Fida, Abida, et al. “SAFETY OF HIGH INTENSITY ACCELERATED CORNEAL COLLAGEN CROSS-LINKING IN KERATOCONUS PATIENTS ON BASIS OF ENDOTHELIAL CELL DENISITY”. Journal of Ayub Medical College Abbottabad, vol. 30, no. 4, Nov. 2018, pp. 501-5, https://www.jamc.ayubmed.edu.pk/index.php/jamc/article/view/3509.