Purpose: To evaluate the efficacy and stability of implantation of 5 mm diameter intrastromal corneal ring segments (ICRS) with a modified base (800 µm) in the treatment of astigmatism after penetrating keratoplasty (PK). Materials and methods: A retrospective case-series study was performed in a cornea-keratoconus service in Buenos Aires (Argentina). We included patients with a history of keratoconus who underwent PK and had residual high astigmatism (>5.0 diopters [D]) after 2 years. These patients had undergone 800 µm width ICRS implantation between 2002 and 2019, with at least 2 years of postoperative follow-up. The main outcomes were uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively) and topographic astigmatism, evaluated before ICRS implantation and 2 years postoperatively. Results: Twelve eyes underwent ICRS implantation. The mean topographic astigmatism was 12.9 ± 3.8 D (6.9–19.6) at baseline, which decreased (p < 0.001) to 4.2 ± 2.3 D (0.4–8.8) after ICRS implantation. The baseline UDVA was 1.00 ± 0.21 logarithm of the minimum angle of resolution (LogMAR) (0.6–1.3), whereas the postoperative UCVA was 0.32 ± 0.17 LogMAR (0.1–0.7). The baseline CDVA was 0.63 ± 0.15 LogMAR (0.2–0.8), whereas the postoperative CDVA was 0.12 ± 0.05 LogMAR (0–0.2). The improvement in visual acuity was statistically significant (p < .0.001). Conclusion: The high postoperative astigmatism after PK in eyes with keratoconus decreased following the implantation of ICRS with an 800 µm base width, improving the UDVA and CDVA and achieving refractive stability for at least 2 years postoperatively. Complications were not detected, although a larger cohort should be evaluated in a multicentric setting to confirm these results. Clinical significance: This series clinically proves that ICRS with a base of 800 µm can be an effective option for managing high post-PK astigmatism.