes were obtained from a local abattoir and imaged within 48 hours using MRI at multiple levels of IOP. IOP was controlled with a gravity perfusion system and a cannula inserted into the anterior chamber. T2-weighted imaging was performed to the eyes serially at 0 mmHg, 10 mmHg, 20 mmHg and 40 mmHg of IOP using a 9.4 Tesla MRI scanner. Manual morphometry was conducted using 3D visualization software to quantify IOP-induced effects at the globe scale (e.g. axial length and equatorial diameters) or optic nerve head scale (e.g. canal diameter, peripapillary sclera bowing). Measurement sensitivity analysis was conducted to determine measurement precision. High-field MRI revealed an outward bowing of the posterior sclera and anterior bulging of the cornea due to IOP elevation. Increments in IOP from 10 to 40 mmHg caused measurable increases in axial length in 6 of 7 eyes of 7.9±5.7% (mean±SD). Changes in equatorial diameter were minimal, 0.4±1.2% between 10 and 40 mmHg, and in all cases less than the measurement sensitivity. The effects were nonlinear, with larger deformations at normal IOPs (10–20mmHg) than at elevated IOPs (20–40mmHg). IOP also caused measurable increases in the nasal-temporal scleral canal diameter of 13.4±9.7% between 0 and 20 mmHg, but not in the superior-inferior diameter. This study demonstrates that high-field MRI can be used to visualize and measure simultaneously the effects of IOP over the whole globe, including the effects on axial length and equatorial diameter, posterior sclera displacement and bowing, and even changes in scleral canal diameter. The fact that the equatorial diameter did not change with IOP, in agreement with previous studies, indicates that a fixed boundary condition is a reasonable assumption for half globe inflation tests and computational models. Our results demonstrate the potential of high-field MRI to contribute to understanding ocular biomechanics, and specifically of the effects of IOP in large animal models.

show abstract

Section: Discussionmentioning

confidence: 99%

Whole-globe biomechanics using high-field MRI

Voorhees

Jan

et al. 2017

Experimental Eye Research

View full text Add to dashboard Cite

show abstract

“…CCT is reportedly thinner in people of African ancestry (Chua et al, 2014; Sample et al, 2009). Although the mechanism is unclear, thinner CCT has been reported as a strong predictor of POAG risk (Deol et al, 2015; Gordon et al, 2002; Sng et al, 2017). Thicker CCT is associated with ocular hypertension and glaucoma suspect status in adults and children (Gordon et al, 2002; Muir et al, 2004).…”

Section: Genetic Analyses Of Poag-associated Traits (Endophenotypes)mentioning

confidence: 99%

Major review: Molecular genetics of primary open-angle glaucoma

Liu

Allingham

2017

Experimental Eye Research

127

106

View full text Add to dashboard Cite

Glaucoma is a leading cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), the most common type, is a complex inherited disorder that is characterized by progressive retinal ganglion cell death, optic nerve head excavation, and visual field loss. The discovery of a large, and growing, number of genetic and chromosomal loci has been shown to contribute to POAG risk, which carry implications for disease pathogenesis. Differential gene expression analyses in glaucoma-affected tissues as well as animal models of POAG are enhancing our mechanistic understanding in this common, blinding disorder. In this review we summarize recent developments in POAG genetics and molecular genetics research.

show abstract

“…5 Keratoconus, Fuchs' dystrophy, Glaucoma, Marfan syndrome, and post-LASIK patients have been found to have low CH and CRF. [6][7][8][9][10][11][12][13] The corneal visualization Scheimpflug technology tonometer (Corvis ST tonometry: CST; Oculus, Wetzlar, Germany) was introduced more recently and allows quantitative and visual assessment of the biomechanical properties of the cornea. 14 The Corvis ST is a noncontact tonometer with an integrated ultra-high-speed Scheimpflug camera, enabling the direct visualization of corneal movement during the application of a rapid air-puff.…”

Section: Clinical Evaluation Of the Biomechanical Changes Occurring Imentioning

confidence: 99%

Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes

Gatinel¹

2017

International Journal of Keratoconus and Ectatic Corneal Diseases

View full text Add to dashboard Cite

The induction of cross-links in corneal tissue appears to be a promising technique to increase its stiffness and this has been the basis of treatment of keratoconus (KC) and corneal ectatic disease. However, there exists a striking discrepancy between the reported biomechanical effects of corneal collagen cross-linking (CXL) in vitro compared to in vivo, and this has not received much attention in the literature. Despite the documentation of an increase in corneal stiffness in vitro by many investigators, reports that provide evidence of measurable and consistent biomechanical changes in corneal rigidity in vivo after CXL are lacking. Indeed, the absence of documented in vivo biomechanical improvement in CXL-treated corneas is a conundrum, which needs to be further explored. To explain this discrepancy, it has been postulated that biomechanical changes induced by CXL are too subtle to be measured by currently available diagnostic tools or have characteristics not discernible by these technologies. However, the dynamic bidirectional applanation device (Ocular Response Analyzer) and dynamic Scheimpflug analyzer instruments (Corvis ST) have demonstrated the ability to quantify even subtle biomechanical differences in untreated KC corneas of different ectatic degree, and document the reduction in corneal hysteresis (CH) and corneal resistance factor (CRF) in situations where the corneal stiffness is reduced, such as after laser in situ keratomileusis and surface ablation procedures. It has also been possible to demonstrate an altered CH and CRF in patients with diabetes, smoking habit, glaucoma, Fuchs’ dystrophy, and corneal edema. It is puzzling that these diagnostic tools could document subtle biomechanical changes in these situations, yet fail to measure the purported changes induced by CXL on corneas with progressive KC. This failure to document significant and consistent biomechanical changes in corneal rigidity could suggest that CXL does not induce a simple reversal of the particular biomechanical deficits that characterize KC, or make the cornea significantly more resistant to bending forces as has been widely postulated. The absence of measurable biomechanical change in living KC corneas after CXL could be a consequence of biomechanical strengthening which is insignificant compared to the marked weakening caused by preexisting alteration of the collagen structure, disorganization of collagen fiber intertwining, and compromised structural–mechanical homogeneity that are hallmarks of keratoconic disease, especially in corneas with progressive KC. The changes in the cornea induced by CXL that have been described in vivo may instead be driven by a wound healing process in response to the removal of the corneal epithelial layer and subsequent exposure to riboflavin and ultraviolet-A (UVA). This paper will present evidence that sustains this hypothesis. How to cite this article Gatinel D. Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes. Int J Kerat Ect Cor Dis 2017;6(1):34-41.

show abstract

Corneal hysteresis and its relevance to glaucoma

Cited by 108 publications

References 53 publications

Whole-globe biomechanics using high-field MRI

Whole-globe biomechanics using high-field MRI

Major review: Molecular genetics of primary open-angle glaucoma

Reevaluating the Effectiveness of Corneal Collagen Cross-linking and Its True Biomechanical Effect in Human Eyes

Contact Info

Product

Resources

About