Predescemetocele: A distinct clinical entity

The pre-Descemet's layer (Dua's layer, also known as the Dua-Fine layer and the pre-posterior limiting lamina layer): Discovery, characterisation, clinical and surgical applications, and the controversy

The pre-Descemet's layer/Dua's layer, also termed the Dua-Fine layer and the pre-posterior limiting lamina layer, lies anterior to the Descemet's membrane in the cornea, is 10 μm (range 6-16) thick, made predominantly of type I and some type VI collagen with abundant elastin, more than any other layer of the cornea. It has high tensile strength (bursting pressure up to 700 mm of Hg), is impervious to air and almost acellular. At the periphery it demonstrates fenestrations and ramifies to become the core of the trabecular meshwork, with implications for intraocular pressure and glaucoma. It has been demonstrated in some species of animals. The layer has assumed considerable importance in anterior and posterior lamellar corneal transplant surgery by improving our understanding of the behaviour of corneal tissue during these procedures, improved techniques and made the surgery safer with better outcomes. It has led to the innovation of new surgical procedures namely, pre-Descemet's endothelial keratoplasty, suture management of acute hydrops, DALK-triple and Fogla's mini DALK. The discovery and knowledge of the layer has introduced paradigm shifts in our age old concepts of Descemet's membrane detachment, acute corneal hydrops in keratoconus and Descemetoceles, with impact on management approaches. It has been shown to contribute to the pathology and clinical signs observed in corneal infections and some corneal dystrophies. Early evidence suggests that it may have a role in the pathogenesis of keratoconus in relation to its elastin content. Its contribution to corneal biomechanics and glaucoma are subjects of current investigations.

Whole Corneal Descemetocele

Background and Objectives: To report a case of microbial keratitis complicated by severe corneal melting and whole corneal descemetocele. Methods: A 72-year-old male farmer presented with a right corneal ulcer involving nearly the entire cornea, which was almost completely melted down with the remaining Descemet's membrane (DM). The pupil area was filled with melted necrotic material, with the intraocular lens partially protruding from the pupil and indenting the DM. Corneal optical coherence tomography (OCT) examination revealed a corneal thickness of 37 µm that was attached to its back surface, with the iris and a part of the intraocular lens (IOL) protruding through the pupil. The patient was hospitalized and treated with local and systemic antibiotics until control of the inflammation was achieved. Corneoscleral transplantation plus excision/transplantation of the corneal limbus were performed, and the entire corneal limbus was lamellarly incised. After completely suturing all around the transplanted corneoscleral graft, the anterior chamber was formed. Postoperative treatment included local antibiotics, anti-inflammatory drugs, and cycloplegic drops. Results: There was no recurrence of infection, and the corneal epithelium gradually regenerated and covered the whole graft. Visual acuity was light perception at 6 months after the surgery. The patient was satisfied that the globe was preserved and did not wish to undergo any further treatment. Conclusions: Corneoscleral transplantation is preferred for the treatment of large-sized descemetoceles with active microbial keratitis and extensive infiltrates, especially in cases where the whole cornea has transformed into a large cyst.

[On the issue of separate designation of the pre-Descemet's layer in the structure of the cornea]

The five-layer structure of the cornea has been generally accepted in anatomy for the last 70 years. Since the beginning of 2000, publications about lamellar keratoplasty have appeared, in which during the operation it was necessary to isolate the Descemet's membrane (DM). Several options for the formation of a big bubble have been described; in the most frequently used type, the presence of remnants of thin stromal tissue on the isolated DM were found. In 2013 an English group of researchers headed by H. Dua tried to prove that this thin strip of the stroma in DM is the sixth layer of the cornea. However, there is a sufficient number of publications that refute this "discovery". In Russian scientific literature there has been no discussion of a «new» layer of the cornea. Only recently one article has been published, which raised the issue of this separate layer in the cornea. Our group of authors has also entered this discourse, believing that it is possible to distinguish terminologically the pre-Descemet's layers, but only as part of the corneal stroma, without attributing it with numerous functions and features.

[On the issue of separate designation of the pre-Descemet's layer in the structure of the cornea]

In 2013, based on the results of an experimental pneumodissection of the cornea, English ophthalmologist H. Dua postulated the existence of a previously unknown pre-Descemet's layer (PDL) with unique characteristics. However, the need to revise the traditional concepts of the corneal structure raises reasonable doubts among many researchers. This article discusses the question of whether the structural features of the pre-Descemet's layer can be a sufficient basis for designating it as a separate anatomical unit.

[On the issue of allocating the pre-Descemet's layer in the corneal structure]

Selective keratoplasty is known to be based on surgical manipulations aimed at dosed isolation of layered grafts in the corneas of the donor and the recipient. Some technological features of obtaining transplants have served as the basis for expanding the understanding of the corneal structure. Thus, analysis of the process of corneal stroma pneumodissection for isolation of the Descemet's membrane led to a suggestion that there was another layer in the cornea, it was designated as the pre-Descemet's layer. This article discusses the practicability of separating the pre-Descemet's layer from the perspective of structural, functional and surgical anatomy.

Was it thickened Dua's layer? Clinical, tomographical, and histopathological correlation: A case report

A 62-year-old female developed pseudophakic bullous keratopathy after cataract surgery and underwent Descemet stripping automated endothelial keratoplasty (DSAEK). Intraoperatively, a white opacified pre-Descemet's layer was noticed after scoring and removal of trypan blue stained Descemet's membrane (DM), and endothelium complex. It was removed using internal limiting membrane peeling forceps and sent for histopathological evaluation along with DM-endothelium complex and epithelium. Preoperative, intraoperative, and postoperative clinical, tomographical, and histopathological data confirmed thickened PDL or Dua's layer. This is a rare encounter with scarred PDL or Dua's layer during DSAEK surgery.

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.