18 Pre-Descemet Endothelial Keratoplasty in Scarred Cornea The cornea is a transparent structure that allows passage of light into the eye and forms the first refractive media that the ray of light embarks upon before hitting the lens and retina. Any disruption in the normal architecture of the corneal lamellae leads to scarring of the corneal stroma, which can be a response to surgery, trauma, or viral or bacterial keratitis. Trauma to the clear cornea often leads to opacity and scarring, which vary in intensity depending on the type and duration of the episode of injury. The cells responsible for scar deposition are fibroblastic cells derived from stromal keratocytes.1 Following trauma the proximal keratocytes undergo apoptosis, and keratocytes that are distal to the wound become active fibroblasts.1,2 Healed corneal scars are often long-lasting and disrupt vision for millions of patients worldwide. Currently, surgical replacement of the stroma is the only successful approach for restoration of vision in scarred corneas. The treatment of corneal scars depends on the depth of the scar and fibrosis. Superficial keratectomy is performed for scar tissue that lies close to the epithelium and is quite superficial. The corneal epithelial surface cells are first removed, and then scar tissue is peeled off the front of the cornea. The epithelial cells then heal over the wound, usually in about a week’s time. Phototherapeutic keratectomy is often employed when the corneal scar tissue extends into the upper parts of the corneal stroma or is very irregular in nature. Anterior lamellar keratoplasty is performed for corneal scars that involve the stroma and have a healthy endothelium. Involvement of the endothelium with the stromal scar necessitates an endothelial keratoplasty (EK) procedure along with the removal of scarred corneal tissue. The surgical procedure to be performed in such a scenario depends on the extent of corneal involvement, and it may range from penetrating keratoplasty (PK) to Descemet stripping endothelial keratoplasty (DSEK), Descemet membrane endothelial keratoplasty (DMEK), Descemet stripping automated endothelial keratoplasty (DSAEK), or Descemet membrane automated endothelial keratoplasty (DMAEK). Pre-Descemet endothelial keratoplasty (PDEK)3,4 is a new variant of EK procedures that, unlike other EK procedures, facilitates the use of infant, young, and adult donor tissue. PK as a procedure is faced with several difficulties, including the shortage of donor tissue, postsurgical complications associated with the use of drugs to prevent immune rejection, and a significant increase in the occurrence of glaucoma. On the other hand, EK procedures focus on the transplant of corneal endothelium, yielding better visual results but still facing the need for donor tissue. Because PDEK allows the use of infant and young donor tissue4 it increases the donor tissue pool, which is seen as advantageous. The use of infant donor tissue for scarred cornea cases has helped a great deal in the clearance of corneal scar due to bullous keratopathy. The infant donor tissue is virtually rich in endothelial cell density count that probably translates into faster and better visual recovery (► Fig. 18.1, ► Fig. 18.2, ► Fig. 18.3, ► Fig. 18.4). Adequate visualization of the intraocular structures is essential in complex cases of scarred cornea. An endoilluminator facilitates surgery because the scarred cornea, when illuminated by obliquely falling light, allows better visualization and comprehension of graft orientation and positioning.5 Correction of any other associated intraocular condition, such as lens removal and intraocular lens (IOL) placement, should be performed before a PDEK procedure to enhance the chances of graft survival and mitigate the issue of constant irritation, which could be of concern at a later stage. In cases associated with IOL decentration, subluxation, or the need for a secondary IOL fixation, glued IOL fixation is performed in all cases, followed by pupilloplasty, which helps to narrow the pupil.6 This facilitates adequate formation of the anterior chamber and also prevents air diversion in the vitreous cavity. Aphakic and pseudophakic bullous keratopathy is one of the major indications for corneal grafting in many developing countries,7,8,9 and many patients in developing countries (e.g., India) do not seek surgical treatment until their bullous lesions are severe and the disease is advanced. The advantages of performing a PDEK in complex cases of bullous keratopathy is that PDEK requires a smaller incision rather than an “open-sky” condition, and the integrity of the corneal surface in PDEK eyes is preserved without corneal incisions or sutures, eliminating the epithelium-related complications (e.g., epithelial defect and ulcer) and the suture-related complications (e.g., loose suture, infection, and neovascularization) of conventional PK. However, in cases of bullous keratopathy with severe subepithelial opacity and/or obvious stromal scar, we always scrape off the epithelium to enhance the intraoperative visualization of intraocular structures. This may often function as superficial keratectomy. The corneal surface can be reepithelialized in 3 to 4 days. Although PDEK has unique advantages, it is a more technically challenging procedure in the treatment of complex bullous keratopathy because combined procedures (e.g., anterior vitrectomy, IOL removal, etc.) are necessary in eyes with intraocular comorbidities. Because PDEK is more difficult to perform than PK, the combined procedures will definitely challenge the surgeon’s skills. Another problem challenging PDEK surgeons is the assessment of postoperative functional vision before PDEK surgery. Because complicated intraocular comorbidities accompany bullous keratopathy, a clear cornea does not guarantee good postoperative vision. It is difficult for surgeons to choose the perfect time for IOL implantation.
18.1 Introduction
18.2 Our Surgical Experience
18.3 Discussion
Ento Key
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