Scleral Transillumination-Guided Trocar Placement During Vitrectomy in Highly Myopic Eyes: A Case Report

High myopia can make pars plana vitrectomy technically challenging because axial elongation may increase the distance between the conventional trocar insertion site and the posterior pole. Accordingly, more posterior trocar placement has been proposed to improve access of vitreoretinal instruments to the retinal surface. We report two myopic eyes in which scleral transillumination was used intraoperatively to assess the posterior edge of the ciliary body and to guide trocar placement when needed. Case 1 underwent surgery for a macular hole, and Case 2 underwent surgery for macular hole retinal detachment. In both cases, involving the right eye, an intraocular light pipe was inserted through the superonasal trocar and directed toward the superotemporal sclera under reduced room and microscope illumination. The resulting transillumination boundary was marked externally. In Case 1, the trocar was placed at the conventional insertion site, and scleral transillumination was performed intraoperatively to assess the relationship between the transillumination boundary and the ciliary body. The boundary was located approximately 6 mm posterior to the corneal limbus, and intraoperative indentation confirmed that it corresponded to the posterior edge of the ciliary body. Postoperative anterior segment optical coherence tomography (AS-OCT) showed a ciliary body length of around 6.6 mm. In Case 2, scleral transillumination was used to guide trocar placement. The initial illumination border was observed approximately 6 mm posterior to the limbus and was used as a reference for trocar insertion. However, further peripheral observation revealed an additional posterior dark band approximately 9 mm from the limbus. External marking and indentation of this band corresponded to the posterior edge of the ciliary body, and postoperative AS-OCT showed a ciliary body length of around 9.9 mm. These preliminary observations from two highly myopic eyes suggest that scleral transillumination may be a useful intraoperative method for estimating the posterior edge of the ciliary body and guiding trocar placement. In Case 2, the initial transillumination boundary was located anterior to an additional peripheral dark band, which appeared to correspond more closely to the actual posterior edge of the ciliary body. Nevertheless, for practical vitrectomy, the anterior illumination boundary provided a sufficiently posterior and safe landmark for trocar placement. This technique should be considered selectively in highly myopic eyes with axial elongation rather than in eyes with normal or short axial length. Further studies are needed to determine the generalizability of these findings.