d. Patch graft

• Corneal patch graft

Crescentic or circular corneal patch graft provides a favorable anatomical result in patients with concomitant autoimmune disease. Vascular ingrowth, chronic epithelial defect, rapid suture loosening, and dissolution of the transplanted tissue are all frequent complications [102]. The new alternative is to use as donor tissue the lenticule obtained during small incision refractive lenticule extraction (SMILE) [103].

• Scleral patch graft

Scleral tissue from cadaveric eyeballs provides tectonic stability and is often used in conjunction with cyanoacrylate glue. It is an easy, inexpensive, and effective surgical solution for perforations that are 3– 5 mm in size [104]. However, like corneal patch graft, it is associated with a high risk of graft vascularization and opacification, postoperative irregular astigmatism and is limited by the availability of donor tissue [88].

• Tenon's patch graft (TPG)

Tenon's patch graft (TPG) is a simple and affordable method used for perforations of 3–5 mm, benefiting from the autologous nature of the graft [105].

	- Crescentic lamellar keratoplasty is commonly used in cases of significant thinning of the marginal area of the cornea in the case of PUK. It involves the placement of a ring-shaped lamellar graft on the periphery of the cornea and attachment with sutures to the host cornea. The size of the graft depends on the shape and size of the thinning zone. The visual acuity obtained after this procedure is reported to be significantly better compared to total LK. Several modifications of this technique exist [107].
	- Compressive crescentic (C-shaped) lamellar keratoplasty comprises the use of undersized crescentic donor tissue and tight sutures, causing a flattening perpendicular to the circumference and correcting the steepening and high astigmatism that occurs in the course of the disease [4, 108].
	- Lamellar corneoscleroplasty can restore ocular integrity and maintain the angle structures when scleral melting is present as well [109].
	- Superficial anterior lamellar keratoplasty (SALK): Decentrated large-diameter SALK has the potential to be used successfully in PUK [110].
	- Deep anterior lamellar keratoplasty (DALK) preserves the host endothelium and Descemet's membrane. Decetrated DALK has shown favorable results in PUK with corneal melt [5].
