Posterior Lamellar Corneal Research Articles

Transmigration of neutrophils across the avascular corneal endothelium

Aims/Purpose: The corneal endothelium (CE) functions as a tight barrier to regulate nutrient and fluid influx into the corneal stroma. During corneal infections, leukocytes infiltrate the cornea through the conjunctival lymphoid reservoir or via angiogenesis directed by the limbus. In a previous study, neutrophils were found to migrate across the corneal endothelium (CE) upon stimulation with IFN‐γ, mediated by ICAM‐1 [1]. We aim to further elucidate the transmigration of neutrophils across the CE as a possible third route for corneal infiltration.Methods: CE tissue samples were obtained from patients with corneal disease that underwent posterior lamellar corneal transplantation or penetrating keratoplasty. Confocal immunofluorescence microscopy was used to study the expression and distribution of adhesion molecule ligands for leukocyte adhesion and the spatial distribution of neutrophils within the CE.Results: Multiple events of infiltrating neutrophils across the CE monolayer were identified, with the paracellular route being the preferred mode of migration. The expression of the leukocyte ligand ICAM‐1 appeared diffuse but heterogeneous across the CE.Conclusions: Using high‐end microscopy, we found neutrophil infiltration through the CE monolayer and confirmed the presence of ICAM‐1 on the apical surface of CE cells. These data imply that there is a third pathway of corneal immunity. This has implications for anti‐inflammatory therapies instilled systemically or topically and warrants further investigation.References Elner VM, et al., Intercellular adhesion molecule‐1 in human corneal endothelium. Modulation and function. Am J Pathol. 1991.

EndoArt®: results in patients with glaucoma drainage devices

EndoArt® (Eye Yon Medical, Ness Ziona, Israel) is anovel artificial corneal inner layer transplant and an innovative treatment alternative for patients at high risk for graft failure after posterior lamellar corneal transplantation (EK). We present the initial results of the EndoArt® implantation in patients with glaucoma drainage devices (GDD). In this study 12eyes with GDD were retrospectively evaluated. All had ahigh risk of transplant rejection in cases of EK (previous other glaucoma surgery in addition to GDD, n = 8, condition following Descemet membrane endothelial keratoplasty, DMEK, n = 9, uveitis, n = 2, or synechiae, n = 2). The EndoArt® was secured with agas bubble and one to three holding sutures. The preoperative and postoperative best spectacle-corrected visual acuity (BSCVA) and central corneal thickness (CCT) were determined. The need for additional gas injections (rebubbling) was analyzed. Octafluoropropane (C3F8) 12% was used in nine patients and sulfur hexafluoride (SF6) 20% in three patients as anterior chamber tamponade to ensure adhesion of the EndoArt®. At least one rebubbling was necessary in four eyes. The preoperative BSCVA was 1.6 (± 0.5) logMAR and significantly improved to 1.1 (± 0.6) logMAR after 12weeks (p = 0.028). The preoperative CCT was 719 µm ± 145.7, which significantly decreased to 622.4 µm ± 174.9 after six weeks (p = 0.004) and to 591.7 µm ± 190.8 after 12weeks (p = 0.096). In one eye, the prosthesis was explanted due to a suspected fibrotic remodelling of the cornea following multiple previous DMEKs. EndoArt® led to asignificant improvement in BSCVA and reduction in CCT; however, there was ahigh rebubbling rate in patients with GDD. In high-risk patients, the use of EndoArt® may be advantageous in avoiding graft failure after EK.

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.

Экспериментальное обоснование использования 1% раствора гидроксипропилметилцеллюлозы для защиты эндотелия заднего послойного трансплантата роговицы при его выкраивании низкоэнергетическим фемтосекундным лазером по инвертированной методике

Purpose. To evaluate experimentally endothelial cell loss of animal's cornea during inverted posterior lamellar corneal graft preparation technique by low-energy femtosecond laser with and without ophthalmic viscosurgical device (OVD) – 1% hydroxypropyl methylcellulose (HPMC) solution application. Material and methods. Posterior lamellar corneal grafts were created using a femtosecond laser (FSL). In the control group (n=16), a few drops of corneal storage solution were applied to the endothelium just before applanation, in the experimental group (n=16) – 1% HPMС. The quality of the applanation were monitored using an integrated in laser OCT system. The endothelial viability was determined using live/dead cells assay and the grafts were examined on a confocal laser scanning microscope. The obtained images were analyzed to count live and dead endothelial cells (EC). To assess the state of collagen fibers of the stromal side of the graft, samples from the control and experimental groups were examined using a scanning electron microscope (SEM). Results. According to the OCT, in all samples of both groups, a flat profile of the contact zone between the laser head and the endothelial monolayer was observed during applanation. The difference between the number of live and dead ECs was statistically significant between both groups. There were 2854 [2819; 2879] live cells/mm² in the control group, and 3477 [3426; 3719] live cells/mm² in the experimental group (p<0.001). Thus, the number of dead ECs in the control group was 710 [649; 728] cells/mm² . The number of dead ECs in the experimental group was 402 [366; 427] cells/mm² (p<0.001). When analyzing the images obtained on a SEM, the preservation of the architectonics of the graft collagen fibers with their single defibrations in both groups was observed. Conclusion. Application of 1% HPMC provides protection for endothelial cells from damage during posterior laser dissection using an FSL. In the study group, the number of endothelial cells was 9.92% higher than in the control group. The presence of the OVD layer in the interface between the head of the FSL and the EC did not affect the formation of an effective laser cut and did not reduce the quality of the stromal surface of the graft. The inverted technique FSL cut using a 1% solution of HPMC on the surface of the endothelium may be recommended for use in clinical practice. Key words: endothelium, keratocytes, corneal transplantation, keratoplasty, posterior lamellar keratoplasty, femtosecond laser, ophthalmic viscosurgical device, hydroxypropyl methylcellulose, confocal microscopy, scanning electron microscopy

Descemet Stripping Automated Endothelial Keratoplasty versus Descemet Membrane Endothelial Keratoplasty for Fuchs Endothelial Corneal Dystrophy: A National Registry-Based Comparison

To compare the outcome between posterior lamellar corneal transplant procedures for Fuchs endothelial corneal dystrophy, taking preoperative patient characteristics in consideration. Surgical methods compared were Descemet membrane endothelial keratoplasty (DMEK), Descemet stripping automated endothelial keratoplasty (DSAEK), and DSAEK with concomitant cataract surgery (phacoemulsification plus DSAEK). Registry-based study with propensity score matching. One thousand six hundred seventy-seven patients from all Swedish corneal transplantation units treated from 2012 through2019. All patients undergoing endothelial keratoplasty performed from 2012 through 2019 with completed 2-year follow-up data reported to The Swedish Corneal Transplant Register were included, totaling 1677 patients. Three comparable groups (DMEK, DSAEK, and phacoemulsification plus DSAEK) with 216 patients in each group were generated with propensity score matching based on preoperative visual acuity, age, sex, year of surgery, and preoperative risk factors such as inflammation, vascularization, and glaucoma. Best-corrected visual acuity (BCVA) at the 2-year follow-up, frequency of graft dislocation, graft rejection episodes, and graft failure within 2 years including primary graft failure. The preoperative corneal status was affected more severely in the DSAEK group before matching. In the matched groups, the median BCVA 2 years after surgery was 0.1 logarithm of the minimum angle of resolution (logMAR) in both the DMEK and the phacoemulsification plus DSAEK groups and 0.15 logMAR in the DSAEK group (P= 0.001). The frequency of graft dislocation was higher among the patients undergoing phacoemulsification plus DSAEK, but the frequency of graft failure and primary graft failure was higher in the DMEK group. Visual acuity improved in most patients (90%) with all 3 surgical methods. However, DMEK and phacoemulsification plus DSAEK reached higher levels of visual acuity 2 years after surgery, and phacoemulsification plus DSAEK was superior considering graft survival rate. All 3 surgical procedures showed both strengths and weaknesses, suggesting that the choice of surgical method should be individualized, taking into consideration not only the cornea, but each patient's complete medical status as well as the entire course of postoperative medical care. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

New findings on the immune response following corneal transplantation

AbstractWe performed a multi‐centre, cross‐sectional analysis of the current immunological status of human full thickness (FT) and posterior lamellar (PL) corneal transplant (CT) recipients and control subjects using multiple technology platforms. The primary goal of this study was to define pathways associated with adverse immune responses to corneal transplantation and to generate and compare comprehensive, pathway‐based profiles of immune activity in CT acute rejection (AR). The secondary goal was to identify a composite biomarker of CT AR. Clinical details, including a comprehensive clinical examination, and blood samples, enabling analysis of peripheral blood mononuclear cell (PBMC) DNA, RNA and phenotype, were collected from adults with clinically diagnosed AR of FL‐CT (n = 35) and PL‐CT (n = 21) along with Stable CT recipients (n = 177) and adults with non‐transplanted corneal disease (n = 40). For those with AR, additional samples were collected 3 months later. CT acute rejection was clinically diagnosed and defined as precipitates on the corneal graft but not on the peripheral recipient cornea, either scattered or in the form of a Khodadoust line along with an increase in central corneal thickness. Immune cell analysis was performed by whole‐genome microarrays (whole blood) and high dimensional multi‐colour flow cytometry (peripheral blood mononuclear cells). For both, no activation signature was identified within the B cell and T cell repertoire at the time of AR diagnosis. Nonetheless, in FT‐ but not PL‐CT recipients, AR was associated with differences in B cell maturity and regulatory CD4+ T‐cell frequency compared to stable allografts. Our results suggest that, in contrast to solid organ transplants, genetic or cellular assays of peripheral blood are unlikely to be clinically exploitable for prediction or diagnosis of AR. However, further investigation of circulating B cell and T cell subpopulations may provide insights into the regulation of anti‐donor immune response in human CT recipients with differing AR risk.

Technology for obtaining an ultrathin posterior lamellar corneal graft at the Eye Tissue Bank

Objective: to develop technologies for preoperative preparation of the posterior lamellar corneal graft based on our own formulation of the preservation medium for optimal dehydration of the donor cornea and a technique for cutting out an ultrathin flap using an optimized method at the Eye Tissue Bank. Materials methods. In a series of experimental studies, we obtained data on the hydration level of cadaveric donor corneas that were preserved in various solutions at different observation periods. Using 16 corneas, analytical weighing and pachymetry were performed via optical coherence tomography in the experimental (n = 8) and control (n = 8) groups. Morphological and functional characteristics of the corneal endothelium were then assessed. At the next stage of work, ultrathin grafts were formed from 16 corneas after hypothermic preservation in the experimental (n = 8) and control (n = 8) solutions by single-pass microkeratome, followed by microscopy of the samples using a scanning electron microscope. Results. After the first days of preservation in the proposed solution, there was dehydration of 9% cornea in the experimental group in comparison with the samples of the control group. After 4 days of preservation, there was no reliable difference found between the groups (p > 0.05) in the study of the endothelial cell viability of ultra-thin corneal grafts by immunofluorescent microscopy using the «Live and dead» marker. Scanning electron microscopy revealed that corneal stromal collagen fibers, preserved in the proposed medium, retained their integrity. Conclusion. The proposed technology can be recommended for use at eye banks for formation of an ultra-thin corneal graft at the preoperative stage.

Risk factors for donor endothelial loss in eye bank-prepared posterior lamellar corneal tissue for descemet stripping automated endothelial keratoplasty.

The aim of this study was to investigate donor, tissue, and precut procedure risk factors for endothelial cell density (ECD) loss in posterior lamellar corneal tissue preparation by an eye bank for Descemet stripping automated endothelial keratoplasty. A total of 259 corneoscleral rims precut by the Singapore Eye Bank from October 2011 to August 2013 were evaluated. Donor characteristics, tissue characteristics, and precut procedure parameters were analyzed. The mean donor age was 57.18 ± 11.35 years, and the mean cutting transition time was 4.16 ± 0.75 seconds. The mean ECD was 2826 ± 225 and 2787 ± 224 cells per square millimeter before and after precutting, respectively, with an average ECD change of -1.38% ± 3.28%. The precutting procedure failure rate was 1.2%. Mutivariate regression analysis showed that an older donor age, a higher ECD before cutting, and a slower cutting transition speed were significant factors. Corneas with an ECD >2800 cells per square millimeter before precutting, cutting transition time >5.5 seconds, and corneas with donor age >65 years were significantly more likely to have greater than 5% ECD loss after precutting (odds ratio, 6.42, 1.66, and 1.62; 95% confidence interval, 1.44-29.43, 1.45-2.72, and 1.66-5.82, respectively). Donor source, death-to-preservation time (range, 0.67-10.88 hours), death-to-precutting time (range, 0-7 days), and graft thickness (range, 43-232 μm) were not statistically significant factors. The ECD loss in the precut tissue prepared by the eye bank was very low. The risk factors identified provide better understanding of how to improve the quality and safety profiles when preparing graft tissue for Descemet stripping automated endothelial keratoplasty.

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.

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).

A Prospective Study Comparing EndoGlide and Busin Glide Insertion Techniques in Descemet Stripping Endothelial Keratoplasty

To compare a new insertion method using an EndoGlide (Angiotech/Network Medical Products) with the standard Busin glide (Moria USA) assisted insertion of the posterior lamellar corneal graft in Descemet stripping endothelial keratoplasty (DSEK). Prospective, consecutive, comparative, nonrandomized study. Surgery was performed between October 2008 and October 2010 in 52 eyes of 52 consecutive patients with endothelial dysfunction suitable for DSEK. Twenty-two consecutive eyes underwent the new EndoGlide-assisted insertion of donor lenticule and 30 eyes underwent the surgery using the Busin glide. Six-month follow-up data are available for all patients. Clinical details, best-corrected visual acuity, manifest refraction, intraoperative and postoperative complications, and corneal endothelial cell loss were assessed at 6 months after DSEK. At 6 months after surgery, the best-corrected visual acuity was similar in both groups (0.13 logarithm of the minimal angle of resolution in the EndoGlide eyes as compared with 0.15 logarithm of the minimal angle of resolution in the Busin group; P = .34). Mean spherical equivalent was 0.65 diopter (D) and 0.51 D, and mean refractory cylinder was 1.39 D and 1.08 D, respectively (P = .40). The endothelial cell loss was much lower in the EndoGlide group (25.76%) as compared with the Busin group (47.46%; P < .0001). In conclusion, the new EndoGlide results in significantly less endothelial cell loss than Busin glide donor insertion in DSEK. The visual outcomes and refractive changes were similar in both groups.

Simultaneous phacoemulsification, lens implantation and endothelial keratoplasty: Triple procedure

Simultaneous Descemet stripping endothelial keratoplasty, phacoemulsification, and intraocular lens implantation are indicated in Fuchs' dystrophy with associated cataract. Compared to the standard method of the triple procedure which includes penetrating keratoplasty, this new method has the advantages of sutureless surgery, small limbal incision, faster recovery, less surface problems, less astigmatism, stronger tensile strength and more predictable calculation of the intraocular lens power. This is the first report of such a combination of procedures in our literature. A 76-year-old woman suffered from a gradual bilateral visual loss. The best corrected visual acuity was 20/60 (right eye) and finger counting at 1m (left eye). Corneal thickness was 590 microm and 603 microm, respectively. A marked cornea guttata and nuclear cataract were present in both eyes. Phacoemulsification, lens implantation, and Descemet stripping were done in the left eye. The posterior lamellar corneal graft, 8.0 mm in diameter and about 150 microm thick, was bent and inserted through the limbal incision. The air was injected into the anterior chamber to attach the graft to the recipient stroma. The cornea remained clear, and the transplant was attached during a two-year follow-up. Visual acuity was 20/40 after two months, and 20/25 after one year. CONCLUSION. The new technique proved itself as a good choice for the treatment of a mild Fuchs' dystrophy associated with cataract.

Descemet Stripping Endothelial Keratoplasty: Effect of the Surgical Procedure on Corneal Optics

To determine the changes in corneal optical performance after posterior lamellar corneal transplantation. Retrospective case series. The anterior segment in four eyes of four patients who underwent Descemet stripping endothelial keratoplasty (DSEK) with cataract extraction and intraocular lens (IOL) implantation were imaged with the Visante anterior segment optical coherence tomography [OCT] (Carl Zeiss Meditec, Dublin, California, USA). The curvature of the posterior surface of the donor graft was compared with that of the host cornea, and corneal thickness was measured. All eyes had a hyperopic refractive error after surgery. The posterior corneal curvature after surgery was more than that before surgery. Average preoperative keratometry was 43.4 diopters (D), and after surgery, it was 42.8 D using keratometry. However, when the postsurgical corneal power was calculated using the Gaussian optics method, the average value was 40.8 D. The addition of a donor corneal graft to the posterior surface of decompensated corneas may lessen the effective optical power of the cornea and may have implications for IOL power calculations in these eyes.

Corneal Imaging with Anterior Segment Optical Coherence Tomography for Lamellar Keratoplasty Procedures

To assess and describe the uses of anterior segment optical coherence tomography (OCT) in the evaluation of the cornea before and after lamellar corneal transplantation procedures. Prospective, noncomparative, observational case series. Seven eyes of seven patients undergoing anterior and posterior lamellar corneal transplantation procedures at the Singapore National Eye Centre were included in the study. High-resolution anterior segment OCT scans of the cornea and anterior segment were performed both before and after lamellar transplantation procedures on the cornea with the Visante anterior segment OCT system (Visante OCT; Carl Zeiss Meditec, Inc, Dublin, California, USA), and the imaging findings were correlated with the clinical picture. Measurements of lamella thickness were performed with the software provided. Anterior segment OCT images were able to provide valuable information on donor apposition, Descemet membrane detachment after deep anterior lamellar keratoplasty (DALK), posterior lamellar dislocation, primary graft failure, and anterior chamber crowding with consequent chamber angle encroachment and pupillary block after Descemet stripping automated endothelial keratoplasty (DSAEK). Anterior segment OCT is a valuable imaging tool for assessing the feasibility of lamellar transplantation surgery in the diseased cornea and in the management of surgical complications after such procedures.

Femtosecond-laser–assisted Descemet's stripping endothelial keratoplasty

To our knowledge, we describe the first patient with pseudophakic bullous keratoplasty treated with femtosecond-laser-assisted endothelial keratoplasty. A 5.5 mm corneoscleral tunnel incision was made; after Descemet's membrane was stripped, an 8.0 mm posterior lamellar corneal disk prepared with a femtosecond laser was inserted into the anterior chamber against the recipient cornea without the use of corneal sutures. Four months postoperatively, the posterior corneal disk was clear and the induced astigmatism was 2.1 diopters, demonstrating a functional corneal endothelial layer. The femtosecond laser offers a new surgical approach for minimally invasive endothelial keratoplasty in corneal endothelial disorders.

Microkeratome Versus Femtosecond Laser Predissection of Corneal Grafts for Anterior and Posterior Lamellar Keratoplasty

To compare 2 different techniques for predissection of human anterior and posterior lamellar corneal grafts for eye bank storage. A mechanical microkeratome (group 1, N = 5) and a femtosecond laser (group 2, N = 5) were used to dissect intended 350-microm-deep lamellar planes in deepithelialized donor corneas mounted on an artificial anterior chamber. These corneas were replaced in Optisol GS at 4 degrees C postoperatively and examined 2 days later to simulate a clinical scenario. Ultrasonic pachymetry of corneal lamellar sections was measured before and after separation of the lamellar grafts. Group 1 sections were separated by the mechanical microkeratome, whereas group 2 sections were manually separated 2 days after laser dissection. Endothelial cell viability was evaluated in posterior grafts. Total corneal thicknesses immediately before dissection were 559 +/- 61 (group 1) and 578 +/- 79 microm (group 2; P = 0.46). Immediate postdissection anterior and posterior graft thicknesses were 361 +/- 68 and 203 +/- 74 microm (group 1), respectively. Achieved anterior and posterior graft thicknesses 2 days later were 282 +/- 44 and 413 +/- 35 microm (group 1) and 324 +/- 112 and 397 +/- 51 microm (group 2), respectively. Percentage of devitalized endothelial cells were 3.4% +/- 1.6% (group 1) and 1.6% +/- 1.2% (group 2; P = 0.35). Centralized predissection by both techniques, cold storage, and shipping by airmail results in viable grafts without significant endothelial cell loss 2 days later.

Initial Results of Small Incision Deep Lamellar Endothelial Keratoplasty (DLEK)

To evaluate the results of replacing the posterior stroma and endothelium, using small incision deep lamellar endothelial keratoplasty (DLEK) surgical technique, in patients with corneal endothelial dysfunction. Noncomparative case series. Fifteen eyes of 15 patients (six males and nine females) with endothelial dysfunction were included in this study. Through a 5-mm scleral incision, a deep lamellar pocket was created across the cornea, followed by excision of an 8.0-mm disk of posterior lamellar corneal tissue. Same size lamellar donor disk was prepared and placed in position without the need of suture fixation. Best spectacle-corrected visual acuity (BSCVA), refraction, endothelial cell density, corneal topography, and corneal thickness were analyzed. Average BSCVA preoperative was 20/200 (range 20/40 to hand movements (HM)), improving to 20/50 (range 20/20 to 20/120) at a mean follow-up of 7.2 months. Average refractive astigmatism at last follow-up was 1.46+/-1.21 diopters (range, 0 to 4 diopters). Preoperative average donor endothelial cell density was 2047+/-311 cells/mm2, and that at last follow-up was 1732+/-514 cells/mm2. Preoperative average pachymetry was 801.4+/-211.3 microm, improving to 553+/-90.4 microm at last follow-up. Initial results with small incision DLEK procedure indicate that it is a safe procedure that provides healthy donor endothelial cell count and function postoperatively, with encouraging visual results.

Finite-Element Modeling of Posterior Lamellar Keratoplasty: Construction of Theoretical Nomograms for Induced Refractive Errors

Purpose: To estimate the theoretical corneal refractive error induced by mechanical weakening effects from posterior lamellar keratoplasty (PLKP) in the human cornea. Methods: The refractive effects of PLKP are simulated by finite-element modeling (FEM) as a mathematical function of the thickness of the excised posterior lamellar corneal button, with a nonlinear formulation of stress-strain relation for the corneal material. A theoretical nomogram was developed to correlate the refractive changes to button thickness. Results: The predicted refractive change after PLKP is less than 1 dpt for a 170-µm thickness posterior corneal button over a broad range of Young’s modulus.Thicker buttons result in greater surgically induced refractive errors. Conclusions: According to FEM analysis, the excision of a posterior lamellar button of less than 170 µm thickness produces a minimal predicted refractive change (<1 dpt) in the cornea after PLKP.

Depth predictability of stromal pockets in the posterior cornea.

To evaluate the predictability of the depth of stromal pockets made in the posterior cornea for the excision of anterior or posterior lamellar corneal buttons with a planned thickness. Stromal corneal pocket dissections were created in human eye bank eyes by making a peripheral arcuate keratotomy incision at 60, 80, or 95% of central pachymetry and creating a pocket from the bottom of the incision across the cornea. Pocket depth was measured by pachymetry immediately after surgery and by light microscopy. Mean achieved central pocket depth differed by 0.03+/-0.03 mm from the intended depth. Variation in depth across the pocket decreased from 0.07+/-0.02 mm for pockets made at 60% of the intended depth to 0.05+/-0.01 mm for pockets made at 80% depth, and 0.04+/-0.02 mm for pockets made at 95% depth (p < 0.01). Pachymetric and histological measurements of relative pocket depth averaged 64+/-9% and 73+/-7%, respectively, for pockets made at 60% of the intended depth, 82+/-7% and 86+/-3% for pockets made at 80% depth, and 91+/-7% and 92+/-3% for pockets made at 95% depth. The difference between pachymetric and histological relative pocket depth measurements decreased with deeper pocket depth (p < 0.01). In the posterior cornea, stromal pockets can be created to within 30 microm from the intended depth. Variation in depth throughout the pocket decreases with deeper pocket depth. Pachymetry is a reliable method to check the achieved pocket depth during surgery; the accuracy of pachymetry readings improves with deeper pocket depth.