Role of the Vitreous in Ocular Biomechanics
DOI:
https://doi.org/10.48560/rspo.25884Keywords:
Posterior Eye Segment, Biomechanical Phenomena, Vitreous Body, Kinetics, posterior vitreous detachmentAbstract
INTRODUCTION: Characterization of ocular biomechanics is necessary to fully understand the development of vitreoretinal traction, retinal tears, and detachment. Few studies have tried to characterize the viscoelastic properties of the vitreous and all previous studies have used either ex vivo human eyes or in vivo animal eyes. Our objective was to analyze, in vivo, the role of the vitreous in ocular biomechanics.
MATERIAL AND METHODS: Prospective longitudinal study that included 24 patients submitted to unilateral pars plana vitrectomy (PPV) for vitreous opacities or epiretinal membrane. Ocular biomechanics were analyzed with Oculus Corvis ST® one week before and one month after surgery. The whole eye movement (WEM) was analyzed separately as a function of posterior segment compression. Posterior vitreous detachment (PVD) was access with 55o optical coherence tomography. The fellow non-operated eyes were used as control. Non-parametric tests were used, and the significance level was set at 5%.
RESULTS: After PPV, we observed changes in biomechanics towards a softer corneal behavior, namely a reduction in SP-A1 (p=0.009). However, intraocular pressure (IOP) was also lower (p=0.034). WEM distance decreased after vitrectomy (p=0.020). There were no significant differences in fellow non-operated eyes. A cross-sectional comparison before PPV showed that eyes with PVD at the macula also have a shorter WEM distance (p=0.047). There were no significant differences according to the reason for PPV (vitreous opacities in 16 eyes or epiretinal membrane in 8 eyes).
CONCLUSION: This study shows changes in response to an air pulse after PPV, which suggests a role of the vitreous in ocular biomechanics. Due to lower IOP after surgery, no definite conclusions may be drawn regarding corneal measurements and indexes. More importantly, we observed changes that relate to the posterior segment of the eye, namely the vitreous. A decrease in WEM distance conveys a reduction in anterior-posterior deflection and reduced compression of the posterior segment. Lower IOP alone would produce the opposite effect. Eyes with PVD may also have reduced WEM. Together these findings demonstrate, for the first time in vivo, that the attached vitreous exerts a centripetal force on the globe.
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