Direct measurement of corneal tissue water content by reflection imaging at Terahertz Frequencies

Abstract

 

Purpose

 

Many pathologies such as Fuchs’ endothelial Dystrophy and pseudophakic bullous keratopathy result in increased corneal tissue water content (CTWC). However, accurate, non-invasive, in vivo measurement of CTWC remains elusive. This study reports direct, non-contact measurement of CTWC in rabbit models using a novel reflectomertry technique based on Terahertz (THz) frequency illumination and imaging.

 

Methods

 

THz reflectivity images of 12 in vivo rabbit cornea were acquired using novel imaging optics. Controls images of healthy cornea were acquired, then CTWC was perturbed through surgical stripping of Descemet’s membrane. The resulting increase in corneal issue water was monitored by THz imaging and compared with that computed by CCT measurements acquired with ultrasound pachymetry. THz imagery and pachymetry monitoring were performed over 5 hours following Descemet’s membrane stripping. The animals were then euthanized, corneas were resected and sectioned, and the success of membrane stripping verified histologically.

 

Results

 

Clear and consistent increases in THz derived CTWC were observed and statistically significant correlations with increasing pachymetry measurements were demonstrated. THz reflection imaging achieved a minimum detectable water concentration difference of < 1.5% using 650 GHz illumination. THz images obtained with ~ 2 mm spatial resolution showed changes in tissue water content distribution throughout the entire extent of the cornea and correlated with the actual water content of the corneas.

 

Conclusions

 

THz imaging can provide direct measurement of CTWC in in-vivo. The technique is non-contact, sensitive, and does not rely on assumptions of healthy cornea central thicknesses. This allows the technology to be robust to physiologic variation and feasible to be translated into clinical application.  

 

Figure 1: (a) Central cornea thickness (CCT) and computed corneal tissue water content as a function of time following corneal tissue water content perturbation procedure. (b) Images (650 GHz illumination) of cornea eye displaying reflectivity decrease from correlated with drop in corneal water content.