Corneal Transplantation and Glaucoma

Abstract

Glaucoma is the leading cause of irreversible vision loss post-keratoplasty and an important cause of graft failure. With newer techniques, such as lamellar, endothelial, and laser-assisted keratoplasty as well as keratoprosthesis gaining popularity, clinicians will need to consider the incidence, risks, evaluation, and management of glaucoma for each type of keratoplasty when determining which type of transplant may be most appropriate. A comprehensive literature search of glaucoma in the setting of corneal transplantation was performed and serves as the basis for this review. Preexisting glaucoma and aphakia are notable risk factors. Patients that are candidates for deep anterior lamellar keratoplasty may benefit from reduced rates of post-keratoplasty glaucoma. Although glaucoma also complicates eyes with Descemet stripping endothelial keratoplasty, the severity is less and the intraocular pressure is more easily controlled when compared to penetrating keratoplasty. Endothelial keratoplasty creates unique perioperative issues mostly related to management of anterior chamber air bubbles.     

A novel method of tunnel creation using intraoperative optical coherence tomography-guided deep anterior lamellar keratoplasty

The big bubble technique has become the technique of choice for performing deep anterior lamellar keratoplasty (DALK) since its inception in 2002. The main challenge with this technique is in achieving a big bubble while preventing inadvertent perforation of the Descemet’s membrane. Although femtosecond lasers have increased the safety, accuracy, and predictability of corneal dissection in DALK, the challenge of achieving a big bubble still exists. To overcome this challenge, Zeimer Z8 Femto LDV has launched a new software module for DALK, which has an added advantage of real-time optical coherence tomography–assisted femtosecond tunnel creation for achieving a big bubble.     

Descemetocele

A corneal descemetocele, the anterior herniation of an intact Descemet membrane through an overlying stromal defect, is a rare, but serious outcome of progressive corneal ulceration and mandates urgent intervention owing to the imminent risk of perforation. Various ocular and systemic abnormalities that can lead to the formation of descemetocele include microbial keratitis, neurotrophic keratopathy, dry eye disorders, and corneal inflammation associated with immune-mediated disorders. The primary aim of management of a descemetocele remains prompt restoration of ocular integrity to prevent the rupture of the Descemet membrane and further complications. Medical therapy is instituted immediately while deciding on the most suitable operative modality for an individual case. Commonly available treatment options include therapeutic bandage contact lenses, tissue adhesives, amniotic membrane transplantation, corneal patch grafts, penetrating or lamellar keratoplasty, and conjunctival flaps. Infrequently, platelet-rich fibrin membrane grafting and umbilical cord patch transplantation have also been tried with success. The surgical strategy and the outcome are commonly determined by the size, location, and etiology of descemetoceles. Despite the availability of all these treatment options, ambiguity remains about management. We review the available literature on pathogenesis, causes, presentation, differential diagnoses, and management of this disorder and also discuss our experience.     

Pathogenesis and treatments of TGFBI corneal dystrophies

Transforming growth factor beta-induced (TGFBI) corneal dystrophies are a group of inherited progressive corneal diseases. Accumulation of transforming growth factor beta-induced protein (TGFBIp) is involved in the pathogenesis of TGFBI corneal dystrophies; however, the exact molecular mechanisms are not fully elucidated. In this review article, we summarize the current knowledge of TGFBI corneal dystrophies including clinical manifestations, epidemiology, most common and recently reported associated mutations for each disease, and treatment modalities. We review our current understanding of the molecular mechanisms of granular corneal dystrophy type 2 (GCD2) and studies of other TGFBI corneal dystrophies. In GCD2 corneal fibroblasts, alterations of morphological characteristics of corneal fibroblasts, increased susceptibility to intracellular oxidative stress, dysfunctional and fragmented mitochondria, defective autophagy, and alterations of cell cycle were observed. Other studies of mutated TGFBIp show changes in conformational structure, stability and proteolytic properties in lattice and granular corneal dystrophies. Future research should be directed toward elucidation of the biochemical mechanism of deposit formation, the relationship between the mutated TGFBIp and the other materials in the extracellular matrix, and the development of gene therapy and pharmaceutical agents.     

Preferred practice pattern and observed outcome of deep anterior lamellar keratoplasty – A survey of Indian corneal surgeons

Purpose:This study aimed to assess the preferred surgical technique and outcome of deep anterior lamellar keratoplasty (DALK) among corneal surgeons in India.Methods:An online questionnaire-based cross-sectional survey was conducted among members of the Cornea Society of India (CSI) with experience of performing >10 DALK procedure. The responses pertaining to their surgical experience, preferred technique, complications, and outcome of DALK were collected and analyzed.Results:A total of 156 responses were received. In total, 35.9% of participants reported annual keratoplasty of >50, and DALK constituted >25% surgeries for 25% of participants. Ectatic corneal disorder was reported as the most common indication for DALK by 71.6% of the respondents. Big-bubble (BB) DALK (W_A-1.82) was the most preferred technique, along with suction trephine (50%) for partial trephination and bottom port cannula (45.5%) for BB formation. On statistical analysis, no difference was observed in the surgeon reported success rate of BB formation with or without anterior lamellar keratectomy (ALK) (χ2 (1,156) = 3.1498, P = 0.08) or paracentesis (χ2 (1,156) = 0.2737, P = 0.60) before stromal air injection, and method of stromal air injection (χ2 (1,156) = 4.7325, P = 0.09). Conversion to penetrating keratoplasty was reported by 16% of participants in >25% cases, while 66.7% reported in <10% cases. Cataract and double anterior chamber were the most common complications. 50% of participants suggested that >20 procedures are required to overcome the learning curve.Conclusion:BB DALK is the most commonly practiced DALK technique, and its success is independent of ALK and paracentesis being performed prior to air injection and method of air injection (cannula/needle).     

Resource maximization during COVID-19 crunch – A novel graft marking technique to use one cornea for two recipients for either Descemet membrane endothelial keratoplasty or deep anterior lamellar keratoplasty

During pandemic, eye banks worldwide faced drastic reduction of corneal retrieval. Since precut tissues are uncommon in India, the onus is on corneal surgeons to maximize the donor corneal usage. The stumbling block making the stromal part unusable in the graft preparation of the Descemet membrane endothelial Keratoplasty is the stromal window creation to place the orientation mark on the stromal side of the folded graft. To overcome this, we simply marked directly on the folded Descemet graft, after partly stripping it from the donor cornea. Then, we unfolded, punched, and created two grafts after completely stripping it, retaining the Descemet part for the endothelial Keratoplasty and the stromal part for lamellar Keratoplasty. Initially, we used a special F marker, and later we marked an L using just a spatula. This simple technique needing no extra donor tissue or instrumentation maximizes the tissue utility with proper patient selection.     

Pathogenesis of Keratoconus: The intriguing therapeutic potential of Prolactin-inducible protein

Keratoconus (KC) is the most common ectatic corneal disease, with clinical findings that include discomfort, visual disturbance and possible blindness if left untreated. KC affects approximately 1:400 to 1:2000 people worldwide, including both males and females. The aetiology and onset of KC remains a puzzle and as a result, the ability to treat or reverse the disease is hampered. Sex hormones are known to play a role in the maintenance of the structure and integrity of the human cornea. Hormone levels have been reported to alter corneal thickness, curvature, and sensitivity during different times of menstrual cycle. Surprisingly, the role of sex hormones in corneal diseases and KC has been largely neglected. Prolactin-induced protein, known to be regulated by sex hormones, is a new KC biomarker that has been recently proposed. Studies herein discuss the role of sex hormones as a control mechanism for KC onset and progression and evidence supporting the view that prolactin-induced protein is an important hormonally regulated biomarker in KC is discussed.     

Corneal transplantation after failed grafts: Options and outcomes

Corneal transplantation is the most commonly performed human tissue transplantation procedure worldwide. Because of the large number of transplants, corneal graft failure has become one of the most common indications for corneal transplantation. The relatively recently developed lamellar transplant techniques have brought about specific potential complications leading to graft failure that may require different approaches to repeat transplantation other than penetrating keratoplasty. On the other hand, these new lamellar techniques also provide novel ways of rescuing failed penetrating grafts, with potential advantages over successive penetrating keratoplasties, such as reduced intraoperative risks and faster visual rehabilitation. We summarize the incidence and risk factors of graft failure for penetrating and lamellar (stromal and endothelial) corneal transplants and discuss the various surgical alternatives currently available to rescue such failed grafts, with a focus on the reported outcomes and limitations.     

Intraocular pressure measurement after corneal transplantation

Measurement of intraocular pressure is an integral part of a comprehensive ocular examination, especially after a surgical intervention that can affect aqueous humor flow dynamics. Most of the intraocular pressure measurement devices are designed for “normal” corneas and may not be accurate in eyes after corneal transplantation where there is altered corneal morphology. Raised intraocular pressure and glaucoma are known postoperative complications after transplantation, and therefore, accurate intraocular pressure measurement is essential. We review the effect of abnormal corneal curvature, corneal thickness, and different biomechanical properties in the context of corneal transplantation on intraocular pressure measurement using a number of devices.