Split cornea transplantation: relationship between storage time of split donor tissue and outcome. Ophthalmology. 2013;120:899-907. [PMID: 23399381 DOI: 10.1016/j.ophtha.2012.11.012]

Challenges of DMEK Technique with Young Corneal Donors' Grafts: Surgical Keys for Success-A Pilot Study

PURPOSE

To report on the surgical maneuvers recommended for a successful unfolding of very young donors in order to accomplish an uneventful Descemet Membrane Endothelial Keratoplasty (DMEK) surgery.

METHODS

Five patients (three females and two males, mean age 71.2 ± 6.7 years) with Fuchs endothelial cell dystrophy who underwent DMEK with very young donors (between 20 and 30 years old) were included. The following demographic data were assessed: donor's age, donor's endothelial cell density (ECD), preservation time, recipient's age and sex and unfolding surgical time. Best-corrected visual acuity (BCVA; decimal system), ECD and corneal central thickness (CCT) were assessed preoperatively and at 6-month follow-up.

RESULTS

Donors' mean age was 23.6 ± 3.6 years (range 21 to 30) and the mean ECD was 2748.6 ± 162.6 cells/mm2. All of them underwent an uneventful DMEK as a single procedure performed by one experienced surgeon (MAG) with a mean unfolding time of 7.2 ± 4.9 min (range 4 to 15). The essential steps, including patient preparation as well as DMEK graft implantation, orientation, unrolling and centering are detailed. At 6 months, BCVA was 0.6 ± 0.2, ECD was 1945.0 ± 455.5 cells/mm2 and CCT was 497.0 ± 19.7 microns.

CONCLUSIONS

We hereby present the keys to overcome tightly scrolled grafts of very young donors, which prove perfectly suitable for DMEK surgery. The graft shape tends towards a double-roll and specific maneuvers are strongly recommended.

Microbiological Testing of Split-Cornea Transplantation

PURPOSE

By splitting a donor cornea into an anterior and a posterior donor lamella, the need for donor tissue can be reduced in times of lack of donors. Current eye bank regulations limit the use of each donor cornea to one recipient.

METHODS

The anterior lamella not applied to the patient after each sterile DMEK preparation performed was stored for one week and was microbiologically controlled on day 7.

RESULTS

Between October 2020 and December 2021, microbiological controls of 108 consecutive anterior lamellae were performed at the Department of Ophthalmology, University of Duesseldorf, without any contamination found.

CONCLUSION

Our data suggest split-cornea transplantation is a microbiologically safe procedure.

Effect of Collagenase A on Descemet Membrane Endothelial Keratoplasty Scroll Tightness

PURPOSE

The scrolling properties of the Descemet membrane endothelial keratoplasty (DMEK) graft are essential for surgical success. Currently, there is limited knowledge on what dictates the tightness of the DMEK scroll. The purpose of this study was to determine the impact of temperature and protein digestion on DMEK graft scroll tightness.

METHODS

For the temperature experiment, a total of 28 eyes were used for this study. Scrolls in the cold group were kept at 4°C while scrolls in the hot group were kept at 37°C. Scroll width was recorded at the 5-, 15-, and 30-minute mark. For the protein digestion experiment, a total of 18 eyes were exposed to collagenase A (10 CDU/mL) in Optisol solution. Scroll width was recorded at the time points of 1, 3, 5, 10, and 20 minutes.

RESULTS

The results of the temperature experiment did not yield any statistically significant changes in the mean scroll width of the DMEK scrolls across both temperature ranges and observation times. For the protein digestion experiment, the mean scroll width grew from 1.85 mm to 2.13 mm from the beginning of the experiment until the final observation at 20 minutes. This is a 14.7% change over 20 minutes with a P value (<0.001), exemplifying a statistically significant change in scroll width.

CONCLUSIONS

Temperature did not have any significant effect over scroll tightness, but scroll tightness decreased with collagenase exposure.

Preincubation of donor tissue with a VEGF cytokine trap promotes subsequent high-risk corneal transplant survival

AIMS

Pathological neovascularisation of the host bed and the transplant itself is the main risk factor for graft rejection after corneal transplantation. This study aims to prevent this process by preincubation of the corneal donor tissue ex vivo with an antivascular endothelial growth factor (VEGF) cytokine trap blocking additional postsurgical hemangiogenesis and lymphangiogenesis to promote high-risk graft survival.

METHODS

The donor tissue was preincubated with a VEGFR1R2 cytokine trap for 24 hours prior to murine high-risk corneal transplantation (human IgG Fc was used as the control). The distribution of VEGFR1R2 Trap in the cornea was investigated by immunohistochemistry. Corneas were excised to quantify the blood vessels (BVs) and lymphatic vessels (LVs) and draining lymph nodes (dLNs) were harvested to analyse the phenotype of dendritic cells (DCs) and T cells at week 1, 2 and 8 post-transplantation. Graft survival was compared between preincubation with VEGFR1R2 Trap and human IgG Fc in high-risk recipients.

RESULTS

VEGFR1R2 Trap was present in the graft for at least 2 weeks after surgery and additionally diffused into the corneal recipient. BVs, LVs and macrophages in the whole cornea were significantly decreased 1-week and 2-week post-transplantation (p<0.05). In dLNs the frequency of CD11c+DCs was significantly reduced, whereas CD200R+ regulatory DCs were significantly increased after keratoplasty (p<0.05). Furthermore, long-term high-risk graft survival was significantly improved (p<0.01).

CONCLUSIONS

Preincubation of corneal donor tissue with a VEGFR1R2 cytokine trap can significantly promote subsequent high-risk corneal transplant survival and thereby opens new treatment avenues for high-risk corneal transplantation.

Does Storage Time Affect the Outcomes of Split Corneal Transplantation to Reduce Corneal Donor Shortage? A Retrospective Study

Split cornea transplantation can reduce the shortage of donor corneas. Therefore, this study aimed to evaluate the effect of split graft storage time on the outcomes of split corneal transplantation through Descemet membrane endothelial keratoplasty (DMEK) and deep anterior lamellar keratoplasty (DALK) surgeries. Split corneal transplantation was performed in 80 eyes using 41 donor corneas. The mean before and after splitting storage times and total storage times were recorded. Donor corneal buttons and split grafts were stored in short-term solution at 4°C. In both surgeries (DMEK and DALK), donor corneas were divided into groups depending on their storage times. Mean postoperative 12th month best corrected visual acuity (BCVA), endothelial cell density (ECD), endothelial cell loss (ECL), central corneal thickness (CCT), refractive spherical equivalent (RSE), refractive astigmatism, and complication rates were compared among the groups. Correlation between storage times and 1-year BCVA, ECL, and complication rates were assessed. Clinical outcomes of the groups 1 year after the surgeries were also compared. DALK and DMEK were performed in 41 and 39 eyes, respectively. Storage times were not correlated with 1-year DMEK outcomes and only weakly correlated with post-DALK ECD, ECL, and RSE values. Except for CCT in those that underwent DALK, the outcomes of DMEK and DALK surgeries with stored and non-stored split grafts were not significantly different (P = .02). The storage times of donor corneas and split grafts do not have any impact on outcomes.

[Efficient Use of Corneal Grafts through Multimodal Donor Tissue Splitting]

BACKGROUND

The reduced availability of corneal donor tissue in Ukraine requires the most effective use of the available grafts. The present work describes and evaluates a method to obtain several small diameter corneal grafts from a single donor cornea ("multimodal donor tissue splitting").

MATERIAL AND METHODS

This retrospective cohort study includes keratoplasty procedures performed at the Department of Corneal Pathology, State Institution, "The Filatov Institute of Eye Diseases and Tissue Therapy of the National Academy of Medical Sciences of Ukraine", Odessa, Ukraine. The method of graft preparation includes either lamellar dissection of the entire graft or partial lamellar dissection to obtain two lamellar and/or full-thickness grafts. Grafts were not only cut in a circular manner, but the individual shape was also adjusted to match the shape of non-circular corneal defects.

RESULTS

A total of 324 keratoplasties between January 2016 and December 2017, using 270 grafts, were included. In 54 cases (including 34 emergency situations), one transplant was used for two recipients. Of these, 43 were therapeutic keratoplasties and 11 peripheral lamellar keratoplasties due to grade III - IV recurrent pterygia. In two cases, two grafts for one patient were dissected from a single donor cornea. Out of 43 patients with curative keratoplasty, visual acuity improved in 28 eyes (65.1%) or remained unchanged in 15 eyes (34.9%). Postoperative visual acuity was dependent on the initial state of the eye, the localisation, the depth and the area of the corneal defect. In eyes with peripheral corneal localisation of ulcerations, even in the presence of corneal perforation, good functional results were obtained.

CONCLUSION

If two or more grafts are obtained from a single donor cornea for different kinds of keratoplasty procedures, this reduces the need for corneal graft tissue and, consequently, the cost of preservation. Especially in regions with a high shortage of donor tissue, this provides additional tissue capacities for emergency situations.

Mechanical Stability of Cryopreserved Split-Thickness Tectonic Corneal Grafts

PURPOSE

To evaluate the influence of cryopreservation on the pressure-strain relationship of microkeratome dissected anterior stromal grafts (ASGs).

METHODS

Partial thickness ASGs were created from 7 pairs of human corneas and randomized to immediate grafting or grafting after 3 months of cryopreservation at -80°C into a whole globe ex vivo corneal perforation model. High frequency ultrasound speckle tracking was used to calculate the cross-sectional axial and lateral strains in each graft at increasing intraocular pressure (IOP) from 5 to 30 mm Hg. The mean axial and lateral strains were compared between the paired groups.

RESULTS

The mean axial and lateral strains were not significantly different between the cryopreserved and noncryopreserved ASGs. The mean lateral strains at 30 mm Hg in the noncryopreserved and cryopreserved grafts were 2.4% ± 2.1% and 1.4% ± 0.7% (P = 0.294), respectively. The mean axial strains at 30 mm Hg in the noncryopreserved and cryopreserved grafts were -7.8% ± 3.3% and -5.5% ± 3.0% (P = 0.198), respectively. A linear pressure-strain relationship was found for all grafts at physiologic IOP.

CONCLUSIONS

ASGs cryopreserved at -80°C maintain their IOP-strain relationship compared with noncryopreserved ASGs at physiologic pressures, supporting the potential use of cryopreserved human corneal stroma for patch grafting procedures.

Outcome of Descemet Membrane Endothelial Keratoplasty Using Corneas from Donors ≥80 Years of Age

PURPOSE

The purpose of this study was to investigate whether corneas from donors ≥80 years old are suitable for Descemet membrane endothelial keratoplasty (DMEK).

DESIGN

Retrospective, comparative, interventional case series.

METHODS

Records of 1,765 consecutive DMEKs were reviewed and matched with corresponding donor tissue data. Older donors (≥80 years of age) were compared to younger donors (<80 years). Outcome measurements in DMEK recipients included best spectacle-corrected visual acuity (BSCVA), endothelial cell density (ECD), central corneal thickness (CCT) at 3 and 6 months and at 1, 2, and 3 years' follow-up and re-bubbling rates.

RESULTS

Of 1,748 DMEKs, 284 (16.2%) were performed with older donor lamellae (mean donor age, 83.96 ± 3.19 years; range, 80-94 years) and 1,464 (83.7%) with younger donor tissue (mean donor age, 65.27 ± 9.57 years; range, 17-79). BSCVA results were comparable for all postoperative time points. CCT results for younger donors were more favorable in the early postoperative course (P < 0.001 at 6 months; and P < 0.001 at 1 year), whereas mid-term results were comparable in both groups. ECD values were significantly higher in donors <80 years of age preoperatively and during the first 2 postoperative years (P ≤ 0.024). Overall re-bubbling rates were comparable in both groups.

CONCLUSIONS

Older donors, ≥80 to 94 years of age, seem to produce comparable mid-term functional results following DMEK surgery compared to younger donors. The use of corneas from donors aged ≥80 for DMEK surgery may therefore be a promising approach to counteract global donor shortage.

Approaches toward enhancing survival probability following deep anterior lamellar keratoplasty

The greatest advantage of deep anterior lamellar keratoplasty over full-thickness corneal transplantation is the elimination of graft failure caused by endothelial rejection. Despite this advantage, a deep anterior lamellar keratoplasty graft can fail because of several factors, such as complications related to the donor-recipient interface, graft epithelial abnormalities, graft vascularization, stromal graft rejection, and recurrence of herpetic keratitis. Increased deep anterior lamellar keratoplasty graft survival is mainly built upon optimization of the ocular surface to provide a hospitable environment for the graft. Any predisposing factors for graft epithelial abnormalities, corneal neovascularization, and preexisting vernal keratoconjunctivitis should be identified and treated preoperatively. Prompt recognition and appropriate treatment of interface-related complications and stromal graft rejection usually result in good anatomic outcomes, with no detrimental effects on vision.

Descemet membrane endothelial keratoplasty (DMEK): an update on safety, efficacy and patient selection

Descemet membrane endothelial keratoplasty (DMEK) is gaining popularity worldwide as a procedure to address corneal endothelial dysfunctions. Its perfect anatomical result improves outcomes and expedites visual recovery. This review addresses important aspects of safety, efficacy and patient selection.

Postoperative pain following Descemet membrane endothelial keratoplasty (DMEK): a prospective study

PURPOSE

To evaluate postoperative pain following Descemet membrane endothelial keratoplasty (DMEK).

METHODS

Seventy-one patients completed perioperatively (day before surgery, day of surgery, 1st, 2nd, and 3rd day after surgery) four different questionnaires (a hospital internal protocol, QUIPS, PainDETECT®, and SF36) regarding their pain and other clinical parameters such as constipation, tiredness, vertigo, sleep disorders, concentration disorders, nausea, and emesis. All standardised questionnaires were evaluated to quantify average pain intensity as well as maximum pain intensity (NRS, 0 [no pain] to 10 [maximal pain], respectively). Analgesic treatment and intraocular pressure (IOP) during the perioperative stay were documented.

RESULTS

Mean average pain intensity was 0.70 ± 1.64 before surgery, 1.97 ± 2.05 on the day of surgery, 1.39 ± 1.68 on day 1, 0.87 ± 1.36 on day 2, and 0.81 ± 1.24 on day 3 after surgery. Maximum pain intensity was 0.65 ± 1.81 before surgery, 3.35 ± 2.98 on the day of surgery, 2.68 ± 2.99 on day 1, 1.49 ± 2.15 on day 2, and 1.26 ± 2.02 on day 3 after surgery. During the first three postoperative days, over 90% of the patients stated no or well tolerable pain. Eighty-three percent had postoperatively no need for analgesics at all. On the first two postoperative days, maximum IOP correlated significantly with reported increased maximum pain intensity (p = 0.043 and p = 0.029, respectively). All patients had very little problems with constipation, tiredness, vertigo, sleep disorder, concentration disorders, nausea, and emesis.

CONCLUSIONS

DMEK is associated with low postoperative pain intensity. Strong pain increase may indicate IOP elevation and should be further investigated and treated.

CLINICAL TRIAL REGISTRATION

German Clinical Trial Register (DRKS00013995).

Descemet's Membrane Endothelial Keratoplasty with Split Corneal Grafts: The Influence of Tamponade Material and Endothelial Storage Time

Purpose: The aim of this study was to describe the clinical outcome of Descemet's membrane endothelial keratoplasty (DMEK) performed with split corneal grafts and to evaluate the influence of tamponade material and endothelial storage time on DMEK success. Material and Method: The records of 43 patients who underwent DMEK surgery with a split corneal graft were reviewed. Diagnosis of the patients, preoperative and postoperative best-corrected visual acuity (BCVA), corneal and endothelial storage time, tamponade material, complications, and success rates were specifically tabulated. Results: The most common indication for DMEK was pseudophakic bullous keratopathy (n = 25, 58.2%). Re-bubbling was needed in 10 cases (23.2%), and a re-DMEK was scheduled in 2 cases and penetrating keratoplasty in 4 cases (9.3%). BCVA improved significantly postoperatively (p < .001). There was an insignificant trend towards a lower re-bubbling rate and better long-term anatomic outcome in favor of 20% SF6 group compared to air tamponade (p = .18 and p = .25). There was no significant difference between the early endothelial transplant (<24 h) and delayed endothelial transplant (3 to 14 days) groups for anatomic success, corneal thickness or BCVA (p = .94, p = .13 and p = .35). Conclusion: The success rate of DMEK was satisfactory with split corneal grafts. There was no adverse influence of delayed endothelial transplantation on clinical outcome. The success rate of 20% SF6 tamponade was slightly better than room air.

[10 years of Descemet membrane endothelial keratoplasty in Fuchs endothelial corneal dystrophy : What have we learned?]

BACKGROUND AND OBJECTIVE

Descemet membrane endothelial keratoplasty (DMEK) has increased in popularity since its introduction over 10 years ago. This article presents a summary of the experiences of the past years collected at the Department of Ophthalmology at the University of Cologne.

METHODS

A literature review of DMEK studies primarily from the Department of Ophthalmology at the University of Cologne, Germany was carried out. Own experiences in the fields of donor selection and graft preparation, DMEK surgery, complication management and postoperative treatment are summarized.

RESULTS

Since the introduction of DMEK experience has been gained and ongoing improvements have occurred ranging from donor-recipient allocation to postoperative follow-up. These led to a better reproducibility of the intervention for the surgeon, to a better postoperative result and to a reduction of the complication rate.

DISCUSSION

The DMEK represents a safe and individualized procedure for endothelial transplantation for corneal endothelial dysfunction. Continuing development of the method leads to optimization and safer results.

Immune reactions after modern lamellar (DALK, DSAEK, DMEK) versus conventional penetrating corneal transplantation

In the past decade, novel lamellar keratoplasty techniques such as Deep Anterior Lamellar Keratoplasty (DALK) for anterior keratoplasty and Descemet stripping automated endothelial keratoplasty (DSAEK)/Descemet membrane endothelial keratoplasty (DMEK) for posterior keratoplasty have been developed. DALK eliminates the possibility of endothelial allograft rejection, which is the main reason for graft failure after penetrating keratoplasty (PK). Compared to PK, the risk of endothelial graft rejection is significantly reduced after DSAEK/DMEK. Thus, with modern lamellar techniques, the clinical problem of endothelial graft rejection seems to be nearly solved in the low-risk situation. However, even with lamellar grafts there are epithelial, subepithelial and stromal immune reactions in DALK and endothelial immune reactions in DSAEK/DMEK, and not all keratoplasties can be performed in a lamellar fashion. Therefore, endothelial graft rejection in PK is still highly relevant, especially in the "high-risk" setting, where the cornea's (lymph)angiogenic and immune privilege is lost due to severe inflammation and pathological neovascularization. For these eyes, currently available treatment options are still unsatisfactory. In this review, we will describe currently used keratoplasty techniques, namely PK, DALK, DSAEK, and DMEK. We will summarize their indications, provide surgical descriptions, and comment on their complications and outcomes. Furthermore, we will give an overview on corneal transplant immunology. A specific focus will be placed on endothelial graft rejection and we will report on its incidence, clinical presentation, and current/future treatment and prevention options. Finally, we will speculate how the field of keratoplasty and prevention of corneal allograft rejection will develop in the future.

Evolution of Consecutive Descemet Membrane Endothelial Keratoplasty Outcomes Throughout a 5-Year Period Performed by Two Experienced Surgeons

PURPOSE

To assess the evolution of clinical outcomes of more than 1300 Descemet membrane endothelial keratoplasties (DMEKs) alone or in combination with cataract surgery (triple DMEK) throughout a 5-year period at a single center, performed by 2 already experienced DMEK surgeons.

DESIGN

Retrospective trend study.

METHODS

Review of charts between July 2011 and July 2016 at the Department of Ophthalmology, University of Cologne, Germany.

RESULTS

A total of 1340 out of 1340 eyes with sufficient information were included. Six-month and 12-month best spectacle-corrected visual acuity (logMAR) had already reached high levels for the surgeries performed in 2011 (0.10 ± 0.06 and 0.09 ± 0.07, respectively) and did not further improve in later years (P = .272). Likewise, endothelial cell loss (ECL) and central corneal thickness (CCT) reached comparable levels independently of the year of surgery (average 12-month ECL was 38% ± 15% and average 6-month CCT decrease was 19% ± 11%). However, there was a decrease in the rebubbling rate, from 68% in 2011, 67% in 2012, and 70% in 2013 to 53% in 2014, 29% in 2015, and 16% in 2016, which was associated with the introduction of 20% sulfur hexafluoride (SF₆) instead of room air for anterior chamber tamponade in 2015 (n = 986; P < .001). The percentage of severe complications after DMEK surgery also decreased significantly with surgeons' growing experience (P < .001; 95% confidence interval [0.09; 0.12]) over the years.

CONCLUSIONS

After an initial learning curve in DMEK surgery, results of visual acuity and ECL do not seem to further improve. However, the complication rate continuously declines, at least over the subsequent 5-year period analyzed herein.

Impact of donor graft quality on deep anterior lamellar Keratoplasty (DALK)

Background

To evaluate main features of donor tissue that may influence clinical outcome or complication rate after deep anterior lamellar keratoplasty (DALK).

Methods

Donor tissue parameters of 84 consecutive corneal donor grafts used for big-bubble DALK surgery between June 2011 and December 2014 in 84 eyes of 84 patients with disorders of anterior corneal stroma were correlated to clinical outcome parameters of recipient eyes 12 months after surgery and 3 months after total suture removal. Main donor tissue parameters included age), post-mortem time, overall preservation time, preservation time after split and prior to transplantation, and preservation technique. Clinical outcome parameters included best spectacle corrected visual acuity (BSCVA), central corneal thickness (CCT), endothelial cell density (ECD) and complication rates. Pearson’s correlation, linear regression analysis for clinical outcome parameter and logistic regression analysis for postsurgical complication rates were applied.

Results

Corneal donors were mean aged 67.4 ± 12.5 years with a post-mortem time of 20.7 ± 14.7 h and ECD of 2641.0 ± 362.8 cells/mm². Overall preservation time was 16.3 ± 6.3 days. Recipients showed mean BSCVA 12 months postoperatively of 0.60 ± 0.36 logMAR, endothelial cell loss was 4 ± 16%, and central corneal thickness was 571.7 ± 54.2 μm. 3 months after total removal of sutures, BSCVA was 0.20 ± 0.10 logMAR, endothelial cell loss was 17 ± 24%, and central corneal thickness was 590.9 ± 55.5 μm. Loosening of sutures occurred in 20%, and Descemet detachment in 16%. None of the clinical outcome parameters or complication rate after DALK showed a significant association with donor tissue parameters.

Conclusions

Donor corneas, independent of excision techniques or preservation method, with donor age ≤ 88 years, post-mortem time ≤ 63 h, overall preservation time ≤ 14 days for cold storaged donor tissue and ≤35 days for organ culture, and preservation time after split prior to grafting ≤96 h, seem to be applicable as safe donor tissue for DALK surgery.

A comparative study: deep anterior lamellar keratoplasty for corneal dystrophies using two different donor stromal tissues

PURPOSE

This study aimed to present a comparison of early postoperative results of deep anterior lamellar keratoplasty (DALK) surgery performed using the two different corneal graft sources.

MATERIALS AND METHODS

This retrospective clinical study included the surgery performed on 26 eyes of 26 patients who underwent DALK for the stromal dystrophies. At the time of surgery, donor stromal tissue for DALK was sourced using the two different preparatory techniques. For 14 cases (Group 1), the donor grafts were prepared quickly by removing the descemet's membrane (DM) without much care after the exposure of the bare DM in the recipient cornea. For 12 cases (Group 2), the grafts for DALK surgery had already been prepared during a previous descemet's membrane endothelial keratoplasty (DMEK).

RESULTS

The groups differed statistically regarding the blue staining of the grafts at the time of surgery and on the first day post-DALK. The first day after surgery, 14 (100%) grafts were clear in Group 1, while eight (66.7%) grafts were clear and four (33.3%) were edematous in Group 2 (p = 0.019). Bubbling was performed in three (25.0% of Group 2) of the four cases on the first day post-DALK, while none of the patients in Group 1 underwent this procedure (p = 0.47). The postoperative increase in visual acuity was higher in Group 1 in the early postoperative period (p = 0.012).

CONCLUSION

During the early postoperative period, complications (as graft edema, detachment, re-bubbling) were observed more frequently in the DALK operations performed with stromal tissue having blue stain remaining from the DMEK performed on the same day and in the same session.

Paradigm shifts, peregrinations and pixies in ophthalmology

Human ingenuity is challenged by defending vision, our highest bandwidth sense. Special challenges are presented by the replacement or repair of highly specialized but scarce tissue within the constraints of transparency, tissue shape and alignment, tissue borders and pressure maintenance. Many, mostly destructive, surgical procedures were developed prior to an understanding of underlying pathophysiology. For a number of conditions, both reconstructive and destructive procedures co-exist, yet there are few guidelines as to the better approach. Because the consequences of these procedures may take many years to surface (consistent with a stem cell role in long-term tissue maintenance), guidance may be provided by the elucidation of underlying principles from these approaches. Illustrative examples from clinical, basic research and biotechnology, particularly relating to pterygium, ocular surface squamous neoplasia, dry-eye syndrome, corneal rehabilitation and replacement, cataract surgery, strabismus surgery and bionic eye research, are described. An unexpected consequence of bionic device development has been an appreciation of the sophistication of tissues being replaced, given the limitations of available biomaterials. Examples of how this has provided insights into ocular disease will be illustrated. Stem cell and biomaterial technologies are starting to impact at a time when cost-effectiveness is under scrutiny. Both efficacy and cost will need to be considered as these interventions are introduced. It appears that the paradigm shift rate is accelerating and there is evidence of this in ophthalmology. Lessons learned from the areas of destructive versus reconstructive surgery and the limitations of development of bionic replacements will be used to illustrate how new procedures and technologies can be developed.

Two-Year Course of Corneal Densitometry After Descemet Membrane Endothelial Keratoplasty

PURPOSE

To investigate the 2-year course of corneal densitometry following Descemet membrane endothelial keratoplasty (DMEK) for Fuchs endothelial dystrophy (FED).

DESIGN

Retrospective, interventional case series.

METHODS

Densitometry values (corneal light backscatter in grayscale units) measured by Scheimpflug-based imaging and clinical records of 160 eyes of 160 patients undergoing DMEK for FED were reviewed. Outcome measures included densitometry data in 4 corneal layers (anterior layer [AL], central layer [CL], posterior layer [PL], and total layer [TL]) and 2 annuli (central annular zone 0-2 mm and peripheral zone 2-10 mm), central corneal thickness (CCT), best spectacle-corrected visual acuity (BSCVA), and endothelial cell density (ECD) prior to DMEK and at 1, 3, 6, 12, and 24 months postoperatively.

RESULTS

Corneal densitometry decreased in all 4 layers over 2 years after DMEK surgery. Regarding TL 0-2 mm, the reduction of corneal light backscatter was statistically significant for all follow-up time points compared with preoperative values (P < .001) and compared in between follow-up periods (P ≤ .010). Corneal light backscatter reduction was significantly higher in the center (0-2 mm) than in the periphery (2-10 mm) for all layers at 12 and 24 months (P ≤ .002). ECD and CCT did not correlate with corneal densitometry, whereas BSCVA correlated moderately for TL 0-2 mm (P = .026; r = 0.449) and TL 2-10 mm (P = .001; r = 0.585) at 12 months.

CONCLUSIONS

Corneal light backscatter showed a significant reduction after DMEK surgery in Fuchs endothelial dystrophy over a period of 2 years, more pronounced in the corneal center, apparently in association with visual acuity improvement.

[Update: Deep anterior lamellar keratoplasty (DALK) for keratoconus. When, how and why]

BACKGROUND

The treatment of keratoconus has been significantly expanded in recent years. In addition to the previous options for correction by fitting hard contact lenses and penetrating keratoplasty (PK), corneal cross-linking and lamellar transplantation techniques have been added.

OBJECTIVE

The aim of this review article is to highlight currently available options for minimization of complications and standardization of deep anterior lamellar keratoplasty (DALK) for keratoconus.

MATERIAL AND METHODS

This article summarizes our own data and gives a review of the literature in PubMed.

RESULTS

Performing DALK can provide keratoconus patients with corneal grafts with considerably longer graft survival and a reduced risk of complications.

CONCLUSION

The DALK procedure provides numerous advantages over PK, especially the reduced intraoperative opening of the eye, which thus reduces the risk of serious intraoperative complications. A further benefit is the complete absence of postoperative endothelial immune reactions as the recipient's endothelium remains untouched. The absence of endothelial immune reactions is especially advantageous for young patients with keratoconus and patients with an increased risk of graft rejection, e.g. in atopic dermatitis; however, there are also typical complications of DALK that do not occur during PK. The outlined strategies for standardization of DALK and avoidance of intraoperative and postoperative complications should make DALK safer and more reproducible and lead to possible establishment as a standard procedure in keratokonus.

[Complications of deep anterior lamellar keratoplasty. Avoid, recognize and treat]

Deep anterior lamellar keratoplasty (DALK) offers tremendous advantages over penetrating keratoplasty (PK). Intraoperative safety is increased due to reduced opening of the eye interoperatively and the fact that no endothelial graft rejection can take place as the patient's own corneal endothelium is retained. Despite these advantages the number of DALK procedures performed each year in Germany remains constant at a low level. One reason could be that the DALK technique offers some complexity and at the same time intraoperative conversion to PK has to be performed in some cases due to rupture of Descemet's membrane. Moreover, interface-related and DALK-specific complications exist which can contribute to an unfavorable visual outcome. Most of these complications, such as incomplete attachment of Descemet's membrane or opacification within the interface between Descemet's membrane and the posterior corneal stoma can be resolved by adequate measures making PK for revision barely necessary. As visual acuity does not differ between PK and DALK, the benefits of DALK - lack of endothelial immune reaction and increased ocular stability during surgery - outweigh the risk of additional complications and DALK should therefore be performed whenever appropriate.

Impact of Donor Age on Descemet Membrane Endothelial Keratoplasty Outcome: Evaluation of Donors Aged 17-55 Years

PURPOSE

To investigate whether the impression held by Descemet membrane endothelial keratoplasty (DMEK) surgeons that young donors are less suitable for DMEK is reflected in 1-year postoperative results.

DESIGN

Retrospective, comparative, interventional case series.

METHODS

Records of 1084 consecutive DMEKs were reviewed and matched with corresponding donor tissue data. Young donors (aged ≤55 years; subgroups: 10-40, 41-55) were compared with old donors (>55 years; subgroups: 56-65, >65). Outcome measures in DMEK recipients included best spectacle-corrected visual acuity (BSCVA), endothelial cell density (ECD), central corneal thickness (CCT) at 6 and 12 months, and rebubbling rate.

RESULTS

Out of 529 included DMEKs, 94 (17.8%) were performed with young donor lamellae (mean donor age 49.31 ± 6.35 years; range: 17-55 years) and 435 (82.2%) with older donor tissue (mean age 70.68 ± 7.77 years; range: 56-90 years). Postoperative BSCVA, ECD, and CCT results were comparable in both groups at 6 and 12 months without statistically significant differences. Overall rebubbling rate in the young donor group was 42.6% and in the old donors was 53.3% (P = .058). Complication rates also did not differ significantly.

CONCLUSION

Younger donor age seems not to affect the clinical outcome of DMEK surgery negatively within the first postoperative year, suggesting donor corneas with donor age down to 17 years as safe donor tissue for DMEK surgery.

An Analysis of Factors Influencing Quality of Vision After Big-Bubble Deep Anterior Lamellar Keratoplasty in Keratoconus

PURPOSE

To identify causes of reduced visual acuity and contrast sensitivity after big-bubble deep anterior lamellar keratoplasty (DALK) in keratoconus.

DESIGN

Prospective interventional case series.

METHODS

This study included 36 eyes in 36 patients with keratoconus who underwent DALK using the big-bubble technique. A bare Descemet membrane was achieved in all cases. Univariate analyses and multiple linear regression were used to investigate recipient-, donor-, and postoperative-related variables capable of influencing the postoperative quality of vision, including best spectacle-corrected visual acuity (BSCVA) and contrast sensitivity.

RESULTS

The mean patient age was 27.7 ± 6.9 years, and the patients were followed for 24.6 ± 15.1 months postoperatively. The mean postoperative BSCVA was 0.17 ± 0.09 logMAR. Postoperative BSCVA ≥20/25 was achieved in 14 eyes (38.9%), whereas a BSCVA of 20/30, 20/40, or 20/50 was observed in 15 eyes (41.7%), 6 eyes (16.6%), and 1 eye (2.8%), respectively. Preoperative vitreous length was significantly associated with postoperative BSCVA (β = 0.02, P = .03). Donor-recipient interface reflectivity significantly influenced scotopic (β = -0.002, P = .04) and photopic (β = -0.003, P = .02) contrast sensitivity. The root mean square of tetrafoil was significantly negatively associated with scotopic (β = -0.25, P = .01) and photopic (β = -0.23, P = .04) contrast sensitivity. Recipient age, keratoconus severity, donor-related variables, recipient trephination size, and graft and recipient bed thickness were not significantly associated with postoperative visual acuity or contrast sensitivity.

CONCLUSION

Large vitreous length, higher-order aberrations, and surgical interface haze may contribute to poor visual outcomes after big-bubble DALK in keratoconus.

[Current treatment options with artificial corneas: Boston Kpro, Osteo-odontokeratoprosthesis, Miro Cornea® and KeraKlear®]

BACKGROUND

Although corneal transplant surgery in avascular normal risk eyes is becoming even more minimally invasive and successful, treatment options for difficult to treat patients with high risk eyes are still limited. In these cases HLA typed allogeneic transplants and artificial corneas (keratoprostheses) can be used.

METHODS

This article combines a review of the literature in PubMed and own clinical experiences on the use of artificial corneas in high risk eyes. Osteo-odontokeratoprosthesis (OOKP), Boston Kpro, Miro Cornea® and KeraKlear® corneas were used as clinical keratoprostheses.

RESULTS

Worldwide, the most experience exists for the use of Boston Kpro and OOKP in high risk eyes. Miro Cornea® and KeraKlear® are new procedures where only preliminary results are available and further evaluation is necessary. The longest experience and best anatomical long-term results have been achieved with OOKPs. Comparable cohorts are available for the Boston Kpro. The function of all keratoprostheses is threatened by secondary glaucoma. Implantation of the KeraKlear® prosthesis remains difficult. The Miro Cornea® shows an initially stable integration behavior.

CONCLUSION

Keratoprostheses, such as the Boston Kpro and OOKP are valid treatment options for eyes which are not open to therapy with allogeneic corneal transplantation. Modern implants such as KeraKlear® prosthesis and Miro Cornea® need further prospective clinical evaluation.

Graft epithelial defects after deep anterior lamellar keratoplasty

PURPOSE

The aim of this study was to report the incidence of epithelial defects and identify donor factors that might correlate with the presence of epithelial defects and graft reepithelialization time after a deep anterior lamellar keratoplasty (DALK).

METHODS

In this retrospective study, 283 consecutive keratoconic eyes underwent DALK using donor corneas of different qualities, ranging from fair to excellent. The donor data included age and sex, cause of death, death-to-preservation time, preservation-to-surgery time, epithelial and stromal status, endothelial cell density and morphology, and graft rating. On the first postoperative day, the corneal surface was carefully examined before and after the application of fluorescein stain, and the patients were followed up daily until complete reepithelialization occurred. A multivariate regression analysis was used to assess the correlation between donor characteristics and graft epithelial defects on postoperative day 1.

RESULTS

The mean donor and recipient ages were 33.5 ± 13.2 and 27.6 ± 7.9 years, respectively. Two hundred sixty-four (93.3%) grafts had epithelial defects on day 1. The epithelial defects completely healed after 3.5 ± 2.7 (range, 1-37) days. In the univariate analysis, the presence of epithelial defects on postoperative day 1 had a significant correlation with donor preservation-to-surgery time (P = 0.01), epithelial sloughing (P < 0.001), and graft rating (P = 0.004). In the multivariate analysis, only donor epithelial sloughing significantly influenced the presence of epithelial defects on postoperative day 1 (odds ratio = 9.26, P < 0.001).

CONCLUSIONS

Graft epithelial defects were very common after DALK. The epithelial status of donors was the only independent factor predictive of the surface integrity on the first postoperative day.

A year of cornea in review: 2013

PURPOSE

The goal of this study was to provide an update of significant corneal literature published in 2013.

DESIGN

This study is a systematic literature review.

METHODS

We conducted a systematic review of the English-language literature published from January 1, 2013, to December 31, 2013, using the following PubMed search and Medical Subject Headings terms: cornea transplantation, keratoplasty, Descemet membrane endothelial keratoplasty, Descemet stripping endothelial keratoplasty, cross linking, pre-Descemet's layer, Rho-associated kinase, keratoprosthesis, infectious keratitis, corneal dystrophy, corneal astigmatism, and keratoconus.

RESULTS

This review summarizes relevant and innovative original articles, review articles, and novel techniques from the following journals: American Journal of Ophthalmology, British Journal of Ophthalmology, Cornea, Graefe's Archive for Clinical and Experimental Ophthalmology, Investigative Ophthalmology & Visual Science, JAMA Ophthalmology, Journal of Cataract and Refractive Surgery, Journal of Refractive Surgery, and Ophthalmology. Case reports, abstracts, letters to the Editor, and unpublished work were excluded, as well as articles e-published ahead of print in 2012 that were discussed in the previous review. One hundred twenty-seven articles met the criteria for this review.

CONCLUSIONS

This review summarizes significant cornea-related literature from 2013.

Spontaneous long-term course of persistent peripheral graft detachments after Descemet's membrane endothelial keratoplasty

BACKGROUND

Peripheral corneal graft detachment after Descemet's membrane endothelial keratoplasty (DMEK) is a frequently occurring postoperative complication. The natural course of these persistent peripheral detachments over time is not known.

METHODS

166 patients were surveyed by slit-lamp-adapted optical coherence tomography (SL-OCT) directly after surgery, during first postoperative week, 4 weeks, 3, 6 and 12 months, postoperatively. Patients with a persistent peripheral graft detachment 4 weeks after DMEK (n=16) were observed for their spontaneous course up to 1 year postoperatively.

RESULTS

Persistent graft detachments could be characterised into two phenotypes: peripheral roll (n=11; 69%) and laminar detachment (n=5; 31%). Maximal length of the detachment did not change in peripheral rolls during observation period (12 months vs 4 weeks, 578±122 µm vs 593±106 µm, p=0.74), whereas laminar detachments spontaneously attached to the host's stroma (12 months vs 4 weeks, 0 µm vs 1088±295 µm, p≤0.001). Central corneal thickness and (peripheral) corneal thickness above the detached area did not significantly change in either group.

CONCLUSIONS

Persistent peripheral graft detachments after DMEK occurred in 10% of patients and had two distinct OCT-phenotypes. Peripheral rolls did not change during the first 12 months, postoperatively. By contrast, peripheral laminar detachments attached spontaneously even months after surgery. Corneal thickness reduction was only observed above peripheral laminar detachment, but not above peripheral rolls.

Effect of donor graft quality on clinical outcomes after deep anterior lamellar keratoplasty

PURPOSE

The aim of this study was to determine the effect of donor features, including age, death-to-preservation time, preservation-to-surgery time, graft rating, and endothelial cell features, on visual and refractive outcomes and complications occurring after deep anterior lamellar keratoplasty (DALK) in patients with keratoconus.

METHODS

In this retrospective study, 290 consecutive keratoconic eyes underwent DALK using donor corneas of different qualities, ranging from fair to excellent. Donor corneas were stored in intermediate-term storage medium. Donor data included age and sex, death-to-preservation time, preservation-to-surgery time, epithelial and stromal status, endothelial cell density and morphology, and graft rating. Postoperative outcomes included visual acuity, refractive error, epithelial problems, suture-related complications, graft rejection, and graft transparency. A multivariate regression analysis was used to assess the correlation between donor characteristics and postoperative outcomes.

RESULTS

Mean donor and recipient ages were 33.4 ± 13.1 and 27.7 ± 8.0 years, respectively. The mean follow-up period was 38.2 ± 20.2 months. The presence of epithelial defects on postoperative day 1 had a significant correlation with donor epithelial sloughing (R = 0.26, P < 0.001), preservation-to-surgery time (R = 0.21, P = 0.001), and graft rating (R = -0.17, P = 0.004). Graft stromal edema on postoperative day 1 was significantly correlated with donor epithelial sloughing (R = 0.31, P < 0.001), preservation-to-surgery time (R = 0.24, P < 0.001), and graft rating (R = -0.28, P < 0.001). Suture-related complications, graft rejection episodes, graft clarity, visual acuity, and refractive outcomes at the final follow-up examination were found to have no correlations with any donor factors.

CONCLUSIONS

The use of low-quality donors for DALK increased the rate of epithelial defects and stromal edema immediately postoperatively. However, the donor features had no influence on visual and refractive outcomes and complications.

Dehydration of corneal anterior donor tissue with polyethylene glycol (PEG)-enriched media

Anterior donor grafts (including scleral rim, without Descemet membrane) increase in thickness and become hazy upon storage in organ culture (OC) medium. Transfer of these grafts to standard dehydration media just before transplantation does not reduce their thickness to normal. Therefore, we assessed the efficacy of different media enriched with polyethylene glycol (PEG) as dehydrating agents for organ-cultured anterior donor grafts. Grafts were harvested and stored in the commercial OC medium 'Max' (without dextran) for 1 week, and subsequently dehydrated in the standard commercial dehydration medium 'Jet' (with dextran) supplemented with 4-20% PEG3350, or 'Max' supplemented with 20% PEG6000 and PEG20.000, or 5-20% PEG35.000. Central corneal thickness (CCT), as assessed by anterior segment-optical coherence tomography, and transparency were evaluated before, and at 1, 4 and 7 days of dehydration. Transfer of grafts after 1 week of OC (average 1,200 µm) to 'Jet' supplemented with PEG3350 revealed a concentration-dependent effect of dehydration; CCT was restored to normal (500-600 µm) when 10% PEG3350 was added. However, transparency was only temporarily restored; after 1 day, the grafts turned hazy. In contrast, grafts transferred to 'Max' supplemented with 20% PEG35.000 were transparent throughout the evaluation period, but were dehydrated to beyond normal levels (average 300 µm). 'Max' supplemented with 5% PEG35.000 dehydrated grafts to normal values and restored transparency throughout. Thus, dehydration of anterior donor grafts prior to surgery in dextran-free OC medium supplemented with 5% PEG35.000 reduces graft thickness to normal and may facilitate anterior keratoplasty procedures.

Donor cornea quality used for penetrating keratoplasty vs deep anterior lamellar keratoplasty

Deep anterior lamellar keratoplasty (DALK) has recently been introduced as an alternative procedure to penetrating keratoplasty (PK) for corneal pathologies not affecting the corneal endothelium. DALK does not rely on donor endothelium and requires less rigid criteria for donor corneal tissue quality. Therefore, DALK makes it possible to use donor corneas deemed unsuitable for PK. Furthermore, lamellar keratoplasty allows acellular corneal tissue to be transplanted. As a result, long-term preservation techniques are being revisited to increase the availability of donor corneas and subsequently alleviate constraints of availability, cost, storage, and transportation in many countries. The recent alterations in corneal transplantation techniques and hence the type of donor cornea tissues used for each technique, may require corneal surgeons and eye banks to reevaluate their selection criteria. The purpose of this systematic review is to present an updated analysis on the type and quality of donor corneas used for PK and DALK, assess the influence of donor and eye bank factors on the quality of donor corneas, and determine whether any of these donor factors affect clinical outcomes, complications, and graft survivals.

A cost-minimization analysis of tissue-engineered constructs for corneal endothelial transplantation

Corneal endothelial transplantation or endothelial keratoplasty has become the preferred choice of transplantation for patients with corneal blindness due to endothelial dysfunction. Currently, there is a worldwide shortage of transplantable tissue, and demand is expected to increase further with aging populations. Tissue-engineered alternatives are being developed, and are likely to be available soon. However, the cost of these constructs may impair their widespread use. A cost-minimization analysis comparing tissue-engineered constructs to donor tissue procured from eye banks for endothelial keratoplasty was performed. Both initial investment costs and recurring costs were considered in the analysis to arrive at a final tissue cost per transplant. The clinical outcomes of endothelial keratoplasty with tissue-engineered constructs and with donor tissue procured from eye banks were assumed to be equivalent. One-way and probabilistic sensitivity analyses were performed to simulate various possible scenarios, and to determine the robustness of the results. A tissue engineering strategy was cheaper in both investment cost and recurring cost. Tissue-engineered constructs for endothelial keratoplasty could be produced at a cost of US$880 per transplant. In contrast, utilizing donor tissue procured from eye banks for endothelial keratoplasty required US$3,710 per transplant. Sensitivity analyses performed further support the results of this cost-minimization analysis across a wide range of possible scenarios. The use of tissue-engineered constructs for endothelial keratoplasty could potentially increase the supply of transplantable tissue and bring the costs of corneal endothelial transplantation down, making this intervention accessible to a larger group of patients. Tissue-engineering strategies for corneal epithelial constructs or other tissue types, such as pancreatic islet cells, should also be subject to similar pharmacoeconomic analyses.

[Standardized Descemet membrane endothelial keratoplasty (DMEK): technique and latest results]

BACKGROUND

The procedure of posterior lamellar keratoplasty has now become established as first choice therapy for the treatment of corneal endothelial diseases, with Descemet membrane endothelial keratoplasty (DMEK) as the most recent refinement of endothelial keratoplasty techniques. In this study the outcome of 400 consecutive cases after standardized no-touch DMEK was evaluated.

METHODS

This was a non-randomized retrospective clinical study of 400 consecutive eyes in 321 patients who underwent standard DMEK. Outcome measures included best corrected visual acuity (BCVA) preoperatively and postoperatively at 1, 3 and 6 months, endothelial cell density (ECD), pachymetry and complications within the first 6 months. In addition two subgroups were analyzed (subgroup I cases 1-200 and subgroup II cases 201-400).

RESULTS

At 6 months postoperatively 80 % of all eyes had a BCVA of ≥ 20/25 (≥ 0.8), 44 % of ≥ 20/20 (≥ 1.0) and 14 % of ≥ 20/18 (≥ 1.2). There were no significant differences between the two subgroups. The mean ECD preoperatively was 2,542 (± 217) cells/mm(2) and 6 months postoperatively 1,622 (± 500) cells/mm(2). The mean ECD decrease was 36 % 6 months after DMEK. No difference between the subgroups was noted. In 5 % a re-operation was needed of which 75 % were performed in subgroup I.

CONCLUSION

With the standardized no-touch DMEK technique a rapid and nearly complete visual rehabilitation as well as ECD values similar to earlier endothelial keratoplasty techniques can be achieved. Therefore DMEK may become the preferred treatment for corneal endothelial disorders.

[DALK and penetrating laser keratoplasty for advanced keratoconus]

BACKGROUND

In cases of contact lens intolerance and/or central corneal scars, corneal transplantation is indicated for advanced keratoconus. This can be performed as deep anterior lamellar keratoplasty (DALK) or as penetrating keratoplasty (PKP). The German keratoplasty registry shows that the proportion of anterior lamellar grafts in Germany has remained stable at approximately 5 % in recent years.

METHODS

Up to now DALK has not been technically standardized but can result in a good visual acuity using the big bubble technique if Descemet's membrane is laid bare intraoperatively. In 10-20 % a conversion to PKP is required if perforation of Descemet's membrane occurs. In cases of advanced keratoconus PKP is still the method of first choice especially after corneal hydrops due to rupture of Descemet's membrane. Non-contact excimer laser trephination seems to be especially beneficial for eyes with iatrogenic keratectasia after LASIK and those with repeat grafts in cases of keratoconus recurrence due to the graft being too small. For donor trephination from the epithelial side, an artificial chamber is used. Wound closure is achieved by a double running cross-stitch suture according to Hoffmann. Graft size is adapted individually depending on corneal size (as large as possible and as small as necessary). Limbal centration is given priority intraoperatively due to optical displacement of the pupil.

RESULTS

Prospective clinical studies have shown that the technique of non-contact excimer laser PKP improves donor and recipient centration, reduces vertical tilt and horizontal torsion of the graft in the recipient bed, thus resulting in significantly less all-sutures-out keratometric astigmatism (2.8 D versus 5.7 D), higher regularity of the topography (SRI 0.80 vs. 0.98) and better visual acuity (0.80 vs. 0.63) in contrast to the motor trephine. The stage of the disease does not influence functional outcome after excimer laser PKP.

CONCLUSIONS

In cases with optimal course DALK achieves the same visual outcome as mechanical PKP but the healthy endothelium can be preserved and endothelial immune reactions are prevented in keratoconus. In contrast to the undisputed clinical advantages of excimer laser keratoplasty with orientation teeth/notches in keratoconus, the major disadvantage of femtosecond laser application is still the necessity of suction and applanation of the cone during trephination.

Use of accidentally torn descemet membrane to successfully complete descemet membrane endothelial keratoplasty

PURPOSE

To describe the use of an accidentally torn Descemet membrane (DM) to successfully complete Descemet membrane endothelial keratoplasty (DMEK) surgery.

METHODS

Retrospective, observational case series of 3 eyes of 3 patients undergoing DMEK with a DM accidentally torn into 2 pieces during graft preparation. The mean outcome measures included best-corrected visual acuity, endothelial cell density, and central corneal thickness, before and at 1, 3, and 6 months after the DMEK surgery was performed.

RESULTS

During graft preparation, immediately before transplantation, a large tear within the 8.0-mm marking line of the DM occurred, resulting in a DM torn into 2 pieces. In all the eyes, both pieces were successfully implanted into the anterior chamber, unfolded and attached to the posterior corneal stroma, one after the other. Six months after the surgery was performed, the best-corrected visual acuity ranged between 20/30 and 20/25. Endothelial cell loss was about 30% (range 28%-32%) 6 months after the surgery. Pachymetry findings showed normal corneal thickness 6 months after the surgery. All corneas remained clear without any signs of graft failure within 6 months of follow-up.

CONCLUSIONS

DMEK surgery can be successfully completed despite the accidental tearing of donor DMs during the preparation of DMEK grafts by the sequential implantation of both DM pieces.

Epoxy cross-linked collagen and collagen-laminin Peptide hydrogels as corneal substitutes

A bi-functional epoxy-based cross-linker, 1,4-Butanediol diglycidyl ether (BDDGE), was investigated in the fabrication of collagen based corneal substitutes. Two synthetic strategies were explored in the preparation of the cross-linked collagen scaffolds. The lysine residues of Type 1 porcine collagen were directly cross-linked using l,4-Butanediol diglycidyl ether (BDDGE) under basic conditions at pH 11. Alternatively, under conventional methodology, using both BDDGE and 1-Ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as cross-linkers, hydrogels were fabricated under acidic conditions. In this latter strategy, Cu(BF₄)₂·XH₂O was used to catalyze the formation of secondary amine bonds. To date, we have demonstrated that both methods of chemical cross-linking improved the elasticity and tensile strength of the collagen implants. Differential scanning calorimetry and biocompatibility studies indicate comparable, and in some cases, enhanced properties compared to that of the EDC/NHS controls. In vitro studies showed that human corneal epithelial cells and neuronal progenitor cell lines proliferated on these hydrogels. In addition, improvement of cell proliferation on the surfaces of the materials was observed when neurite promoting laminin epitope, IKVAV, and adhesion peptide, YIGSR, were incorporated. However, the elasticity decreased with peptide incorporation and will require further optimization. Nevertheless, we have shown that epoxy cross-linkers should be further explored in the fabrication of collagen-based hydrogels, as alternatives to or in conjunction with carbodiimide cross-linkers.

"OSMO-UT-DSAEK" using THIN-C medium

BACKGROUND

When performing ultra-thin Descemet's stripping automated endothelial keratoplasty (UT-DSAEK), the quality of the stromal interface and stromal thickness seem to be critical for visual outcome. The aim of this study was to investigate whether additional osmotic deswelling prior to UT-DSAEK improves the quality of the cut surface and leads to a more reliable and deeper cut in UT-DSAEK ("OSMO-UT-DSAEK").

METHODS

Seventeen human donor corneas not usable for transplantation were used in this experiment. After standard deswelling with culture Medium II, ten corneas were randomly assigned to be additionally deswollen within THIN-C medium. The other remaining seven corneas were put back into culture Medium II. All corneas were placed in an artificial anterior chamber system (Moria); a double path cutting procedure using a microkeratome (Moria) was then performed. Corneal thickness was measured by ultrasound biomicroscopy and in paraffin-embedded slides, followed by histological grading of the cut surface.

RESULTS

Stromal interface smoothness significantly improved after preconditioning in THIN-C medium (Pearson P = 0.019). The correlation of the corneal thickness obtained by UBM (mean 706 ± SD 208 μm) and histology (mean 530 ± SD 159 μm) was not significant (Pearson r = 0.11, P > 0.05, mean difference 247, 95 % CI [+50;+304]). We found no significant correlation between the microkeratome setting and the actual thickness of the lenticule measured in histological analysis in both media as well as for the first and second cut (first cut: Pearson r = 0.9, P = 0.1, 95 % CI [-10;+96], second cut: Pearson r = 0.9, P = 0.4, 95 % CI [-10;+22]).

CONCLUSION

Preconditioning of corneas with THIN-C medium significantly improved the quality of the graft interface in UT-DSAEK, but did not significantly improve the cut precision of the microkeratome.