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

Maja M Rogala,Jerzy Detyna,Agnieszka Antończyk,Daniel Lewandowski,Monika E Danielewska

doi:10.1371/journal.pone.0228920

Maja M Rogala, Jerzy Detyna + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0228920

Copy DOI

Abstract

The purpose of this study was to ascertain the relationships between the amplitude of the corneal pulse (CP) signal and the parameters of corneal biomechanics during ex-vivo intraocular pressure (IOP) elevation experiments on porcine eyes with artificially induced ocular pulse cycles. Two experiments were carried out using porcine eyes. In the first one, a selected eye globe was subjected to three IOP levels (15, 30 and 45 mmHg), where changes in physical ocular pulse amplitude were controlled by infusion/withdrawal volumes (ΔV). In the second experiment, six eyes were subjected to IOP from 15 mmHg to 45 mmHg in steps of 5 mmHg with a constant ΔV, where corneal deformation parameters were measured using Corvis ST. In both experiments, at each IOP, the CP and IOP signals were acquired synchronically using a non-contact ultrasonic distance sensor and a pressure transmitter, respectively. Based on the amplitudes of the CP and IOP signals ocular pulse based corneal rigidity index (OPCRI) was calculated. Results indicate positive correlations between ΔV and the physical ocular pulse amplitude, and between ΔV and the corneal pulse amplitude (both p < 0.001). OPCRI was found to increase with elevated IOP. Furthermore, IOP statistically significantly differentiated changes in OPCRI, the amplitudes of CP and IOP signals and in most of the corneal deformation parameters (p < 0.05). The partial correlation analysis, with IOP as a control variable, revealed a significant correlation between the length of the flattened cornea during the first applanation (A1L) and the corneal pulse amplitude (p = 0.002), and between A1L and OPCRI (p = 0.003). In conclusion, this study proved that natural corneal pulsations, detected with a non-contact ultrasonic technique, reflect pressure-volume dynamics and can potentially be utilized to assess stiffness of the cornea. The proposed new rigidity index could be a simple approach to estimating corneal rigidity.

Highlights

The first experiment showed that the elevation of intraocular pressure (IOP) results in an increase of physical ocular pulse amplitude (OPAp) for the same infusion/withdrawal volume
For the first ex-vivo inflation experiment, the results show that both physical ocular pulse amplitude (OPAp) and corneal pulse amplitude (CPA) positively correlate with infusion/withdrawal volume
Summarizing, this study revealed that the corneal biomechanical changes related to increase in IOP can be detected by observing natural corneal pulsations with a non-contact ultrasonic technique

Summary

Introduction

The dynamic deformation response of the cornea is described by its viscoelastic properties and originates mainly from molecular rearrangement as a response to the mechanical load application [11,12]. The cornea, as an integral part of the outer ocular coat, is directly subjected to the internal load of the IOP [13,15]. As it was reported earlier [7,16,17,18], IOP itself affects stiffness of the ocular shell. 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]

Objectives

Methods

Results

Discussion

Conclusion