Stromal Thickness Research Articles

Corneal Biomechanical Properties after Small Incision Lenticule Extraction Surgery on Thin Cornea

ABSTRACT Purpose To explore the biomechanical changes in thin corneas after the small incision lenticule extraction (SMILE) surgery. Methods This prospective survey screened patients scheduled for the SMILE surgery from November 2017 to March 2018. Patients with thin corneas (central corneal thickness [CCT] ≤500 μm) and those with normal corneal thickness (CCT > 500 μm) were enrolled. Corneal biomechanics were examined by the ocular response analyser and Corvis ST, preoperatively and at 1 day, 3 weeks, and 3 months postoperatively. Results Twenty-seven patients (46 eyes) with mean spherical equivalent of −5.1 ± 1.7 D were assigned to the thin cornea group, and 28 (45 eyes) cases with mean spherical equation of −5.3 ± 1.8 D were assigned to the control group. Safety and efficacy did not differ between the two age- and refraction-matched groups (safety index, 1.15 ± 0.14 vs 1.14 ± 0.17 [P = .7]; efficacy index, 1.11 ± 0.13 vs 1.16 ± 0.22 [P = .2]). All biomechanical parameters changed significantly after SMILE. The thin cornea group showed less decrease in the second applanation time (A2 Time), stiffness parameters at first applanation (SP-A1). Pooling data from two groups, lower CCT was correlated with less A2 Time change (r = 0.37, P < .01) and less SP-A1 change (r = −0.33, P < .01). Less bIOP change was correlated with higher residual stromal thickness index and thicker CCT (P = .003, R2 = 0.12). Conclusion Over a short-term observation period, less corneal biomechanic deterioration may have contributed to the safety of SMILE on thin cornea.

Queratoplastia lamelar vs Queratoplastia penetrante

Introducción: El queratocono es un proceso progresivo, bilateral, asimétrico, no inflamatorio del espesor estromal, en el que la forma normal de la córnea se distorsiona y desarrolla una deformación similar a un cono, que modifica y altera progresivamente la visión y la hace cada vez más borrosa, con la aparición de una disminución de la agudeza visual por aumento de la miopía, astigmatismo regular o irregular, y el desarrollo de opacidades corneales.&#x0D; Objetivos: Realizar una revisión sistemática de la literatura en el periodo 2014-2018 sobre la eficacia de la queratoplastia lamelar frente a la queratoplastia penetrante en el tratamiento quirúrgico del queratocono. Material y Métodos: Se realizó una revisión sistemática de la literatura que incluyó metaanálisis con nivel de evidencia tipo A, se emplearon buscadores científicos como Elsevier, Scopus, Pubmed, Cochrane Library, Scielo en el período 2014 – 2018, sobre la eficacia de la queratoplastia lamelar frente a la técnica penetrante en el tratamiento quirúrgico del queratocono. Se incluyeron 23 artículos tipo Metaanálisis, revisiones sistemáticas y ensayos clínicos sobre el tema.&#x0D; Resultados: Se revisaron 24 artículos científicos publicados en las revistas Elsevier, Scopus, Pubmed, Cochrane Library, Scielo en el período 2014 – 2018. De la revisión efectuada se pudo determinar la efectividad de la Queratoplastia Lamelar y sus potencialidades en la Oftalmología.&#x0D; Conclusión: De acuerdo a la evidencia revisada, se concluye que la técnica de queratoplastia lamelar resulta ser más eficaz y con menos taza rechazo endotelial frente a la queratoplastia penetrante dentro del tratamiento quirúrgico de queratocono

The best optical zone for small-incision lenticule extraction in high myopic patients.

Small-incision lenticule extraction (SMILE) is an effective and safe procedure for the correction of myopia due to minimally invasive and noncorneal flap surgery. However, the SMILE procedure has certain requirements for corneal cap thickness, attempted refractive correction, residual stromal bed thickness, and optical zone diameter, which sometimes make surgeons hesitant to choose SMILE or other refractive surgeries. The requirements limit its use in patients with high myopia. The purpose of this review was to find the optimal parameters of SMILE through discussing the best optical zone for high myopic patients, the visual quality of different optical zones, the choice of corneal cap thickness, and their effects on corneal biomechanical parameters, so surgeons can provide reference recommendations for patients with high myopia in choosing a reasonable and safe procedure.

CORNEAL EPITHELIAL AND STROMAL CHANGES AFTER MYOPIC PHOTOREFRACTIVE KERATECTOMY

Purpose: to evaluate the corneal epithelial and stromal Changes after myopic photorefractivekeratectomy (PRK) Patient and methods: The study was established in Sohag Refractive Center,Sohag, Egypt, from October 2017 till November 2018. It included 50 eyes of 28 patients with agerange from 20 to 40 years old who subjected to PRK for the correction of myopia or compoundmyopic astigmatism. AS-OCT (Avanti - Optovue Taiwan) and corneal topography using Sirius Scheimpflug Placido topography (CSO, Florence, Italy) were done for all eyes pre and post-myopicphotorefractive keratectomy (PRK). Results: The study was conducted on 50 eyes of 28 patients, 6were operated on uniocular. 24 eyes were for females (48 %) and 26 eyes were for males (52 %)with their mean age 28.12 ± 6.22. the study showed a generalized pattern of decreased epithelialthickness in the period of the 1st month after performing PRK with significant P value for repeatedmeasures over 6 months for all parts of the cornea except for the superior part which was notstatistically significant. As regards the stromal thickness, the study showed a generalized pattern ofdecrease of the stromal thickness among the 6 months period after performing PRK. Conclusion:Epithelial thickness showed a decrease of thickness mainly in the central part except the superiorpart which was relatively the thickest. As regards the stromal thickness, all corneal showed significant change of stromal thickness after 1 month of PRK except the central part

Temporal redistribution of cap and residual stromal thickness after SMILE.

To investigate corneal sublayer alterations during the postoperative period after small-incision lenticule extraction (SMILE). Synslaser clinic, Oslo, Norway. Retrospective. Patients who underwent SMILE for treating myopia were included. The thicknesses of the corneal epithelium, cap, stromal part of the cap (StromaCap), residual stromal bed (StromaRes), and total stroma (StromaTot) were measured using spectral-domain optical coherence tomography at 1 day, 1 week, 1 month, 3 months, and 6 months postoperatively. Postoperative changes in the corneal sublayer thicknesses were analyzed and correlated with changes in spherical equivalence and anterior and posterior keratometry (K). The study was based on analyses of the right eyes of 51 patients. From 1 day to 6 months postoperatively, the corneal epithelium, cap, StromaCap, StromaRes, and StromaTot thicknesses increased from 54.4 ± 4.0 µm to 57.3 ± 5.2 µm; 137.1 ± 5.5 µm to 140.3 ± 5.1 µm; 82.7 ± 5.9 µm to 82.8 ± 6.3 µm; 375.0 ± 40.8 µm to 381.4 ± 30.6 µm; and 457.6 ± 41.1 µm to 462.1 ± 36.7 µm, respectively. Between 1 month and 6 months postoperatively, the increase in anterior K correlated significantly with the thickening of the cap (r = 0.37, P = .03) and the stromal component of the cap (r = 0.36, P = .04) within the central cornea. The post-SMILE remodeling behavior between the anterior (StromaCap) and posterior (StromaRes) stroma were dissimilar. There was a significant correlation between changes in anterior K and the central cap and the stromal component of the cap. This might be because of biomechanical changes, tissue remodeling, and wound healing or a combination of some or all of the aforementioned processes.

Evaluation of corneal sublayers thickness and corneal parameters in patients with Parkinson’s disease

Purpose The aim of this study was to compare the blink rate (BR), tear tests, corneal parameters, and the thickness of each corneal sublayer in patients with Parkinson’s disease (PD) and healthy individuals. Methods A total of 64 eyes from 64 patients with PD and 64 eyes from 64 age- and sex-matched healthy individuals were included in this study. All participants underwent a detailed neurological and ophthalmological evaluation. The severity of disease was measured according to Hoehn–Yahr (H–Y) scale. The blink rate (BR), Schirmer test, and tear break-up time (TBUT) scores were assessed. Corneal parameters were measured using Pentacam. Additionally, the thickness of the corneal epithelium, Bowman layer, stroma, and Descemet membrane-endothelium complex were measured on the central cornea with anterior segment module of spectral domain optical coherence tomography (AS-OCT). Results The BR, Schirmer’s test, TBUT, pachymetric measurements, Bowman layer, and stromal thickness values of the patient group were significantly lower than those of the control group. The disease duration and disease severity were significantly negative correlated with the pachymetric measurements and stromal thickness. Also, the values of TBUT and the score of Schirmer test were significantly positive correlated with the pachymetric measurements and stromal thickness. Conclusions A reduced BR and poor tear quality in the PD, can result in reduced pachymetric measurements and stromal thickness.

Comparison of the therapeutic effects between topical 8-oxo-2′-deoxyguanosine and steroid in ocular chemical burn experimental model

Abstract Purpose To compare the effects of topical 8-oxo-dG and steroids on ocular chemical burn mice model Methods We created ocular chemical burn models with 8-week-old BALB/c mice (n=45) by applying 0.1M sodium hydroxide(NaOH); the mice were then treated with 8-oxo-dG eye drops 10 mg/ml, 0.1% fluorometholone ophthalmic suspension, and phosphate buffered saline (PBS) twice daily. After seven days, clinical findings such as corneal integrity, clarity, and neovascularization were assessed. Histology, immunohistochemistry, inflammatory cytokine levels using real time polymerase chain reactions (PCRs), and amount of total reactive oxygen species in the corneas of the mice were also compared. Results Topical application of 8-oxo-dG and steroid resulted in a significant improvement of epithelial defects and clarity, compared to PBS (each p&amp;lt;0.05). Stromal thickness in cornea was also decreased in the 8-oxo-dG and steroid treated mice, compared to PBS-treated controls. (p&amp;lt;0.001) The expressions of F4/80 and neutrophil elastase-positive inflammatory cells in the stroma, and IL-1β and IL-6 cytokine levels in whole cornea were significantly reduced in the 8-oxo-dG group, compared to PBS group (each p&amp;lt;0.05). Conclusion In the ocular chemical burn experimental model, topical 8-oxo-dG showed excellent anti-inflammatory effects those were not inferior than topical steroids.

Femtosecond laser-assisted Descemet's stripping endothelial keratoplasty: a prospective study of 6-month visual outcomes, corneal thickness and endothelial cell loss.

To report 6-month outcomes of visual acuity, the corneal thickness and endothelial cell density (ECD) in patients undergoing femtosecond laser-assisted Descemet's stripping endothelial keratoplasty (FS-DSEK). This prospective, consecutive, interventional series examined 25 eyes of 25 patients who underwent FS-DSEK for Fuchs endothelial dystrophy and bullous keratopathy. The pre-cut corneal endothelial graft thickness (CET) was 150µm. Best-corrected visual acuity (BCVA), central corneal thickness (CCT), donor CET, recipient corneal stromal thickness (CST) and ECD were assessed at 1week and 1, 2, 3 and 6months postoperatively. The mean BCVA at 6months was 0.76 ± 0.35 logMAR units, improving from 1.54 ± 0.52 logMAR. CCT decreased significantly, from 759.8 ± 152.4µm at 1week to 631.7 ± 79.7µm at 6months (P = 0.001) postoperatively. CET recovered to 153.4 ± 33.7µm (P = 0.076) at 6months as pre-cut status. The CST decreased from 561.5 ± 96.3µm at 1week to 479.7 ± 57.9µm at 6months (P < 0.001). Preoperatively, the donor ECD was 2747.6 ± 255.4 cells/mm2, and the ECD decreased to 1729.1 ± 562.9 cells/mm2 at 6months, for a peak ECD loss of 36.86%. A greater decrease in CST observed from 1week to 6months postoperatively correlated with a lower ECD loss (P = 0.019) and a lower preoperative ECD (P = 0.012). However, a thinner CET correlated with a higher preoperative ECD (P = 0.028). FS-DSEK is a safe and effective surgical alternative for corneal endothelial decompensation. The donor ECD and its changes could be used as predictive factors for the improvement of CST and CET.

High Fluence Increases the Antibacterial Efficacy of PACK Cross-Linking.

Photoactivated chromophore for keratitis cross-linking (PACK-CXL) is used as an adjunct therapy to antibiotic medication in infectious keratitis. This experimental study aimed at quantifying the PACK-CXL efficacy as a function of UV fluence using several bacterial strains and irradiated volumes. Six distinct bacterial strains, including standardized strains and clinically isolated strains from patients with keratitis, were analyzed. Bacterial concentrations between 10 and 10 cells/mL were used (simulating small corneal ulcers). Volumes of either 11 μL (≈285 μm stromal thickness) or 40 μL (≈1000 μm stromal thickness) were irradiated within a microtiter plate at different fluences (5.4-27 J/cm) and irradiances (3, 9 and 18 mW/cm). The ratio of bacterial killing (B†) was determined to evaluate the antimicrobial efficacy of PACK-CXL. B† was similar (51 ± 11%) in bacterial concentrations between 10 and 10 per ml. In 11 μL volume, Staphylococcus aureus (SA) 8325-4 ATCC 29213, Bacillus subtilis (BS) 212901, and Pseudomonas aeruginosa (PA) 2016-866624 were most sensitive to PACK-CXL at 5.4 J/cm (on average B† = 49 ± 8%), whereas Klebsiella oxytoca (KO) 2016-86624 (B† = 25%) was least sensitive. When irradiating a larger volume, B† was on average lower in 40 μL (19 ± 18%), compared with 11 μL (45 ± 17%, P < 0.001). By contrast, applying a higher UV fluence increased B† of SA ATCC 29213, from 50% at 5.4 J/cm to 92% at 10.8 J/cm, to 100% at 16.2 J/cm and above. Applying higher UV fluences substantially increases the bacterial killing rates. Safety limits for clinical application require further investigation.

HSV-1 infection and pathogenesis in the tree shrew eye following corneal inoculation.

Herpes simplex virus type I (HSV-1) infection causes inflammation in the cornea known as herpes simplex virus keratitis (HSK), a common but serious corneal disease. It is not entirely clear whether the virus during recurring infection comes from the trigeminal ganglia or the eye tissue, including the retina and ciliary ganglion. Because the tree shrew is closely related to primates and tree shrew eye anatomic structures are similar to humans, we studied HSV-1 corneal infection in the tree shrew. We found that HSK symptoms closely mimic those found in human HSK showing typical punctiform and dendritic viral keratitis during the acute infection period. Following the HSV-specific lesions, complications such as stromal scarring, corneal thickening (primary infection), opacity, and neovascularization were observed. In the tree shrew model, following ocular inoculation, the cornea becomes infected, and viral protein can be detected using anti-HSV-1 antibodies in the epithelial layer and retina neuronal ganglion cells. The HSV-1 transcripts, ICP0, ICP4, and LAT can be detected at 3days post-infection (dpi), peaking at 5dpi. After 2weeks, ICP4 and ICP0 transcripts are reduced to a basal level, but the Latency Associated Transcripts (LATs) continue to accumulate. Interestingly, after the acute infection, we still detected abundant active HSV-1 in tree shrew eyes. Further, we found HSV-1 persistent in the ciliary ganglion and cornea. These findings are discussed in support of the tree shrew as a non-human primate HSK model, which could be useful for mechanistic studies of HSK.

Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography.

PurposeTo image, track and map the nerve fiber distribution in excised rabbit corneas over the entire stromal thickness using micro-optical coherence tomography (µOCT) to develop a screening tool for early peripheral neuropathy.MethodsExcised rabbit corneas were consecutively imaged by a custom-designed µOCT prototype and a commercial laser scanning fluorescence confocal microscope. The µOCT images with a field of view of approximately 1 × 1 mm were recorded with axial and transverse resolutions of approximately 1 µm and approximately 4 µm, respectively. In the volumetric µOCT image data, network maps of hyper-reflective, branched structures traversing different stromal compartments were segmented using semiautomatic image processing algorithms. Furthermore, the same corneas received βIII-tubulin antibody immunostaining before digital confocal microscopy, and a comparison between µOCT image data and immunohistochemistry analysis was performed to validate the nerval origin of the tracked network structures.ResultsSemiautomatic tracing of the nerves with a high range of different thicknesses was possible through the whole corneal volumes, creating a skeleton of the traced nerves. There was a good conformity between the hyper-reflective structures in the µOCT data and the stained nerval structures in the immunohistochemistry data.ConclusionsThis article demonstrates nerval imaging and tracking as well as a spatial correlation between µOCT and a fluorescence corneal nerve standard for larger nerves throughout the full thickness of the cornea ex vivo.Translational RelevanceOwing to its advantageous properties, µOCT may become useful as a noncontact method for assessing nerval structures in humans to screen for early peripheral neuropathy.

Systemic Sclerosis Dermal Fibroblasts Induce Cutaneous Fibrosis Through Lysyl Oxidase-like 4: New Evidence From Three-Dimensional Skin-like Tissues.

Systemic sclerosis (SSc) is a clinically heterogeneous disease characterized by increased collagen accumulation and skin stiffness. Our previous work has demonstrated that transforming growth factor β (TGFβ) induces extracellular matrix (ECM) modifications through lysyl oxidase-like 4 (LOXL-4), a collagen crosslinking enzyme, in bioengineered human skin equivalents (HSEs) and self-assembled stromal tissues (SAS). We undertook this study to investigate cutaneous fibrosis and the role of LOXL-4 in SSc pathogenesis using HSEs and SAS. SSc-derived dermal fibroblasts (SScDFs; n = 8) and normal dermal fibroblasts (NDFs; n = 6) were incorporated into HSEs and SAS. These 3-dimensional skin-like microenvironments were used to study the effects of dysregulated LOXL-4 on ECM remodeling, fibroblast activation, and response to TGFβ stimulation. SScDF-containing SAS showed increased stromal thickness, collagen deposition, and interleukin-6 secretion compared to NDF-containing SAS (P < 0.05). In HSE, SScDFs altered collagen as seen by a more mature and aligned fibrillar structure (P < 0.05). With SScDFs, enhanced stromal rigidity with increased collagen crosslinking (P < 0.05), up-regulation of LOXL4 expression (P < 0.01), and innate immune signaling genes were observed in both tissue models. Conversely, knockdown of LOXL4 suppressed rigidity, contraction, and α-smooth muscle actin expression in SScDFs in HSE, and TGFβ-induced ECM aggregation and collagen crosslinking in SAS. A limitation to the development of effective therapeutics in SSc is the lack of in vitro human model systems that replicate human skin. Our findings demonstrate that SAS and HSE can serve as complementary in vitro skin-like models for investigation of the mechanisms and mediators that drive fibrosis in SSc and implicate a pivotal role for LOXL-4 in SSc pathogenesis.

Wide Stromal Mapping Using an Anterior Segment Optical Coherence Tomography.

PurposeTo quantify and assess the reproducibility of the corneal stromal thickness profiles captured by the SD-OCT. Secondly, we correlated the zonal thicknesses to the age, gender and axial length.MethodsWe included 227 normal eyes of 227 patients with a maximum hypermetropia of +5 and myopia of –6 diopters (D). Subjects with an intraocular pressure exceeding 22 mm Hg, evidence of cataract formation, history of ophthalmic surgery or disease were excluded. Lastly, reproducibility was evaluated in a subset of 50 participants by means of an identical scan protocol repeated by 2 different OCT operators.ResultsStromal values were consistently thicker in the peripheral cornea (p<0.001). Age was negatively correlated with approximately every sector of the stroma with notable exceptions of the center (r=0.117, p=0.088) and the superior inner (r=0.057, 0.409), middle (r=0.086, p=0.209) and outer locations (r=0.120, p=0.079). There was no statistical significance in most sectors when looking at the axial length, gender and K1/K2. This method was highly reproducible in terms of both the ICC and COV.ConclusionCorneal stromal mapping is highly reproducible and shows a negative correlation to age. Additionally, the periphery of the stroma is consistently thicker to the center. Other variables like gender and axial length show no relationship to the corneal stroma.

An Exclusively Whole-Plant-Food Diet in the Improvement of Fuchs’ Endothelial Corneal Dystrophy

Fuchs’ endothelial corneal dystrophy (FECD) is a progressive disorder of the corneal endothelium characterized by endothelial cell functional abnormalities and loss of visual acuity. Chronic oxidative stress plays a key role in disease progression. We present the case of a 69-year-old woman with an 18-year history of FECD that improved after dietary intervention with an exclusively whole-plant-food diet free of added salt, oil, and sugar. An eye exam 1 month prior to dietary intervention indicated that her uncorrected visual acuity was 20/50 -1 OD and 20/100 OS. The exam also showed 3+ guttae OD and 4+ guttae OS and intraocular pressures of 23 OD and 16 OS by applanation. After approximately 30 days on an exclusively whole-plant-food diet, the patient reported improved vision. An eye exam indicated that her visual acuity was 20/40 without correction with only trace stromal thickening and no edema in both eyes. Intraocular pressures were 17 OD and 15 OS by applanation. This case suggests an exclusively whole-plant-food diet may be beneficial in the treatment of FECD.

Deep anterior lamellar keratoplasty techniques; predescemetic versus big bubble: Anterior segment optical coherence tomography study

To compare the visual and refractive outcomes and anterior segment optical coherence tomography (AS-OCT) findings of 2different deep anterior lamellar keratoplasty (DALK) techniques in the treatment of advanced keratoconus with and without successful big bubble formation. In this retrospective comparative case series, data from 79consecutive eyes of 69patients who underwent either big bubble (group 1, n: 62) or manual DALK (group 2, n: 17) were analyzed. The visual and refractive results, keratometric values and residual stromal thickness were assessed. Patients were seen at 1, 3, 6 and 12 months after the procedure and 1 month after complete suture removal. A big bubble was successfully obtained in 62eyes (78.5%; group 1) and manual dissection was performed in the 17remaining eyes (21.5%; group 2). The final best spectacle-corrected visual acuity (BSCVA) was 0.38 logMAR and 0.55 logMAR in Group 1 and 2, respectively (P<0.05). At the final visit, BSCVA≤0.30 logMAR was achieved in 80% and 60.8% of eyes in Groups 1 and 2, respectively (P<0.001). Groups 1 and 2 were comparable in terms of mean keratometry: 47.80D±2.81D (range, 41.30D to 54.2D) versus 45.90D±3.62D (range, 41.10D to 53.8 D), respectively; (P=0.56) and keratometric astigmatism: 3.81D± 2.1D (range, 1.0D to 6.20D) versus 3.56D±1.92D (range 1.2D to 6.85D), respectively; (P=0.40) at the final follow-up. The mean residual stromal thickness was 36.90±17.80μm in group 2. The presence of residual posterior corneal stroma when big bubble formation is not successfully achieved in DALK is correlated with lower postoperative visual acuity.

Decellularized Porcine Cornea-Based Hydrogels for Regeneration of Corneal Epithelium and Stroma

Hydrogels derived from decellularized tissues provide superior biocompatibility, tenability and tissue-specific extracellular matrix (ECM) components. Based on the preparation of decellularized porcine cornea (DPC), here we developed an injectable hydrogel, characterized the biocompatibility and transparency, and evaluated the use to repair corneal stromal defect in rabbit. Upon cross-linking with N-cyclohexyl-N′-(2-morpholinethyl) carbodiimide metho-p-toluenesulfonate (CMC), the DPC-based hydrogel assumed favorable transparency, exhibited distinct mechanical properties and preserved the ECM components of native porcine cornea (NPC). In vitro experiments showed that the hydrogel maintained the phenotype, supported the proliferation and promoted the ECM synthesis of corneal fibroblasts. When injected on rabbit corneas, the hydrogel rapidly covered, solidified and formed a smooth surface upon the focal defect. Corneal epithelium was fully regenerated within 3 days. The thickness of corneal epithelium and stroma was restored at 12 weeks postoperatively without significant inflammation and scar formation. Notably, the hydrogel showed no harmful effects on the resident stroma and endothelium. Considering to the advantages of low cost and ease of production and use, the DPC-based hydrogel may represent a promising biomaterial for corneal epithelial and stromal regeneration.

Analysis of light scattering ability of the cornea before and after endothelial keratoplasty

To evaluate light scattering ability of the cornea before and after Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK) endothelial keratoplasty. The study included 70 patients (70 eyes) who had undergone DSAEK and DMEK (35 patients, 35 eyes in each group). In addition to standard ophthalmological examinations before and during the one-year follow-up after surgery, the patients had their central corneal thickness, stromal thickness, thickness of the interface area and the graft measured with optical coherence tomography (Optovue, U.S.A.). Intensity of light scattering by corneal structures was evaluated using Pentacam HR (Oculus, Germany) topographer with proprietary software and algorithms for calculation of corneal transparency. Comparison of the outcomes revealed that indices of general integral and stromal light-scattering were higher in patients after DSAEK. Integral light scattering in the interface and graft areas in the DMEK group was significantly lower than in the DSAEK group during the whole follow-up period. The reason for decrease of visual acuity after endothelial keratoplasty, regardless of the surgery type, may be higher light-scattering ability of patient's corneal stroma due to residual opacifications. Better visual acuity outcomes after DMEK in comparison to DSAEK are associated with higher transparency of the interface and graft areas. The suggested new method of assessing the intensity of light-scattering allows more precise evaluation of the influence of light-scattering ability of the stroma, interface and corneal graft after different modifications of endothelial keratoplasty, considering the respective layer thickness and excluding the influence of light scattering on the air-epithelium interface.

Effectiveness of the Goldmann Applanation Tonometer, the Dynamic Contour Tonometer, the Ocular Response Analyzer and the Corvis ST in Measuring Intraocular Pressure following FS-LASIK

ABSTRACTPurpose: To test the performance of the four tonometers in providing IOP measurements that were free of the effects of corneal biomechanics changes caused by refractive surgery.Methods: Four tonometers were employed to provide IOP measurements for 65 participants who accepted Femtosecond laser-assisted LASIK (FS-LASIK). The measurements included GAT-IOP by the Goldmann Applanation Tonometer, DCT-IOP by the Dynamic Contour Tonometer, Goldmann-correlated IOP (ORA-IOPg) and corneal-compensated IOP (ORA-IOPcc) by the Ocular Response Analyzer, and uncorrected IOP (CVS-IOP) and biomechanically corrected IOP (CVS-bIOP) by the Corvis ST. Statistical analyses were performed to assess the association of the differences in IOP caused by FS-LASIK with central corneal thickness (CCT), mean corneal curvature (Km), age, refractive error correction (REC), optical zone diameter (OZD), ablation zone diameter (AZD), residual stromal bed thickness (RSB) and RSB ratio (RSB/CCT). Multiple linear regression models were constructed to explore factors influencing IOP changes.Results: All four tonometers exhibited significant differences between IOP measurements taken pre and post-surgery except for CVS-bIOP in the low to moderate myopia group (t = 1.602, p = .12). CVS-bIOP, followed by DCT-IOP, provided the best agreement between pre and post-FS-LASIK measurements with the lowest differences in IOP and the narrowest limits of agreement. The pre-post IOP differences were also significantly associated with the reduction in CCT in only GAT-IOP, ORA-IOPg, and CVS-IOP. CVS-bIOP and ORA-IOPcc were the only measurements that were not correlated with CCT, Km or age both before and after FS-LASIK.Conclusions: The biomechanically corrected bIOP from the Corvis ST provided post-FS-LASIK measurements that were in closest agreement with those obtained before surgery. In comparison, GAT-IOP, ORA-IOPg, ORA-IOPcc, and CVS-IOP appeared to be more influenced by the changes in corneal biomechanics caused by FS-LASIK.

Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability

PurposeTo examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements. MethodsRepeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated. ResultsIntraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20–30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements. ConclusionAS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 μm for intraobserver repeatability and ≤ ±3.7 μm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.

Efficacy and Safety of Transglutaminase-Induced Corneal Stiffening in Rabbits.

PurposeTo evaluate the biomechanical efficacy and safety of in vivo microbial transglutaminase (Tgases)-induced corneal crosslinking in a rabbit model.MethodsA total of 34 white New Zealand rabbits were divided into two groups, a biochemistry group and a photochemistry group. The right eye of every rabbit was treated and left eyes served as negative controls. In the biochemistry group, a 1 U/mL solution of crosslinking agent microbial Tgases (Tgases CXL) was applied to the corneal surface, while in the photochemistry group, clinical ultraviolet A-riboflavin crosslinking (UVA/RF CXL) was used. Efficacy and safety evaluated on the 14th day after the procedures. Twelve pairs of corneal strips were harvested from the eyes of 12 euthanized rabbits in every group, and uniaxial tensile tests were performed to evaluate ex vivo biomechanical effects. The CXL-treated eye to its corresponding untreated eye ratio of tangent modulus were calculated. Another five pairs of corneal button were excised from euthanized animals in every group for corneal stroma and endothelium staining to evaluate changes in keratocyte distribution and endothelial cell damage.ResultsIn tensile tests, tangent modulus was statistically higher in the Tgases CXL groups under 1.0 MPa (26.59 ± 4.54 vs. 21.47 ± 4.72 MPa, P = 0.04) and 1.5 MPa (29.75 ± 5.01 vs. 20.47 ± 6.63 MPa, P = 0.00). The tangent modulus ratio of Tgases group (1.72 ± 1.0 vs. 1.05 ± 0.22, P = 0.04) was significantly higher than that of UVA/RF under 1.5-MPa stress. The distribution of keratocytes in the corneal stroma and the morphologies of endothelial cells were similar in Tgases CXL-treated and untreated corneas. However, in the UVA/RF CXL group, keratocytes in the anterior half of stromal thickness were lost, and clear endothelial cell apoptosis was observed.ConclusionsTgases-CXL effectively stiffened the cornea and caused no damage to the endothelium and keratocytes in the cornea. This crosslinking method could be useful as a next-generation treatment for corneal ectasia and could replace CXL of photochemistry.Translational RelevanceThese findings may give a new hope to biomechanically compromised corneal disease due to mechanical forces, such as corneal ectasia and keratoconus. A next-generation treatment to these corneal diseases due to mechanical forces may be designed based on the new findings.