Background: Keratoconus is an idiopathic, noninflammatory, ectatic corneal disease that causes progressive vision loss. Although the disease is bilateral, its effects are usually asymmetric. It causes paraxial stromal thinning and weakening, leading to corneal surface distortion. Vision loss in keratoconus is caused primarily by irregular astigmatism and myopia and secondarily by corneal scarring. Objective: To study the effect and safety of Femtosecond assisted implantation of INTACs on corneal endothelium using specular microscopy. Patients and methods: This was a prospective comparative study conducted on 20 eyes attended the outpatient clinic of the Ophthalmology Department at Al-Azhar University Hospital (Cairo) from October 2018 to October 2029 with Keratoconus who had implantation of intracorneal ring segments (INTACS). The effect and safety of femtosecond assisted implantation of INTACs on corneal endothelium using specular microscopy were studied. Results: Regarding preoperative ophthalmic data, the mean preoperative intraocular pressure (IOP) was (17.5 ± 2.3) mmHg, the mean preoperative uncorrected visual acuity (UCVA) was (0.17 ± 0.1), and the mean preoperative best corrected visual acuity (BCVA) was (0.5 ± 0.17).  Regarding preoperative corneal topography data, the mean preoperative spherical equivalent was -5.94 ± 3.2 D. The mean preoperative cylinder was (-3.5 ± 1.68) D, and the mean preoperative topographic K values was (48.3 ± 3.9) D. Regarding preoperative specular microscopy data, the mean preoperative endothelial cell number was 2822.5 ± 321.9. The mean preoperative coefficient of variation was 29.2 ± 4, and the mean preoperative percentage hexagonal cell count was 54.6 ± 7.7 %. There were significant increase in post-operative best corrected visual acuity (BCVA), and best corrected visual acuity (BCVA) assessments in keratoconus eyes (p < 0.01 respectively). By using ROC-curve analysis, femtosecond assisted implantation of implantation of intracorneal ring segments (INTACS) predicted endothelial cell number improvement, with fair (72%) accuracy, sensitivity= 40% and specificity= 95% (p < 0.01). Conclusion: The intrastromal ring was a stent designed to alter the corneal curvature and reduce refractive errors resulting from irregularities of corneal ectasia. The ring may improve the effect of optical correction with glasses or contact lenses.