Femtosecond laser–assisted nanothin DSAEK using optical coherence tomography–guided pachymetric oversizing: outcomes and risk factors for failure

Technical Summary: Femtosecond Laser–Assisted Nanothin DSAEK with OCT-Guided Pachymetric Oversizing

Problem Statement
Endothelial keratoplasty has largely replaced penetrating keratoplasty for isolated endothelial dysfunction, offering faster visual rehabilitation. While Descemet membrane endothelial keratoplasty (DMEK) offers superior visual outcomes, Descemet stripping automated endothelial keratoplasty (DSAEK) preserves handling advantages. Conventional DSAEK grafts (≥100 µm) result in slower visual recovery compared to ultrathin (50–100 µm) or nanothin (≤50 µm) variants. However, achieving consistently thin planar grafts is technically demanding. Standard femtosecond laser (FSL) platforms often limit the minimum cutting depth to approximately 125 µm from the endothelial surface, restricting the creation of true nanothin grafts. Furthermore, existing nanothin techniques are predominantly microkeratome-based, and FSL-only approaches have been largely confined to laboratory settings or the ultrathin range. There is a need for a reproducible FSL method to produce nanothin grafts (50–75 µm) while maintaining safety and precision, particularly in complex eyes with anterior segment comorbidities.

Methodology
This retrospective interventional case series analyzed 18 consecutive DSAEK procedures performed by a single surgeon between June 2022 and October 2025. The study focused on a specific donor preparation technique combining femtosecond laser dissection with intraoperative optical coherence tomography (OCT) guidance and a strategy of pachymetric oversizing.

• Donor Preparation: Donor corneas were processed using a Victus® FSL platform equipped with real-time intraoperative OCT. The core innovation was "pachymetric oversizing," where the corneal thickness was intentionally overestimated in the planning software. This allowed the cutting plane to be set closer to the endothelium than standard platform limits would permit, targeting a graft thickness of 50–75 µm.
• Laser Parameters: The lenticule was fashioned with a bed-cut close to the Descemet membrane and an internal side-cut directed toward the endothelium (7.8–8.1 mm diameter). Specific energy settings included 0.95 µJ for the bed (5.5/5.5 µm spacing) and 1.10 µJ for the rim (5.5/2.0 µm spacing).
• Surgical Technique: Following FSL cutting, the lenticule was manually dissected using a Sinskey hook and blunt spatulas to avoid endothelial contact. The graft was inserted via a 4.0–4.5 mm incision, primarily using a Busin glide pull-through technique.
• Study Population: The cohort was highly complex, with 83.3% (15/18) of cases involving comorbidities such as prior graft failure (re-transplantation), aphakia, glaucoma drainage devices, iris abnormalities, or prior posterior vitrectomy.
• Outcome Measures: Clinical success was defined at one year as a clear graft with improved visual acuity and no need for re-transplantation. Outcomes included intraoperative and 1-month graft thickness, best-corrected visual acuity (BCVA), and endothelial cell density (ECD).

Key Contributions

1. Reproducible Nanothin Preparation: The study demonstrates that FSL-assisted donor preparation, utilizing pachymetric oversizing and real-time OCT monitoring, can reproducibly produce nanothin DSAEK grafts with a mean thickness of approximately 50 µm at one month.
2. Overcoming Platform Limitations: The "oversizing" strategy effectively circumvents the minimum depth limitations of standard FSL platforms, enabling safe dissection planes closer to the endothelium without perforation, specifically in regular, homogeneous corneas.
3. Risk Factor Analysis in Complex Cohorts: The paper provides exploratory data on success rates in a complex cohort, identifying that primary cases (no prior graft) were significantly more likely to succeed than re-transplant cases, while prior graft failure showed a trend toward lower success rates.

Results

• Graft Thickness: The mean intraoperative graft thickness was 57.0 µm (range 38–74 µm), decreasing to a mean of 49.9 µm at one month (range 30–79 µm).
• Clinical Success: Clinical success was achieved in 10 of 18 eyes (55.6%).
• Visual Outcomes: Postoperative BCVA was significantly better in successful cases compared to failures (median 0.52 vs. 1.60 LogMAR; P=0.001). Preoperative BCVA did not differ between groups.
• Risk Factors:
  • Primary vs. Re-transplantation: Primary cases achieved success in 87.5% of instances, whereas re-transplantation cases had a 30% success rate (P=0.041 for primary success; P=0.070 trend for re-transplant failure).
  • Graft Diameter: Successful cases had significantly larger graft diameters (mean 7.9 mm) compared to failures (mean 7.6 mm; P=0.037).
  • Other Factors: Aphakia, prior posterior vitrectomy, iris abnormalities, and glaucoma drainage devices did not show statistically significant associations with failure in this small cohort, though glaucoma devices showed a non-significant trend toward lower success.
• Endothelial Cell Density (ECD): One-year ECD was available for 8 eyes (mean 1,338.3 cells/mm²).
• Complications: Complications were infrequent, including one retinal detachment and one DALK melting (both in failure cases). No graft rejections or rebubbling were recorded.

Significance and Claims
The authors claim that this technique enables the reproducible preparation of ultrathin/nanothin DSAEK grafts even in complex eyes, bridging the gap between the handling advantages of DSAEK and the visual potential of thinner grafts. The study highlights that while precise donor preparation is critical, patient selection remains a dominant determinant of success; specifically, primary cases are more likely to succeed than those with prior graft failures. The authors emphasize that these findings are exploratory due to the small sample size and heterogeneous cohort, serving as hypothesis-generating data rather than definitive conclusions. They assert that the combination of FSL, pachymetric oversizing, and intraoperative OCT offers a viable pathway to achieving nanothin grafts that were previously difficult to obtain with femtosecond technology alone.