How to perform trephination?

Corneal Trephination Technique

Corneal trephination is performed using either mechanical trephines or femtosecond laser-assisted techniques, with the choice depending on the specific clinical scenario, equipment availability, and surgeon preference. 1

Mechanical Trephination

Technique

• Trephination for penetrating keratoplasty (PK) involves using either same-size or oversize trephines for donors and recipients 1
• The size of the trephine is determined by the size of the defect and whether the graft's edge will impinge on the pupil 1
• Axial length and graft-host disparity significantly impact postoperative refractive error:
  • Same-size grafts in short eyes typically result in postoperative hyperopia 1
  • Oversized grafts in eyes with long axial lengths typically result in myopia 1
• For peripheral pathology that is annular in nature, a concentric donut or partial crescentic graft may be required 1

Considerations

• Central grafts are usually circular in shape 1
• Peripheral grafts are technically more difficult and often associated with modest postoperative astigmatism 1
• In some cases, a full-thickness patch or crescentic graft may be needed 1
• Less graft/host-size disparity tends to induce less myopic shift 1

Femtosecond Laser-Assisted Trephination

Technique

• Femtosecond laser-assisted keratoplasty (FLAK) utilizes the femtosecond laser for trephining both donor and recipient corneas 1
• The same pattern of laser trephination is used for both donor and recipient 1
• Trephination patterns include:
  • Top-hat pattern (preserves more host endothelium) 1
  • Mushroom pattern 1
  • Zigzag pattern 1

Advantages

• Creates additional wound surface area resulting in faster wound healing and stronger wound 1
• Allows for earlier suture removal and quicker visual rehabilitation 1
• Improves control of wound shape and postoperative astigmatism 1
• Provides greater mechanical stability 1
• Reduces astigmatism in the early postoperative period (though this benefit doesn't persist beyond 6 months) 1

Limitations

• Access, logistics, cost, and lack of insurance reimbursement limit its use 1
• Studies show no long-term benefit compared to mechanical trephination 1

Special Applications

Deep Anterior Lamellar Keratoplasty (DALK)

• The femtosecond-assisted big-bubble technique utilizes a femtosecond laser program to trephine the cornea 1
• After trephination, a big bubble is created using a needle or cannula to bare Descemet's membrane 1
• A femtosecond laser-trephined cornea is then sutured onto the recipient bed 1
• Using a customized trephination pattern (such as "zigzag") combined with the big bubble DALK technique can improve wound integrity and healing 1

Peripheral Thinning and Ectasia

• When ectasia occurs in the far periphery, a lamellar graft can be performed for tectonic support as a primary procedure 1
• Additional PK can be performed later for visual rehabilitation 1

Complications and Pitfalls

• Perforation of the cornea during DALK procedures may require conversion to PK 1
• Irregular astigmatism is a common postoperative problem with rotational autografts 1
• Care should be taken to avoid having the graft-host junction too close to the pupil, which can cause postoperative distortion 1
• Suture-related complications include breakage, irritation, infection, or rejection 1
• When corneal thinning extends near the limbus, PK is more challenging and carries a greater risk of failure 1

By selecting the appropriate trephination technique and pattern based on the specific clinical scenario, surgeons can optimize outcomes for patients requiring corneal transplantation.