Lamellar Techniques Research Articles

Equine lamellar energy metabolism studied using tissue microdialysis

Failure of lamellar energy metabolism may contribute to the pathophysiology of equine laminitis. Tissue microdialysis has the potential to dynamically monitor lamellar energy balance over time. The objectives of this study were to develop a minimally invasive lamellar microdialysis technique and use it to measure normal lamellar energy metabolite concentrations over 24 h. Microdialysis probes were placed (through the white line) into either the lamellar dermis (LAM) (n = 6) or the sublamellar dermis (SUBLAM) (n = 6) and perfused continuously over a 24 h study period. Probes were placed in the skin dermis (SKIN) for simultaneous comparison to LAM (n = 6). Samples were collected every 2 h and analysed for glucose, lactate, pyruvate, urea and glycerol concentrations. LAM was further compared with SUBLAM by simultaneous placement and sampling in four feet from two horses over 4 h. Horses were monitored for lameness, and either clinically evaluated for 1 month after probe removal (n = 4) or subjected to histological evaluation of the probe site (n = 10).There were no deleterious clinical effects of probe placement and the histological response was mild. Sample fluid recovery and metabolite concentrations were stable for 24 h. Glucose was lower (and lactate:glucose ratio higher) in LAM compared with SUBLAM and SKIN (P < 0.05). Pyruvate was lower in SUBLAM than SKIN and urea was lower in LAM than SKIN (P < 0.05). These differences suggest lower perfusion and increased glucose consumption in LAM compared with SUBLAM and SKIN. In conclusion, lamellar tissue microdialysis was well tolerated and may be useful for determining the contribution of energy failure in laminitis pathogenesis.

Surgical strategies to improve visual outcomes in corneal transplantation

The recent years have brought about a sea change in the field of corneal transplantation with penetrating keratoplasty being phased to newer lamellar keratoplasty techniques for a variety of corneal pathology. Improved and innovative surgical techniques have allowed selective replacement of diseased host corneal layers with pre-prepared healthy donor corneal lamellae for anterior corneal disorders such as keratoconus and posterior corneal disorders such as Fuch's corneal endothelial dystrophy. The results of lamellar techniques are encouraging, with rapid visual rehabilitation and vastly reduced risk of immune-mediated transplant rejection. The techniques of deep anterior lamellar keratoplasty and Descemet's stripping endothelial keratoplasty (DSAEK) continue to evolve with advent of femtosecond lasers and newer concepts such as pre-conditioned donor corneas for Microthin DSAEK and Descemet's membrane keratoplasty. This review describes the current developments in lamellar keratoplasty, including the futuristic approach using cell therapy to restore vision in corneal blindness.

Immunreaktionen nach DMEK, DSAEK und DALK

The aim of this study is to describe incidence, diagnosis and therapy for endothelial immune reactions after modern lamellar corneal transplantat surgery (DMEK, DSAEK, DALK). A PubMed-based literature review and our own clinical and experimental data are evaluated. There is no longer an endothelial immune reaction after DALK for keratoconus. DMEK significantly reduces the risk for endothelial immune reactions after surgery for Fuchs dystrophy. Modern lamellar corneal transplant techniques such as DALK and DMEK have nearly abolished the risk for endothelial immune reactions in the avascular recipient bed.

Deep anterior lamellar keratoplasty using an original manual technique

AimsTo evaluate the clinical findings and visual outcomes of deep anterior lamellar keratoplasty (DALK) using an original manual dissection technique.Methods288 eyes (268 patients) with corneal pathologies without endothelial involvement were...

Corneal Transplantation: Changing Techniques

Corneal Transplantation: Changing Techniques

Hemi-automated lamellar keratoplasty (HALK)

AimTo describe a hybrid technique for anterior lamellar keratoplasty in corneas with topographical irregularities that circumvents the limitations of the microkeratome, namely reproduction of surface irregularities in the lamellar cut...

A Stepwise Approach to Donor Preparation and Insertion Increases Safety and Outcome of Descemet Membrane Endothelial Keratoplasty

Lamellar techniques for selective replacement of diseased corneal structures have recently been improved. Descemet membrane endothelial keratoplasty (DMEK) allows the sole replacement of the endothelium--Descemet membrane layer (EDM). However, wide-spread use of DMEK is currently limited because of problems with donor preparation namely the tearing of the Descemet membrane and the difficulty to unfold the EDM graft in the anterior chamber (AC). A standardized DMEK procedure that allows safe preparation of EDM, atraumatic introduction of EDM into the AC, reliable orientation of EDM during surgery, and stepwise unfolding within the AC is described in 80 patients. Visual acuity and corneal endothelial cell density were assessed. A stepwise approach using a novel bimanual underwater technique to harvest EDM from donor corneal buttons allows reproducible generation of grafts without tearing the Descemet membrane. Injection of the EDM roll into the AC is achieved by use of a standard injector cartridge, whereas the depth of AC is maintained by an irrigation handpiece. Marks at the margin of EDM allow orientation. Finally, unfolding EDM in the AC is achieved by sequential use of water jets and air bubbles. In the early phase of the learning curve, 4 patients were regrafted because of graft failure. Endothelial cell density decreased from 2600 6 252 to 1526 6 341 cells per square millimeter 1 month after DMEK. A novel technique for graft preparation and EDM injection results in improved safety with a high rate of successful DMEKs.

Deep Lamellar Keratoplasty After Resolution of Hydrops in Keratoconus

Deep anterior lamellar keratoplasty (DALK) using Anwar's big-bubble technique is contraindicated in cases of previous hydrops because of the risk of Descemet membrane (DM) rupture at the hydrops scar. Improved manual lamellar dissection techniques down to the deepest stromal layers now enable manual DALK surgery for previous hydrops with the possibility of obtaining good vision, as an alternative to conventional penetrating keratoplasty. Two retrospective case reports of manual DALK in patients with previous hydrops. A 12-year-old boy, with keratoconus and resolved hydrops in his left eye with deep stromal scarring, underwent bilateral manual DALK without baring of the DM. An intraoperative microperforation occurred in his left eye and was managed by intracameral injection of air to seal the perforation. Eleven months after his right DALK and 10 months after his left DALK, his right best spectacle-corrected visual acuity (BSCVA) was 20/20, and his left BSCVA was 20/25. The right cornea was clear, whereas the left cornea had minimal residual deep stromal scarring. Endothelial cell count by specular microscopy was 2611 cells per square millimeter in the right eye and 2193 cells per square millimeter in the left eye. A 28-year-old man, with keratoconus and resolved hydrops in his right eye with deep stromal scarring, underwent right manual DALK without baring of the DM. Nine months postoperatively, his right BSCVA was 20/30, and the graft was clear. Endothelial cell count by specular microscopy was 3148 cells per square millimeter in the right eye. DALK can be performed in patients with previous hydrops. A controlled deep manual dissection technique without baring the DM is advocated. Good final BSCVA can be achieved despite leaving a thin residual layer of the stroma unexcised.

Cost-effective Tattooing

Corneal staining (tattooing) has been advocated in the management of patients with corneal leucomata, iris malformations or following iridotomies. Functional visual benefits can result from the reduction of aberrant light directed through iris defects that may cause glare and light scatter, in addition to cosmetic improvements for those with opacification. Inks, classified as stationery or cosmetic products, offer an economic alternative to currently available classical corneal staining agents (metallic salts). Furthermore, they may be used to good clinical effect with an intrastromal lamellar pocket technique.

Glaukom und Keratoplastik

Glaucoma and corneal disorders are often associated and are of diagnostic, therapeutic and prognostic relevance for each other. Glaucoma is already present in approximately 15% of eyes prior to keratoplasty, whereas in addition approximately 15% of cases are diagnosed following corneal transplantation. Corneal opacities, surface irregularities and pachymetric deviations from the norm can have a negative impact on tonometry, perimetry and morphological glaucoma diagnosis. Digital and intracameral tonometry as well as flash VEP to determine the visual potential can be helpful in this setting. Increased intraocular pressure (IOP), long-term application of antiglaucomatous medication or the use of antimetabolites in glaucoma surgery can all induce keratopathy. Therefore, intraocular pressure should be regulated prior to corneal transplantation. Risk factors for the evolution of glaucoma following corneal transplantation are the specific indication and surgical technique (e. g. combined corneal and cataract/vitreoretinal surgery), as well as postoperative steroid application and chamber angle synechiae. Unpreserved glaucoma medication without pro-inflammatory effects should be preferred following keratoplasty. In the long term surgery to control IOP is required in approximately 25% of eyes. The wider use of lamellar techniques for corneal transplantation is likely to reduce the incidence of secondary glaucoma.

Comparison of Outcomes of Lamellar Keratoplasty and Penetrating Keratoplasty in Keratoconus

To compare outcomes after penetrating keratoplasty (PK) and two techniques of deep anterior lamellar keratoplasty (DALK) in patients with keratoconus. Retrospective cohort study. One hundred and twenty-five corneal transplantations comprising 100 PK and 25 DALK procedures for keratoconus at the Singapore National Eye Centre from April 1992 through December 2006 were included. DALK was performed with the modified Anwar technique (descemetic or DALKa group) in 14 eyes and manual lamellar keratoplasty (predescemetic or DALKm group) was performed in 11 eyes. At 12 months, the DALKa and PK groups achieved a logarithm of the minimum angle of resolution mean best spectacle-corrected visual acuity (BSCVA) of 0.15 and 0.27, respectively (P = .26), whereas the mean BSCVA of the DALKm group was 0.41 compared with the PK group (P = .12). Significance level was achieved between the DALKa and DALKm groups (P = .013). There was no significant difference in the mean spherical equivalent (P = .72) and astigmatism (P = .88) between the PK and DALK groups. The DALK group had a significantly lower incidence of complications compared with PK cases, including allograft rejection and glaucoma. Graft survival rate of both the PK and DALKa groups was 100%, whereas that of the DALKm group was 73% at 3 years after surgery (P = .000 between PK and DALKm groups). Visual acuity outcomes of the DALKa technique are comparable with those of PK for keratoconus, whereas DALK surgery results in fewer postoperative complications than PK. DALKa is emerging as a preferred choice among the lamellar techniques for better optical outcome. Further studies are required to provide long-term analysis of these results.

Keratoplasty: laminate or penetrate?

A number of corneal disorders sooner or later call for a decision as to whether corneal grafting is necessary. In contrast to the current gold standard, penetrating keratoplasty (PKP), former lamellar techniques had the disadvantage of worse visual outcomes due to interface problems. A number of recent new technical developments have led to a 'renaissance' of various lamellar keratoplasty methods. Deep anterior lamellar keratoplasty (DALK) avoids the risk of endothelial immune reactions. However, visual outcomes are comparable to PKP only is complete baring of Descemet's membrane is achieved. In Descemet stripping (automated) endothelial keratoplasty [DS(A)EK], a variation of posterior lamellar keratoplasty, only the diseased endothelium is removed with the Descetmet membrane (descemetorhexis). The lamellar, endothelium-bearing graft can subsequently be implanted via a corneoscleral/corneal tunnel, whereby little astigmatism is induced. The main advantage of DS(A)EK compared to PKP is faster visual recovery with almost unaltered refraction, although visual acuity is often slightly lower. However, valid study results are still lacking for this new surgical technique to allow a long-term comparison of the new techniques with conventional penetrating keratoplasty.

Schicht für Schicht - Die maβgeschneiderte Keratoplastik

Penetrating keratoplasty represented the gold standard in corneal transplantation for more than a century. Recent refinements of surgical technique and instrumentation have allowed for a shift towards the transplantation of selected components of the cornea as opposed to full thickness transplantation. Depending on the lamellar technique chosen, the main advantages of lamellar component surgery over penetrating surgery may include a reduced rate of endothelial failure secondary to immunological rejection and faster visual rehabilitation. This brief review discusses the indications for penetrating and lamellar techniques and compares advantages and disadvantages of these treatment modalities.

Corneal oedema after cataract surgery: predisposing factors and corneal graft outcome

Pseudophakic bullous keratopathy (PBK) is one of the main indications for corneal transplantation. Graft survival and visual outcome in this group are often poorer than for other indications. The aim of this study was to find risk factors for developing corneal oedema after cataract surgery and factors that influence the subsequent survival of the graft and the visual outcome. We carried out an observational, retrospective cohort study using data from the Swedish Cornea Transplant Register and patient medical records. A total of 273 patients whose indication for corneal transplantation was corneal oedema after cataract surgery were included in the study. Multiple logistic regression analysis and, where appropriate, univariate analyses were applied. A total of 43% of the patients developed persistent corneal oedema immediately after cataract surgery, the main risk factors for which were phacoemulsification and pre-existing endothelial disease. Almost a third (32%) of the transplants for PBK failed within 2 years, for which rejection and other postoperative complications increased the risk. Half (50%) the patients had visual acuity < or = 0.1 at 2 years after keratoplasty. Comorbidity, increasing duration of the bullous keratopathy and increasing age affected the visual outcome negatively. Phacoemulsification was a risk factor for immediate persistent corneal oedema after cataract surgery, although it did not increase the overall risk of developing PBK. However, transplants for immediate PBK had a better survival rate than those for later onset PBK. Shorter duration of PBK and intraocular lens exchange at the time of penetrating keratoplasty increased the likelihood of good visual acuity.

Langzeitergebnisse nach Iridozyklektomie bei Iristumoren

The aim of this study was to evaluate the long-term survival rate and functional results after iridocyclectomy. Between 1980 and 2002 39 patients (26 female and 13 male) ranging in age from 20 to 79 years (median m = 58 years) underwent iridocyclectomy for a tumour of periphery iris by means of a lamellar technique or by trepanating. Follow-up time ranged from 3 months to 24 years (m = 11.2 years). In 21 cases (54 %) there was a malignant tumour including 20 melanomas (mostly spindle-cell and mixed-cell melanomas) and one filiae of a bronchial carcinoma. There was a variety of histopathological entities in the 18 benign lesions (46 %). Naevi were the most frequent. The outcome was satisfactory: 57 % of the patients kept a visual acuity of > 0.5. Three eyes had to be enucleated. The rate of recurrence was 10 % (4 cases). The Kaplan-Meyer estimate for the 10-year-survival of the patients with a malignant iris tumour was 77 %. Two patients died of metastic melanoma following spindle-cell and mixed-cell melanoma. The long-term functional results after Iridocyclectomy are good, whereas complications and recurrences are rare. The 10-year-survival is high. Over a long period iridocyclectomy is a recommendable surgical procedure for removal of progredient tumours of the anterior uvea.

Anterior segment optical coherence tomography in eye injuries

To evaluate the usefulness of anterior segment optical coherence tomography (AS OCT) for initial diagnosis and for monitoring treatment results in eye injury cases. We examined 38 eyes of 34 patients with different types of ocular injuries: penetrating injury (eight eyes), perforating injury (two eyes), intraocular foreign body (four eyes), ocular burn (nine eyes), contusion (13 eyes), and lamellar laceration (two eyes). The mean age of the patients was 33.8 years. AS OCT examination was performed at the initial visit, directly after injury, and repeated as treatment progressed. Both anterior chamber components and corneal pachymetry were evaluated. Slit-lamp examination did not provide a clear diagnosis in three eyes after contusion because of a nontransparent cornea. In one case of a 44-year-old male patient, only corneal edema was noticed during slit-lamp examination, whereas AS OCT revealed Descemet's membrane detachment. In a 17-year-old male patient with blood infiltrating the cornea, OCT revealed acute angle closure with a pupillary block. In patients with corneal burns, OCT was valuable for monitoring the corneal healing progress after amniotic membrane application. OCT was also useful for determining whether a lamellar or penetrating technique should be applied in patients that qualified for corneal transplantation. In patients with foreign bodies, AS OCT was helpful in establishing the localization and size of the foreign body. AS OCT is a very valuable tool in ophthalmic departments dealing with ocular trauma, for early diagnosis and for monitoring treatment progress.

Descemet’s Stripping Automated Endothelial Keratoplasty

Taken together, causes of endothelial decompensation represent a major indication for corneal transplantation. Posterior lamellar grafts allow patients with endothelial failure to avoid many of the complications associated with the full thickness penetrating keratoplasty. Evolving over the last decade, Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) represents the latest incarnation of posterior lamellar grafting techniques. This article contains four case reports from the cornea clinic where the author is a resident, and a review of literature highlighting the benefits of posterior lamellar grafting.

Impact of new lamellar techniques of keratoplasty on eye bank activity

Deep anterior lamellar keratoplasty (DALK) has become an increasingly popular alternative to penetrating keratoplasty in patients with stromal corneal pathologies. The main advantages of DALK are: prevention of long-term endothelial loss, elimination of allograft reaction and short topical steroid treatment with lower risks of glaucoma, cataract and infection. Because this technique enables surgeons to use corneal grafts with low endothelial density, the aim of this paper was to determine whether this type of innovation has had a significant impact on eye bank activity. We reviewed our corneal graft activity over a 40-month period and assessed the proportion of deep lamellar and penetrating keratoplasties. During the same period, we also evaluated our eye bank activity and recorded the utilisation of grafts with endothelium abnormalities, which were only suitable for lamellar techniques. Deep lamellar keratoplasty represented 29.8% (85 out of 285) of corneal transplantations. Forty-eight percent of all corneas stored at the local eye bank were unsuitable for penetrating keratoplasty; 36.6% of those were not suitable for endothelial deficiencies. Among these, 72.7% were used for DALK and 27.3% were rejected. This permitted a 24.5% increase in corneal grafting activity. In contrast, Descemet's membrane was removed at the time of surgery in 12% of corneas with healthy endothelium, which was used for deep lamellar keratoplasty. Deep anterior lamellar keratoplasty development and close collaboration between eye banks and surgeons can induce a significant increase in corneal grafting. This could be a partial solution in countries confronted with corneal graft shortages.

Deep anterior lamellar keratoplasty

Recent advances in surgical technique have promoted a paradigm shift in the surgical treatment of corneal disease. Penetrating keratoplasty is now being replaced by various types of lamellar techniques that aim to replace damaged tissue only, while maintaining healthy tissue intact. This review focuses on recent advances in deep anterior lamellar keratoplasty. The concept of creating a deep lamellar bed for lamellar keratoplasty is not new, but exposing Descemet's membrane was a tedious, time consuming procedure. New techniques that use air and ophthalmic viscosurgical devices to directly expose Descemet's membrane have dramatically reduced surgery time, while improving the safety of performing surgery. The indications for deep anterior lamellar keratoplasty have expanded from keratoconus and hereditary dystrophies, to include severe ocular surface disease and cases following infection and corneal perforation. Deep anterior lamellar keratoplasty can be considered as the first choice of surgery for a wide range of corneal disease, with bullous keratopathy as the only absolute contraindication.

Microwave irradiated collagen tubes as a better matrix for peripheral nerve regeneration

Collagen is one of the best materials used for nerve guide preparation due to its biocompatibility and desirable tensile strength. In this work, we have compared regeneration and functional reinnervation after sciatic nerve resection with bioresorbable crosslinked collagen guides in 10 mm gap. The crosslinking was carried out either with glutaraldehyde (GTA) or microwave irradiation (MWI). The multilayered collagen membrane used for nerve guides are prepared by lamellar evaporation technique. Functional evaluations of the regenerated nerves were performed by measuring the sciatic functional index (SFI), nerve conduction velocity (NCV), and electromyography (EMG). Transmission electron microscopic studies showed growth of axonal cable with fewer myelinated axons, Schwann cells and more unmyelinated axons present in the case of group treated with uncrosslinked collagen tubes after 1 month of implantation. However, we have observed more myelinated axons in the case of autograft, GTA, and MWI crosslinked collagen tube implants across the gap of 1 cm after the same period of implantation. Smaller myelinated fiber diameter was observed in the case of GTA crosslinked collagen tube group when compared with the autograft and MWI collagen tube groups. There were more myelinated axons during the 3rd and 6th months postoperatively using these conduits as substantiated by light microscopic studies of the regenerated nerve. The conduction velocity and recovery index improved significantly after 5 months reaching the normal values in the autograft and MWI crosslinked collagen groups compared to GTA and uncrosslinked collagen tubes.