**2. Corneal transplant techniques**

Corneal grafting techniques date back to the latter part of the 19th century and the earlier part of the 20th century as exemplified by pioneer ophthalmologists such as Reisinger, von Hippel and Elsching.

Penetrating Keratoplasty refers to the full thickness replacement of a diseased cornea with a healthy donor tissue. This technique may be used or to provide tectonic support in case of corneal thinning and perforation, either in case of keratoconus, bullous keratopathy, corneal dystrophies and degeneration, trauma or any other causes of corneal decompensation. Because of the "open sky" exposure of the intraocular contents during this kind of surgery, IOP control is an important step to avoid the risk of intraoperative expulsive choroidal haemorrhage. Using a calliper the horizontal and vertical diameters of the recipient's cornea are measured and the size of the graft is determined base on pathology and clinical judgement. Traditionally is used a size disparity in which the donor tissue is 0.25 mm larger than that of the recipient. The centre of the recipient cornea is marked so as the periphery with a radial keratotomy marker stained with ink. Then, while preparing the donor tissue punching the corneal button, the recipient cornea is cut by a trephine and the trephination is stopped as soon as aqueous egress shows the anterior chamber has been entered. Suction is released and the viscoelastic is then injected; the recipient button is excised using forceps and corneal scissors. Then the donor button is placed over the recipient bed and sutured in

Diagnosis and Treatment of a Rare Complication

**3. Retention of Descemet's membrane** 

considered an essentially refractive neutral transplant procedure.

Fig. 1.a Retained Descemet's membrane after PK treated with YAG laser

firmly press the donor tissue against the recipient cornea.

humour nutrients.

After Penetrating Keratoplasty: Retained Descemet's Membrane 121

Retention of the host's Descemet's membrane is a complication which can occur during the course of a penetrating keratoplasty (but also DALK and DSAEK present retention of Descemet's complications) and which eventually leads to loss of graft clarity by clouding or by coming into contact with the graft endothelium. Penetrating keratoplasty is a common technique with good prognosis value and has been the first choice for corneal endothelial decompensation even if in the last years for this kind of diseases DSAEK is preferred in order to its minimal sequelae. DSAEK requires much less manipulation of the recipient cornea and anterior chamber, compared with the earlier PK and DALK procedure and this help to minimize intraoperative and postoperative complications. Moreover DSAEK technique does not induce significative alterations of corneal topography so that it could be

Postoperative complications of penetrating keratoplasty include high or irregular astigmatism, prolonged wound healing, late wound dehiscence with trauma, suture-related infections, vascularisation, and graft rejection. The most postoperative complication with DSAEK, instead, is that sometimes the donor tissue detaches in the early postoperative period (from 1 day to 1 week after surgery) so that additional air must to be injected to again

In addition, retention of the host's Descemet's membrane can be seen as a rare complication of these surgical techniques. The retained Descemet's membrane can compromise endothelial tissue by contact injury or by limiting diffusion of aqueous

place with four cardinal sutures whose depth is typically 90% of the corneal thickness. After placement of the 12 o'clock suture, particular attention is paid to the 6 o'clock suture because these two sutures follow a vertical line and bisect the entire donor button such as the two at 3 and 9 o'clock. The rest of the sutures could be a combination of interrupted and running sutures.

But since the advent of penetrating keratoplasty surgeons have recognized the undesirable postoperative consequences of full-thickness corneal surgery such as high astigmatism, unpredictable refractive outcomes and prolonged visual rehabilitation. That's why ophthalmologists have conceptualized more selective transplanting techniques such as deep stromal and endothelial keratoplasty.

Lamellar keratoplasty involves placing a partial thickness donor corneal graft within a recipient corneal bed prepared by lamellar dissection of abnormal corneal tissue. It could be considered an alternative surgical option to penetrating keratoplasty in many specific cases such as all the ectactic corneal disorders that don't affect the endothelial cell layer. Lamellar keratoplasty offers several advantages over traditional PKP by avoiding complications associated with the "open sky" surgery and decreasing allograft rejection. The goal of this kind of surgery is a sufficient restoration of optical clarity of the central cornea; achievement of this objective is dependent upon a clean and complete posterior lamellar dissection of the host's corneal stroma from Descemet's membrane. An inadequate dissection could result in stromal and interface opacification and irregular astigmatism.

Descemet's stripping automatic endothelial keratoplasty (DSAEK) has become the preferred method of corneal transplantation for endothelial disease with improved safety, reduced astigmatism, and faster visual recovery. It is often performed with topical anaesthesia and monitored intravenous sedation. With the patient in a supine position, the horizontal corneal diameter of the recipient eye is measured with callipers to guide the selection of an appropriate donor tissue diameter. A 5 mm temporal clear corneal or sclera tunnel incision is made in the recipient eye. If the recipient epithelium is hazy or scarred it can be removed and this usually improves the view into the eye. Multiple ink points around the entire diameter of recipient cornea are used to lightly mark the surface of the recipient cornea to delineate the area for Descemet's membrane removal. The recipient endothelium, in fact, should only be stripped from the area that will be covered by the donor tissue because any stripped area not covered with donor tissue will become oedematous. To prevent this occurrence some surgeons score an area somewhat smaller than the planned donor diameter. Trypan blue could also be introduced in the anterior chamber to improve membrane visualization during the stripping. Descemet's membrane is then scored in a circular pattern along the perimeter of the area to be removed with a modified hook. During the scoring and stripping steps the anterior chamber can remain formed by continuous infusion of balanced salt solution or air (we prefer to avoid the use of viscoelastic because, if it will not be completely removed before inserting the donor button, it will impair donor adherence).

After the donor tissue is inserted the anterior chamber is inflated by injecting air or balanced salt solution which allows the posterior portion of the donor tissue to unfold. The anterior chamber is then completely filled with air to firmly press the donor tissue up against the recipient cornea.
