Corneoscleral stiffening increases IOP spike magnitudes during rapid microvolumetric change in the eye

Abstract

Factors governing the steady-state IOP have been extensively studied; however, the dynamic aspects of IOP are less understood. Clinical studies have suggested that intraocular pressure (IOP) fluctuation may be associated with glaucoma risk. This study aims to investigate how stiffening of corneoscleral biomechanical properties affects IOP spikes induced by rapid microvolumetric change. Porcine eyes (n = 25 in total) were subjected to volumetric infusions before and after external treatment of a circular area (11 mm diameter) in either the central cornea or posterior sclera. The treated area in the control group was immersed in phosphate-buffered saline (PBS) for 40 min, while the treated area of the chemical crosslinking group was immersed in 4% glutaraldehyde/PBS for 40 min. A subset of the sham-treated eyes was also subjected to volumetric infusions at a raised steady-state IOP. The magnitude of IOP spikes increased after localized chemical crosslinking of either the cornea (27.5% increase, p < 0.001) or the sclera (14.3% increase, p < 0.001) with corneal crosslinking having a stronger effect than scleral crosslinking (p = 0.018). We also observed that raising the steady-state IOP from 15 to 25 mmHg resulted in marked increase in IOP spike magnitudes by 63.9% (p < 0.001). These results suggested that an increased corneoscleral stiffness could significantly increase IOP spike magnitudes at the same volumetric change. Corneal stiffness appeared to have a strong impact on the IOP spike magnitude and may play a major role in regulating rapid volume-pressure dynamics. An increase in steady-state IOP also resulted in larger IOP fluctuations due to the increased “apparent” stiffness of the ocular shell, suggesting a potential interaction between the magnitude of IOP and its fluctuations. Corneoscleral properties may represent additional pathways for understanding and managing glaucoma risk and warrant future investigation.

Corneal pulsation and biomechanics during induced ocular pulse. An ex-vivo pilot study

“…Hence, the corneal stiffness growth, concurrent with the IOP raise, prevents tissue ability to deform (represented by CPA) but also causes an increase in the amplitude of IOP changes (represented by OPAp). These findings are in agreement with a study by Clayson et al [20] on porcine eyes, which showed that the induced corneal stiffening, obtained by crosslinking treatment, and the IOP rise significantly impact the magnitude of IOP spikes. In human studies, the positive correlation between IOP and OPA has been also reported in healthy subjects [58] as well as in patients with ophthalmic diseases [7,19] showing increased mechanical resistance of the ocular wall at high IOP.…”

“…In turn, the corneal mechanical resistance influences IOP fluctuations, e.g. Ocular Pulse Amplitude (OPA) and IOP spikes, as it has recently been proven in both in-vivo [7,19] and exvivo studies [20].…”

Ocular Pulse Elastography: Imaging Corneal Biomechanical Responses to Simulated Ocular Pulse Using Ultrasound

“…4). This difference can be explained by the known nonlinear mechanical behavior of the cornea, 33,34 which manifests as a more compliant response at lower IOP and a stiffer response at higher IOP. It is noted that the effect of baseline IOP on ocular pulse-induced corneal strains was not linear (Fig.…”

Age Distribution and Associated Factors of Cornea Biochemical Parameter Stress-Strain Index in Chinese Healthy Population

“…Consistent with the study of Eliasy, neither bIOP or CCT were signi cantly correlated with SSI 8 , but SSI was found to be positively correlated with IOP. It was not surprising, since SSI re ected the corneal stiffness, and IOP measurement was affected by corneal stiffness 10,34 . While it was emphasized that bIOP can exclude the in uence of corneal thickness and age on intraocular pressure measurement 35 , and can re ect more accurate intraocular pressure [36][37][38] .…”

“…However, since cornea is consist of a viscoelastic material, and its stress-strain behavior of biological tissue is nonlinear 6,7 , the cornea shows the biomechanical properties of changes while under different intraocular pressure load. It is always a di cult problem to evaluate corneal biomechanics without the in uence of intraocular pressure in vivo [8][9][10] .…”