Age-related changes in dynamic moduli of ovine vitreous

Colter, Jourdan; Williams, Alex G.; Moran, Patrick; Coats, Brittany

doi:10.1016/j.jmbbm.2014.09.004

Cited by 22 publications

(15 citation statements)

References 43 publications

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“…Colter et al (2015) investigated age-related changes in the mechanical properties of the vitreous humor using sheep eyes. 23 By testing whole ovine vitreous with the hyaloid membrane, they found that the dynamic moduli of the adult vitreous was about 2 times lower than infant vitreous, albeit not statistically significant. More recently, Shultz et al (2019) analyzed 190 whole human vitreous body samples extracted from donors aged 33 to 92 via shear rheology.…”

Section: Aging Of the Vitreous Humormentioning

confidence: 98%

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

Tram

Maxwell

Swindle-Reilly

2020

Current Eye Research

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Research on the vitreous humor and development of hydrogel vitreous substitutes have gained a rapid increase in interest within the past two decades. However, the properties of the vitreous humor and vitreous substitutes have yet to be consolidated. In this paper, the mechanical properties of the vitreous humor and hydrogel vitreous substitutes were systematically reviewed. The number of publications on the vitreous humor and vitreous substitutes over the years, as well as their respective testing conditions and testing techniques were analyzed. The mechanical properties of the human vitreous were found to be most similar to the vitreous of pigs and rabbits. The storage and loss moduli of the hydrogel vitreous substitutes developed were found to be orders of magnitude higher in comparison to the native human vitreous. However, the reported modulus for human vitreous, which was most commonly tested in vitro, has been hypothesized to be different in vivo. Future studies should focus on testing the mechanical properties of the vitreous in situ or in vivo. In addition to its mechanical properties, the vitreous humor has other biotransport mechanisms and biochemical functions that establish a redox balance and maintain an oxygen gradient inside the vitreous chamber to protect intraocular tissues from oxidative damage. Biomimetic hydrogel vitreous substitutes have the potential to provide ophthalmologists with additional avenues for treating and controlling vitreoretinal diseases while preventing complications after vitrectomy. Due to the proximity and interconnectedness of the vitreous humor to other ocular tissues, particularly the lens and the retina, more interest has been placed on understanding the properties of the vitreous humor in recent years. A better understanding of the properties of the vitreous humor will aid in improving the design of biomimetic vitreous substitutes and enhancing intravitreal biotransport.

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Section: Aging Of the Vitreous Humormentioning

confidence: 98%

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

Tram

Maxwell

Swindle-Reilly

2020

Current Eye Research

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“…This approach has been found to be successful in understanding age-related changes in the mechanics of brain tissue, vitreous, and other biological materials. 16 , 17 For this study, we selected sheep as the non-human model to evaluate age- and region-related changes in retinal vasculature. Sheep have a holangiotic vascular pattern like humans and a well-defined retinal structure.…”

mentioning

confidence: 99%

Morphological Analysis of Retinal Microvasculature to Improve Understanding of Retinal Hemorrhage Mechanics in Infants

Byrne

McMillan

Coats

2020

Invest. Ophthalmol. Vis. Sci.

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Citation: Byrne MP, McMillan KR, Coats B. Morphological analysis of retinal microvasculature to improve understanding of retinal hemorrhage mechanics in infants. Invest Ophthalmol Vis Sci. 2020;61(3):16. https://doi.org/10.1167/iovs.61.3.16 PURPOSE.In this experimental study, we quantify retinal microvasculature morphological features with depth, region, and age in immature and mature ovine eyes. These data identify morphological vulnerabilities in young eyes to inform the mechanics of retinal hemorrhage in children. METHODS.Retinal specimens from the equator and posterior pole of preterm (n = 4) and adult (n = 9) sheep were imaged using confocal microscopy. Vessel segment length, diameter, angular asymmetry, tortuosity, and branch points were quantified using a custom image segmentation code. Significant differences were identified through twoway ANOVAs and correlation analyses. RESULTS.Vessel segment lengths were significantly shorter in immature eyes compared to adults (P < 0.003) and were significantly shorter at increasing depths in the immature retina (P < 0.04). Tortuosity significantly increased with depth, regardless of age (P < 0.05). These data suggest a potential vulnerability of vasculature in the deeper retinal layers, particularly in immature eyes. Preterm retina had significantly more branch points than adult retina in both the posterior pole and equator, and the number increased significantly with depth (P < 0.001). CONCLUSIONS.The increased branch points and decreased segment lengths in immature microvasculature suggest that infants will experience greater stress and strain during traumatic loading compared to adults. The increased morphological vulnerability of the immature microvasculature in the deeper layers of the retina suggest that intraretinal hemorrhages have a greater likelihood of occurring from trauma compared to preretinal hemorrhages. The morphological features captured in this study lay the foundation to explore the mechanics of retinal hemorrhage in infants and identify vulnerabilities that explain patterns of retinal hemorrhage in infants.

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“…A number of studies have quantified the mechanical properties of the mammalian vitreous using bulk measurements (Bettelheim and Wang, 1976; Weber et al, 1982; Tokita et al, 1984), magnetic microrheology (Lee et al, 1992, 1994; Watts et al, 2014), in vivo visual tracking (Zimmerman, 1980), acoustic and magnetic resonance imaging (MRI) techniques (Walton et al, 2002; Stein et al, 2018), and shear rheometry (Nickerson et al, 2005, 2008; Suri and Banerjee, 2006; Swindle et al, 2008; Swindle-Reilly et al, 2009, 2016; Sharif-Kashani et al, 2011; Filas et al, 2014; Colter et al, 2015; Silva et al, 2017; Shafaie et al, 2018). In recent years, shear rheometry has become a common technique for testing the vitreous humor, since this technique can report various rheological properties pertaining to the viscoelasticity of the vitreous gel.…”

Section: Introductionmentioning

confidence: 99%

“…While the vitreous is well-known to liquefy with age, age-related changes in the mechanical properties of the vitreous remain elusive. Colter et al (2015) is the only paper to date that investigated age-related changes in the mechanical data of the vitreous humor, using ovine eyes. The authors claimed that the storage and loss moduli of the adult ovine vitreous were lower than those of the infant vitreous and higher than those of the premature vitreous.…”

Section: Introductionmentioning

confidence: 99%

Rheological Properties and Age-Related Changes of the Human Vitreous Humor

Tram

Swindle-Reilly

2018

Front. Bioeng. Biotechnol.

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The vitreous humor is a fragile, transparent hydrogel situated between the lens and the retina, occupying 80% of the eye's volume. Due to its viscoelastic behavior, the vitreous serves as a mechanical damper for the eye, absorbing impacts, and protecting the lens and retina. The vitreous liquefies with age, which compromises its function as a shock absorber and causes complications including retinal detachment, macular holes, and vitreous hemorrhage. Studies on the viscoelastic properties of the vitreous have been limited. Rheological testing of the vitreous has commonly been done on non-primate mammalian species. Human vitreous rheological properties have been previously reported; however, various measurement techniques were used, resulting in data that differed by orders of magnitude. Shear rheometry is commonly used to characterize soft tissues and hydrogels such as the vitreous humor. However, no human vitreous rheological data have been reported using this technique, preventing direct comparison to other published work. Additionally, no age-related changes in the mechanical properties of the human vitreous humor have been reported. Human vitreous samples (n = 39, aged 62 ± 15 years) were tested using a shear rheometer. Small amplitude oscillatory shear and creep experiments were performed. The linear viscoelastic region of the human vitreous was found to be below 1% strain. The solid phase of the old human vitreous was found to be stiffer than the young human vitreous and the porcine vitreous. The stiffness of the human vitreous gel also appeared to be positively correlated with age. Vitreous dehydration due to a decrease in hyaluronic acid concentration with age was proposed to cause the stiffening of the solid phase of the vitreous gel. Vitreous liquefaction, therefore, might be characterized as a simultaneous increase in liquid volume and localized stiffening of the vitreous gel. The phase separation of the vitreous humor with age has been hypothesized as the cause of many vitreous-related complications. This study provides viscoelastic properties and age-related changes of the human vitreous humor, which will aid in the design of biomimetic vitreous substitutes, enhancement in analyzing intravitreal transport of therapeutics, and understanding the pathological conditions of the vitreous humor.

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Age-related changes in dynamic moduli of ovine vitreous

Cited by 22 publications

References 43 publications

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

Morphological Analysis of Retinal Microvasculature to Improve Understanding of Retinal Hemorrhage Mechanics in Infants

Rheological Properties and Age-Related Changes of the Human Vitreous Humor

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