pre-Descemet Layer Research Articles

Relationship of posterior peripheral corneal layers and the trabecular meshwork: an immunohistological and anatomical study

Background/AimWith the popularity of endothelial keratoplasty (EK) procedures, Descemet membrane (DM) EK and pre-Descemet EK, considerable work has been done on understanding the posterior corneal anatomy. Most of the information...

Comparative posterior corneal profile of keratoconus hydrops versus Haab's striae in congenital glaucoma.

Keratoconus eyes develop corneal decompensation more often compared to eyes with primary congenital glaucoma (PCG) following Descemet's membrane (DM) tear. This study was conducted to compare the posterior corneal morphology in areas with DM breaks with regards to DM and pre-Descemet's layer (PDL) between the two. In this cross-sectional comparative study, anterior segment optical coherence tomography (AS-OCT) scans of the posterior cornea of advanced keratoconus eyes with hydrops ( n = 12), PCG eyes with Haab's striae ( n = 15), and healthy control eyes ( n = 14) were compared for DM-PDL morphology. These were further corroborated by the histopathology of corneal buttons from keratoconus ( n = 14) and PCG ( n = 13) cases obtained following penetrating keratoplasty and compared with controls (enucleated retinoblastoma globes, n = 6) on light microscopy and collagen IV immunostaining. AS-OCT showed a thicker median DM/PDL complex in PCG (80 µm) versus keratoconus eyes (36 µm, P = 0.01; Kruskal-Wallis test). The median height and length of detached DM-PDL were significantly more in keratoconus versus PCG (145 μm, 1766.1 ± 1320.6 μm vs. 26.5 μm, 453.3 ± 303.2 μm, respectively, P = 0.012; Kruskal-Wallis test). Type-1 DM/PDL detachment (seen as a characteristic taut chord) in keratoconus (90%) was the most common morphological pattern versus intracameral twin protuberance (92%) following DM breaks in PCG. Histopathology confirmed thicker DM in PCG (median: 63.4 μm) versus keratoconus eyes (median: 33.2 µm) or controls (27.1 μm) ( P = 0.001; Kruskal-Wallis test). Greater height/length of DM/PDL detachment compounded by poor healing response (lower DM/PDL thickness) probably causes more frequent corneal decompensation in keratoconus eyes when compared to PCG eyes following DM tears.

Diamond ophthalmic burr-assisted deep anterior lamellar keratoplasty – Case series

This case series presents a simple technique using the diamond ophthalmic burr (DOB) to perform successful deep anterior lamellar keratoplasty (DALK) in cases where the big-bubble technique is unsuitable or intraoperative Descemet membrane perforation occurs. Five patients underwent DOB-assisted DALK, and postoperative outcomes were evaluated, including best-corrected visual acuity, corneal astigmatism, residual host tissue thickness, and postoperative endothelial cell count. Manual corneal lamellar dissection was performed, followed by DOB-assisted pre-Descemet layer polishing and donor graft attachment using 16 (10-0) Monofilament Nylon sutures. The postoperative visual acuity significantly improved. DOB-assisted DALK is a viable alternative.

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 700mm 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.

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

Selective exchange of pathologically altered retinal layers is currently considered the most practical approach in corneal transplantation. Deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK) are often performed as pathogenetically substantiated transplantation methods. The technique and the course of surgery, possible complications, and achieved outcomes, among other things, depend largely on the pre-Descemet's layer, which was described more than 10 years ago by several ophthalmologists in varying detail. In view of this, the main issue discussed in literature is the following: is the pre-Descemet's layer (Dua's layer) a separate (new) layer of the cornea, or is it an integral part of the stroma (the Feizi stroma)? This article continues the discussion on «separate designation of the pre-Descemet's layer in the structure of the cornea» and presents the view of the authors on this problem based on own experience, literature data, anatomical subdisciplines, as well as specific aspects of ophthalmological terminology, and with the use of extrapolation and analogies.

Adding to the results of the discussion on the need to separately designate the pre-Descemet’s layer in the corneal structure

The article summarizes the outcomes of the discussion concerning the need to designate the pre-Descemet's layer (PDL) in the cornea as a separate anatomical structure. Considering the differences in opinions on this highly debated topic, various studies suggested a compromised, purely terminological solution - to limitedly separate the PDL as a deep stromal layer of the cornea.

Inadvertent Viscoelastic Separation of the Pre-Descemet (Dua) Layer in Deep Anterior Lamellar Keratoplasty With Structural Features Revealed by Polarization Microscopy.

Deep anterior lamellar keratoplasty (DALK) is a corneal transplant technique that removes the host stroma down to either the pre-Descemet (Dua) layer or Descemet membrane. It is most common for the big bubble technique to create a cleavage plane between the posterior stroma and the pre-Descemet layer. This is advantageous because the pre-Descemet layer has been found to be much stronger than Descemet membrane, and makes the procedure easier to perform. In this report, we present an uncommon viscoelastic-related complication of DALK that resulted in excising the pre-Descemet layer and allowing it to be studied using polarization microscopy. DALK was performed using a standard big bubble technique. Postoperatively, a double anterior chamber was found to have been created by the inadvertent passage of an ophthalmic viscoelastic device (OVD) through the pre-Descemet layer. This resulted in the OVD being trapped between the pre-Descemet layer and Descemet membrane. The pre-Descemet layer was then resected in a subsequent operation. The pre-Descemet layer and posterior stroma were studied by polarization microscopy using Sirius Red histochemical staining to elucidate the orientation of the collagen fibers. The pre-Descemet layer is composed of lamellar arrays of collagen that have consistent polarization properties within each layer but show variable polarization of the strands, indicative of anisotropic strand orientation. The degree of variable polarization of the pre-Descemet layer is distinct from the overlying posterior stroma. Injecting an OVD into a big bubble in DALK may result in it being trapped between the pre-Descemet layer and Descemet membrane. The pre-Descemet layer shows alternating layers of varying polarization of collagen. This anisotropic structure helps explain the basis for the additional strength that the pre-Descemet layer is known to have.

Posterior corneal morphological changes in primary congenital glaucoma.

Purpose:To compare posterior corneal morphology between older treated and younger untreated children with primary congenital glaucoma (PCG) using anterior segment optical coherence tomography (ASOCT) and intraoperative OCT (iOCT), respectively.Methods: In this comparative study, ASOCT of older PCG children were compared with iOCT of younger untreated PCG patients. Differences between the two groups with respect to posterior corneal morphology were studied.Results: Observed morphological patterns within posterior cornea in older treated (age: 72–300 months) children (87 eyes) included Descemet’s membrane (DM) excrescences (70%), thickened DM (35%), intracameral twin protuberances (92%), and DM detachment (26%). Changes within pre-Descemet’s layer (PDL) (28%) included thickening, breaks, and detachments. Extent of Haab’s striae was associated with thickness of DM/PDL complex (P = 0.008) when analyzed in the treated group. In contrast, in the untreated group (n = 53 eyes, age 1–63 months), posterior corneal changes were limited to diffuse hyper-reflectivity of the DM/PDL complex, with absence of DM tears.Conclusion: Posterior cornea thickens and Haab’s striae become more circumscribed in eyes of older treated children compared to untreated PCG eyes, probably reflecting a healing response of posterior cornea over time.

Are fenestrations in peripheral pre-Descemet’s layer the route for intracameral air bubble migration during femtosecond LASIK?

Femtosecond laser assisted in situ keratomileusis (FS-LASIK) is associated with the creation of cavitation gas bubbles in the stromal dissection plane. Intraoperative intracameral migration of these air bubbles is a rare complication observed during the procedure. At present, it is postulated that the air bubbles created during the photodisruptive process migrate into the anterior chamber via the Schlemm’s canal and trabecular meshwork. This theory; however, does not explain the extremely rare occurrence of this complication. Recently, the pre-Descemet’s layer (PDL) and the presence of fenestrations in its periphery have been described in literature. We present an alternative pathomechanism for intracameral air bubble migration during FS-LASIK based on the anatomical relationship of fenestrations in the peripheral PDL and the termination of Descemet membrane. We propose that the air bubbles migrate directly from the laser dissection plane into the anterior chamber via the fenestrations in the peripheral PDL in cases where the Descemet membrane terminates proximal to the fenestrations. The anatomical variability in the termination of the Descemet membrane in relation to the fenestrations in the peripheral PDL may explain why the complication is not observed in a significant proportion of cases where the LASIK flap border lies in close proximity to the limbus.

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.

Mooren's ulcer with nonrhegmatogenous Descemet's membrane detachment (type-1), persisting after cataract surgery with clear cornea

Acute hydrops is very rarely reported in the setting of Mooren's ulcer. Our patient with bilateral Mooren's ulcer, being managed with immunomodulation, presented with sudden decrease in vision in the left eye, and was diagnosed to have acute hydrops with a type1 non-rhegmatogenous pre-Descemet's layer and Descemet's membrane detachment.(DMD) Her corneal stromal edema resolved with conservative management and she regained a vision of 20/80 following cataract surgery, with an evident persistent DMD and a clear cornea.

A unique pre‐endothelial layer at the posterior peripheral cornea: ultra‐structural study

AbstractPurposeTo investigate the ultrastructure of a unique pre‐endothelial layer (PENL) of the posterior peripheral cornea and compare their fibers to those of the limbus and sclera.MethodsTen anonymous‐donor human sclera–corneal rings (leftover after corneal transplants) were processed for electron microscopy. Semi‐thin sections were examined using an Olympus BX53 microscope, and ultrathin sections were studied using a JOEL 1400 transmission electron microscope.ResultsA unique pre‐endothelial layer (PENL) was identified at the posterior peripheral cornea a radial distance of 70 µm – 638 µm, from the Descemet’s membrane endpoint (DME). At 272 µm distance from the DME, the posterior pre‐limbal cornea contained 5 layers; basement membrane (BM), pre‐Descemet’s layer (PDL), Descemet’s layer (DM), and a pre‐endothelial layer (PENL) between the DM and endothelium (EN). As the DM runs towards the central stroma, the PENL thins out gradually and disappears at a distance of 638 µm from DME. The layer contained an electron‐dense sheath with periodic structures (narrow‐spacing fibers), wide‐spacing fibers, and numerous microfibrils. The typical elastic fibers were composed of an elastic core surrounded by microfibrils. These were present in sclera and limbus but were not observed in the PENL.ConclusionsThe present study revealed the existence of a new acellular PENL, and it can be considered as another layer of the pre‐limbal peripheral posterior cornea. Knowledge of the PENL layer may help with understanding the pathology of endothelial dystrophies and pre‐DM dystrophies. PENL fibers were similar in structure to the fibers of trabecular meshwork described previously.

Dynamics of Big Bubble Formation During Deep Anterior Lamellar Keratoplasty in Eyes with Advanced Keratoconus.

PurposeTo study the dynamics of big bubble (BB) formation in eyes with advanced keratoconus (KC) during deep anterior lamellar keratoplasty (DALK).MethodsA retrospective review of medical records and videos of DALK surgeries performed during the period from January 2013 to December 2019 on keratoconic eyes. Eyes with formed BB, in the presence of a relatively clear stroma, were included. We studied the following parameters the location of BB commencement, duration from the start of the bubble until complete formation, and the pattern of air passage during the formation process.ResultsA total of 37 eyes met the inclusion criteria. Type 1 BB was formed in 22 eyes with a mean formation time of 1.9 ± 1.1 seconds and a mean bubble diameter of 7.6 ± 1.1 mm. Type 1 BB started in the center as a small dome expanding centrifugally with preceding localized stromal whitening in 19 eyes and without whitening in three eyes. Type 2 BB was formed in 14 eyes with a mean formation time of 0.3 ± 0.12 seconds and a mean bubble diameter of 7.4 ± 1.8 mm. Type 2 BB started in the center in 13 eyes and the mid periphery in one eye, through either direct access to the plane between Descemet’s membrane and the pre-Descemet’s layer in six eyes, or preceded by a small intrastromal bubble in eight eyes. Mixed bubble was observed in one eye, which started as a small central Type 1 BB followed by the rapid formation of a Type 2 BB.ConclusionEyes with KC are associated with central commencements of both Type 1 and Type 2 BB during DALK. Duration of BB formation was significantly faster in Type 2 BB, with most starting as a small intrastromal bubble before air gain access to the plane between DM and stroma.

The Descemet Membrane in Primary Congenital Glaucoma.

To evaluate Descemet membrane (DM) morphology in eyes with primary congenital glaucoma (PCG) in vivo using high-definition anterior segment optical coherence tomography (ASOCT) and on histopathology. Corneal scans of patients with PCG (22 eyes of 15 patients) were evaluated for DM morphology and anterior chamber angle using ASOCT. The DM thickness in PCG eyes was compared with fellow eyes (8 eyes) of unilateral patients with PCG and healthy controls (12 eyes) on ASOCT. The DM morphology was also compared on the histopathology of corneal tissues (9) obtained from PCG eyes after keratoplasty and enucleated eyes of retinoblastoma (6 controls) on light microscopy with immunostaining for collagen IV. On ASOCT, all affected eyes showed the presence of either a thickened DM complex or a hyper-reflective double layer representing the thickened DM and pre-Descemet layer (PDL), unlike a single membrane in the controls and fellow eyes. On ASOCT, among patients with PCG, the DM showed significant thickening (32.0 ± 11.2 μm) versus fellow eyes (14.4 ± 3.3 μm) and controls (11.5 ± 1 μm) (P < 0.001; analysis of variance). The thickened DM complex continued peripherally into the trabecular meshwork as an abnormal membrane in 16/22 affected eyes. On histopathology, thickening of DM was also more among PCG eyes (median: 67.9 μm range: 27.2-214.9) versus controls (median: 27.7 μm, range: 22.1-36.1; P = 0.005) as also of PDL (median: 14 μm, range: 5.9-30.5) of PCG versus (median 3.5, range: 1.3-6.7 μm) in controls; P = 0.014. Thickening of DM and PDL occurs in eyes with PCG and is seen to have a peripheral extension upto the angle recess.

“Descemet Membrane Detachment”: A Novel Concept in Diagnosis and Classification

To examine the optical coherence tomography (OCT) and histologic features of Descemet membrane detachment (DMD) to ascertain the involvement of the pre-Descemet layer (PDL). Retrospective, observational case series. Clinical, histopathologic, and OCT features of a cohort of 41 cases with diagnosis of DMD from 4 centers were studied. OCT images were evaluated independently by 3 observers for number of detached layers (1 or 2), reflectivity, configuration (straight line or wavy), distance from posterior stroma, and presence or absence of a tear with any scrolling of the torn edges. Five had a histology specimen. The main outcome measure was the involvement of the PDL in DMD and its confirmation by histology. Three types of DMD were identified: type 1, where the PDL and DM were detached together; type 2, where only the DM was detached; and mixed, where the PDL and DM were detached but also separated from each other. These were further found to be rhegmatogenous or nonrhegmatogenous depending on the presence of absence of a tear in DM or both layers. Histology confirmed involvement of PDL in all 5 cases and showed it to be infiltrated by cells in 3 of 5 cases. The PDL is involved in DMD. This fact significantly changes our understanding of DMD and could have implications for management. The detached PDL can be infiltrated with cells. A prospective study in relation to etiology and types of DMD is needed.

Surgical Corneal Anatomy in Deep Anterior Lamellar Keratoplasty: Suggestion of New Acronyms.

Deep anterior lamellar keratoplasty (DALK) is the ideal surgery for corneal stromal diseases with a healthy endothelium. This technique offers substantial advantages compared with penetrating keratoplasty, primarily the avoidance of endothelial rejection and longer graft survival. Several DALK techniques have been described and classified into 2 categories, descemetic DALK (dDALK) and predescemetic DALK (pdDALK) depending on whether Descemet membrane-endothelium was thought to be exposed or minimal residual stroma was left behind. This classification was crucial to identify the conditions to achieve good visual outcomes with pdDALK techniques. The recent description of Dua's layer, also known as the pre-Descemet layer, has demonstrated that a very thin layer of stroma exists in some instances where Descemet membrane was thought to be completely exposed. This concept has generated a discrepancy between the previous and current applications of the terms "dDALK" and "pdDALK." We offer a summary of the published literature and a proposal for a new and more appropriate DALK nomenclature. We suggest adding the terms subtotal anterior lamellar keratoplasty (STALK) and total anterior lamellar keratoplasty (TALK).

Elastin Content and Distribution in Endothelial Keratoplasty Tissue Determines Direction of Scrolling

Descemet membrane endothelial keratoplasty (DMEK) and pre-Descemet endothelial keratoplasty (PDEK) tissues always scroll with the endothelial cells (EC) outside. We designed a study to understand the reason for this behavior. Experimental study. Elastin content in Descemet membrane (DM), pre-Descemet layer (PDL), central and peripheral stroma, sclera, and trabecular meshwork were measured by the Fastin elastin assay kit. Distribution of elastin in DM, PDL, and anterior lens capsule (ALC) were examined by immunohistology. The effect of recombinant elastase enzyme and the effect of complete removal of EC and epithelial cells on the scrolling of DM and ALC, respectively, were studied. PDL showed the highest elastin content among the different tissues studied. Elastin localized as a distinct anterior band in the DM and was uniformly distributed in the PDL demarcating the latter from corneal stroma. Enzymatic treatment of DM with elastase reversed scrolling and corresponded with degradation or disappearance of elastin. Removal of EC did not affect the direction of scrolling. ALC behaved in the same manner with regard to distribution of elastin, scrolling, and removal of epithelial cells. This pattern of elastin distribution in DM explains why DMEK and PDEK tissues always scroll with the EC outside. This behavior is not influenced by the EC. High elastin content and uniform distribution in the PDL suggest a structural difference from the posterior stroma.

Triple chamber: a clinical rarity after deep anterior lamellar keratoplasty and role of optical coherence tomography in management

To report a case demonstrating triple chamber following deep anterior lamellar keratoplasty (DALK) and its successful intra-operative optical coherence tomography-guided management. Case report of a young male with macular corneal dystrophy, who underwent DALK in his left eye by Big-Bubble technique. The surgery was uneventful. On the first post-operative day, triple chamber was observed and followed-up with serial clinical photography and anterior segment optical coherence tomography. Due to decrease in graft clarity and increase in volume of the two extra chambers, interface drainage along with descemetopexy was undertaken 4days later. The compartments constituting the triple chamber were those in-between the donor tissue and host pre-Descemet layer (Dua's layer), the latter and host Descemet membrane and the true anterior chamber. Presence of viscoelastic in the interface was identified as the cause. Microscope integrated optical coherence tomography (MiOCT) guided drainage followed by intracameral air tamponade ensured near total disappearance of the two extra chambers at the end of surgery. Examination on the next day confirmed complete apposition of the graft and host. To the best of our knowledge, this is a unique demonstration of Dua's layer in vivo by slit lamp biomicroscopy and description of MiOCT guided management of triple chamber.

Dynamics of big bubble formation in deep anterior lamellar keratoplasty by the big bubble technique: invitro studies.

To examine the movement of air injected in the cornea in simulated deep anterior lamellar keratoplasty (DALK), from the needle tip to the formation of different types of big bubbles (BB) and to ascertain how air travels through the stroma and pre-Descemet's layer [Dua's layer (PDL)] to create a type-1 (air between PDL and deep stroma) and type-2BB (air between PDL and Descemet's membrane). Air was injected in 57 sclerocorneal discs and the passage recorded. Leaking points and sites of commencement of type-1 and type-2BB were examined by scanning electron microscopy. Stromal distribution of air pockets was studied by light microscopy. Uninjected corneas served as controls. Injected air followed a consistent pattern, initially as radial tracks to the limbus, then as circumferential bands along the limbus and finally centripetally to create predominantly a type-1BB. Type-2BB started at the periphery, by air emerging through clusters of tiny fenestrations discovered in the periphery of PDL. Fifteen to 20 such clusters were also seen in control samples on either side of the Descemet's attachment. Type-1BB was formed by air emerging through wide spaces between lamellae of deep stroma. Histologically, the circumferential band revealed an aggregation of air pockets in the mid-stroma. The consistent pattern of passage of air is indicative of the architecture and microanatomy of the corneal stroma where collagen lamellae are orthogonally arranged centrally and as a circular annulus at the periphery. The novel peripheral fenestrations explain the peripheral commencement of a type-2BB and the escape of air into the anterior chamber during DALK.

Pre-Descemets endothelial keratoplasty: the PDEK clamp for successful PDEK.

PurposeTo design and produce a clamp that enables good handling of donor sclera-corneal disks, allows air to be injected in the corneal stroma and consistently provides pre-Descemets endothelial keratoplasty (PDEK) tissue by creation of a type-1 big bubble (BB) avoiding a type-2BB by shutting the fenestrations in the periphery of the pre-Descemets layer and preventing escape of air.Patients and methodsA clamp with spring loaded handles attached to two rings of 9 mm diameter and 1 mm width with a side port for insertion of a needle for air injection was designed and produced. The clamp was tested in 20 human donor sclera-corneal disks and refined over three prototypes. The final design was used for PDEK in 8 patients.ResultsThe clamp was able to prevent any escape of air or the formation of a type-2BB. By preventing air leak, it provided better control over the volume of air injected allowing for consistent formation of a type-1BB, which could be expanded to its full diameter by advancing the tip of the needle into the bubble cavity. Centration of tissue in the clamp was important. The clamp was used successfully to obtain PDEK tissue from 8 donor sclara-corneal disks for transplant in three eyes with pseudophakic bullous keratopathy and five eyes with pseudophakia and Fuchs' endothelial dystrophy.ConclusionThe PDEK clamp is a simple and useful instrument that will give surgeons the confidence of consistently obtaining PDEK tissue with ease and without the risk of separating the Descemets membrane in a type-2BB.