Surgical outcomes of phototherapeutic keratectomy on Epithelial basement membrane dystrophy, and the characterisation of Bowman´s Layer

Abstract: Background. Epithelial basement membrane dystrophy (EBMD) is a common disease of the anterior cornea that can lead to problems with vision and/or painful recurrent erosions of the corneal epithelium. Several treatment options have been used, but recurrence of EBMD after treatment is a problem. Excimer laser phototherapeutic keratectomy (PTK) has become an increasingly popular surgical option in recent years due to its accuracy, reproducibility, and good clinical outcomes. When treating EBMD with PTK, the anterior corneal structures including the epithelium, Bowman´s layer (BL), and subbasal nerves are disrupted or removed completely. Little is known about how BL, nerves, and the stroma recover after PTK treatment, or how they could influence recurrence of EBMD symptoms. Additionally, very little is known about the properties and actual thickness of BL in-vivo.Aims. To improve the understanding and management of EBMD by investigating the clinical diagnosis and treatment of EBMD and its relationship to Bowman´s layer.Method. An excimer laser was used to treat EBMD patients at the Department of Ophthalmology during the period 2001-2010. IVCM was used to perform pre- and postoperative examinations. In particular, images of anterior corneal structures, cells, and nerves in high-resolution were obtained. Additionally, a group of over 100 healthy volunteers underwent a full ophthalmic examination including IVCM. Other subjects examined in this work included a group of 17 patients who underwent full-thickness transplantation of the cornea.Results and conclusions. Clinical follow-up revealed that PTK is an effective method of alleviating the clinical symptoms of EBMD, but the dystrophy can recur with time. Recurrence can be divided into clinical and morphologic types, and may depend upon treatment parameters including the type and depth of ablation. IVCM was found to be a useful screening tool pre- and postoperatively, and could prevent patients with symptoms, but no visible signs of EBMD on slit lamp examination, to go undiagnosed and untreated. BL was found to play a role in regenerative wound healing after PTK, and was also found to be important regarding the treatment and recurrence of EBMD. BL may present a physical barrier that protects the subepithelial nerve plexus thereby facilitating sensory recovery, and BL may also serve as a barrier that prevents direct traumatic contact with the corneal stroma, avoiding a stromal wound healing response. To aid in accurate assessment of BL in patients, an in vivo method for determining BL thickness was developed. This method could be an important tool to aid in clinical assessment and planned treatments of the anterior cornea. Using this tool, a large inter-individual variability in BL thickness and a strong negative correlation of BL thickness with age were found in a healthy population. Using IVCM, it was also found that subbasal nerves are pathologically reduced in EBMD compared to a healthy population, and that this nerve deficit does not improve in the long term after PTK treatment.