Deep Anterior Lamellar Keratoplasty for Keratoconus: Multisurgeon Results

Correlation between Corneal Volume and Corneal Biomechanics and Corneal Volume Significance in Staging and Diagnosing Keratoconus

Purpose

To investigate the relationship between corneal volume (CV) at different zones and corneal biomechanics in keratoconus (KC) along with the significance of CV in diagnosing and staging KC.

Methods

This prospective clinical study included 456 keratoconic eyes (Group B) and 198 normal eyes (Group A). Using the topographic KC classification method, Group B was divided into subgroups based on severity (mild, moderate, and severe). The CVs of the 3 mm, 5 mm, and 7 mm zones and biomechanical parameters were obtained by Pentacam and Corvis ST. The diagnostic utility of multirange CVs at different disease stages and severity was determined using a receiver operating characteristic (ROC) curve analysis.

Results

The CV of the 7-mm zone had the strongest correlation with A1V, A2T, PD, DA ratio max (2 mm), DA ratio max (1 mm), ARTh, integrated radius, SPA1, and CBI (p < 0.01). The CVs of the Group B subgroups were significantly lower than those of Group A for each diameter range (p < 0.05). There were significant differences between the severe, mild, and moderate subgroups for the 3 mm zone (p < 0.05, all). The 3 mm zone CV exhibited better diagnostic ability in each group for distinguishing KC from the normal cornea (Groups A vs. B: area under the ROC curve (AUC) = 0.926, Groups A vs. B1: AUC = 0.894, Groups A vs. B2: AUC = 0.925, Groups A vs. B3: AUC = 0.953).

Conclusion

The CV significantly decreased in keratoconic eyes. Progressive thinning in the 3 mm zone may be a valuable measurement for detecting and staging KC. Combining the CV examination with corneal biomechanical information may effectively enhance the ability to detect KC.

Outcomes of large-diameter deep anterior lamellar keratoplasty and converted two-piece mushroom penetrating keratoplasty for herpetic corneal scars

PURPOSE

To report the clinical outcomes of large diameter deep anterior lamellar keratoplasty (DALK) and converted two-piece microkeratome-assisted mushroom keratoplasty (MK) for herpetic corneal scars.

METHODS

In this single-centre study, large diameter (9 mm) DALK was attempted in consecutive patients with herpetic corneal scars. In case of macroperforation or unsatisfactory clearance of the optical zone, the procedure was intraoperatively converted to two-piece microkeratome-assisted MK. Outcome measures were best spectacle-corrected visual acuity (BSCVA), refractive astigmatism, endothelial cell density (ECD), immunologic rejection, herpetic recurrence and graft failure rates in the two groups.

RESULTS

DALK was successfully performed in 98 of 120 eyes, while the remaining 22 eyes required intraoperative conversion to MK. At 5 years, mean logMAR BSCVA was 0.10 ± 0.12 in the DALK group and 0.09 ± 0.15 in the MK group (P = 0.75). Refractive astigmatism at 5 years was 2.8 ± 1.4 D in the DALK group and 3.0 ± 1.7 D in the MK group (P = 0.67). ECD was higher in the DALK group than in the MK group at all time points (P < 0.001), with a mean annual cell loss of 10.9% after MK and 4.2% after DALK. The 5-year risk for immunologic rejection (DALK: 3%, MK: 5%, P = 0.38), herpetic recurrence (DALK: 6%, MK: 9%, P = 0.38), and graft failure (DALK: 4%, MK: 5%, P = 0.75) were comparable in both groups.

CONCLUSION

Large diameter (9 mm) DALK yields excellent visual and clinical outcomes in eyes with herpetic corneal scars. In case of intraoperative complications, DALK can be converted to two-piece microkeratome-assisted MK to maximize the refractive benefit of a large diameter graft while minimizing the risk of endothelial failure.

Keratoconus and Personality Traits: A Case-Control Study

PURPOSE

The aim of this study was to delineate the personality traits of patients affected by keratoconus (KC) compared with a group of nonkeratoconic controls matched in age and sex.

METHODS

In this prospective interventional case-control study, 60 consecutive subjects (30 KC cases and 30 healthy controls), aged 18 to 30, were enrolled at the time of their first encounter at the ophthalmology unit of the Fondazione Policlinico "Tor Vergata", Roma. After completing the ophthalmic evaluation, participants were asked to respond to the National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25). A complete psychiatric assessment was performed, including the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (SCID-5); the Symptom Check List-90-Revised (SCL-90); the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego-Modified (TEMPS-M); and the NEO Five-Factor Inventory (NEO-FFI).

RESULTS

Cases had lower quality of life than controls, as demonstrated by lower scores in all NEI VFQ-25 subdomains. Nine patients with KC (30.0%) were diagnosed by the SCID-5 with at least 1 cluster C personality disorder, resulting in a 9-fold increased risk compared with controls. Moreover, keratoconic patients showed a more pronounced psychosomatic symptomatology (SCL-90) and a characteristic neurotic temperament (TEMPS-M and NEO-FFI).

CONCLUSIONS

Our results support the hypothesis that subjects with KC feature dysfunctional coping mechanisms and personality traits, which might already be present at the first clinical encounter. Ophthalmologists should question the mental and emotional status of patients with KC and be especially careful in managing these patients.

Retrospective Analysis of a New Intrastromal Dissection Technique Using the Retinal Reflex for Deep Anterior Lamellar Keratoplasty

PURPOSE

The purpose of this study was to describe a new surgical technique for deep anterior lamellar keratoplasty.

METHODS

All pupils in the recipient eyes were dilated preoperatively. Vertical grooving was performed using a crescent blade with a width of 5 mm and a depth of one-third to half corneal thickness on the temporal side of the limbus. Stromal dissection was performed as close as possible to Descemet membrane by observing the gap between the gold line by retinal reflex and the front edge of the crescent blade. Lamellar dissection was performed along the lamellar plane using corneal dissectors. The ophthalmic viscoelastic device was injected into the intrastromal pocket to separate the anterior and posterior stroma and an anterior corneal lamella was excised. A donor cornea was sutured into the recipient bed.

RESULTS

In 18 eyes, none of the patients had Descemet membrane rupture during surgery. The mean postoperative residual stromal thickness was 80 ± 31 μm. The mean central corneal thickness after surgery was 660 ± 69 μm. At the last follow-up, the cornea was cleared in all 18 eyes on slit-lamp examination.

CONCLUSIONS

We estimated the residual stromal thickness based on the gap between the gold line by the retinal reflex and crescent blade, and intrastromal lamellar dissection was performed using a smooth corneal dissector. Consequently, the surface of stromal dissection was smooth, and the residual stromal thickness was even.

Comparison of Femtosecond Laser Assistance and Manual Trephination in Deep Anterior Lamellar Keratoplasty in the Treatment of Keratoconus: A Meta-Analysis

PURPOSE

To compare the efficacy and safety of femtosecond laser-assisted deep anterior lamellar keratoplasty (F-DALK) with those of manual-trephination DALK (M-DALK) in treating keratoconus.

DESIGN

Systematic review and meta-analysis.

METHODS

Through November 2022, we comprehensively searched PubMed, EMBASE, the Cochrane Library, and 4 Chinese databases. Studies that involved comparisons between F-DALK and M-DALK groups and that reported on relevant efficacy and/or safety parameters were included. Primary outcomes were uncorrected- and corrected-distance visual acuity and intraoperative complication rates. Secondary outcomes were spherical equivalent, topographic astigmatism, refractive cylinder, mean keratometry, endothelial cell density, suture removal time, and postoperative complication rates. These data were analyzed using Cochrane Review Manager software version 5.3.

RESULTS

This meta-analysis included 9 nonrandomized controlled studies involving 1713 eyes. In eyes treated with F-DALK, corrected-distance visual acuity at 1 to 6 months (weighted mean difference = -0.07 [95% confidence interval {CI} -0.10 to -0.03]; I2 = 0%; P < .001) after surgery was better and intraoperative Descemet membrane perforation occurred less often (odds ratio = 0.53 [95% CI 0.31-0.92]; I2 = 6%; P = .02) than in eyes treated with M-DALK. No clinically significant differences in other outcomes were found among the groups.

CONCLUSIONS

Both F-DALK and M-DALK are safe and efficacious for patients with keratoconus. Compared with M-DALK, F-DALK can provide better early visual acuity and reduce the intraoperative perforation rate, and its likely improvements to long-term visual quality and endothelial cell preservation warrant further investigation. In addition, the 2 techniques seem to be comparable regarding refractive outcomes and other complications.

Incidence and management of early postoperative complications in lamellar corneal transplantation

PURPOSE

To provide a comprehensive review of the incidence, risk factors, and management of early complications after deep anterior lamellar keratoplasty (DALK), Descemet stripping automated keratoplasty (DSAEK), and Descemet membrane endothelial keratoplasty (DMEK).

METHODS

A literature review of complications, that can occur from the time of the transplant up to 1 month after the transplant procedure, was conducted. Case reports and case series were included in the review.

RESULTS

Complications in the earliest postoperative days following anterior and posterior lamellar keratoplasty have shown to affect graft survival. These complications include, but are not limited to, double anterior chamber, sclerokeratitis endothelial graft detachment, acute glaucoma, fluid misdirection syndrome, donor-transmitted and recurrent infection, and Uretts-Zavalia syndrome.

CONCLUSION

It is essential for surgeons and clinicians to not only be aware of these complications but also know how to manage them to minimize their impact on long-term transplant survival and visual outcomes.

EBEI: A new index of eye bank efficiency

PURPOSE

To describe a new proxy of the Eye Bank (EB) activity named "Eye Bank Efficiency Index" (EBEI), calculated as the ratio between the number of corneal tissues distributed by an EB within a certain time period, and the difference between the number of procured and discarded tissues.

METHODS

To demonstrate the effectiveness of the new metric as compared to traditional statistics, an analysis was conducted using data from the largest Italian Eye Bank (Fondazione Banca degli Occhi del Veneto Venice, Italy). Collected data included: the number of corneas retrieved, the number of discarded grafts, and the number of distributed tissues. The analysis focused on three defined timeframes: January to December, March to May (the "Italian Lockdown period"), and June to December (the "Italian post-lockdown period").

RESULTS

In 2020, the annual variation of the EBEI showed a significant increase of up to 3.4% compared to the previous year (0.986 in 2019; 1.020 in 2020), but then gradually decreased to 0.993 in 2022. However, during the months of lockdown in 2020, there was a significant decline of -13.8% in the EBEI compared to the same period in the previous year. The variation in the EBEI during the post-lockdown months was minimal in 2020 and 2021, with the lowest EBEI value of 0.976 being reached in 2022 (-7.8% compared to 2019).

CONCLUSION

The EBEI is a simple and reliable new measure of the EB activity. Its widespread adoption could ensure a more accurate and reliable analysis of EB data for academic, political, and economic purposes.

Modified big bubble technique for deep anterior lamellar keratoplasty in keratoconus

We describe a modified technique for deep anterior lamellar keratoplasty with three modifications in big bubble pneumodissection technique; including two staged stromal trephination to avoid inadvertent full-thickness trephination, deep bevel-up needle air injection for better visualization and deeper air injection and, vicoseperation by refilling the pre-Descemet space with a viscoelastic after removing the air bubble for safe removal of the deep stromal layers. Patients with advanced keratoconus underwent deep anterior lamellar keratoplasty with pneumodissection by two-staged trephination followed by bevel-up needle deep air injection and viscoseperation. The big bubble was successfully formed in all cases and there was no case with the rupture of the Descemet's membrane (DM) during air injection or baring of DM.

A 7-year review of clinical characteristics, predisposing factors and outcomes of post-keratoplasty infectious keratitis: the Nottingham infectious keratitis study

Background/objectives

Post-keratoplasty infectious keratitis (PKIK) is a unique sight-threatening clinical entity which often poses significant therapeutic challenges. This study aimed to examine the clinical presentation, risk factors, management, and clinical outcomes of PKIK.

Methods

This was a retrospective study of all patients who presented to the Queen's Medical Centre, Nottingham, with PKIK between September 2015 and August 2022 (a 7-year period). Relevant data on types of keratoplasty, clinical presentations, causative microorganisms, management, and outcome were analyzed.

Results

Forty-nine PKIK cases, including four cases of interface infectious keratitis, were identified during the study period. The most common graft indications for PKP, DALK and EK were failed grafts (9, 37.5%), keratoconus (6, 54.5%) and Fuchs endothelial corneal dystrophy (FECD; 8, 57.1%), respectively. Staphylococcus spp. were the most commonly identified organisms (15, 50.0%). Bullous keratopathy (18, 36.7%), ocular surface disease (18, 36.7%), and broken/loose sutures (15, 30.6%) were the most common risk factors. Concurrent use of topical steroids was identified in 25 (51.0%) cases. Of 31 functioning grafts at presentation, 12 (38.7%) grafts failed at final follow-up with 15 (48.4%) patients retaining a CDVA of ≥1.0 logMAR. The overall estimated 5-year survival rate post-PKIK was 55.9% (95% CI, 35.9%-75.9%), with DALK having the highest survival rate [63.6% (95% CI, 28.9%-98.3%)], followed by EK [57.1% (95% CI, 20.4%-93.8%)] and PKP [52.7% (95% CI, 25.1%-80.3%)], though no statistical difference was observed (p=0.48).

Conclusions

PKIK represents an important cause of IK and graft failure. Bullous keratopathy, OSD and suture-related complications are the commonest risk factors, highlighting the potential benefit of prophylactic topical antibiotics (for unhealthy ocular surface) and early suture removal (where possible) in reducing the risk of PKIK. Graft survival may be higher in lamellar keratoplasty following PKIK but larger studies are required to elucidate this observation.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Comparison of Robot-Assisted and Manual Cannula Insertion in Simulated Big-Bubble Deep Anterior Lamellar Keratoplasty

This study aimed to compare the efficacy of robot-assisted and manual cannula insertion in simulated big-bubble deep anterior lamellar keratoplasty (DALK). Novice surgeons with no prior experience in performing DALK were trained to perform the procedure using manual or robot-assisted techniques. The results showed that both methods could generate an airtight tunnel in the porcine cornea, and result in successful generation of a deep stromal demarcation plane representing sufficient depth reached for big-bubble generation in most cases. However, the combination of intraoperative OCT and robotic assistance received a significant increase in the depth of achieved detachment in non-perforated cases, comprising a mean of 89% as opposed to 85% of the cornea in manual trials. This research suggests that robot-assisted DALK may offer certain advantages over manual techniques, particularly when used in conjunction with intraoperative OCT.

Intraoperative OCT for Lamellar Corneal Surgery: A User Guide

Intraoperative OCT is an innovative and promising technology which allows anterior and posterior segment ocular surgeons to obtain a near-histologic cross-sectional and tomographic image of the tissues. Intraoperative OCT has several applications in ocular surgery which are particularly interesting in the context of corneal transplantation. Indeed, iOCT images provide a direct and meticulous visualization of the anatomy, which could guide surgical decisions. In particular, during both big-bubble and manual DALK, the visualization of the relationship between the corneal layers and instruments allows the surgeon to obtain a more desirable depth of the trephination, thus achieving more type 1 bubbles, better regularity of the plane, and a reduced risk of DM perforation. During EK procedures, iOCT supplies information about proper descemetorhexis, graft orientation, and interface quality in order to optimize the postoperative adhesion and reduce the need for re-bubbling. Finally, mushroom PK, a challenging technique for many surgeons, can be aided through the use of iOCT since it guides the correct apposition of the lamellae and their centration. The technology of iOCT is still evolving: a larger field of view could allow for the visualization of all surgical fields, and automated tracking and iOCT autofocusing guarantee the continued centration of the image.

Clinical comparison of manual and laser-cut corneal tunnel for intrastromal air injection in femtosecond laser-assisted deep anterior lamellar keratoplasty (DALK)

PURPOSE

The most crucial step in deep anterior lamellar keratoplasty (DALK) is to achieve a bare Descemet's membrane. We aimed to assess a new femtosecond laser software that allows for a precise intrastromal tunnel creation for big bubble (BB) air injection using a real-time microscope-integrated optical coherence tomography.

MATERIALS AND METHODS

A retrospective review of 61 eyes of 61 patients with keratoconus. Before introducing the new software update, DALK was performed using a partial-assisted femtosecond laser (partial-thickness circular cut followed by a lamellar cut) with manual intrastromal tunnel creation (partial FS-DALK group). After the software update, the femtosecond laser created the intrastromal tunnel (full FS-DALK group).

RESULTS

In the full FS-DALK group, the BB's formation was significantly higher (64.3% vs. 36.4%, p = 0.04), and surgery time was shorter (21.8 ± 5.1 vs. 25.6 ± 6.8 min, p = 0.025) than in the partial FS-DALK. Penetrating keratoplasty conversion rate (7.1% vs. 15.1%, p = 0.432) was similar between the groups. Both groups showed statistically significant improvement in uncorrected and corrected distance visual acuity, central corneal thickness, surface asymmetry, and regularity indices. Endothelial cell density loss at 12 and 18 months was lower in the full compared with the partial FS-DALK group (12 months:10.0% vs. 16; 18 months: 10.7 vs. 16.5%, p < 0.001 for both comparisons).

CONCLUSIONS

Creating the intrastromal guiding tunnel using FS laser for air injection resulted in a higher rate of BB formation, reduced long-term endothelial cell loss, and operating room time.

Deep Anterior Lamellar Keratoplasty: Can All Ruptures Be Fixed?

PURPOSE

The aim of this study was to report our experience in managing different types of Descemet membrane (DM) ruptures during deep anterior lamellar keratoplasty (DALK).

METHODS

This study was a retrospective, consecutive, interventional case series of 1573 DALK procedures conducted on 1244 patients, performed between 2002 and 2017. Inclusion criteria consisted of a minimum of 24-month follow-up. DM rupture incidence, location, and surgical approach for repair were recorded. Postoperative measures were investigated only in eyes that experienced DM ruptures and included best spectacle-corrected visual acuity, endothelial cell loss, double anterior chamber, pupillary block, need for rebubbling, graft clarity, and rejection episodes.

RESULTS

One thousand four hundred forty-three eyes met the inclusion criteria. DM ruptures occurred in 119 eyes (8.25%). Seventy-eight percent of DM ruptures were microruptures (≤2 mm), and they occurred more frequently during manual DALK cases. Macroruptures were less frequent (22%), and they occurred more frequently during subtotal and total anterior lamellar keratoplasty (STALK-TALK) cases. In general, DM ruptures mainly occurred in the peripheral cornea (95% of cases). One hundred (84%) of the 119 ruptures resolved by the first postoperative day. Nineteen cases (16%) developed double anterior chamber; all resolved by using different strategies. No intraoperative penetrating keratoplasty conversion was recorded. Pupillary block occurred in 7 cases (5.9%), but no Urrets-Zavalia syndrome was observed. The average postoperative endothelial cell loss was 410 ± 39 cells/mm 2 (19%) at 1-year follow-up, and there was no significant difference between cases requiring a rebubbling and cases that did not ( P = 0.896). All grafts but one were clear at the last follow-up. Graft failure from endothelial decompensation occurred in this lone case (0.8%).

CONCLUSIONS

It is worth trying to repair all DM ruptures in DALK, and immediate penetrating keratoplasty conversion should be avoided. Understanding the physiomechanical mechanisms in DALK allows to correctly choose a proper rescue strategy to successfully repair DM ruptures.

"Groove and Peel" Deep Anterior Lamellar Keratoplasty: How Deep Can You Go?

PURPOSE

The aim of the current research was to measure the thickness of the residual central corneal bed after performing the manual "Groove and Peel" deep anterior lamellar keratoplasty (GP-DALK) technique on human cadaveric eyes.

METHODS

The manual GP-DALK technique was performed on 6 human cadaver eyes by an experienced corneal surgeon. After surgery, the eye globes were fixed in 10% buffered formalin and embedded in paraffin. For each eye, 4-μm-thick hematoxylin and eosin sections involving the pupillary axis were obtained and examined. Using an image-processing software, 2 observers measured the corneal thickness of the residual central corneal bed and the peripheral corneal rims.

RESULTS

The overall mean central corneal bed thickness was 35.5 ± 12.9 μm, whereas the mean right and left peripheral rim thicknesses were 993.0 ± 141.1 and 989.3 ± 147.1 μm, respectively ( P = 0.0006 ). In most corneas, the level of dissection reached almost to the pre-Descemetic collagen (Dua) layer.

CONCLUSIONS

The GP-DALK technique is effective in removing most of the corneal stroma and may be non-inferior to "big-bubble" deep anterior lamellar keratoplasty in some cases.

Effect of Covid-19 on Eye Banks and Corneal Transplantations: Current Perspectives

The coronavirus disease 2019 (COVID-19) pandemic exerted a great impact on medical practice, which was reframed according to the actual needs. Ophthalmological services and procedures including corneal transplantation did not represent an exception. The adoption and implementation of new standard operating procedures as well as of new technologies for remote consultation and smart-working reshaped daily activities of both eye bankers, physicians, researchers, and patients. Regulatory restrictions were issued redefining corneal donor eligibility criteria, as well as handling and harvesting procedures of donor ocular tissues. Surgical schedules underwent an abrupt contraction with prioritization of urgent procedures. Local lockdowns and confinement strategies resulted in both a reduction and redirection of research activities. The evaluation of SARS-CoV-2 colonization of ocular tissues, long-term corneal storage techniques, new disinfection strategies, split corneal transplants and cell-based therapies for the treatment of corneal disease peaked in the pipeline. Aim of this article is to summarizes the overall impact of the pandemic on the corneal transplantation machinery, and the current and future perspectives for the corneal transplant community.

Ex Vivo Evaluation of a Pressure-Sensitive Device to Aid Big Bubble Intrastromal Dissection in Deep Anterior Lamellar Keratoplasty

Purpose

To develop and perform ex vivo testing for a device designed for semiquantitative determination of intracorneal dissection depth during big bubble (BB) deep anterior lamellar keratoplasty.

Methods

A prototype device connected to a syringe and cannula was designed to determine depth of intrastromal placement based on air rebound pressure emitted by a software controlled generator. Ex vivo testing of the device was conducted on human corneas mounted on an artificial anterior chamber in three experiments: (1) cannula purposely introduced at different depths measured with anterior segment optical coherence tomography, (2) cannula introduced as per the BB technique, and (3) simulation of the BB technique guided by the device.

Results

A positive pressure differential and successful BB were observed only when the cannula was positioned within 150 microns from the endothelial plane. In all successful BB cases (21/40), a repeatable increase in tissue rebound pressure was detected, which was not recorded in unsuccessful cases. The device was able to signal to the surgeon correct placement of the cannula (successful BB) in 16 of 17 cases and incorrect placement of the cannula (unsuccessful BB) in 8 of 8 cases (94.1% sensitivity, 100% specificity).

Conclusions

In our ex vivo model, this novel medical device could reliably signal cannula positioning in the deep stroma for effective pneumatic dissection and possibly aid technical execution of BB deep anterior lamellar keratoplasty.

Translational Relevance

A medical device that standardizes big bubble deep anterior lamellar keratoplasty could increase the overall success rate of the surgical procedure and aid popularization of deep anterior lamellar keratoplasty.

Femtosecond laser-assisted Bowman layer transplantation for advanced keratoconus

BACKGROUND/AIMS

To assess the technical feasibility and outcomes of femtosecond laser-assisted Bowman layer transplantation (FLABOLT) in stabilizing progressive, advanced keratoconus, which is ineligible for corneal crosslinking.

METHODS

This single-center retrospective study included 50 eyes of 49 patients with progressive advanced keratoconus, ineligible for corneal crosslinking, that underwent FLABOLT with both the donor graft and recipient mid-stromal pocket using a femtosecond laser.

RESULTS

The mean follow-up was 13.2 ± 4.9 months (range 7-35 months). Donor graft preparation and accurate dissection of the recipient mid-stromal pocket were successful in 96% and 100% of cases, respectively. The mean maximum keratometry decreased by 1.93 D at 6 months after surgery and there was no change in the mean preoperative best contact lens-corrected visual acuity (BCLVA). Three eyes developed hydrops postoperatively and recovered after clinical treatment. One eye that achieved useful BCLVA postoperatively, worsened 2 years after the surgery due to progressive corneal scarring and required corneal transplantation for visual rehabilitation. Preoperative corneal scarring was a risk factor for BCLVA loss. All other eyes remained stable (92%), and no other procedure was required until the last follow-up.

CONCLUSION

In this series, FLABOLT was successfully performed as an alternative to stabilize advanced progressive keratoconus. This technique is highly reproducible for graft preparation and recipient pocket dissection when assisted by femtosecond laser. Despite promising initial results, more studies with longer follow-up periods are needed to evaluate the effectiveness of FLABOLT in stabilizing advanced progressive keratoconus.

Outcomes of Conventional 8.0-mm Versus Large 9.0-mm Diameter Deep Anterior Lamellar Keratoplasty for Keratoconus

PURPOSE

The purpose of the study was to compare the clinical outcomes of large 9.0-mm diameter and conventional 8.0-mm big-bubble deep anterior lamellar keratoplasty (DALK).

METHODS

In this comparative, retrospective interventional case series, medical records of 124 cases of large 9.0-mm diameter DALK from January 2017 to December 2019 and 133 conventional 8.0-mm DALK from January 2014 to December 2016 performed by a single surgeon for the indication of keratoconus were reviewed. Main outcome measures were best spectacle-corrected visual acuity (BSCVA), refractive astigmatism (RA), and postoperative complication rates.

RESULTS

Postoperative logarithm of the minimum angle of resolution BSCVA did not significantly differ between 9.0-mm and 8.0-mm DALK at any time points. Although the cumulative percentage of eyes achieving Snellen BSCVA of 20/40 or better was comparable between groups (9.0-mm DALK: 93%, 8.0-mm DALK: 90%, P = 0.571), the cumulative percentage of eyes achieving 20/20 or better (9.0-mm DALK: 44%, 8.0-mm DALK: 26%, P = 0.01) and 20/25 or better (9.0-mm DALK: 74%, 8.0-mm DALK: 59%, P = 0.03) was significantly higher in the 9.0-mm DALK group. RA was significantly lower in the 9.0-mm DALK group compared with the 8.0-mm DALK group during all time points (P < 0.001). The percentage of eyes with RA less than or equal to 4.0 D was significantly lower in the 9.0-mm DALK patients (90%) compared with in 8.0-mm DALK group (72%) (P = 0.002). Postoperative complication rates were similar between groups.

CONCLUSIONS

Compared with conventional 8.0-mm DALK, large 9.0-mm DALK can provide superior visual outcomes at higher levels of Snellen BSCVA and significantly lower degrees of astigmatism without an increased risk of immune rejection and graft failure.

Indications and techniques of corneal transplants performed in one center in Southern Poland, in the years 2001–2020

Purpose

The study aimed to evaluate changes over a period of time in techniques and indications for corneal transplantation in a single center in Poland.

Methods

Retrospective analysis of corneal transplants performed at the Ophthalmology Department of the District Railway Hospital in Katowice in 2001–2020. Data on indications and surgical technique were collected.

Results

A total of 3021 corneal transplantations were performed in the years 2000–2020. The most common technique was penetrating keratoplasty (69,54%), then lamellar grafts—both anterior and posterior (19,63%), and limbal grafts (10,82%). Only in 2007 the number of lamellar keratoplasties exceeded the number of penetrating grafts and accounted for 108 (54,55%), including 85 (42,93%) of Descemet Stripping Automated Endothelial Keratoplasty. The only noticeable trend in changing techniques was a decrease in the number of performed deep anterior lamellar keratoplasties (r 2 = -0.21) over the last seven years. Main indications included bullous keratopathy (23,22%), following keratoconus (18,59%), leukoma (14,67%), keratitis and perforation (14,3%), Fuchs dystrophy (11,4%), and regrafts (7,22%). Leukoma and bullous keratopathy as an indications for corneal transplant have been declining over the years (r2 = 0.60 and r2 = 0.30 respectively). Consecutively, indications such as fuchs dystrophy, regraft and keratitis perforation have increased (r2 = 0.05, r2 = 0.50, r2 = 0.33)

Conclusions

The number of keratoplasties gradually increased from 2001 to 2020. It could be possible that the development and spread of new therapeutic alternatives, like corneal cross-linking and scleral lenses, have contributed to the decrease in deep anterior lamellar keratoplasty performed. There was an increasing trend in the percentage of penetrating keratoplasties for failed grafts, Fuchs dystrophy and infectious keratitis.

Rediscovering a valuable manual Deep Anterior Lamellar Keratoplasty (DALK) technique: Outcomes of 42 "Peeling-off" DALK

PURPOSE

Residual bed thickness in DALK should be less than 80μm to provide optimal visual outcomes. "Peeling-off" is a manual DALK technique, which separates the anterior stroma by pulling the deep stromal lamellae following the plane of their lowest adhesion, which is usually very deep. The purpose of this study is to measure the residual bed thickness achievable with this technique.

METHODS

Retrospective case series of "Peeling-off" DALK cases performed between January 2014 and January 2021 with at least 1 year of follow-up. Indications for DALK, intraoperative and postoperative complications, residual recipient bed thickness at 1 day and at 1 month after surgery, and postoperative best corrected visual acuity (BCVA) at 1 year of follow up were evaluated.

RESULTS

42 eyes (42 patients) underwent DALK performed with "Peeling-off" technique. Indications for surgery were keratoconus in 33 eyes and stromal scar in 9 eyes. "Peeling-off" technique was used as a rescue approach to perform a DALK after a failed Big-Bubble in all cases, and also failed Air-Visco-Bubble in some cases. No intraoperative and postoperative complications were recorded. Residual recipient bed thickness was deep and regular, measuring 42 microns at 1 day postoperative (range 21-65 microns) and 23 microns (range 17-26 microns) at 1 month postoperative. Mean postoperative BCVA at 1 year of follow up was 0.18 logMAR ± 0.09.

CONCLUSION

"Peeling-off" DALK is a valuable manual technique that achieves a deep stromal plane with optimal visual outcomes.

Impact of vaccination on keratoplasty

PURPOSE OF REVIEW

Corneal graft rejection has been reported after coronavirus disease 2019 (COVID-19) vaccination. The purpose of this review is to evaluate the literature regarding corneal graft rejection after vaccination, including rejection rates and risk factors. We aim to create a framework to identify patients who are at higher risk for graft rejection and may warrant consideration of prophylactic interventions.

RECENT FINDINGS

Graft rejection has been reported following administration of mRNA, viral vector, and inactivated whole-virion COVID-19 vaccines. Most cases had additional risk factors associated with rejection. Vaccination increases circulation of proinflammatory cytokines, CD4+ and CD8+ T-cell responses, and antispike neutralizing antibody, all of which may contribute to graft rejection. Two prospective studies have found no relationship between recent vaccination and rejection but 20% of cornea specialists report to have seen a vaccine-associated rejection and 22% recommend delaying vaccination in certain circumstances. Many specialists recommend prophylactic topical corticosteroids before and after vaccination to mitigate rejection risk but there is no evidence to support this practice on a wider scale.

SUMMARY

Our framework identified 96.8% of penetrating keratoplasty patients with vaccine-associated rejection as higher risk. Further research is needed in order to develop evidence-based guidelines.

Visual Outcomes of Microkeratome-Assisted Anterior Lamellar Keratoplasty in Keratoconus: 5-Year Results

Purpose

To report 5-year results of microkeratome-assisted anterior lamellar keratoplasty (MK-ALK) in cases of keratoconus.

Methods

Patients with advanced keratoconus and the thinnest corneal location 300 μ or more were recruited. A Carriazo–Barraquer microkeratome was used to remove a 200-μ cap from the recipient cornea, and to prepare a 300-μ anterior stromal graft from a donor cornea. A full-thickness crescentic incision was made in the posterior stromal recipient bed using a 6.5-mm suction trephine. The donor was sutured to the recipient bed using interrupted nylon sutures. The minimum follow-up was five years.

Results

Twelve eyes of 12 patients were included. The mean age was 26 ± 8 years. None of the patients required conversion to penetrating keratoplasty. Mean logMAR uncorrected and best spectacle-corrected visual acuity, respectively, improved from 1.56 ± 0.24 and 1.18 ± 0.32 preoperatively, to 0.63 ± 0.38 and 0.18 ± 0.12, five years after surgery (P=0.001for both). There was also a statistically significant reduction of mean manifest spherical equivalent, refractive cylinder, and mean keratometry readings. Posterior stromal striations occurred in all patients immediately after surgery but resolved after a maximum of 3 months. At five-years, anterior segment optical coherence tomography revealed a clear interface in all cases and a mean graft thickness of 328 ± 27 μ.

Conclusion

MK-ALK is a safe and effective procedure for advanced keratoconus. Where feasible, it may be the best choice for patients at high risk of poor outcomes with penetrating keratoplasty, such as young patients with atopic keratoconjunctivitis or Down's syndrome.

Current Perspectives on Corneal Transplantation

Disease of the cornea is the third leading cause of blindness worldwide. Corneal graft surgery is one of the most successful forms of solid organ transplantations in humans, with ever-increasing developments in surgical technique. To date, approximately 4504 corneal transplants are performed in the United Kingdom each year. While full thickness transplantation was the most commonly performed keratoplasty over the last few decades, selective lamellar transplantation of the diseased layers of the cornea has been universally adopted. This comprehensive review aims to provide an updated synthesis on different types of corneal transplantations, their treatment outcomes, and the associated complications of each procedure in both adult and paediatric population. In addition, we also present an up-to-date summary of the emerging therapeutic approaches that have the potential to reduce the demand for donor-dependent keratoplasty.

Keratoconus: An updated review

Keratoconus is a bilateral and asymmetric disease which results in progressive thinning and steeping of the cornea leading to irregular astigmatism and decreased visual acuity. Traditionally, the condition has been described as a noninflammatory disease; however, more recently it has been associated with ocular inflammation. Keratoconus normally develops in the second and third decades of life and progresses until the fourth decade. The condition affects all ethnicities and both sexes. The prevalence and incidence rates of keratoconus have been estimated to be between 0.2 and 4,790 per 100,000 persons and 1.5 and 25 cases per 100,000 persons/year, respectively, with highest rates typically occurring in 20- to 30-year-olds and Middle Eastern and Asian ethnicities. Progressive stromal thinning, rupture of the anterior limiting membrane, and subsequent ectasia of the central/paracentral cornea are the most commonly observed histopathological findings. A family history of keratoconus, eye rubbing, eczema, asthma, and allergy are risk factors for developing keratoconus. Detecting keratoconus in its earliest stages remains a challenge. Corneal topography is the primary diagnostic tool for keratoconus detection. In incipient cases, however, the use of a single parameter to diagnose keratoconus is insufficient, and in addition to corneal topography, corneal pachymetry and higher order aberration data are now commonly used. Keratoconus severity and progression may be classified based on morphological features and disease evolution, ocular signs, and index-based systems. Keratoconus treatment varies depending on disease severity and progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, while severe cases that cannot be managed with scleral contact lenses may require corneal surgery. Mild to moderate cases of progressive keratoconus may also be treated surgically, most commonly with corneal cross-linking. This article provides an updated review on the definition, epidemiology, histopathology, aetiology and pathogenesis, clinical features, detection, classification, and management and treatment strategies for keratoconus.

Microscope-Integrated Intraoperative Optical Coherence Tomography-Guided Big-Bubble Deep Anterior Lamellar Keratoplasty

PURPOSE

The purpose of this study was to evaluate the feasibility of microscope-integrated intraoperative optical coherence tomography (OCT) for real-time quantitative analysis of surgical planes in big-bubble deep anterior lamellar keratoplasty (DALK).

METHODS

In this interventional case series, intraoperative OCT-guided big-bubble DALK was performed in 16 consecutive eyes of 16 patients with keratoconus. Trephination depth was measured using the intraoperative OCT caliper tool. Aiming for a depth within 150 μm from the endothelial surface, the trephination groove was extended to a deeper plane using a 15-degree blade. Repeat OCT scans were taken to measure residual stromal thickness before insertion of the DALK probe from the bottom of the extended trephination. Caliper measurements, success rate of pneumatic dissection, and complications were recorded.

RESULTS

After trephination, residual stromal thickness exceeded 150 μm in all eyes and averaged 257.1 ± 42.5 μm. In each case, the initial trephination groove was extended to a depth within 150 μm from the endothelial surface (118.9 ± 27.1 μm). Big-bubble formation was achieved in 12 eyes (75%). Type 1 bubble was obtained in 11 eyes. Perforation requiring conversion to penetrating keratoplasty occurred in 4 eyes during insertion of the cannula into a residual stromal bed of <100 μm (n = 2; 63 and 75 μm) or layer-by-layer dissection (n = 2).

CONCLUSIONS

Quantitative analysis of intraoperative OCT scans can be used to assist decision-making on whether to proceed with pneumatic dissection or extend the trephination groove, thereby facilitating insertion of the injection cannula at the desired stromal depth.

A simple surgical technique for splitting a single donor cornea for performing deep anterior lamellar keratoplasty and Descemet membrane endothelial keratoplasty without using a microkeratome

Purpose:

To describe a simple manual surgical technique for splitting a single-donor eye for performing both deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK) without using a microkeratome.

Methods:

Twenty-three eyes with anterior stromal pathology and 23 eyes with irreversible endothelial dysfunction were evaluated for keratoplasty at a tertiary eye care referral center. Twenty-three healthy donor corneas were split into two parts. The Descemet’s membrane was stripped and used for DMEK. The stripped stroma was used for DALK. Best-corrected visual acuity (BCVA) of both DALK and DMEK, endothelial cell density, and endothelial cell loss in DMEK were noted at 1-year follow-up, along with any intraoperative or postoperative complications and failures.

Results:

In the DALK group, mean BCVA improved from 1.264 ± 0.25 log Mar preoperatively to 0.355 ± 0.27 log Mar at 12 months follow-up. There were no complications and failures. In the DMEK group, mean BCVA improved from 1.537 ± 0.61 log Mar preoperatively to 0.592 ± 0.67 log Mar and the mean donor ECD was 3071.66 (range, 2783–3487) cells/mm² preoperatively, which was reduced to 1989.33 (range, 1546–2543) cells/mm² at 12 months follow-up indicating a mean endothelial cell loss of 35%. The failure rate was 21.7%.

Conclusion:

This study demonstrates that with a single donor corneal tissue, both DALK and DMEK can be performed successfully without any complications. Our technique will help corneal surgeons in all developing countries to cost effectively perform more lamellar surgeries and help in reducing the magnitude of corneal blindness without the need for expensive microkeratomes.

Preferred practice pattern and observed outcome of deep anterior lamellar keratoplasty - A survey of Indian corneal surgeons

Purpose

This study aimed to assess the preferred surgical technique and outcome of deep anterior lamellar keratoplasty (DALK) among corneal surgeons in India.

Methods

An online questionnaire-based cross-sectional survey was conducted among members of the Cornea Society of India (CSI) with experience of performing >10 DALK procedure. The responses pertaining to their surgical experience, preferred technique, complications, and outcome of DALK were collected and analyzed.

Results

A total of 156 responses were received. In total, 35.9% of participants reported annual keratoplasty of >50, and DALK constituted >25% surgeries for 25% of participants. Ectatic corneal disorder was reported as the most common indication for DALK by 71.6% of the respondents. Big-bubble (BB) DALK (WA-1.82) was the most preferred technique, along with suction trephine (50%) for partial trephination and bottom port cannula (45.5%) for BB formation. On statistical analysis, no difference was observed in the surgeon reported success rate of BB formation with or without anterior lamellar keratectomy (ALK) (χ2 (1,156) = 3.1498, P = 0.08) or paracentesis (χ2 (1,156) = 0.2737, P = 0.60) before stromal air injection, and method of stromal air injection (χ2 (1,156) = 4.7325, P = 0.09). Conversion to penetrating keratoplasty was reported by 16% of participants in >25% cases, while 66.7% reported in <10% cases. Cataract and double anterior chamber were the most common complications. 50% of participants suggested that >20 procedures are required to overcome the learning curve.

Conclusion

BB DALK is the most commonly practiced DALK technique, and its success is independent of ALK and paracentesis being performed prior to air injection and method of air injection (cannula/needle).

Corneal neovascularisation following deep anterior lamellar keratoplasty for corneal ectasia: incidence, timing and risk factors

BACKGROUND

The purpose of this study was to evaluate the incidence, timing and risk factors of corneal neovascularisation (NV) after deep anterior lamellar keratoplasty (DALK) for corneal ectasia.

METHODS

This study included 616 eyes who underwent DALK between 2012 and 2020 in two tertiary referral centres. In one centre topical corticosteroids were discontinued after complete suture removal 1 year after surgery, whereas in the other they were discontinued 3-4 months after surgery. The presence and severity of corneal NV was ascertained based on slit lamp photographs. Potential risk factors for corneal NV were evaluated using the Cox proportional hazards model.

RESULTS

The cumulative incidence of corneal NV was 8.7% at 1 year after surgery and 13.2% at 5 years. Mean time interval from surgery to development of corneal NV was 12.8±16.2 months, with 68.9% of cases occurring before complete suture removal. Early discontinuation of topical steroids, older age and ocular allergy were associated with an increased risk of developing corneal NV (respectively, HR=2.625, HR=1.019, HR=3.726, all p<0.05).

CONCLUSIONS

The risk of corneal NV is higher in the first year following DALK. Early discontinuation of topical steroids, ocular allergy and older age are significant predictors of corneal NV.

Unexplained Bilateral Simultaneous Corneal Graft Rejection in a Healthy 18-Year-Old Male

PURPOSE

To report a rare case of unexplained bilateral corneal graft rejection one year after penetrating keratoplasty (PK) in an otherwise healthy individual, who was compliant with topical fluorometholone maintenance therapy.

OBSERVATIONS

An 18-year-old gentleman, who underwent successful, sequential, non-simultaneous, bilateral PK for advanced keratoconus, presented one year later with an acute endothelial rejection episode involving both eyes simultaneously. The rejection episode was reversed with a high dose of intravenous (IV) methylprednisolone pulse therapy over three days, topical cyclosporine-A 1%, and prednisolone acetate 1%, and then maintained on cyclosporine-A 1% eye drops, as the patient was a steroid responder. Conclusion and importance: Bilateral corneal graft rejection, although rare, can occur even several months after successful PK. Prompt management is crucial for the successful reversal of an acute corneal graft rejection episode. In steroid responders, Cyclosporine-A 1% can play a role in reducing the need for, or frequency of, potent steroid eye drops in the acute phase, and as a long-term steroid-sparing agent for maintenance.

Five-year Outcomes of Converted Mushroom Keratoplasty from Intended Deep Anterior Lamellar Keratoplasty (DALK) Mandate 9-mm Diameter DALK as the Optimal Approach to Keratoconus

PURPOSE

To compare the 5-year outcomes of 9-mm-deep anterior lamellar keratoplasty (DALK) for keratoconus with those of conversions to mushroom keratoplasty (MK).

DESIGN

Retrospective cohort study.

METHODS

The setting was the Ospedali Privati Villa Igea, Department of Ophthalmology, Forlì, Italy. The study population consisted of the medical records of all attempted DALK procedures (416 eyes) for the indication of keratoconus performed between January 2012 and January 2018; 68 eyes (16.4%) were converted to MK and analyzed as a separate cohort. The mean follow-up time was 33.8 ± 15.1 months. Procedure(s) consisted of 9-mm DALK and MK (9-mm anterior lamella with 6-mm posterior lamella). Outcome measurements were best-corrected visual acuity (BCVA), refractive astigmatism, and endothelial cell loss (ECL) at 5 years.

RESULTS

Average BCVA at 5 years was 0.06 ± 0.07 in the DALK group and 0.09 ± 0.15 in the MK group (P = .88). Refractive astigmatism following suture removal (all visits later than 12 months) was slightly less in the DALK cohort (5-year DALK = 2.16 ± 1.40 diopter [D]; MK = 3.02 ± 0.89 D; P = .04; mean difference = 0.86 D [95% confidence interval [CI]: 0.71-1.01]). ECL was significantly higher in the MK group than in the DALK group at all follow-up intervals (5-year DALK = 19.36 ± 21.47%; MK = 56.61 ± 15.82%; P < .001). The total all-cause graft failure rate at 5 years was 0.58% for DALK (2 of 348) cases and 5.88% for MK (4 of 68) cases.

CONCLUSIONS

Excellent 5-year visual and clinical outcomes associated with a 2-piece MK in cases converted from intended DALK mandate large-diameter DALK (9 mm) as the optimal surgical approach to keratoconus.

Femtosecond Laser-Assisted Deep Anterior Lamellar Keratoplasty for Keratoconus: Multi-surgeon Results

PURPOSE

To compare the clinical outcomes in femtosecond laser-assisted deep anterior lamellar keratoplasty (F-DALK) to manual non-laser deep anterior lamellar keratoplasty (M-DALK) for keratoconus in a multi-surgeon public healthcare setting.

DESIGN

Single-center, comparative, retrospective interventional case series.

METHODS

Population: Consecutive cases of keratoconus treated with big-bubble F-DALK from August 1, 2015, to September 1, 2018 and big-bubble M-DALK from September 1, 2012, to September 30, 2016.

SETTING

Moorfields Eye Hospital, London.

OBSERVATIONS

Data on preoperative status, operative details, intraoperative and postoperative complications, secondary interventions, and visual outcomes were archived on a customized spreadsheet for analysis. MainOutcomeMeasures: Rate of intraoperative perforation and conversion to penetrating keratoplasty (PK) and the percentage of patients, post removal of sutures (ROS), with corrected distance visual acuity (CDVA) ≥20/40.

RESULTS

We analyzed 58 eyes of 55 patients who underwent F-DALK and 326 eyes of 309 patients who underwent M-DALK. Intraoperative perforation of Descemet membrane occurred in 15 of 58 (25.9%) F-DALK cases compared to 148 of 326 (45.4%) M-DALK cases (P = .006). Intraoperative conversion to PK was carried out in 2 of 58 (3.4%) F-DALK cases compared to 80 of 326 (24.5%) M-DALK cases (P = .001). Post ROS, 86.5% of F-DALK eyes had a CDVA of ≥20/40 (15 ± 7.3 months after surgery) compared to 83.7% of M-DALK eyes (24.9 ± 10.6 months) (P = .825).

CONCLUSION

Laser automation of some steps in DALK for keratoconus may reduce the rate of intraoperative Descemet perforation and the conversion to PK in a multi-surgeon setting.

Corneal transplantation after failed grafts: Options and outcomes

Corneal transplantation is the most commonly performed human tissue transplantation procedure worldwide. Because of the large number of transplants, corneal graft failure has become one of the most common indications for corneal transplantation. The relatively recently developed lamellar transplant techniques have brought about specific potential complications leading to graft failure that may require different approaches to repeat transplantation other than penetrating keratoplasty. On the other hand, these new lamellar techniques also provide novel ways of rescuing failed penetrating grafts, with potential advantages over successive penetrating keratoplasties, such as reduced intraoperative risks and faster visual rehabilitation. We summarize the incidence and risk factors of graft failure for penetrating and lamellar (stromal and endothelial) corneal transplants and discuss the various surgical alternatives currently available to rescue such failed grafts, with a focus on the reported outcomes and limitations.

Evaluation of the risk factors associated with conversion of intended deep anterior lamellar keratoplasty to penetrating keratoplasty

Background/aims

To identify and evaluate risk factors associated with the need to convert intended deep anterior lamellar keratoplasty (DALK) to penetrating keratoplasty (PK).

Methods

Retrospective institutional cohort study including all consecutive eyes undergoing intended DALK between May 2015 and October 2018 at ‘Villa Igea’ Hospital (Forli, Italy). The indications for surgery were categorised as (1) keratoconus without scarring; (2) keratoconus with scarring; (3) non-keratoconus without scarring; and (4) non-keratoconus with scarring. Multivariate binary logistic regression analysis was performed, introducing, as independent variables, those that reached a significance level of less than 0.05 in univariate analysis. The main outcome measure was whether or not conversion to a PK occurred.

Results

705 eyes were included, with conversion to PK occurring in 16.2% (n=114) of cases. The factors that remained significant in multivariate analysis were corneal scarring (OR=3.52, p<0.001), manual dissection (OR=42.66, p<0.001), type 2 bubble (OR=90.65, p<0.001) and surgeon inexperience (OR=10.86, p<0.001). A receiver operating characteristic (ROC) curve based on the factors significant in the multivariate binary logistic regression analysis achieved a sensitivity of 89.5% (95% CI 82.3% to 94.4%) and a specificity of 80.2% (95% CI 76.8% to 83.3%) with an area under the ROC curve of 0.91 (95% CI 0.88 to 0.93) (p<0.001)

Conclusion

Occurrence of a type 2 bubble, the need for manual dissection, the presence of scarring and surgeon inexperience are independent risk factors for the need to convert intended DALK to PK. Correct identification and management of the type of bubble achieved during pneumatic dissection is instrumental in minimising the rate of conversion to PK.