Infectious keratitis following corneal transplantation: A long-term cohort study.

BACKGROUND: To assess the long-term incidence and risk factors for post-keratoplasty infectious keratitis (IK), associated ocular pathogens, and antibiotic resistance profiles. METHODS: Cohort study including 2553 consecutive penetrating, endothelial, and anterior lamellar keratoplasties performed between 1992 and 2020. Medical and microbiological records of patients clinically diagnosed with IK were retrospectively reviewed. MAIN OUTCOME MEASURES: cumulative incidence of IK, infectious agent species, and antibiotics resistance profiles. RESULTS: The average follow-up time after transplantation was 112 ± 96 months. Eighty-nine IK episodes were recorded; microbiological tests were positive in 55/89 (62%). The cumulated incidence of postoperative IK was 5.50%/10.25% at 10/20 years. The occurrence of at least one episode of IK after transplantation was associated with lower graft survival in the long term (p < 0.0001). Rejection risk (adjusted Hazard Ratio, 2.29) and postoperative epithelial complications (HR, 3.44) were significantly and independently associated with a higher incidence of postoperative IK. Infectious agents included 41 bacteria, 10 HSV, 6 fungi, and 1 Acanthamoeba. The rate of antibiotic resistance was 0% for vancomycin, 13% for fluoroquinolones, 20% for rifamycin, 59% for aminoglycosides, and 73% for ticarcillin. In 41% of cases, patients were under prophylactic topical antibiotics before the infectious episode. Topical antibiotics were significantly associated with increased resistance to penicillin, carbapenems, and aminoglycosides. CONCLUSION: IK (mainly bacterial) is a frequent complication of corneal transplantation in the long term. Vancomycin and fluoroquinolones can be considered as first-line treatments. Prolonged postoperative antibiotic preventive treatment is not advisable as it may increase antibiotic resistance.

Development, structure, and bioengineering of the human corneal stroma: A review of collagen-based implants.

Bio-engineering technologies are currently used to produce biomimetic artificial corneas that should present structural, chemical, optical, and biomechanical properties close to the native tissue. These properties are mainly supported by the corneal stroma which accounts for 90% of corneal thickness and is mainly made of collagen type I. The stromal collagen fibrils are arranged in lamellae that have a plywood-like organization. The fibril diameter is between 25 and 35 nm and the interfibrillar space about 57 nm. The number of lamellae in the central stroma is estimated to be 300. In the anterior part, their size is 10-40 µm. They appear to be larger in the posterior part of the stroma with a size of 60-120 µm. Their thicknesses also vary from 0.2 to 2.5 µm. During development, the acellular corneal stroma, which features a complex pattern of organization, serves as a scaffold for mesenchymal cells that invade and further produce the cellular stroma. Several pathways including Bmp4, Wnt/ß-catenin, Notch, retinoic acid, and TGF-ß, in addition to EFTFs including the mastering gene Pax-6, are involved in corneal development. Besides, retinoic acid and TGF- ß seem to have a crucial role in the neural crest cell migration in the stroma. Several technologies can be used to produce artificial stroma. Taking advantage of the liquid-crystal properties of acid-soluble collagen, it is possible to produce transparent stroma-like matrices with native-like collagen I fibrils and plywood-like organization, where epithelial cells can adhere and proliferate. Other approaches include the use of recombinant collagen, cross-linkers, vitrification, plastically compressed collagen or magnetically aligned collagen, providing interesting optical and mechanical properties. These technologies can be classified according to collagen type and origin, presence of telopeptides and native-like fibrils, structure, and transparency. Collagen matrices feature transparency >80% for the appropriate 500-µm thickness. Non-collagenous matrices made of biopolymers including gelatin, silk, or fish scale have been developed which feature interesting properties but are less biomimetic. These bioengineered matrices still need to be colonized by stromal cells to fully reproduce the native stroma.

Multimodal imaging of Hurler syndrome-related keratopathy treated with deep anterior lamellar keratoplasty.

BACKGROUND: Hurler syndrome-associated keratopathy is an exceedingly rare corneal disorder that requires corneal transplantation in advanced stages. Precise assessment of the corneal condition is necessary for deciding which type of keratoplasty (i.e., deep anterior lamellar or penetrating) should be proposed. We aimed to confront the results of multimodal imaging with those of histology in a case of Hurler syndrome-associated keratopathy. CASE PRESENTATION: A 16-year-old patient with Hurler's syndrome treated with hematopoietic stem cell transplantation was referred for decreased vision related to advanced keratopathy. The patient was treated with deep anterior lamellar keratoplasty (DALK) in both eyes with uncomplicated outcome. Visual acuity improved from 0.1 (20/200) preoperatively to 0.32 (20/63) and 0.63 (20/32) after transplantation. The corneal endothelial cell density was 2400 cells/mm2 in both eyes 3 years after transplantation. In vivo confocal microscopy (IVCM) and spectral domain optical coherence tomography (SD-OCT) were performed preoperatively. The corneal buttons retrieved during keratoplasty were processed for histology. In SD-OCT scans, corneal opacities appeared as diffuse stromal hyperreflectivity associated with increased corneal thickness. IVCM showed diffuse cytoplasmic granular hyperreflectivity and rounded/ellipsoid aspects of keratocytes, presence of small intracellular vacuoles, and hyperreflective epithelial intercellular spaces. Bowman's layer was thin and irregular. The corneal endothelium was poorly visualized but no endothelial damage was observed. Histology showed irregular orientation and organization of stromal lamellae, with the presence of macrophages whose cytoplasm appeared clear and granular. A perinuclear clear halo was visible within the epithelial basal cells. Bowman's layer featured breaks and irregularities. CONCLUSIONS: The observed corneal multimodal imaging features in mucopolysaccharidosis-related keratopathy were concordant with histology. Compared with standard histology, multimodal imaging allowed additional keratocyte features to be observed. It revealed both morphological and structural changes of all corneal layers but the endothelium. This information is essential for therapeutic management which should include DALK as the first-choice treatment in case of impaired visual acuity.

Assessment of Confocal Microscopy for the Diagnosis of Polymerase Chain Reaction-Positive Acanthamoeba Keratitis: A Case-Control Study.

PURPOSE: To determine in vivo confocal microscopy diagnostic criteria to diagnose Acanthamoeba keratitis (AK) using polymerase chain reaction (PCR) as the reference diagnostic technique. DESIGN: Retrospective case-control study. Data were recorded prospectively and analyzed retrospectively. PARTICIPANTS: Fifty patients with PCR-positive AK (study group) and 50 patients with bacterial, fungal, viral, or immune keratitis featuring negative Acanthamoeba PCR results (control group). METHODS: In vivo confocal microscopy performed at the acute stage of keratitis. MAIN OUTCOME MEASURES: Presence of in vivo confocal microscopy images suggestive of AK. Multivariate logistic regression was used to determine the relationship between types of images and presence of PCR-positive AK. RESULTS: The following 4 types of images were associated significantly with PCR-positive AK (P < 0.05): bright spots (round or ovoid hyperreflective objects with no double wall; diameter, <30 µm); target images (hyperreflective objects with hyporeflective halo; diameter, <30 µm); clusters of hyperreflective objects (diameter, <30 µm); and trophozoite-like objects (diameter, >30 µm). Specificity of both target and trophozoite images was 100%. This figure was 98.2% for clusters and 48.2% for bright spots. If the diagnosis of AK was made on presence of target images, clusters or trophozoite images (at least 1 of the 3 features), the positive predictive value of confocal microscopy was 87.5% and the negative predictive value was 58.5%. CONCLUSIONS: Acanthamoeba keratitis is a serious vision-threatening disease. In vivo confocal microscopy can help in this challenging diagnosis, especially when PCR is delayed, shows negative results, or is not available. Target images and trophozoite-like images are pathognomonic of AK. Clusters of hyperreflective objects are highly specific of AK. However, the overall sensitivity of in vivo confocal microscopy features of AK is low. In addition to the clinical features, microbiological tests (direct examination and cultures of corneal scrapings), and PCR, in vivo confocal microscopy allows for more rapid diagnosis and treatment initiation, potentially leading to an improved outcome.

Incidence of Intraocular Pressure Elevation and Glaucoma after Lamellar versus Full-Thickness Penetrating Keratoplasty.

PURPOSE: To analyze the cumulated incidence of glaucoma after penetrating keratoplasty (PK), anterior lamellar keratoplasty (ALK), and endothelial keratoplasty (EK). DESIGN: Cohort study. Data were recorded prospectively and analyzed retrospectively. PARTICIPANTS: A total of 1657 consecutive eyes of 1657 patients undergoing corneal transplantation between 1992 and 2013. METHODS: Penetrating keratoplasty (date range, 1992-2013), ALK (date range, 2002-2013), and Descemet's stripping automated EK (date range, 2006-2013). MAIN OUTCOME MEASURES: Postoperative intraocular pressure (IOP), glaucoma treatments, and glaucoma-related loss of vision (loss of central visual function resulting in absence of light perception or light perception limited to the temporal visual field). Cox proportional hazard regression model was used to analyze risk factors for glaucoma after keratoplasty. RESULTS: The 10-year cumulated incidence of elevated IOP and elevated IOP requiring treatment was 46.5% and 38.7%, respectively. In multivariate analysis, 4 variables were significantly associated with a higher incidence of elevated IOP requiring treatment after keratoplasty: preoperative glaucoma or IOP >20 mmHg (adjusted hazard ratio [HR], 1.56; P < 0.001), penetrating keratoplasty (PK) (adjusted HR, 1.12 vs. ALK and 1.10 vs. EK; P < 0.001), postoperative lens status (adjusted HR vs. phakic eyes: 1.15 for posterior chamber intraocular lens, 1.43 for anterior chamber intraocular lens [IOL], 2.83 for aphakic eyes; P < 0.001), and IOL exchange or removal during surgery (adjusted HR, 1.48; P < 0.001). Recipient age, preoperative diagnosis, filtering surgery before keratoplasty, vitrectomy associated with keratoplasty, and filtering surgery associated with keratoplasty were significantly associated with a higher incidence of elevated IOP requiring treatment after keratoplasty in univariate analysis but not in multivariate analysis. The 10-year probability of loss of vision related to glaucoma was 1.0% after EK, 2.1% after ALK, and 3.6% after PK (P = 0.036). CONCLUSIONS: The incidence of elevation of IOP after keratoplasty and development of glaucoma are significantly decreased with ALK and EK compared with PK. We believe this is due to diminished surgery-induced damage to the anterior chamber angle and trabecular meshwork, and reduced postoperative use of steroids.

Corneal radius of curvature after anterior lamellar versus penetrating keratoplasty.

BACKGROUND: Keratoplasty may induce major spherical refractive error related to abnormal corneal radius of curvature (CRC). METHODS: Two hundred and thirty-eight consecutive eyes of 238 patients with clear graft and at least one postoperative Orbscan examination performed after suture removal (average follow-up time, 86 months) were retrospectively analyzed. Anterior lamellar keratoplasties (ALK group, n = 119) and penetrating keratoplasties (PK group, n = 119) were matched for preoperative diagnosis and lens status. RESULTS: The average postoperative, suture-out, Orbscan 3-mm CRC was 7.17 mm with a wide 95 % confidence interval [6.26 mm; 8.37 mm]. It was 7.05 mm in the ALK group and 7.31 mm in the PK group (p < 0.01). In the ALK group, this figure was 7.00 mm for oversized grafts and 7.67 mm for non-oversized grafts (p < 0.001). CRC values were significantly lower for eyes with keratoconus (7.00 mm) or stromal scar after infectious keratitis (7.06 mm) compared with stromal scar after trauma (7.74 mm) or stromal dystrophies (8.17 mm). Values were significantly lower for big-bubble ALKs (6.92 mm) and manual dissection-ALKs (7.14 mm) compared with PKs (7.31 mm) and microkeratome-assisted ALKs (7.45 mm). The average Orbscan 3-mm SimK cylinder, irregularity, and refractive power symmetry index were, respectively, 4.7 D/4.8 D/1.9 D for ALKs and 5.2 D/4.8 D/1.8 D for PKs (p = 0.99). CONCLUSIONS: The CRC is lower after ALK compared with PK, and features important variability. In eyes with ALK, non-oversized grafts result in postoperative CRC close to normal values and corneal diseases associated with stromal thinning and DALK result in lower postoperative CRC.

Long-term results of deep anterior lamellar versus penetrating keratoplasty.

OBJECTIVE: To compare deep anterior lamellar keratoplasty (DALK) with penetrating keratoplasty (PK) in eyes with corneal diseases not involving the corneal endothelium (keratoconus, scars after infectious keratitis, stromal dystrophies, and trauma). DESIGN: Retrospective, comparative case series. PARTICIPANTS: One hundred forty-two consecutive DALK (DALK group; big-bubble technique or manual lamellar dissection using a slitlamp) and 142 matched PK (PK group). METHODS: Three models were used to describe the postoperative outcomes of the endothelial cell density. A joint regression model was used to predict long-term graft survival. Visual acuity, ultrasound pachymetry, specular microscopy, and optical coherence tomography (OCT) findings were recorded. MAIN OUTCOME MEASURES: Postoperative endothelial cell loss and long-term predicted graft survival. RESULTS: The average 5-year postoperative endothelial cell loss was -22.3% in the DALK group and -50.1% in the PK group (P<0.0001). The early- and late-phase annual rates of endothelial cell loss were -8.3% and -3.9% per year, respectively, in the DALK group and -15.2% and -7.8% per year in the PK group (P<0.001; biphasic linear model). The median predicted graft survival was 49.0 years in the DALK group and 17.3 years in the PK group (P<0.0001). The average visual acuity was lower in the manual dissection subgroup compared with the PK group (average difference, 1.0 to 1.8 line) and with the big-bubble subgroup (average difference, 2.2 to 2.5 lines). The average central corneal thickness at 12 months was 536 µm in the PK group, 523 µm in the big-bubble subgroup, and 562 µm in the manual dissection subgroup (P<0.001). The average thickness of the residual recipient stroma measured by OCT was 87±26 µm in the manual dissection subgroup. No correlation was found between this figure and logarithm of the minimal angle of resolution at any postoperative time point (P>0.05). CONCLUSIONS: Long-term, model-predicted graft survival and endothelial densities are higher after DALK than after PK. The big-bubble technique gives better results than manual dissection and PK. Compared with PK, manual dissection provides higher survival of both the corneal endothelium and graft, but lower visual acuity.

Corneal Epithelial Thickness Mapping in the Diagnosis of Ocular Surface Disorders Involving the Corneal Epithelium: A Comparative Study.

PURPOSE: The purpose of this study was to analyze the role of corneal epithelial thickness (ET) mapping provided by spectral domain optical coherence tomography in the diagnosis of ocular surface disorders (OSDs) involving the corneal epithelium. DESIGN: This was a retrospective comparative study. METHODS: Institutional settings are as follows. Study population includes 303 eyes with an OSD and 55 normal eyes (controls). Observation procedures include spectral domain optical coherence tomography with epithelial mapping in the central 6 mm. Main outcome measures include ET map classification (normal, doughnut, spoke-wheel, localized/diffuse, and thinning/thickening patterns) and ET data and statistics (minimum, maximum, and SD). A quantitative threshold was determined with receiver operating curves to distinguish pathological from normal corneas. Sensitivity and specificity of classification and quantitative data were calculated using all eyes to assess the ability to distinguish corneas with a given corneal disorder from other conditions. RESULTS: Classification of full agreement between 3 readers was obtained in 75.4% to 99.4% of cases. Main OSD features were keratoconus (135 eyes), doughnut pattern (sensitivity/specificity = 56/94%), and max-min ET ≥ 13 µm (84/43%); limbal deficiency (56 eyes), spoke-wheel pattern (66/98%), and max-min ET ≥ 14 µm (91/59%); epithelial basement membrane dystrophy (55 eyes), inferior thickening pattern (55/92%), and central ET > 56 µm (53/81%); dry eye (21 eyes), superior thinning pattern (67/88%), and minimal ET ≤ 44 µm (86/48%); pterygium (10 eyes), nasal thickening pattern (100/86%), and nasal ET > 56 µm (80/71%); and in situ carcinoma (11 eyes), max ET > 60 µm (91/60%), and ET SD >5 µm (100/58%). CONCLUSIONS: The epithelial map pattern recognition combined with quantitative analysis of ET is relevant for the diagnosis of OSDs and for distinguishing various OSDs from each other. Deep learning analysis of big data could lead to the fully automated diagnosis of these disorders.

Multimodal imaging of pre-Descemet corneal dystrophy.

PURPOSE: The aim of this study was to assess structural and histological changes associated with pre-Descemet corneal dystrophy with multimodal in vivo imaging. METHODS: Retrospective case series including eight corneas from four unrelated male patients with pre-Descemet corneal dystrophy characterized by the presence of punctiform gray opacities located just anterior to the Descemet membrane at slit-lamp examination of both eyes. In vivo confocal microscopy images were obtained in the central, paracentral, and peripheral corneal zones from the superficial epithelial cell layer down to the corneal endothelium in both eyes. Spectral domain optical coherence tomography scans (central and limbal zones) and mapping of both corneas were acquired. RESULTS: Diffuse small extracellular stromal deposits, presence of enlarged hyperreflective keratocytes in the posterior stroma with either hyperreflective or hyporeflective intracellular dots, and presence of activated keratocytes in the very anterior stroma were observed in all corneas with in vivo confocal microscopy. Spectral domain optical coherence tomography scans showed a hyperreflective line anterior to Descemet's membrane running from limbus to limbus and associated with a second thinner hyperreflective line just beneath Bowman's layer. Fine hyperreflective particles were observed in the posterior, mid, and anterior stroma on optical coherence tomography scans. CONCLUSION: The clinical presentation and structural anomalies found in isolated sporadic pre-Descemet corneal dystrophy are in favor of a degenerative process affecting corneal keratocytes with no epithelial or endothelial involvement. The maximum damage is found just anterior to the Descemet membrane resulting in pre-Descemet membrane location of stromal opacities. Multimodal imaging of cornea reveals that the disorder affects the whole stroma and it permits better understanding of pre-Descemet corneal dystrophy pathophysiology together with ascertained diagnosis.

Corneal stromal stem cells restore transparency after N2 injury in mice.

Corneal scarring associated with various corneal conditions is a leading cause of blindness worldwide. The present study aimed to test the hypothesis that corneal stromal stem cells have a therapeutic effect and are able to restore the extracellular matrix organization and corneal transparency in vivo. We first developed a mouse model of corneal stromal scar induced by liquid nitrogen (N2 ) application. We then reversed stromal scarring by injecting mouse or human corneal stromal stem cells in injured cornea. To characterize the mouse model developed in this study and the therapeutic effect of corneal stromal stem cells, we used a combination of in vivo (slit lamp, optical coherence tomography, in vivo confocal microscopy, optical coherence tomography shear wave elastography, and optokinetic tracking response) and ex vivo (full field optical coherence microscopy, flow cytometry, transmission electron microscopy, and histology) techniques. The mouse model obtained features early inflammation, keratocyte apoptosis, keratocyte transformation into myofibroblasts, collagen type III synthesis, impaired stromal ultrastructure, corneal stromal haze formation, increased corneal rigidity, and impaired visual acuity. Injection of stromal stem cells in N2 -injured cornea resulted in improved corneal transparency associated with corneal stromal stem cell migration and growth in the recipient stroma, absence of inflammatory response, recipient corneal epithelial cell growth, decreased collagen type III stromal content, restored stromal ultrastructure, decreased stromal haze, decreased corneal rigidity, and improved vision. Our study demonstrates the ability of corneal stromal stem cells to promote regeneration of transparent stromal tissue after corneal scarring induced by liquid nitrogen.

Predicted long-term outcome of corneal transplantation.

OBJECTIVE: To analyze graft survival and the outcome of the corneal endothelium after corneal transplantation in a single model to predict the long-term prognosis of these grafts. DESIGN: Cohort study. Data were recorded prospectively and then analyzed retrospectively. PARTICIPANTS: One thousand one hundred forty-four consecutive eyes of 1144 patients who underwent corneal transplantation between 1992 and 2006. INTERVENTIONS: Penetrating keratoplasty and deep anterior lamellar keratoplasty. MAIN OUTCOME MEASURES: Slit-lamp examination and wide-field specular microscopy results. A joint analysis of endothelial cell loss and time to graft failure was undertaken. From midterm simultaneous analysis of graft survival and endothelial cell loss, long-term graft survival was predicted. RESULTS: The observed 5- and 10-year graft survival estimates were, respectively, 74% and 64%. The average endothelial cell density (cell loss) was 2270 cells/mm(2) before surgery, 1058 cells/mm(2) (-53%) during the sixth postoperative year, and 865 cells/mm(2) (-61%) during the 10th postoperative year. Overall, the predicted graft survival estimate was 27% at 20 years and 2% at 30 years. Both observed and predicted graft survival were higher in patients who had undergone lamellar keratoplasty than in patients who had undergone penetrating keratoplasty and had normal recipient endothelium and higher in patients who had undergone penetrating keratoplasty and had normal recipient endothelium than in patients who had undergone penetrating keratoplasty and had impaired recipient endothelium. CONCLUSIONS: For corneal diseases involving the endothelium, penetrating keratoplasty seems to be a good therapeutic approach in elderly patients because the graft life-span may be similar to the patient life expectancy. Conversely, for younger patients, penetrating keratoplasty is only a midterm therapeutic approach. For corneal diseases not involving the endothelium, deep anterior lamellar keratoplasty seems to be a promising therapeutic approach with higher long-term expected survival.

Donor selection, retrieval and preparation of donor tissue. Donor selection.

Corneal transplantation safety is widely dependent on clinical donor selection. Donor-to-host transmission of rabies and Creutzfeldt-Jakob disease is well established, and it is lethal for the recipient. Taking into consideration this latter figure, contraindications to ocular tissue transplantation include not only rabies, contact with rabies virus, spongiform encephalitis, family history of spongiform encephalitis, recipients of human pituitary-derived hormones before 1987, surgery using dura mater and brain/spinal surgery before 1992, but also CNS diseases of unknown etiology or those with unknown risk of transmission. It has been established that hepatitis B virus and herpes simplex virus can be transmitted by corneal transplantation, and both diseases are contraindications to transplantation. HIV infection, syphilis, hepatitis C, hepatitis A, tuberculosis, HTLV-1 and -2 infection, active leprosy, active typhoid, smallpox and active malaria are also contraindications to ocular tissue transplantation even if no evidence of donor-to-recipient transmission has been demonstrated. A history of corneal refractive surgery in the donor eye, ocular inflammation, retinoblastoma, and malignant tumors of the anterior segment are contraindications to keratoplasty.

Long-Term Results of Cultured Limbal Stem Cell Versus Limbal Tissue Transplantation in Stage III Limbal Deficiency.

We aimed to evaluate efficiency and safety of transplantation of limbal stem cells (LSC) cultured on human amniotic membrane with no feeders and to compare cultured LSC with limbal tissue transplantation. Thirty eyes with stage III LSC deficiency were treated with autologous (autoLSC) or allogeneic (alloLSC) cultured LSC transplantation (prospective phase II clinical trial; average follow-up time, 72 months) or autologous (autoLT) or allogeneic (alloLT) limbal tissue transplantation (retrospective control group; average follow-up time, 132 months) between 1993 and 2014. The 5-year graft survival defined by absence of recurrence of the clinical signs of limbal deficiency was 71% for autoLSC, 0% for alloLSC, 75% for autoLT, and 33% for alloLT. Visual acuity improved by 9.2 lines for autoLSC and 3.3 lines for autoLT. It decreased by 0.7 lines for alloLSC and 1.9 lines for alloLT. Adverse events were recorded in 1/7 autoLSC, 7/7 alloLSC, 6/8 autoLT, and 8/8 alloLT patients. Corneal epithelial defect was the only adverse event recorded after autoLSC, whereas severe sight-threatening adverse events were recorded in the remaining three groups. Compared with failed grafts, successful grafts featured greater decrease in fluorescein staining, greater superficial vascularization-free corneal area, lower variability of the corneal epithelial thickness, and higher corneal epithelial basal cell density. Autologous cultured LSC transplantation was associated with high long-term survival and dramatic improvement in vision and was very safe. Autologous limbal tissue transplantation resulted in similar efficiency but was less safe. Cadaver allogeneic grafts resulted in low long-term success rate and high prevalence of serious adverse events. Stem Cells Translational Medicine 2019;8:1230&1241.

Comparison of techniques used for removing the recipient stroma in anterior lamellar keratoplasty.

OBJECTIVE: To compare 3 techniques used for removing the recipient stroma during anterior lamellar keratoplasty (ALK): the "big-bubble" technique, manual dissection using a crescent blade and slitlamp operating microscope, and microkeratome lamellar cut. DESIGN: Retrospective comparative cohort study of 69 consecutive ALKs and 69 consecutive penetrating keratoplasties (PKs). Manifest refraction, slitlamp examination, Goldmann tonometry, ultrasound pachymetry, specular microscopy, and confocal microscopy findings were recorded. RESULTS: The 12-month graft survival estimate was 98.5% in the ALK group and 94.1% in the PK group (P = .19). Higher endothelial cell density was found after ALK (P < .001). At 12 months (before suture removal), 53% of eyes that underwent ALK and 44% of eyes that underwent PK had 20/40 or better spectacle-corrected visual acuity (P = .24). In keratoconic eyes, these values were 83% and 69%, respectively (P = .18). Significant differences in visual acuity, corneal central thickness, and keratocyte density among ALK subgroups were found, with the best results obtained using the big-bubble technique and the worst results obtained using the microkeratome. In eyes that underwent ALK, visual acuity increased with keratocyte density. CONCLUSIONS: Better results were obtained after ALK vs PK, and the big-bubble technique seemed to provide the best results.

Predictive Factors for Successful Type 1 Big Bubble during Deep Anterior Lamellar Keratoplasty.

OBJECTIVE: Big bubble (BB)-deep anterior lamellar keratoplasty (DALK) has become the reference transplantation technique for corneal stromal disorders. Type 1 BB is the desired aspect but it is not constant. We aimed to determine the predictive factors of type 1 BB success. METHODS: Observational cohort study including 77 consecutive eyes of 77 patients undergoing DALK by one surgeon at a single reference center without any selection. Clinical and spectral domain optical coherence tomography data were collected pre- and postoperatively. RESULTS: Stromal scars were found in 91.8% of cases and were located in the anterior (90.9%), mid (67.5%), and posterior (36.4%) stroma. Type 1 BB (49.3% of cases) was significantly associated with the absence of scars in the posterior stroma, stage 1-3 keratoconus, and deep trephination. Among eyes with posterior scars, type 1 BB was associated with higher minimal corneal thickness, maximum-minimum corneal thickness < 220 µm, and diagnosis other than keratoconus. Eyes with type 1 BB featured significantly thinner residual stromal bed (22 ± 8 µm versus 61 ± 28 µm), thinner corneas at 12, 24, and 36 months, and better visual acuity at 12 months compared with eyes with no type 1 BB. Conversely, no significant differences between both groups were observed for graft survival, visual acuity at 24 and 36 months, and endothelial cell density at 12 and 36 months. CONCLUSION: OCT assessment before DALK is useful for choosing trephination depth that should be as deep as possible and for looking for posterior scars. The BB technique may not be the most appropriate method in keratoconus with posterior scars. Follow-up data do not support the need for conversion to penetrating keratoplasty when type 1 BB cannot be obtained nor does it support the need for performing a penetrating keratoplasty as a first-choice procedure in eyes with posterior stromal scars.

Spectral-domain Optical Coherence Tomography in Limbal Stem Cell Deficiency. A Case-Control Study.

PURPOSE: To evaluate the efficacy of optical coherence tomography (OCT) as a noncontact method for imaging the ocular surface in limbal stem cell deficiency (LSCD) and normal eyes. DESIGN: Retrospective case-control study. METHODS: Setting: Institutional. STUDY POPULATION: Twenty-two eyes with LSCD (study group, 22 patients) and 10 normal eyes (control group, 10 patients). OBSERVATION PROCEDURES: Spectral-domain (SD)-OCT and confocal microscopy in both the limbal and central corneal zones. MAIN OUTCOME MEASURES: Pachymetry data from the central cornea, presence of the palisades of Vogt, limbal crypts, and clear transition between the hyporeflective corneal epithelium and the hyperreflective conjunctival epithelium assessed on cross sections parallel and perpendicular to the limbus and en face sections of the limbal region. Parallel, perpendicular, and en face limbal scores were calculated by adding results of the 4 limbal quadrants. RESULTS: Both the difference between the minimal and the maximal epithelial thicknesses and the epithelial thickness standard deviation were significantly higher in the study group (mean, 47 µm/10 µm) compared with the control group (mean, 8 µm/2 µm). The parallel, perpendicular, and en face limbal scores were significantly lower in the study group (0.1/0.6/0.2) compared with the control group (7.4/4.8/3.5). Poorer visual acuity was significantly associated with higher standard deviation and difference between minimal and maximal corneal epithelial thicknesses (rs, +0.81/+0.77) and lower parallel, perpendicular, and en face limbal scores (-0.82/-0.73/-0.82). CONCLUSIONS: SD-OCT of both the central cornea and limbus with various section orientations is a valuable imaging modality allowing noninvasive and rapid overall precise assessment of both normal and LSCD eyes.

Comparison of optical low-coherence reflectometry and ultrasound pachymetry in measuring corneal graft thickness.

PURPOSE: To compare optical low-coherence reflectometry (OLCR) and ultrasound pachymetry in measuring corneal graft thickness in patients after keratoplasty. METHODS: We retrospectively measured the central graft thickness in 41 eyes of 41 patients with the OLCR pachymeter (Haag Streit, Koeniz, Switzerland) and the SP-2000 contact ultrasound pachymeter (Tomey, Nagoya, Japan). Five separate measurements were performed on each eye with both methods. Mean, SD, repeatability, and coefficient of variation of measurements were calculated, and the correlation between the 2 methods was studied with Spearman regression. RESULTS: Mean central graft thickness was 546 +/- 51 (SD) microm with the contact ultrasound pachymeter and 546 +/- 47 microm with the OLCR pachymeter. The correlation between both methods was strong (rs = 0.96). No significant differences in mean SD of measurements were observed between OLCR pachymetry (mean SD = 4.66 microm) and contact ultrasound pachymetry (mean SD = 4.88 microm). The repeatability of both methods was comparable (P = 0.06) and high (the average coefficient of variation of the central corneal graft thickness was 0.9% with both pachymeters). The postoperative time did not affect the correlation between both pachymeters (P > 0.05). CONCLUSIONS: Central corneal graft thickness values obtained with the OLCR pachymeter were similar to those obtained with a contact ultrasound pachymeter. In some cases of lamellar keratoplasty, the corneal refractive index could change at the interface level that could affect OLCR measurements.

New parameters in assessment of human donor corneal stroma.

PURPOSE: To provide quantitative parameters for assessment of human donor corneal stroma by imaging stromal features of diseased and normal human corneas with full-field optical coherence microscopy (FFOCM), using confocal microscopy (CM) and histology as reference techniques. METHODS: Bowman's layer (BL) thickness and keratocyte density were assessed ex vivo in 23 human donor corneas and 27 human pathological corneas (keratoconus and other corneal disorders) with FFOCM, CM and histology. Stromal backscattering was assessed with FFOCM. Additionally, 10 normal human corneas were assessed in vivo with CM. RESULTS: In FFOCM, the logarithm of the normalized stromal reflectivity was a linear function of stromal depth (R2  = 0.95) in human donor corneas. Compared with keratoconus corneas, human donor corneas featured higher BL thickness (p = 0.0014) with lower coefficient of variation (BL-COV; p = 0.0002), and linear logarithmic stromal reflectivity with depth (higher R2 , p = 0.0001). Compared with other corneal disorders, human donor corneas featured lower BL-COV (p = 0.012) and higher R2 (p = 0.0001). Using the 95% confidence limits of the human donor cornea group, BL thickness < 6.5 µm (sensitivity, 57%; specificity, 100%), BL-COV > 18.6% (79%; 100%) and R2  < 0.94 (93%; 71%) were revealed as indictors of abnormal cornea. In CM, keratocyte density decreased with stromal depth (r = -0.56). The mean overall keratocyte density (cells/mm2 ) was 205 in human donor corneas, 244 in keratoconus, 176 in other corneal disorders and 386 in normal corneas. CONCLUSION: Full-field optical coherence microscopy (FFOCM) provides precise and reliable parameters for non-invasive assessment of human donor corneal stroma during storage, enabling detection of stromal disorders that could impair the results of keratoplasty.