Corneal pulse characteristic in response to elevated intraocular pressure during ocular pulse simulation in porcine eye. A pilot in-vitro study

Abstract

Purpose : To investigate the impact of intraocular pressure (IOP) and the related corneal biomechanical metrics on temporal and spectral parameters of the corneal pulse (CP) signal during ocular pulse cycles induced in porcine eyes in-vitro.

Methods : Four porcine eye globes were obtained from the local abattoir 6 hours post-mortem and tested within the next 12 hours. An infusion needle (19G), connected with a pressure transducer (P-30, WIKA) and a custom made syringe pump, was inserted into the anterior chamber. The pump was used to induce the IOP pulsation simulating the ocular pulse with a frequency of 1.2 Hz, at the IOP levels increased from 15 to 45 mmHg in 5-mmHg steps. The infusion volume was set to obtain an ocular pulse amplitude (OPA) in the range of 2–3 mmHg for the starting IOP, and was constant at each step of the experiment. At each IOP level, three measurements of the CP signal were acquired in a non-contact manner with an ultrasonic transducer synchronically with the IOP signal registered with the pressure transducer. In addition, corneal biomechanical metrics (CBM), including the applanation lengths (A1L, A2L) and velocities (A1V, A2V), peak distance (PD), radius (R) and deformation amplitude (DA) were measured using a dynamic Scheimpflug analyzer (Corvis ST). Raw data were numerically processed to estimate CP parameters such as the root mean square (RMS) value and the amplitude of the first harmonic in the CP power spectrum (ACP1), normalized with respect to the starting values and averaged for each IOP. The backward stepwise regression analysis was applied.

Results : All considered CBM showed significant correlation with IOP (p<0.05). Regression analysis including CBM revealed that for RMS and ACP1 only DA contributed significantly to the models: RMS=0.328+0.374DA (R²=0.596, p<0.001) and ACP1=0.295+0.370DA (R²=0.605, p<0.001). Furthermore, considering pressure parameters, for RMS only IOP contributed significantly to the subsequent model: RMS=1.164−0.016IOP (R²=0.676, p<0.001), while ACP1 was found to be predicted by IOP and OPA: ACP1=0.915−0.017IOP+0.080OPA (R²=0.682, p<0.001 and p=0.045).

Conclusions : CP parameters were found to reflect an increase in IOP and associated changes in corneal apex deformation. Further studies may enrich the CP signal analysis with the ability to assess corneal biomechanics.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.