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A Novel Method for Optical Distortion Quantification

Gerton, Katherine M., MSc1; Novar, Brenda J., MSEM2; Brockmeier, William, BSE3; Putnam, Christopher, OD, PhD, FAAO2*

doi: 10.1097/OPX.0000000000001335
ORIGINAL INVESTIGATIONS

SIGNIFICANCE Optical distortion is the image degradation of a visual target induced by a transparent material. Current Air Force evaluation of distortion is an entirely qualitative assessment of the acceptability of image distortion. The novel, quantitative technique described here is capable of identifying 0.1% distortion across an array of optical samples.

PURPOSE Optical distortion is the effect by which a transparent object spatially warps the perception of a visual target. All U.S. Air Force visors are required to pass military standards outlined in MIL-DTL-43511D (2006). Although specifications for the optical distortion setup and critical areas of vision are outlined, the evaluation technique is entirely qualitative, with a panel of several human evaluators assessing the distortion acceptability. The evaluation is not explicitly tied to a visual acceptability rating and has variable levels of consistency over time or across evaluators and a fabrication tolerance limit of 3% distortion.

METHODS The technique proposed in this article is a modification to the recommended optical tester used to analyze distortion patterns. An image-processing algorithm was developed to analyze patterns of Ronchi grid distortion mathematically to provide a quantitative approach that can subsequently be tied to visual metrics.

RESULTS This effort developed and refined an algorithm that allowed for a standardized assessment creation of high-resolution distortion maps from digital images. A 1-inch-diameter region imaged through ophthalmic material allowed for two-dimensional median filtering down to 15-pixel areas with enhanced contrast between grid lines leading to possible resolution capabilities of 0.10% distortion.

CONCLUSIONS Quantification of the standard for measuring optical distortion is the initial step toward determining the effects of distortions on human visual performance metrics. The future goal for this effort will focus on obtaining empirical results from human experimental efforts and relating the distortion location and magnitude to effects on visual performance activities.

1Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey

2711 Human Performance Wing, Airman Systems Directorate, Bioeffects Division, Optical Radiation Bioeffects Branch, San Antonio, Texas

3Engility Corporation, JBSA Fort-Sam, Houston, Texas *christopher.putnam@us.af.mil

Submitted: February 11, 2018

Accepted: October 7, 2018

Funding/Support: None of the authors have reported funding/support.

Conflict of Interest Disclosure: None of the authors have reported a financial conflict of interest.

Author Contributions and Acknowledgments: Conceptualization: KMG, BJN; Data Curation: KMG, BJN, WB; Formal Analysis: BJN, WB; Funding Acquisition: BJN, CP; Investigation: KMG, WB, CP; Methodology: KMG, WB; Project Administration: CP; Resources: WB; Software: KMG, BJN; Supervision: BJN, CP; Validation: KMG, BJN; Writing – Original Draft: KMG, BJN, WB, CP; Writing – Review & Editing: CP.

The authors would like to acknowledge Dr. Leon McLin for providing his valuable feedback and research experience in the field of vision science.

© 2019 American Academy of Optometry