Suboptimal visual outcome after femto-LASIK ablation in a high myopic patient.

A 28-year-old nurse had an aberration-free femto-laser in situ keratomileusis (LASIK) performed for her myopia of -6.25 -0.50 × 096 and -6.75 -0.50 × 175 in the right and left eye, respectively. Corrected distance visual acuity (CDVA) preoperatively was 20/16. Preoperatively, there were no abnormalities on Scheimpflug imaging, and a pachymetry of 585 µm was measured in both eyes. Flap thickness was 115 µm. The patient was quite nervous during the surgery. Since the surgery, her uncorrected distance visual acuity (UDVA) and CDVA are suboptimal at 20/30 and 20/20 in the right eye, and 20/20 and 20/16 in the left eye. 3 months postoperatively, there is a stable manifest refraction of +0.25 -1.25 × 030 and +0.25 -0.00 × 0. The keratometric astigmatism in the Scheimpflug imaging is 1.2 diopter (D) × 114 and 0.4 D × 78 in the right and left eyes, respectively (FIgures 1 and 2). Thinnest pachymetry is 505 µm and 464 µm in the right and left eye, respectively. Her wavefront analysis shows refraction in a 6 mm zone of -0.99 -1.22 × 32 and -0.91 -0.36 × 136. The cycloplegic refraction is 1.25 -1.00 × 023 and +1.00 -0.25 × 006 (Figures 3 and 4). What is the cause of the suboptimal visual outcome in this case? What would be your treatment strategy to improve visual outcome?

A comparison of keratoconus progression following collagen cross-linkage using standard or personalised keratometry thresholds.

OBJECTIVE: To define how estimates of keratoconus progression following collagen cross-linking (CXL) vary according to the parameter selected to measure corneal shape. MATERIALS AND METHODS: We estimated progression following CXL in 1677 eyes. We compared standard definitions of keratoconus progression based on published thresholds for Kmax, front K2, or back K2, or progression of any two of these three parameters, with the option of an increased threshold for Kmax values ≥ 55D. As corneal thickness reduces unpredictably after CXL, it was excluded from the principal analysis. We then repeated the analysis using novel adaptive estimates of progression for Kmax, front K2, or back K2, developed separately using 6463 paired readings from keratoconus eyes, with a variation of the Bland-Altman method to determine the 95% regression-based limits of agreement (LoA). We created Kaplan-Meier survival plots for both standard and adaptive thresholds. The primary outcome was progression five years after a baseline visit 9-15 months following CXL. RESULTS: Progression rates were 8% with a standard (≥ 1.5D) threshold for K2 or 6% with the static multi-parameter definition. With a ≥ 1D threshold for Kmax, the progression was significantly higher at 29%. With adaptive Kmax or K2, the progression rates were similar (20%) but less than with the adaptive multi-parameter method (22%). CONCLUSIONS: Estimates of keratoconus progression following CXL vary widely according to the reference criteria. Using adaptive thresholds (LoA) to define the repeatability of keratometry gives estimates for progression that are markedly higher than with the standard multi-parameter method.

An in vitro assessment of the thermoreversible PLGA-PEG-PLGA copolymer: Implications for Descemet's membrane endothelial keratoplasty.

BACKGROUND: To explore the use of a thermoreversible copolymer gel coating to prevent donor tissue scrolling in Descemet's membrane endothelial keratoplasty (DMEK). METHODS: PLGA-PEG-PLGA triblock copolymer was synthesised via ring opening polymerisation. Two formulations were fabricated and gelation properties characterised using rheological analyses. Endothelial cytotoxicity of the copolymer was assessed using a Trypan Blue exclusion assay. Thickness of the copolymer gel coating on the endothelial surface was analysed using anterior segment optical coherence tomography (OCT) (RTVue-100, Optovue Inc.). Gold nanoparticles were added to the copolymer to aid visualisation using OCT. Prevention of Descemet membrane donor scrolling was represented via a novel, in vitro, immersion of copolymer coated donor graft material. RESULTS: Two different formulations of PLGA-PEG-PLGA copolymer were successfully fabricated and the desired peak gelling temperature of 24°C was achieved by polymer blending. Application of 20%, 30% and 40% (wt/vol) polymer concentrations resulted in a statistically significant increase in polymer thickness on the endothelium (p < 0.001). There was no detectable endothelial cytotoxicity. The polymer was easy to apply to the endothelium and prevented scrolling of the DMEK graft. CONCLUSION: This PLGA-PEG-PLGA thermoreversible copolymer gel could be exploited as a therapeutic aid for preventing DMEK graft scrolling.

The Vision Correction Questionnaire: an electronic patient-reported outcome measure for refractive surgery.

PURPOSE: To develop a psychometrically robust electronic patient reported outcome measure (ePROM) for refractive surgery. SETTING: Moorfields Eye Hospital, London, United Kingdom. DESIGN: Questionnaire development study. METHODS: Items were derived in 6 domains (spectacle dependence, visual quality, eye comfort, functional freedom, emotional wellbeing, and satisfaction with treatment) from existing Rasch adjusted instruments, patient and surgeon feedback, and refinement in semistructured interviews before administration to a field test cohort (n = 360) of patients undergoing routine refractive surgery. Spectacle dependence and satisfaction with treatment items were used to provide descriptive statistical information only. Contemporary criteria for item reduction and Rasch modeling were applied to the remaining domains. The finalized questionnaire was then administered to a second patient cohort (n = 120) before and after surgery to assess sensitivity to change. RESULTS: A 5-item scale derived for emotional wellbeing was unidimensional and a good fit to the Rasch model with ordered category response profiles, adequate precision (person separation 2.22 logits, reliability coefficient 0.83), and no misfitting items. Mean logit scores were 0.91 higher after treatment (effect size 1.26) suggesting a positive impact on emotional wellbeing. Functional scales could not be derived for visual quality, eye comfort, or functional freedom. Single-item ratings for visual quality and eye comfort were retained in our final 11-item questionnaire. CONCLUSIONS: This short ePROM should integrate well with routine clinical care and clinical trials in refractive surgery. The Rasch adjusted emotional wellbeing scale may help quantify the way patients feel about refractive surgery, with the remaining items providing useful descriptive information.

Personalized Model to Predict Keratoconus Progression From Demographic, Topographic, and Genetic Data.

PURPOSE: To generate a prognostic model to predict keratoconus progression to corneal crosslinking (CXL). DESIGN: Retrospective cohort study. METHODS: We recruited 5025 patients (9341 eyes) with early keratoconus between January 2011 and November 2020. Genetic data from 926 patients were available. We investigated both keratometry or CXL as end points for progression and used the Royston-Parmar method on the proportional hazards scale to generate a prognostic model. We calculated hazard ratios (HRs) for each significant covariate, with explained variation and discrimination, and performed internal-external cross validation by geographic regions. RESULTS: After exclusions, model fitting comprised 8701 eyes, of which 3232 underwent CXL. For early keratoconus, CXL provided a more robust prognostic model than keratometric progression. The final model explained 33% of the variation in time to event: age HR (95% CI) 0.9 (0.90-0.91), maximum anterior keratometry 1.08 (1.07-1.09), and minimum corneal thickness 0.95 (0.93-0.96) as significant covariates. Single-nucleotide polymorphisms (SNPs) associated with keratoconus (n=28) did not significantly contribute to the model. The predicted time-to-event curves closely followed the observed curves during internal-external validation. Differences in discrimination between geographic regions was low, suggesting the model maintained its predictive ability. CONCLUSIONS: A prognostic model to predict keratoconus progression could aid patient empowerment, triage, and service provision. Age at presentation is the most significant predictor of progression risk. Candidate SNPs associated with keratoconus do not contribute to progression risk.

Safety-Net Suture for Aphakic Descemet Membrane Endothelial Keratoplasty.

PURPOSE: The purpose of this research was to describe a low-cost, accessible method for reducing the risk of posterior donor dislocation in Descemet membrane endothelial keratoplasty (DMEK) performed in eyes with aphakia and a large iris defect (unicameral eyes)-the "safety-net suture." METHODS: We review 3 cases of aphakic bullous keratopathy in unicameral eyes treated successfully using DMEK aided by a simple technique to create a temporary, partial barrier between the anterior and posterior chambers. The safety-net suture technique is based on a continuous 10-0 polypropylene suture placed across the anterior chamber in a cat's-cradle pattern anterior to the trabecular meshwork. At the end of surgery, after air tamponade of the DMEK donor, the 10-0 polypropylene suture is removed. RESULTS: All 3 cases were completed with no intraoperative posterior dislocation. A partial postoperative detachment in 1 case was successfully treated with repeat air tamponade. The corneas remain clear in early follow-up, 1 to 10 months after surgery. CONCLUSIONS: The safety-net suture is a simple, low-cost method of reducing the risk of intraoperative posterior dislocation for DMEK in unicameral, aphakic eyes.

Accelerated Pulsed High-Fluence Corneal Cross-Linking for Progressive Keratoconus.

PURPOSE: To report on 2-year results of accelerated corneal collagen cross-linking (CXL) in progressive ectasia using the Avedro KXL system. DESIGN: Prospective interventional case series. METHODS: A total of 870 patients (1,192 eyes) attending Moorfields Eye Hospital after CXL were included. All patients undergoing CXL had progressive keratoconus. Corneas with a minimum stromal thickness <375 µm were excluded. Riboflavin 0.1% soak duration was 10 minutes. High-fluence pulsed UVA was delivered at 30 mW/cm2 for 4 minutes, with a 1.5-second on/off cycle (total energy 7.2 J/cm2). Subjective refractive, corneal tomography, and specular microscopy were performed at baseline, 6, 12, and 24 months postoperatively. The primary outcome measure was a change in maximum keratometry (Kmax) at 24 months. RESULTS: Twelve- and 24-month follow-up data were available on 543 and 213 patients, respectively (mean age 25.4 ± 6.6 years). In mild cones (Kmax < 55 diopter [D]), mean keratometry remained unchanged at 24 months. In more advanced disease, we observed modest corneal flattening compared to baseline (Kmax 63.2 ± 6.5 D vs 61.9 ± 8.1 D, P = .02), but no significant changes in central keratometry (K1 or K2). Keratometric stabilization was confirmed in 98.3% of eyes. Mean CDVA, manifest refraction and endothelial cell density did not change. Overall, 2.7% of eyes lost more than 2 lines of CDVA. CONCLUSION: Accelerated pulsed CXL is a safe, effective, and refractively neutral intervention (at 2 years) to halt disease progression in keratoconus.

LiQD Cornea: Pro-regeneration collagen mimetics as patches and alternatives to corneal transplantation.

Transplantation with donor corneas is the mainstay for treating corneal blindness, but a severe worldwide shortage necessitates the development of other treatment options. Corneal perforation from infection or inflammation is sealed with cyanoacrylate glue. However, the resulting cytotoxicity requires transplantation. LiQD Cornea is an alternative to conventional corneal transplantation and sealants. It is a cell-free, liquid hydrogel matrix for corneal regeneration, comprising short collagen-like peptides conjugated with polyethylene glycol and mixed with fibrinogen to promote adhesion within tissue defects. Gelation occurs spontaneously at body temperature within 5 min. Light exposure is not required-particularly advantageous because patients with corneal inflammation are typically photophobic. The self-assembling, fully defined, synthetic collagen analog is much less costly than human recombinant collagen and reduces the risk of immune rejection associated with xenogeneic materials. In situ gelation potentially allows for clinical application in outpatient clinics instead of operating theaters, maximizing practicality, and minimizing health care costs.

Pyramidal Aberrometry in Wavefront-Guided Myopic LASIK.

PURPOSE: To evaluate measurement repeatability and clinical results for pyramidal aberrometry in routine myopic wavefront-guided laser in situ keratomileusis (LASIK). METHODS: Results from 265 consecutive eyes treated with myopic wavefront-guided LASIK using the Amaris 1050RS Excimer Laser and Peramis pyramidal aberrometer (SCHWIND eye-tech-solutions GmbH) were reviewed. Limits of repeatability were calculated for the aberrometric refraction spherical equivalent and higher order aberrations for the Peramis aberrometer using results from three consecutive scans acquired preoperatively and postoperatively for the first 100 eyes treated. RESULTS: The 95% limits of repeatability for pyramidal aberrometric measurement were: 0.3 diopters (D) for sphere, 0.2 D for cylinder, and 0.1 D (dioptric equivalent) for 3rd and 4th order aberration indices. A total of 95% of eyes were within ±0.50 D of the manifest refraction spherical equivalent target postoperatively. Uncorrected distance visual acuity was 20/20 or better in 96% of 232 eyes with a plano refraction target outcome. A total of 97% of eyes had a refraction cylinder of 0.50 D or less. No eyes lost one or more line of corrected distance visual acuity. CONCLUSIONS: These data demonstrate good measurement repeatability, safety, and efficacy for pyramidal aberrometry in routine myopic LASIK. [J Refract Surg. 2020;36(7):442-448.].

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.

Keratoconus Natural Progression: A Systematic Review and Meta-analysis of 11 529 Eyes.

PURPOSE: We set out to describe the natural history of keratoconus. We included untreated patients, and our key outcome measures were vision, refraction, and corneal curvature. CLINICAL RELEVANCE: Keratoconus affects 86 in 100 000 people, causing visual loss due to increasing irregular corneal astigmatism, and the quality of life declines in patients. Interventions are used to stabilize the disease or improve vision, including corneal cross-linking (CXL) and grafting, but these carry risks. Detailed knowledge of the natural history of keratoconus is fundamental in making informed decisions on when their benefits outweigh these risks. METHODS: We included prospective or retrospective studies of pediatric or adult patients who reported 1 or more of visual acuity, refraction, and corneal curvature measures: steep keratometry (K2), mean keratometry (Kmean), or maximum keratometry (Kmax), thinnest pachymetry, corneal transplantation rates, corneal scarring incidence, and patient-reported outcome measures (PROMs). Databases analyzed included Medline, Embase, CENTRAL, and CINAHL. Searches were carried out until October 2018. Bias assessment was carried out using the Joanna Briggs Institute model of evidence-based healthcare. RESULTS: Our search yielded 3950 publication titles, of which 41 were included in our systematic review and 23 were incorporated into the meta-analysis. Younger patients and those with greater Kmax demonstrated more steepening of Kmax at 12 months. The meta-analysis for Kmax demonstrated a significant increase in Kmax of 0.7 diopters (D) at 12 months (95% confidence interval [CI], 0.31-1.14; P = 0.003). Our meta-regression model predicted that patients had 0.8 D less Kmax steepening over 12 months for every 10-year increase in age (P = 0.01). Patients were predicted to have 1 D greater Kmax steepening for every 5 D of greater baseline Kmax (P = 0.003). At 12 months, there was a significant increase in the average Kmean of 0.4 D (95% CI, 0.18-0.65; P = 0.004). CONCLUSIONS: We report the first systematic review and meta-analysis of keratoconus natural history data including 11 529 eyes. Younger patients and those with Kmax steeper than 55 D at presentation have a significantly greater risk of progression of keratoconus. Closer follow-up and a lower threshold for cross-linking should be adopted in patients younger than 17 years and steeper than 55 D Kmax.

Deep Anterior Lamellar Keratoplasty for Keratoconus: Multisurgeon Results.

PURPOSE: To examine clinical outcomes in deep anterior lamellar keratoplasty (DALK) for keratoconus using contemporary techniques in a multisurgeon public healthcare setting. DESIGN: Consecutive, retrospective case series. METHODS: Setting: Moorfields Eye Hospital, London, United Kingdom. STUDY POPULATION: Consecutive cases of keratoconus treated with non-laser assisted DALK from September 1, 2012, to September 31, 2016. OBSERVATION PROCEDURE: Data on preoperative status, operative details, intraoperative and postoperative complications, secondary interventions, and visual outcomes were archived for analysis. MAIN OUTCOME MEASURES: Graft failure rate and percentage of patients with corrected distance visual acuity (CDVA) ≥20/40 within 1 year of surgery and at final review after suture removal. RESULTS: Three hundred fifty-seven eyes of 338 patients undergoing DALK (91.3% big-bubble technique attempted) were analyzed. A total of 4.2% (95% confidence interval [CI] 2.4%-6.8%) of corneal transplants had failed within the follow-up period (21.8 ± 11.4 months), and 75.9% of eyes had CDVA ≥20/40 within 1 year of surgery, rising to 81% after suture removal. Forty-two primary surgeons (31 trainees) participated. Intraoperative perforation of Descemet membrane occurred in 45.4% of eyes. A total of 24.1% were converted to penetrating keratoplasty (PK) intraoperatively. Conversion to PK increased the risk of transplant rejection (P = .026; odds ratio [OR] 1.94; 95% CI 1.1-3.5) and secondary glaucoma (P = .016; OR 4.0; 95% CI 1.3-12.4). Transplant rejection increased the risk of graft failure both overall (P = .017; OR = 3.9; 95% CI 1.4-11.0) and when cases converted to PK were excluded (P = .028; OR = 3.35; 95% CI 1.1-9.9). CONCLUSION: DALK for keratoconus achieves early results similar to those published for PK in a multisurgeon setting. Conservative management of intraoperative Descemet membrane perforation, where possible, may be safer than conversion to PK.

Methods for the study of near, intermediate vision, and accommodation: an overview of subjective and objective approaches.

PURPOSE: To present an overview of contemporary methods and metrics used to measure near vision, intermediate vision, and accommodation. METHODS: A search in PubMed was performed with the following key phrases: near vision, intermediate vision, objective and subjective methods for the measurement of accommodation. For subjective methods, we included only those that are most widely used, had a scientific evidence of its outcomes, and have an easy availability at the doctor's office. For objective methods, we included those aberrometers or autorefractometers that have been proven to give good repeatability and reproducibility in the study of changes in optical power of the eye along the accommodative process. RESULTS: Near vision should be tested at 40 cm and intermediate vision at 63 or 80 cm. Accommodation should be measured with objective methods such as autorefractometers or aberrometers. CONCLUSIONS: The standardization for the measurement of near and intermediate vision, as well as the reading charts, will facilitate the comparison of visual outcomes between studies. Measurement of accommodation should be performed with objective methods as subjective methods tend to overestimate the accommodative power.

Phakic intraocular lens as a temporary barrier in aphakic Descemet's membrane endothelial keratoplasty.

BACKGROUND: Descemet's membrane endothelial keratoplasty has a lower risk of endothelial rejection than Descemet's stripping automated endothelial keratoplasty. In aphakic eyes requiring endothelial transplantation, approaches aimed at reducing the risk of posterior graft dislocation in Descemet's stripping automated endothelial keratoplasty are not transferable to Descemet's membrane endothelial keratoplasty. TECHNIQUE: Here we describe the use of an implantable collamer lens placed over the iris to provide a temporary intraoperative platform, to facilitate graft unfolding and to avoid posterior graft dislocation in an aphakic, vitrectomised eye with a fixed, dilated pupil in a young patient with chronic uveitis and previous failed Descemet's stripping automated endothelial keratoplasty.

Combined wavefront-guided transepithelial photorefractive keratectomy and corneal crosslinking for visual rehabilitation in moderate keratoconus.

PURPOSE: To present 24-month results from the transepithelial photorefractive keratectomy (PRK)-corneal crosslinking (CXL) trial using simultaneous accelerated CXL and a new tissue-saving ocular wavefront-guided transepithelial PRK algorithm aiming to reverse visual loss in early-stage keratoconus without compromise to stabilization of disease progression. SETTING: Moorfields Eye Hospital, London, United Kingdom. DESIGN: Prospective case series. METHOD: Patients with progressive grades I to III keratoconus and logarithm of the minimum angle of resolution (logMAR) corrected distance vision acuity (CDVA) worse than 0.00 (20/20) were included. Consecutive matched historical controls treated only with accelerated CXL were the control group. The main outcome measure was change in logMAR CDVA. RESULTS: The study group comprised 47 eyes of 47 patients (mean age 24.6 years ± 3.8 [SD]). The CDVA improved from 0.28 ± 0.21 logMAR (20/60) preoperatively to 0.15 ± 0.14 logMAR (20/30) 24 months after transepithelial PRK-CXL (P < .001). Twelve eyes gained and 1 eye lost 2 lines or more of CDVA. The mean stromal ablation depth at the cone apex was 35 ± 15 µm. Significant reductions in the maximum keratometry (K) reading and coma were evident in topographic comparison maps. The controls (n = 47) had no significant changes in CDVA, higher-order aberrations, or K values. The mean K values in both groups were stable from 6 months after treatment. CONCLUSION: Ocular wavefront-guided transepithelial PRK-CXL resulted in significant gains in CDVA without compromising CXL efficacy over a 24-month follow-up.

Organ culture storage of pre-prepared corneal donor material for Descemet's membrane endothelial keratoplasty.

PURPOSE: To evaluate the effect of media composition and storage method on pre-prepared Descemet's membrane endothelial keratoplasty (DMEK) grafts. METHODS: 50 corneas were used. Endothelial wound healing and proliferation in different media were assessed using a standard injury model. DMEK grafts were stored using three methods: peeling with free scroll storage; partial peeling with storage on the stroma and fluid bubble separation with storage on the stroma. Endothelial cell (EC) phenotype and the extent of endothelial overgrowth were examined. Global cell viability was assessed for storage methods that maintained a normal cell phenotype. RESULTS: 1 mm wounds healed within 4 days. Enhanced media did not increase EC proliferation but may have increased EC migration into the wounded area. Grafts that had been trephined showed evidence of EC overgrowth, whereas preservation of a physical barrier in the bubble group prevented this. In grafts stored in enhanced media or reapposed to the stroma after trephination, endothelial migration occurred sooner and cells underwent endothelial-mesenchymal transformation. Ongoing cell loss, with new patterns of cell death, was observed after returning grafts to storage. Grafts stored as free scrolls retained more viable ECs than grafts prepared with the fluid bubble method (74.2± 3% vs 60.3±6%, p=0.04 (n=8). CONCLUSION: Free scroll storage is superior to liquid bubble and partial peeling techniques. Free scrolls only showed overgrowth of ECs after 4 days in organ culture, indicating a viable time window for the clinical use of pre-prepared DMEK donor material using this method. Methods for tissue preparation and storage media developed for whole corneas should not be used in pre-prepared DMEK grafts without prior evaluation.

Global cell-by-cell evaluation of endothelial viability after two methods of graft preparation in Descemet membrane endothelial keratoplasty.

PURPOSE: To describe a novel method of global cell viability assessment for Descemet membrane endothelial keratoplasty (DMEK) and the comparison of two contemporary methods of donor tissue preparation. METHODS: DMEK transplants were prepared using two different methods: liquid bubble separation and manual peeling (n=8 each group). Samples were incubated with Hoechst, calcein-AM and ethidium homodimer prior to mounting on a curved imaging chamber. Z-stacked fluorescence microscopy images were combined to produce an in-focus global image capable of resolving all cell nuclei. Image processing software was used to define a calcein-positive live cell area, count all cell nuclei within this area and subtract ethidium-positive dead cells to derive the total viable endothelial cell count. Corrected global cell density was calculated by dividing the number of viable cells by the graft area, which had been corrected for imaging a curved surface. RESULTS: Corrected global cell density was lower than the central endothelial cell density in both groups: 85.5% of the pre-preparation central endothelial cell density in the peel group and 75.8% in the bubble group. Corrected global cell density was significantly lower in the liquid bubble separation group than in the peel group (p=0.04). CONCLUSIONS: Eye bank estimations of central endothelial cell density overestimate true cell density after graft preparation in DMEK. A peel method is less damaging and more consistent than a liquid bubble method. Cell loss correlated strongly with the degree of stromal hydration prior to bubble separation in the liquid bubble group.

A Comparison of Different Corneal Iontophoresis Protocols for Promoting Transepithelial Riboflavin Penetration.

PURPOSE: To measure corneal riboflavin penetration using different transepithelial iontophoresis protocols. METHODS: Freshly enucleated rabbit eyes were divided into nine treatment groups of 4 eyes. One group, in which 0.1% wt/vol riboflavin was applied for 30 minutes without iontophoresis after corneal epithelial debridement, acted as a control. The remaining groups were treated with an intact epithelium using different riboflavin formulations and varying iontophoresis current, soak, and rinse times. After riboflavin application, eyes were snap frozen in liquid nitrogen. Corneal cross sections 35 µm thick were then imaged immediately by two-photon fluorescence microscopy, using image processing software to quantify stromal riboflavin concentration at different corneal depths. RESULTS: In the epithelium-on iontophoresis treatment groups, greater stromal riboflavin penetration was achieved with higher-concentration riboflavin solutions, greater iontophoresis dosage, and longer solution contact times. A protocol utilizing 0.25% wt/vol riboflavin with benzalkonium chloride (BAC) 0.01% and two cycles of applied current and subsequent soaking (1 mA 5 minutes, soak 5 minutes; 0.5 mA 5 minutes, soak 5 minutes) achieved similar stromal riboflavin penetration to epithelium-off controls. The best-performing non-BAC-containing protocol produced stromal riboflavin penetration approximately 60% that of epithelium-off controls. Riboflavin solutions containing saline resulted in minimal stromal penetration. Riboflavin loading within the epithelium was equivalent to or higher than that in the subjacent stroma, despite rinsing the ocular surface with balanced salt solution. CONCLUSIONS: Modified iontophoresis protocols can significantly improve transepithelial riboflavin penetration in experimental corneal collagen cross-linking.