**Acknowledgements**

This study was supported in part by NIH core grant P30 EY030413 (Bethesda, Maryland), NIH award UL1TR001105 (Bethesda, Maryland), and University of Texas Southwestern Medical Student Research Program (Dallas, TX). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. We would also like to thank Tina Pham, Priya Mekala, and Monica Patel for their help with organizing artifact images and information.
