Development of an Objective Method of Respiratory Protective Mask Lens Fogging: Data Acquisition and Image Processing Proof of Concept

A method that objectively related video image gray scale characteristics to Snellen visual acuity was conceptualized, developed, and evaluated in this investigation as a first step towards development of an objective measure of respirator lens fogging. Seven image processing techniques, including region of interest selection, image filtering, thresholding, removal of border objects, removal of small objects, filling of image holes, and particle detection were applied to images captured on-line with a miniature video camera through goggles with different levels of visual acuity. The image processing sequence was used to assess correlations between image particle counts and known visual acuity scores. A LABVIEW program was developed to determine Snellen visual acuity based on the presence or absence of circles from the processed images. The developed image processing and analysis application correctly identified 20120, 20150, 20170, and 201300 Snellen visual acuity conditions on a consistent basis. Following adjustments to the image thresholding techniques during image processing, program identification success improved for all acuity conditions. These findings indicate that an objective method has been established that can be used to quantify changes in visual acuity due to mask lens fogging.