Doughnut Refractive Lenticule Transplantation for Advanced Keratoconus: A Prospective Study on Visual, Topographic, and Biomechanical Outcomes

Purpose: The aim of this study was to evaluate clinical efficacy, safety, and biomechanical effects of doughnut refractive lenticule transplantation (DRLT) in advanced keratoconus over 16 months. Methods: This prospective interventional study included 41 eyes of 40 patients (aged 11–32 years) with advanced keratoconus, with or without vernal keratoconjunctivitis, conducted at Health Net Hospital, Peshawar (IRB No.: HNH/IRB/2024/07). Donor stromal lenticules from SMILE procedures (−6.00 to −10.00 D) were fashioned into a doughnut shape and implanted into femtosecond laser–created intrastromal pockets to reinforce ectatic corneas. Follow-up over 16 months assessed distance-corrected visual acuity, corneal tomography, and anterior segment OCT. Outcomes included keratometric indices, pachymetry, astigmatism, corneal volume, asphericity, pachymetric progression index (PPI), and ARTmax. Data were analyzed using paired t tests or Wilcoxon signed rank tests, with P < 0.05 considered significant. Results: This study analyzed 41 eyes of 40 patients with advanced keratoconus treated with DRLT. Distance-corrected visual acuity improved from logMAR 1.00 ± 0.20 to 0.30 ± 0.15 at 16 months (mean gain 0.70 logMAR; P < 0.001), with 30% achieving logMAR 0.18 or better. Mean K1 decreased from 52.19 ± 5.38 D to 50.98 ± 5.62 D, K2 from 60.46 ± 6.27 D to 55.29 ± 6.19 D ( P = 0.0021), and Kmax from 70.07 ± 9.72 D to 62.90 ± 7.76 D ( P < 0.001). Topographic astigmatism reduced from 8.27 ± 3.50 D to 4.81 ± 2.55 D ( P < 0.001). The thinnest corneal thickness increased from 410.33 ± 39.23 μm to 443.33 ± 80.68 μm (+33 μm; P = 0.63). Posterior K1 decreased from 7.88 ± 0.49 D to 7.10 ± 0.63 D, K2 from 9.03 ± 0.59 D to 8.38 ± 0.66 D, and Kmax from 9.30 ± 0.57 D to 8.63 ± 0.68 D ( P < 0.05). The final D value reduced from 31.00 ± 4.51 to 14.52 ± 2.05 ( P < 0.0001), Db increased from 19.27 ± 2.55 to 23.65 ± 3.43 ( P = 0.0002), Dp increased from 15.61 ± 2.08 to 29.54 ± 4.83 ( P < 0.0001), and Dt decreased from 5.13 ± 0.91 to 3.82 ± 0.40 ( P < 0.0001), while Da showed no change (3.51 ± 0.36–3.90 ± 0.61; P = 0.57). Pachymetric progression indices increased significantly (PPImin 3.06 ± 0.58–5.55 ± 0.73; PPImax 5.10 ± 0.65–8.85 ± 0.92; PPIavg 3.82 ± 0.61–6.64 ± 0.78; all P < 0.0001), whereas ARTmax decreased from 74 ± 5.9 to 48 ± 6.3 ( P < 0.0001). Corneal thickness spatial profile increased across all zones (0–2 mm, 2–4 mm, 4–6 mm, >6 mm; P <0.0001). Peripheral percentage thickness increase (3–8 mm) rose from 38% ± 6% to 56% ± 6%, and central percentage thickness increase (0–2 mm) rose from 12% ± 3% to 19% ± 3% ( P = 0.0034). Conclusions: DRLT provided significant improvements in visual acuity, keratometric parameters, and corneal biomechanics in advanced keratoconus over 16 months. As a minimally invasive, sutureless, and endothelial-sparing procedure, it may serve as an alternative in cases unsuitable for conventional interventions. Larger controlled studies with longer follow-up are warranted to validate durability and progression control.