Moiré-pattern imaging-based IOP sensing contact lens in a Glaucoma rabbit model

Abstract

Purpose : Continuous monitoring of intraocular pressure(IOP) is necessary for successful treatment of glaucoma since patients can have a wide variation of IOP in circadian pattern and during the medication. This study presents a new method of IOP measurement by generating Moiré imaging pattern that is proportional to the IOP change with a single contact lens(CL) and a virtual second reference image that needs no additional CL

Methods : The IOP of rabbit was controlled by injection of Healon into anterior chamber and checked by tonometer and UBM. After injection of Healon, the Moire pattern on the CL was captured by conventional camera. To measure the IOP change, the Moiré effect is formed by superimposing a camera-captured image on the micro pattern of CL with computer assisted a virtual reference image. To extract IOP data from overlapped Moire patterns, the relative changes in the image pattern were converted into a waveform signals over pixel by pixel by Histograms of Gradient(HOG) algorithm using MATLAB, in which pixel intensity information were converted into the gradient information. Then waveform analysis by Fourier transform provided approach to monitor IOP change.

Results : As increased the IOP in rabbit eye, the Moire pattern on the CL(Fig 1A) was changed accordingly, producing overlapped image patterns(Fig 1B) in proportion to the IOP change. We compared the Moire pattern changes with the anterior chamber angle(ACA) that was measured according to the applied pressure(0-30 mmHg)(Fig 1C). The extracted pattern changes were obtained from overlapping with computer-assisted 2^nd Moire pattern by image analysis, which were proportion to the IOP(Fig 1D) and well coincided with ACA in a number of selected IOPs(Fig 1E).

Conclusions : The Moire pattern on the CL was changed by applied IOP or in glaucoma rabbit where IOP was increased. It was possible to extract the pattern change from computer-assisted image analysis. IOP increase and ACA were correlated in glaucoma rabbit model. In conclusion, IOP was predicted by analyzing the shape of the Moire pattern on the CL according to the pressure.

This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.

 

Representative Moire pattern on CL (A), superimposed patterns with computer assisted a virtual reference image (B) and UBM images showing measurement of ACA. Moire patterns showed their proportional change with different IOPs (D) and correlation with measured ACA according to IOP in Glaucoma rabbit model (E).