Lamellar Corneal Research Articles

Rapid cooling of the amniotic membrane as a model system for the vitrification of posterior corneal lamellae

To vitrify human amniotic membrane specimens so that the maximum of epithelial cells survives in order to develop a procedure for the eventual vitrification of posterior corneal lamellae without using cryoprotective agents. To assess different methods of tissue sample preparation preceding vitrification. In group 1, the amniotic membrane specimens were stretched on nitrocellulose support. In group 2, mechanical pressure was used to remove the excess culture medium between the support and the membrane. The samples were frozen in liquid ethane (-183 °C) and stored in liquid nitrogen. The specimens in the control group were not vitrified. Re-warming was performed at 40 °C. The epithelial cell survival rate was assessed after 1, 3 and 7 days of storage following re-warming using calcein and ethidium homodimer-1 fluorescence. A wide range of values was observed among the different groups and among individual specimens within the groups. Resulting average survival rate was 41 % for group 1 and 53 % for group 2; in several samples the cell survival rate exceeded 70 %. The storage period did not significantly affect the survival rates. The results of the rapid cooling of amniotic membranes in liquid ethane indicate that significant percentage of epithelial cells remain viable after the re-warming.

Bilateral Microkeratome-Assisted Anterior Lamellar Contralateral Corneal Autograft

To present a case in which bilateral microkeratome-assisted contralateral anterior lamellar corneal autografting was used in the treatment of a patient with a stromal scar in one eye and dense amblyopia in the fellow eye. Case report based on chart review. Anterior lamellar flaps were created in both eyes with a microkeratome. Six weeks later, central trephination through both flaps was performed, and the resulting corneal discs were switched. Visual acuity improved to 20/30 in the nonamblyopic eye 1 year after the surgery. Microkeratome-assisted contralateral lamellar autokeratoplasty can be useful in the treatment of an anterior stromal scar when the fellow eye has a clear cornea and poor vision limited by untreatable noncorneal pathology.

Remote Manipulation of Posterior Lamellar Corneal Grafts Using a Magnetic Field

In posterior lamellar keratoplasty procedures such as Descemet stripping endothelial keratoplasty and Descemet membrane endothelial keratoplasty, the lamellar graft is manipulated directly or by injecting an air bubble. This preliminary study sought to evaluate the feasibility of guiding lamellar corneal grafts by generating a magnetic field. Rabbit and porcine Descemet stripping endothelial keratoplasty and Descemet membrane endothelial keratoplasty grafts were manually produced and immersed in a ferromagnetic solution containing nanomagnetic particles conjugated to streptavidin or in gadoteric acid. For the feasibility study, grafts were transferred to an artificial anterior chamber or plastic test tube and a magnetic field was generated with a handheld NdFeB disc magnet. The presence and the sustainability of graft motion were documented under various conditions. For the semiquantitative study, whole or partial grafts were transferred to a plastic test tube after immersion, and the amount of tissue retraction induced by the remote magnet was graded. The grafts were successfully manipulated in all directions by the magnet, from a distance of up to 7 mm. They remained ferromagnetic more than 24 hours after immersion in the ferromagnetic solutions. The degree of retraction was affected by graft size, immersion time, time from immersion, and immersion solution. Posterior lamellar corneal grafts may be made ferromagnetic and remotely manipulated by creation of a magnetic field. The ferromagnetic properties are adjustable. This technique holds promise in attaching and repositioning grafts during keratoplasty. Further research is needed to assess the possible effects of ferromagnetic solutions on corneal endothelial cells and on lamellar graft clarity.

Descemet Stripping Endothelial Keratoplasty

Technical innovations in corneal transplantation have now made it possible to replace only the diseased part of the cornea, rather than the entire cornea as in penetrating keratoplasty (PKP). Patients with endothelial insufficiency due to Fuchs endothelial dystrophy, bullous keratopathy, or endothelial failure after keratoplasty can be treated with the new methods of posterior lamellar corneal transplantation: Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK). It remains unclear which of these methods is better in the individual case. We review the pertinent literature retrieved by a selective search in Medline and the Cochrane Library employing the terms "DMEK," "DSAEK," "DSEK," and "posterior lamellar keratoplasty." The publications considered in this article are those that contain important clinical information on the operative techniques. No randomized controlled trials of these techniques have been published to date. Numerous case series have shown that patients who undergo DSAEK (postoperative visual acuity ≥0.5 in 38-100%), and especially those who undergo it in early or intermediate stages of endothelial insufficiency, achieve a better functional result more rapidly than patients treated with PKP (postoperative visual acuity ≥0.5 in 47-61%). Only 23-47% of DSAEK patients achieve a visual acuity of 0.8 or more, compared to 36-79% of DMEK patients. Moreover, transplant rejection is seen in only 1-3% of cases of DMEK, compared to 0-8% after DSAEK and 1-23% after PKP. Numerous case series show clear advantages of DMEK over DSAEK, which, in turn, has better results than PKP. Nonetheless, randomized controlled trials are needed to determine which operative method is best in each stage of corneal disease.

A Fish Scale–Derived Collagen Matrix as Artificial Cornea in Rats: Properties and Potential

A fish scale-derived collagen matrix (FSCM) is proposed as an alternative for human donor corneal tissue. Light scatter and light transmission of the FSCM were measured and compared with human cornea, and its short-term biocompatibility was tested in a rat model. light scatter was determined with a straylight measuring device, whereas light transmission was measured using a broadband absorption spectrometer. for evaluation of the biocompatibiliy, three approaches were used: the FSCM was implanted as an anterior lamellar keratoplasty (ALK), placed in an interlamellar corneal pocket (IL), and placed subconjunctivally (SC). Transparency, neovascularization, and epithelial damage were followed for 21 days. Morphology and cellular infiltration were assessed histologically. The amount of scattered light was comparable to that seen in early cataract and the percentage of light transmission was similar to the transmission through the human cornea. Implantation of the FSCM as an ALK led to mild haziness only, not obscuring the pupil, despite the development of neovascularization around the sutures; IL placement led to a moderate haze, partly obscuring the pupil, and to (partial) melting of the anterior corneal lamella. The SC group exhibited local swelling and induration, which decreased over time. Histology showed a chronic inflammation varying from mild and moderate in the ALK and IL group, to severe in the SC group. In spite of technical difficulties, it was feasible to use the FSCM for ALK, whereas IL placement led to melting of the anterior lamella. Further studies are necessary for better understanding of its immunogenicity. The light scatter and transmission data show that the first version of this FSCM is comparable to human cornea tissue in this respect.

Einfluss der Spenderlamellendicke auf die Sehschärfe nach „Descemet’s stripping automated endothelial keratoplasty“ (DSAEK)

The aim of this study was to evaluate the effect of donor lamella thickness on postoperative visual acuity after Descemet's stripping automated endothelial keratoplasty (DSAEK). A retrospective analysis of 65 eyes from 61 patients who underwent DSAEK surgery in cases of Fuchs' corneal dystrophy or bullous keratopathy between 2008 and 2011 was performed. The thickness of donor lamella was measured intraoperatively by ultrasonic pachymetry and postoperatively by anterior segment optical coherence tomography (OCT) and correlated to the visual acuity and number of endothelial cells. The donor lamella thickness measured intraoperatively and postoperatively correlated significantly with each other (r = 0.874, p < 0.001). A significant correlation was found between postoperative corneal lamella thickness measured by anterior segment OCT and visual acuity (r = 0.273, p = 0.028) but not between intraoperative donor lamella thickness measured by ultrasonic pachymetry and visual acuity (r = 0.241, p = 0.103). The postoperative endothelial cell number did not show a correlation with either the intraoperatively or the postoperatively measured donor lamella thickness (r = - 0.059, p = 0.731, r = 0.024, p = 0.869, respectively). Corneal lamella thickness < 120µm was found to be correlated with a better visual outcome than in cases of thicker corneas > 120µm. Despite greater difficulty in corneal transplant technique in cases of thinner lamella no increased damage of corneal endothelium was shown. Therefore, DSAEK with corneal lamella thickness < 120µm is an interesting therapeutic alternative to DMEK.

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.

Femtosecond Lasers in Ophthalmology

The use of the femtosecond laser in ophthalmic surgery over the last decade has resulted in the development of innovative procedures. The ultra-short infrared laser pulses of the femtosecond laser can be applied precisely and predictably with minimal collateral tissue damage, making it an ideal tool for highly precise ophthalmic surgery. Flap creation in laserin situkeratomileusis (LASIK) is the most common use of this laser. It can also be used for other corneal refractive procedures, lamellar and full-thickness corneal transplantation, and cataract surgery. This article summarizes recent advanced applying femtosecond laser technology in ophthalmology.

Neurotrophins and Nerve Regeneration-Associated Genes are Expressed in the Cornea After Lamellar Flap Surgery

To determine the in vivo expression of neurotrophins (NTs) and nerve regeneration-associated genes (RAGs) after surgically creating a hinged lamellar corneal flap in thy1-YFP mice. Lamellar corneal flaps with multiple hinges were created in thy1-YFP mice. Mice were killed at weeks 2, 4, and 8. Quantitative polymerase chain reaction was performed to determine the expression of NTs and RAGs in the corneas after lamellar transection. Nerve growth factor (Ngf), brain-derived neurotrophic factor (Bdnf), glial cell-derived neurotrophic factor (Gdnf), neurotrophin 3, neurotrophin 5, small proline-rich repeat protein 1A (Sprr1a), growth-associated protein 43 (Gap43), and beta III tubulin (Tubb3) gene expressions were analyzed. Whole-mount confocal immunofluorescence and Western analyses were performed for localization and abundance of robustly expressed genes. Sprouts of fine YFP-positive fronds emanating from transected (injured) nerve bundles were seen in the flap area at 2 weeks onward. Bdnf and Sprr1a were robustly and significantly expressed at 2 weeks postoperatively (>2-fold increase in expression; P<0.05). Bdnf localized to thy1-YFP+ cells in operated corneas. Sprr1a localized to corneal epithelial cell membranes. At 8 weeks, none of the NTs and RAGs had increased expression. Bdnf (ρ=0.73, P=0.001) and Sprr1a (ρ=0.76, P=0.001) showed a significant positive correlation with beta III tubulin. The neurotrophin Bdnf and RAG Sprr1a are robustly and significantly expressed during corneal nerve regeneration in vivo.

Thygeson Superficial Punctate Keratitis and Scarring

Thygeson superficial punctate keratitis (TSPK), a chronic, inflammatory disease, has traditionally been taught to resolve spontaneously and without scarring. We present 4 cases with TSPK who developed sight-altering scarring after a prolonged disease course. Retrospective chart review of cases seen at the Proctor Medical Group. Patients age ranged from 31 to 68 years. All patients were male and had been symptomatic from 2 to 53 years. Follow-up period ranged from 1 month to 35 years. All 3 patients developed significant corneal scarring. Case 1 had bilateral corneal thickening and a Salzmann nodule with vascularization. Case 2 had bilateral stromal opacification. Case 3 developed corneal scarring to the point of needing an anterior lamellar corneal transplant. Pathological evaluation of this tissue showed disruption of the Bowman layer with band keratopathy, thickening of the basement membrane, and subepithelial fibrosis. The diagnosis of TSPK in these cases was never in doubt, 2 of the cases having been diagnosed by Dr Thygeson. Prolonged corneal inflammation associated with TSPK can cause visually significant scarring of the anterior corneal stroma. In those patients with chronic disease, the use of a topical corticosteroid may be needed not just for comfort but to reduce the risk of corneal scarring.

Outcomes of New Partial-Thickness Corneal Grafts: A Paradigm Shift in Practice, but at What Cost?

Introduction: Over the past 7-8 years, there has been a paradigm shift in the pattern of practice of corneal transplantation. Partial thickness and corneal endothelial cell allografts are now being performed for indications that previously were treated by full-thickness corneal grafts. We examined the evidence for the success of these new lamellar procedures, with a focus on graft survival and visual outcome. Methods: In a prospectively-maintained, national register of >23,000 corneal grafts with up to 25 years of annual follow-up, 2983 lamellar grafts were identified, of which 42% were endokeratoplasties (posterior corneal endothelial cell grafts), 39% were traditional, peripheral lamellar keratoplasties, and 19% were deep anterior lamellar keratoplasties (DALKs). Kaplan-Meier plots were used to determine graft survival times, Cox proportional hazards regression was used for multivariate graft survival analysis, and visual outcomes were investigated using best-corrected Snellen acuity, that is, with any prescribed spectacle lens or contact lens. Results: Kaplan-Meier graft survival at one year was 74% for endokeratoplasties, 80% for traditional lamellar procedures, and 93% for DALKs. The major indications for endokeratoplasty were Fuchs’ dystrophy (47%) and bullous keratopathy (33%). Over the time frame 2004-2012, penetrating corneal grafts performed for either of these indications exhibited significantly better graft survival than did endokeratoplasties for the same indications (p< 0.001). The major indication for DALK was keratoconus (76%). Over the time frame 1995-2012, penetrating corneal grafts performed for keratoconus exhibited significantly better graft survival than did DALKs for keratoconus (p< 0.001). Approximately 80% of lamellar procedures were performed to improve visual acuity, but at the time of most recent follow-up, more patients with penetrating grafts achieved good post-operative Snellen acuity than did those with lamellar grafts. A best-corrected Snellen acuity of 6/12 or better (=20/40 or better) at most recent follow-up was achieved in 18% of endokeratoplasties, 34% of traditional lamellar grafts, and in 37% of DALKs. Surgeons who performed more than 15 lamellar procedures per year achieved significantly better graft survival than those who performed fewer grafts (p=0.02). Conclusion: There appears to be a surgeon learning curve for new lamellar corneal graft procedures. Currently, outcomes in terms of graft survival and visual acuity are better for penetrating grafts than for the newer lamellar procedures, even when matched for era and indication for graft.

Outcomes of New Partial-Thickness Corneal Grafts: A Paradigm Shift in Practice, but at What Cost?

Introduction: Over the past 7-8 years, there has been a paradigm shift in the pattern of practice of corneal transplantation. Partial thickness and corneal endothelial cell allografts are now being performed for indications that previously were treated by full-thickness corneal grafts. We examined the evidence for the success of these new lamellar procedures, with a focus on graft survival and visual outcome. Methods: In a prospectively-maintained, national register of >23,000 corneal grafts with up to 25 years of annual follow-up, 2983 lamellar grafts were identified, of which 42% were endokeratoplasties (posterior corneal endothelial cell grafts), 39% were traditional, peripheral lamellar keratoplasties, and 19% were deep anterior lamellar keratoplasties (DALKs). Kaplan-Meier plots were used to determine graft survival times, Cox proportional hazards regression was used for multivariate graft survival analysis, and visual outcomes were investigated using best-corrected Snellen acuity, that is, with any prescribed spectacle lens or contact lens. Results: Kaplan-Meier graft survival at one year was 74% for endokeratoplasties, 80% for traditional lamellar procedures, and 93% for DALKs. The major indications for endokeratoplasty were Fuchs' dystrophy (47%) and bullous keratopathy (33%). Over the time frame 2004-2012, penetrating corneal grafts performed for either of these indications exhibited significantly better graft survival than did endokeratoplasties for the same indications (p< 0.001). The major indication for DALK was keratoconus (76%). Over the time frame 1995-2012, penetrating corneal grafts performed for keratoconus exhibited significantly better graft survival than did DALKs for keratoconus (p< 0.001). Approximately 80% of lamellar procedures were performed to improve visual acuity, but at the time of most recent follow-up, more patients with penetrating grafts achieved good post-operative Snellen acuity than did those with lamellar grafts. A best-corrected Snellen acuity of 6/12 or better (=20/40 or better) at most recent follow-up was achieved in 18% of endokeratoplasties, 34% of traditional lamellar grafts, and in 37% of DALKs. Surgeons who performed more than 15 lamellar procedures per year achieved significantly better graft survival than those who performed fewer grafts (p=0.02). Conclusion: There appears to be a surgeon learning curve for new lamellar corneal graft procedures. Currently, outcomes in terms of graft survival and visual acuity are better for penetrating grafts than for the newer lamellar procedures, even when matched for era and indication for graft.

Sub Bowman's keratomileusis for the correction of anisometropia after penetrating and lamellar corneal surgery

AbstractPurpose To report the use of Sub Bowman's Keratomileusis (SBK) in the treatment of anisometropia subsequent to Perforating Keratoplasty (PK) and Deep Anterior Lamellar Keratoplasty(DALK).Methods Three patients with compound myopic and hyperopic astigmatism after PK and DALK were submitted to SBK. Treatments were conducted under topical anaesthesia. Femtosecond laser (IntraLase FS., AMO Inc, CA, USA) was used to create a superiorly hinged anterior lamellar flap at 100 microns in a 7.75/8 mm zone. The flap was lifted and a customized wavefront ablation was performed in two cases with the Star S4IR (CustomVue, AMO Inc., CA, USA), and in one case with Technolas z100 (Zyoptix Custom Wavefront, Bausch &amp; Lomb Inc, NY, USA). The flap was then replaced, and the interface was irrigated. Minimum residual pachimetry value was estimated not inferior to 400µm.Results Postoperative controls at 1 and 3 months showed a reduction of anisometropia up to 70% with residual spherical equivalent (SE) not superior to 2.50 dioptersConclusion Sub Bowman's Keratomileusis has been shown to be safe and effective to reduce anisometropia in patients who have previously undergone to PK and DALK.

Usefulness of the optical coherence tomography Spectralis® anterior segment module in the diagnosis and monitoring of corneal pathology

AbstractPurpose The Spectralis® Anterior Segment Module that offers Spectral‐Domain Optical Coherence Tomography (SD‐OCT) Heidelberg Engineering, is a sign of the revolution who are suffering OCT teams nowadays. The aim of our study is to analyze the usefulness of optical coherence tomography of anterior segment in the diagnosis and monitoring of different corneal diseases.Methods Some ophthalmologists explored their patients from department of cornea and ocular superfie under slit lamp and later with the OCT Anterior Segment Module. The Spectralis SD‐OCT offers high quality images of cornea and anterior segment, without any contact and comfort for the patient. Because it is installed on a slit lamp is very intuitive and easy to use, so no special training is required.Results We present several cases where we used optical coherence tomography of anterior segment in the diagnosis of different corneal diseases: degeneration, infections, dystrophies... and also in following various surgical procedures such as intrastromal corneal rings, keratoplasty, lamellar corneal graft and amniotic membrane coatings.Conclusion We believe it is a useful diagnostic tool in every department of cornea, refractive surgery and ocular surface diseases to document, make measurements and studies of evolution and, especially, to evaluate the surgical results.

Endothelial quality of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S): two-year outcome of manual preparation in an ocular tissue bank

To assess the quantitative and qualitative parameters of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S) prepared manually in the Ocular Tissue Bank Prague. All 65 successfully prepared pre-cut posterior corneal lamellae provided for grafting during a 2-year period were analyzed retrospectively. The lamellae, consisting of a central zone of endothelium-Descemet membrane surrounded by a supporting peripheral stromal rim, were prepared manually from corneoscleral buttons having an endothelial cell density higher than 2,500 cells/mm(2). The live endothelial cell density, the percentage of dead cells, the hexagonality and the coefficient of variation were assessed before and immediately after preparation as well as after 2 days of organ culture storage at 31 °C. Altogether, the endothelium of 57 lamellae was assessed. Immediately after preparation, the mean live endothelial cell density was 2,835 cells/mm(2) and, on average, 1.8 % of dead cells were found. After 2 days of storage, the cell density decreased significantly to 2,757 cells/mm(2) and the percentage of dead cells to 1.0 %. There was a significant change in the mean hexagonality and the coefficient of variation after lamellar preparation and subsequent storage. The amount of tissue wasted during the preparation was 23 %. The endothelial cell density of posterior corneal lamellae sent for DMEK-S was higher than 2,700 cells/mm(2) in average with a low percentage of dead cells; 65 pre-cut tissues were used for grafting during a 2-year period.

Semaphorin 7a Links Nerve Regeneration and Inflammation in the Cornea

We determined Semaphorin 7a (Sema7a) localization and abundance in naive corneas and in corneas after nerve-transecting lamellar flap surgery, and determined the effect of Sema7a supplementation on corneal nerve regeneration and inflammation. Immunolocalization and Western blot analyses were performed to evaluate the abundance of Sema7a in naive corneas and corneas undergoing nerve regeneration after lamellar corneal surgery in thy1-YFP+ neurofluorescent mice. We used compartmental cultures of dissociated trigeminal ganglion cells to determine the effect of Sema7a exposure on neurite outgrowth in vitro. Finally, a Sema7a pellet was implanted under the corneal flap after lamellar transection surgery to determine the neuronal and inflammatory effects of Sema7a supplementation in vivo. Sema7a was expressed in the corneal epithelium and stromal keratocytes, but was more abundant in the epithelium (74.3%) compared to the stroma (25.7%, P = 0.02). Sema7a expression was increased significantly in the cornea after lamellar corneal surgery and was localized to stromal cells near the regenerating nerve fronds. Exposure of trigeminal neurites to Sema7a (20 nM) in the side compartment increased neurite length significantly. The implanted Sema7a pellet increased significantly YFP+ inflammatory cell influx into the cornea as well as increased corneal nerve length. Sema7a is expressed constitutively in the cornea, and potently stimulates nerve regeneration and inflammatory cell influx. Therefore, this immune semaphorin links nerve regeneration and inflammatory processes in the cornea.

Corneal Donor Tissue Preparation for Endothelial Keratoplasty

Over the past ten years, corneal transplantation surgical techniques have undergone revolutionary changes1,2. Since its inception, traditional full thickness corneal transplantation has been the treatment to restore sight in those limited by corneal disease. Some disadvantages to this approach include a high degree of post-operative astigmatism, lack of predictable refractive outcome, and disturbance to the ocular surface. The development of Descemet's stripping endothelial keratoplasty (DSEK), transplanting only the posterior corneal stroma, Descemet's membrane, and endothelium, has dramatically changed treatment of corneal endothelial disease. DSEK is performed through a smaller incision; this technique avoids 'open sky' surgery with its risk of hemorrhage or expulsion, decreases the incidence of postoperative wound dehiscence, reduces unpredictable refractive outcomes, and may decrease the rate of transplant rejection3-6.Initially, cornea donor posterior lamellar dissection for DSEK was performed manually1 resulting in variable graft thickness and damage to the delicate corneal endothelial tissue during tissue processing. Automated lamellar dissection (Descemet's stripping automated endothelial keratoplasty, DSAEK) was developed to address these issues. Automated dissection utilizes the same technology as LASIK corneal flap creation with a mechanical microkeratome blade that helps to create uniform and thin tissue grafts for DSAEK surgery with minimal corneal endothelial cell loss in tissue processing.Eye banks have been providing full thickness corneas for surgical transplantation for many years. In 2006, eye banks began to develop methodologies for supplying precut corneal tissue for endothelial keratoplasty. With the input of corneal surgeons, eye banks have developed thorough protocols to safely and effectively prepare posterior lamellar tissue for DSAEK surgery. This can be performed preoperatively at the eye bank. Research shows no significant difference in terms of the quality of the tissue7 or patient outcomes8,9 using eye bank precut tissue versus surgeon-prepared tissue for DSAEK surgery. For most corneal surgeons, the availability of precut DSAEK corneal tissue saves time and money10, and reduces the stress of performing the donor corneal dissection in the operating room. In part because of the ability of the eye banks to provide high quality posterior lamellar corneal in a timely manner, DSAEK has become the standard of care for surgical management of corneal endothelial disease.The procedure that we are describing is the preparation of the posterior lamellar cornea at the eye bank for transplantation in DSAEK surgery (Figure 1).

Corneal Donor Tissue Preparation for Endothelial Keratoplasty

Over the past ten years, corneal transplantation surgical techniques have undergone revolutionary changes1,2. Since its inception, traditional full thickness corneal transplantation has been the treatment to restore sight in those limited by corneal disease. Some disadvantages to this approach include a high degree of post-operative astigmatism, lack of predictable refractive outcome, and disturbance to the ocular surface. The development of Descemet's stripping endothelial keratoplasty (DSEK), transplanting only the posterior corneal stroma, Descemet's membrane, and endothelium, has dramatically changed treatment of corneal endothelial disease. DSEK is performed through a smaller incision; this technique avoids 'open sky' surgery with its risk of hemorrhage or expulsion, decreases the incidence of postoperative wound dehiscence, reduces unpredictable refractive outcomes, and may decrease the rate of transplant rejection3-6. Initially, cornea donor posterior lamellar dissection for DSEK was performed manually1 resulting in variable graft thickness and damage to the delicate corneal endothelial tissue during tissue processing. Automated lamellar dissection (Descemet's stripping automated endothelial keratoplasty, DSAEK) was developed to address these issues. Automated dissection utilizes the same technology as LASIK corneal flap creation with a mechanical microkeratome blade that helps to create uniform and thin tissue grafts for DSAEK surgery with minimal corneal endothelial cell loss in tissue processing. Eye banks have been providing full thickness corneas for surgical transplantation for many years. In 2006, eye banks began to develop methodologies for supplying precut corneal tissue for endothelial keratoplasty. With the input of corneal surgeons, eye banks have developed thorough protocols to safely and effectively prepare posterior lamellar tissue for DSAEK surgery. This can be performed preoperatively at the eye bank. Research shows no significant difference in terms of the quality of the tissue7 or patient outcomes8,9 using eye bank precut tissue versus surgeon-prepared tissue for DSAEK surgery. For most corneal surgeons, the availability of precut DSAEK corneal tissue saves time and money10, and reduces the stress of performing the donor corneal dissection in the operating room. In part because of the ability of the eye banks to provide high quality posterior lamellar corneal in a timely manner, DSAEK has become the standard of care for surgical management of corneal endothelial disease. The procedure that we are describing is the preparation of the posterior lamellar cornea at the eye bank for transplantation in DSAEK surgery (Figure 1).

Effects of Variation in Depth and Side Cut Angulations in LASIK and Thin-flap LASIK Using a Femtosecond Laser: A Biomechanical Study

To study the corneal biomechanical effects of varying LASIK flap depth and side cut angulations and evaluate the relative contribution of the lamellar and side cuts using a femtosecond laser and radial shearing speckle pattern interferometry (RSSPI). Forty-two organ-cultured human corneas were divided into a control group and three investigative groups, each undergoing different incision types at both 90- and 160-μm depth using a femtosecond laser. In the first group, typical LASIK flaps were created; in the second group, only the bed was cut (delamination); and in the third group, side cuts alone were affected. Corneal strain was measured using RSSPI before and after treatment following an increase in hydrostatic pressure from 15.0 to 15.5 mmHg and again after 1 week of incubation in culture medium. The flap group demonstrated a weakening of strength related to the depth of cut, with strain increasing by 9% and 32% at 90 and 160 μm, respectively. Similar changes, 9% and 33%, were observed following execution of side cuts to the same depths. By contrast, strain increase following delamination showed no relationship with depth, increasing by 5% in both instances. When the side cut angle was made more acute, strain decreased with a 2% strain increase being measured after a 90-μm, 150° side cut was created. No significant changes occurred during the period of organ culture. Vertical side cuts through corneal lamellae rather than horizontal delamination incisions contribute to the loss of structural integrity during LASIK flap creation. Angulating side cuts such that the stromal diameter of the flap exceeds its epithelial diameter can decrease this effect.

Inverse Cutting of Posterior Lamellar Corneal Grafts by a Femtosecond Laser

Purpose Posterior lamellar grafting of the cornea has become the preferred technique for treatment of corneal endothelial dysfunction. Posterior lamellar grafts are usually cut by a micro-keratome or a femto-second laser after the epithelial side of the donor cornea has been applanated. This approach often results in variable central graft thickness in different grafts and an increase in graft thickness towards the periphery in every graft. The purpose of this study was to evaluate if posterior lamellar grafts can be prepared from the endothelial side by a femto-second laser, resulting in reproducible, thin grafts of even thickness.Methods A CZM 500 kHz Visumax femto-second laser was used. Organ cultured donor grafts were mounted in an artifical anterior chamber with the endothelial side up and out. Posterior grafts of 7.8 mm diameter and 130 micron thickness were prepared by femto-second laser cutting. A standard DSAEK procedure was performed in 10 patients with Fuchs endothelial dystrophy. Patients were followed-up regularly and evaluated by measurement of complications, visual acuity, corneal thickness (Pentacam HR), and endothelial cell density.Results Femto-laser cutting of grafts and surgery was uncomplicated. Rebubbling was necessary in 5 of 10 cases (normally only in 1 of 20 cases). All grafts were attached and cleared up during the first few weeks. After six months, the average visual acuity was 0.30 (range: 0.16 to 0.50), corneal thickness was 0.58 mm (range 0.51 to 0.63), and endothelial cell density was 1.570 per sq. mm (range: 1.400 to 2.000 cells per sq. mm). The grafts were of uniform thickness, but substantial interface haze was present in most grafts.Conclusions Posterior lamellar corneal grafts can be prepared from the endothelial side using a femto-second laser. All grafts were clear after 6 months with satisfying endothelial cell counts. Poor visual acuity caused by interface scatter was observed in most patients. Femto-second laser cutting parameters needs to be optimised to enable smooth cutting in the posterior stroma.