Abnormal Corneas Research Articles

IOP measurement in abnormal corneas

AbstractElevated intraocular pressure still the major surrogate and risk factor for development and progression of glaucoma. For decades the Goldmann applanation tonometry has been the gold standard for measuring intraocular pressure; however, there are newer methods of measuring intraocular pressure, each one has advantages and disadvantages and depends on the corneal biomechanics parameters. This talk will focus on the different methods and their limitations with regard to measuring intraocular pressure in abnormal corneas.

Intraocular lens power calculation in patients with irregular astigmatism.

Accurate intraocular lens (IOL) calculation in subjects with irregular astigmatism is challenging. This study evaluated the accuracy of using Scheimpflug-derived central 2-mm equivalent keratometry reading (EKR) values for IOL calculation in irregular astigmatism. This retrospective study included subjects (31 eyes of 30 patients) who underwent cataract surgery and IOL calculation using the 2-mm central EKR methods. We compared prediction error (PE) and absolute PE (APE) outcomes using SRK/T and Barrett Universal II formulas for keratometry data obtained from the IOLMaster 500 and Pentacam (anterior corneal sim k) devices. Cataract surgery and IOL calculation using the 2-mm central EKR methods resulted in improved visual acuity (uncorrected: from 1.13 ± 0.38 to 0.65 ± 0.46 logMar, p < 0.01; best-corrected: from 0.45 ± 0.24 to 0.26 ± 0.20 logMar, p < 0.01) after surgery. The percentage of subjects with best-corrected visual acuity of 6/6 was 22%, < 6/9 was 58%, and < 6/12 was 71%. For both the SRK/T and the Barrett formulas, the PE was similar to those obtained by IOLMaster (> 0.14) but lower than those obtained by the anterior corneal sim k (p < 0.02). IOLMaster provided keratometry reading in only 23/31 (74.1%) of cases. The use of Scheimpflug central 2-mm EKR for IOL calculation in irregular astigmatism was beneficial in terms of visual acuity improvement. It had comparable refractive prediction performance to the IOLMaster 500 and better than the anterior corneal sim K. The 2-mm EKR method can be used when IOLMaster cannot provide a reliable reading in abnormal corneas.

Interocular Symmetry Analysis of Corneal Elevation Using the Fellow Eye as the Reference Surface and Machine Learning

Unilateral corneal indices and topography maps are routinely used in practice, however, although there is consensus that fellow-eye asymmetry can be clinically significant, symmetry studies are limited to local curvature and single-point thickness or elevation measures. To improve our current practices, there is a need to devise algorithms for generating symmetry colormaps, study and categorize their patterns, and develop reference ranges for new global discriminative indices for identifying abnormal corneas. In this work, we test the feasibility of using the fellow eye as the reference surface for studying elevation symmetry throughout the entire corneal surface using 9230 raw Pentacam files from a population-based cohort of 4613 middle-aged adults. The 140 × 140 matrix of anterior elevation data in these files were handled with Python to subtract matrices, create color-coded maps, and engineer features for machine learning. The most common pattern was a monochrome circle (“flat”) denoting excellent mirror symmetry. Other discernible patterns were named “tilt”, “cone”, and “four-leaf”. Clustering was done with different combinations of features and various algorithms using Waikato Environment for Knowledge Analysis (WEKA). Our proposed approach can identify cases that may appear normal in each eye individually but need further testing. This work will be enhanced by including data of posterior elevation, thickness, and common diagnostic indices.

Automatic Segmentation of Corneal Microlayers on Optical Coherence Tomography Images.

PurposeTo propose automatic segmentation algorithm (AUS) for corneal microlayers on optical coherence tomography (OCT) images.MethodsEighty-two corneal OCT scans were obtained from 45 patients with normal and abnormal corneas. Three testing data sets totaling 75 OCT images were randomly selected. Initially, corneal epithelium and endothelium microlayers are estimated using a corneal mask and locally refined to obtain final segmentation. Flat-epithelium and flat-endothelium images are obtained and vertically projected to locate inner corneal microlayers. Inner microlayers are estimated by translating epithelium and endothelium microlayers to detected locations then refined to obtain final segmentation. Images were segmented by trained manual operators (TMOs) and by the algorithm to assess repeatability (i.e., intraoperator error), reproducibility (i.e., interoperator and segmentation errors), and running time. A random masked subjective test was conducted by corneal specialists to subjectively grade the segmentation algorithm.ResultsCompared with the TMOs, the AUS had significantly less mean intraoperator error (0.53 ± 1.80 vs. 2.32 ± 2.39 pixels; P < 0.0001), it had significantly different mean segmentation error (3.44 ± 3.46 vs. 2.93 ± 3.02 pixels; P < 0.0001), and it had significantly less running time per image (0.19 ± 0.07 vs. 193.95 ± 194.53 seconds; P < 0.0001). The AUS had insignificant subjective grading for microlayer-segmentation grading (4.94 ± 0.32 vs. 4.96 ± 0.24; P = 0.5081), but it had significant subjective grading for regional-segmentation grading (4.96 ± 0.26 vs. 4.79 ± 0.60; P = 0.025).ConclusionsThe AUS can reproduce the manual segmentation of corneal microlayers with comparable accuracy in almost real-time and with significantly better repeatability.Translational RelevanceThe AUS can be useful in clinical settings and can aid the diagnosis of corneal diseases by measuring thickness of segmented corneal microlayers.

Topography-Guided Ablations: Early US Experience and Utility Across the Refractive Landscape

This paper evaluated topography-guided excimer ablations and recent US experience of this technology. Personal clinical experience, initial approval of the technique, and its application to a potential extended spectrum of clinical conditions was reviewed. Topography-guided ablation can precisely treat corneas with variable topographic indices and attempt to neutralize irregularities by combining myopic and hyperopic ablation profiles. The T-CAT Phase III study demonstrated the safety and efficacy of this technique, which earned FDA approval in 2013. Current literature has reinforced its efficacy and explored off-label investigations, such as its use to improve visual results in abnormal corneas (e.g., keratoconus, post-LASIK ectasia). Topography-guided ablation provides increased quality of vision without necessitating excess tissue removal in otherwise normal, keratoconic, ectatic, or post-corneal transplant eyes. In the future, we will likely see a combination of treatment strategies, enabling ophthalmologists to treat the entire refractive surface and refine these already remarkable results.

Enhanced neural function in highly aberrated eyes following perceptual learning with adaptive optics

Highly aberrated keratoconic (KC) eyes do not elicit the expected visual advantage from customized optical corrections. This is attributed to the neural insensitivity arising from chronic visual experience with poor retinal image quality, dominated by low spatial frequencies. The goal of this study was to investigate if targeted perceptual learning with adaptive optics (AO) can stimulate neural plasticity in these highly aberrated eyes. The worse eye of 2 KC subjects was trained in a contrast threshold test under AO correction. Prior to training, tumbling ‘E’ visual acuity and contrast sensitivity at 4, 8, 12, 16, 20, 24 and 28 c/deg were measured in both the trained and untrained eyes of each subject with their routine prescription and with AO correction for a 6mm pupil. The high spatial frequency requiring 50% contrast for detection with AO correction was picked as the training frequency. Subjects were required to train on a contrast detection test with AO correction for 1h for 5 consecutive days. During each training session, threshold contrast measurement at the training frequency with AO was conducted. Pre-training measures were repeated after the 5 training sessions in both eyes (i.e., post-training). After training, contrast sensitivity under AO correction improved on average across spatial frequency by a factor of 1.91 (range: 1.77–2.04) and 1.75 (1.22–2.34) for the two subjects. This improvement in contrast sensitivity transferred to visual acuity with the two subjects improving by 1.5 and 1.3 lines respectively with AO following training. One of the two subjects denoted an interocular transfer of training and an improvement in performance with their routine prescription post-training. This training-induced visual benefit demonstrates the potential of AO as a tool for neural rehabilitation in patients with abnormal corneas. Moreover, it reveals a sufficient degree of neural plasticity in normally developed adults who have a long history of abnormal visual experience due to optical imperfections.

Prevention of Iatrogenic Keratectasia.

Iatrogenic corneal ectasia is a rare but devastating complication after refractive surgery. While its incidence appears to be declining, it has not been eliminated. Its cause is probably related to a combination of an intrinsic predisposition to ectasia and an additional anatomical destabilising effect from the refractive surgery. Determining which eyes are intrinsically "weak" and exactly how much additional "weakening" an eye can withstand before developing progressive thinning and protrusion are both difficult tasks. The essentially universal availability of corneal topography and the increasing use of corneal tomography have significantly improved our ability to preoperatively diagnose early forms of corneal ectasias, especially keratoconus and pellucid marginal degeneration. Advanced software algorithms have also enhanced the sensitivity and specificity of these technologies. Newer technologies, such as measuring corneal biomechanics and corneal epithelial distribution, will hopefully continue to help us to differentiate normal from abnormal corneas preoperatively. In addition to abnormalities in anterior and posterior corneal curvature, a number of other risk factors for the development of post-refractive surgery ectasia have been proposed, including younger patient age, thinner central corneal thickness, thinner residual stromal bed thickness and high myopia. If the percentage of altered tissue is > 40 %, this is an extremely accurate predictor of corneal ectasia after refractive surgery. While there are a number of effective treatments for iatrogenic corneal ectasia, such as contact lenses, corneal crosslinking, intracorneal rings and corneal transplantation, prevention should be the goal. With newer and better corneal imaging technology to help screen out patients with abnormal corneas along with an improved understanding of exactly how much weakening a given cornea can take, we should be able to minimize this vision threatening complication.

Intra-Ocular Pressure Measurement in a Patient with a Thin, Thick or Abnormal Cornea.

Accurate measurement of intra-ocular pressure is a fundamental component of the ocular examination. The most common method of measuring IOP is by Goldmann applanation tonometry, the accuracy of which is influenced by the thickness and biomechanical properties of the cornea. Algorithms devised to correct for corneal thickness to estimate IOP oversimplify the effects of corneal biomechanics. The viscous and elastic properties of the cornea influence IOP measurements in unpredictable ways, a finding borne out in studies of patients with inherently abnormal and surgically altered corneal biomechanics. Dynamic contour tonometry, rebound tonometry and the ocular response analyzer provide useful alternatives to GAT in patients with abnormal corneas, such as those who have undergone laser vision correction or keratoplasty. This article reviews the various methods of intra-ocular pressure measurement available to the clinician and the ways in which their utility is influenced by variations in corneal thickness and biomechanics.

Ocular response analyzer (ORA) derived parameters compared to Sirius corneal topography in analyzing corneal pathology

Purpose: To evaluate the ability of Ocular Response Analyzer (ORA) to differentiate between normal and abnormal corneas as compared to Sirius corneal topography. Methods: This retrospective study included 302 eyes of 151 patients. All patients underwent evaluation with ORA and Sirius corneal topography. Parameters included disease classification results on both instruments (device software classification), Surface asymmetry index (SAI) on Sirius, Corneal Hysteresis (CH), Corneal Resistant Factor (CRF), Keratoconus Match Index (KMI), Goldmann-correlated intraocular pressure (IOPg), Corneal compensated intraocular pressure (IOPcc) and waveform score (WS) on ORA. Results: On Sirius, 198 eyes (65.6%) were classified as normal. On ORA, 121 eyes (40.1%) were documented as normal. Overall, 105 eyes (34.8%) were classified as normal and 88 eyes (29.1%) with non-normal classification on both Sirius and ORA. Of the 198 eyes classified as normal on Sirius, 53% were classified as normal, 39% as suspect and 8% as mild keratoconus on ORA (47% non-normal). Of the 121 eyes classified as normal on ORA, 87% were classified as normal, 6% as suspect, and 2% as keratoconus compatible on Sirius (13% non-normal). Four percent of the eyes classified as keratoconus compatible on Sirius were classified as normal on ORA. There was a significant difference when comparing normal and non-normal classifications between ORA and Sirius (p < 0.001) with poor agreement (Kappa=0.32). When including only normal and Keratoconus eyes in the analysis, good agreement was found between the two machines (Kappa=0.75). Conclusion: According to our results there seems to be a significant difference between ORA and Sirius in their ability to differentiate between normal and non-normal eyes. As such, we recommend that these devices not to be used interchangeably for assessing patients prior to refractive surgery. Keywords: Cornea; Corneal biomechanics; Keratoconus; Ocular response analyzer; Sirius corneal topo

Reliability of Pentacam HR Thickness Maps of the Entire Cornea in Normal, Post–Laser In Situ Keratomileusis, and Keratoconus Eyes

To measure the repeatability and reproducibility of Pentacam HR system thickness maps for the entire cornea in normal, post-laser insitu keratomileusis (post-LASIK), and keratoconus (KC) eyes. Reliability study. Sixty normal subjects (60 eyes), 30 post-LASIK subjects (60 eyes), and 14 KC patients (27 eyes) were imaged with the Pentacam HR system by 2 well-trained operators. For pachymetry the cornea was divided into 4 zones: a central zone (2-mm diameter) and concentric pericentral zone (2-5mm), transitional zone (5-7mm), and peripheral zone (7-10mm). The 3 concentric zones were subdivided into 8 sectors. Intraobserver repeatability and interobserver reproducibility of entire corneal thickness maps were tested by the repeatability and reproducibility coefficients, intraclass correlation coefficients, coefficient of variation, and 95% limits of agreement. From central to peripheral zones, the precision of corneal thickness measurements became gradually smaller. Central zone repeatability and reproducibility were the best in the normal, post-LASIK, and KC groups. The peripheral superior sectors showed poorer repeatability and reproducibility for all subjects. The intraobserver repeatability and interobserver reproducibility for all zones were ≤19.3μm, ≤22.1μm, and ≤20.7μm, in the normal, post-LASIK, and KC groups, respectively. The intraobserver and interobserver coefficients of variation for all zones were ≤1.3%, ≤1.6%, and ≤1.6% for all 3 groups. Pentacam HR system pachymetry of the entire cornea provided good precision in normal, post-LASIK, and KC corneas. Thickness measurements in the peripheral cornea should be interpreted with caution in abnormal corneas after surgery or with diseases.

Establishment of a transgenic mouse model of corneal dystrophy overexpressing human BIGH3

This study aimed to establish a transgenic mouse model of corneal dystrophy (CD) overexpressing the human transforming growth factor, β-induced, 68 kDa (TGFBI, also known as BIGH3) gene. A purified and linearized recombinant plasmid carrying the expression cassette BIGH3‑IRES‑EGFP was microinjected into the pronuclei of C57BL/6J mouse fertilized eggs under the control of the phosphoglycerate kinase (PGK) promoter. The expression of human BIGH3 in the transgenic mice was confirmed by PCR using DNA extracted from tail tissue. Four founder transgenic mice were identified by PCR and the increased expression of BIGH3 was observed in the corneas of the transgenic mice by RT-PCR and western blot analysis. The abnormal corneas with central opacity were observed in the transgenic mice by corneal photography. We concluded that the exogenous gene, BIGH3, was integrated successfully into the mouse genome through microinjection. In addition, the phenotype observed in this BIGH3 transgenic mouse model was similar to CD. Therefore, this transgenic model may prove useful in the investigation of the pathogenesis of CD.

International Values of Central Pachymetry in Normal Subjects by Rotating Scheimpflug Camera.

In corneal refractive surgery, postoperative ectasia risk assessment routinely includes pachymetric analysis at the apex and thinnest point. We examined whether these data differ worldwide and constructed preliminary country-specific normative thresholds. This was a multicenter, cross-sectional study. Using the Pentacam Eye Scanner (OCULUS GmbH, Wetzlar, Germany), we examined 1 randomly selected eye from each of 555 normal adults (8 countries, 6 continents), measuring the thinnest point location, central pachymetry (thinnest point, pupillary center, and apex), and the apex-thinnest point difference. International differences were assessed by 1-way analysis of variance. Normative thresholds were defined by 2- and 3-SD gates or Tukey method. The thinnest point averaged 0.44 mm temporal and 0.29 mm inferior to the apex. Individual thinnest points located more than 1.0 mm inferior represented fewer than 0.5% of normal corneas (>0.76 mm in the US subgroup). The mean thinnest-point pachymetry was 536 μm overall, and values less than 469 or 435 μm (-2 or -3 SD, respectively) would be expected in less than 2.5% or 0.15% of normal corneas, respectively. The thinnest-point pachymetry averaged 2 to 3 μm thinner than apical (range, 0-32 μm). Differences of greater than 8.5 μm would be expected in less than 0.5% of normal corneas overall. International differences were largely clinically insignificant. Nevertheless, it remains preferable to establish racial/geographic-specific normative values. We defined preliminary generalized and country-specific thresholds useful to the corneal refractive surgeon for identifying potentially abnormal corneas based on common pachymetric parameters, particularly the thinnest point by tomography.

Cornea special edition of veterinary ophthalmology

This special issue of Veterinary Ophthalmology concentrates on a seemingly straightforward tissue: the cornea. Although a relatively simple structure when compared to other ocular tissues such as the retina, the cornea compromises a huge portion of the ophthalmic diseases that we treat as veterinary ophthalmologists. Additionally, because of the cornea’s relative similarity across species, we are in a unique position as veterinary ophthalmologists to characterize spontaneous diseases in other species that can serve as models of human disease, furthering both animal and human health. In this issue, researchers and clinicians strive to improve our understanding of normal corneal homeostasis and wound healing as well as investigate new treatments of common corneal diseases. The review of integrins in normal and abnormal corneas by Dr. Renee Carter is an excellent starting point in furthering our understanding of corneal health and disease. The role of myofibroblasts in the cornea, highlighted in the review by Dr. Kathern Myrna et al., is only just beginning to be understood in humans and will likely prove to be an important factor in modulating corneal wound healing in all species. Both of these papers highlight the amount of work that still needs to be done to fully understand both the normal and diseased cornea. In this issue, we also have the first description of the anatomy of the living equine cornea using confocal microscopy, which is an exciting addition to the advanced diagnostic tools increasingly available to us to understand corneal pathology. Drs. Brian Gilger and Andy Matthew review the classification of immune mediated keratitis in horses. In this review, various forms and treatment options are described, as well as new areas of research to improve our understanding of these sometimes frustrating entities in horses. Dr. Caryn Plummer reviews the use of amniotic membrane use for ocular reconstruction, an underutilized option to improve corneal wound healing in veterinary medicine. Other papers in this issue address methodology to culture primary equine corneal cells, which should provide an excellent foundation for future wounding healing studies. In the area of corneal transplantation, work with allogenic mesenchymal stem cells demonstrates an innovative area of research to improve outcomes in all species (Wee et al.). Wee et al. also research the effect of freezing and thawing corneal prior to transplantation, a step in increasing the possible supply of donor corneas. Other papers in this issue address new treatment techniques and critically analyze success rates of treatment modalities. The practice of evidence based medicine whenever possible should be our goal in veterinary ophthalmology, in spite of the seemingly numerous obstacles placed in our way.1 One crucial element of evidence-based medicine is the peer review process. During the editing of this journal, I have been repeatedly impressed with reviewers who take time out of their busy schedules to provide thoughtful, constructive reviews. Without reviewers generously donating their time, we could not as a profession move forward. I would like to extend my thanks and congratulations to these reviewers who make the extra effort to advance the field of veterinary ophthalmology.

Vision improvement by correcting higher-order aberrations with customized soft contact lenses in keratoconic eyes

Higher-order aberration correction in abnormal eyes can result in significant vision improvement, especially in eyes with abnormal corneas. Customized optics such as phase plates and customized contact lenses are one of the most practical, nonsurgical ways to correct these ocular higher-order aberrations. We demonstrate the feasibility of correcting higher-order aberrations and improving visual performance with customized soft contact lenses in keratoconic eyes while compensating for the static decentration and rotation of the lens. A reduction of higher-order aberrations by a factor of 3 on average was obtained in these eyes. The higher-order aberration correction resulted in an average improvement of 2.1 lines in visual acuity over the conventional correction of defocus and astigmatism alone.

Use of silicone oil in the management of complex retinal detachment -- an Indian experience

In the management of complicated retinal detachments (RD), temporary silicone oil tamponade has been increasingly used. This study reports results and complications of temporary silicone oil tamponade that was used to treat complicated RD associated with multiple etiologies. Between 1988 and 1998, a total of four thousand four hundred and eighty-eight (4488) eyes underwent vitreous surgery and silicone oil tamponade. Outcome measures were: anatomic and functional success and postoperative complications such as cataract, corneal changes, hypotony, and glaucoma. An eye was considered an anatomic success if there was a complete retinal reattachment or macular attachment. Functional success was defined as attainment of visual acuity of 5/200 or better. Multiple logistic regression analysis was performed to elucidate the relationship between various pre- and postoperative variables and outcome measures. Mean follow-up was 17 months, and median, 8 months. Overall, anatomic success was achieved in 73% of the eyes, and functional success, in 47%. After removal of silicone oil, recurrence of retinal detachment was observed in 9% of the eyes; a high percentage (70%) of eyes attained functional success. Postoperative cataract was observed in 65.3%, abnormal corneas in 21.3%, hypotony in 16.9%, and glaucoma in 16.4% of the eyes. Despite the onset of complications related to silicone oil usage, a high rate of reattachment of the retina was observed following vitrectomy and silicone oil tamponade in the management of complex RD associated with multiple etiologies.

Nordic research in ophthalmology.

To provide an overview of some of the current activities in eye research in the Nordic countries. The presentations at the biannual Nordic Congress of Ophthalmology, held in Tampere, Finland in 2002, were reviewed and the contributions found most noteworthy are included in this article along with a limited discussion of each research field. However, space requirements prevented the inclusion of many interesting scientific contributions. Important contributions in various subfields of eye research and ophthalmology are reviewed. These include cornea, cataract, paediatric ophthalmology, glaucoma, diabetic eye disease, age-related macular degeneration, physiology and pharmacology and oncology. Eye research is very active in the Nordic countries and significant contributions are being made to ophthalmology in several fields on a world scale. We hope to continue to review Nordic contributions to eye research after each Nordic Congress of Ophthalmology and plan to make the reviews more systematic and comprehensive in the future.

Standardized color-coded scales for anterior and posterior elevation maps of scanning slit corneal topography

Purpose To find the most appropriate color-coded scales for the anterior and posterior elevation maps of scanning slit topography in the screening of abnormal corneas such as keratoconus. Design Retrospective case-control study. Participants Eighty eyes of 40 normal subjects and 175 eyes of 95 patients with keratoconus. Intervention Anterior and posterior corneal elevations were assessed using Orbscan 2. Best-fit sphere maps were drawn with several color-coded scales: 2-, 5-, 10-, and 20-μm height per each color interval. Main outcome measures The maps were judged to be abnormal when more than three colors (discriminant number) were found within the central 3-mm area. For each color-coded scale, sensitivity, specificity, positive predictive value, negative predictive value, and sensitivity + specificity were calculated. After determining the most appropriate color-coded scales for the anterior and posterior elevation maps, validity of the discriminant number was assessed. By varying the discriminant number from two to eight, receiver operator characteristic (ROC) curves were created using the sensitivity and specificity for each threshold number. Results The highest sensitivity + specificity values and highly balanced predictive values were obtained with the 10- and 20-μm scales for the anterior and posterior elevation maps, respectively. The ROC curve analyses showed that the best discriminant color number is three, indicating that maps with four or more colors within the central 3-mm area are judged abnormal in screening. Conclusions The 10- and 20-μm interval color scales are most appropriate for the anterior and posterior elevation maps of the scanning slit topography, respectively.

Modeling of corneal surfaces with radial polynomials.

We consider analytical modeling of the anterior corneal surface with a set of orthogonal basis functions that are a product of radial polynomials and angular functions. Several candidate basis functions were chosen from the repertoire of functions that are orthogonal in the unit circle and invariant in form with respect to rotation about the origin. In particular, it is shown that a set of functions that is referred herein as Bhatia-Wolf polynomials, represents a better and more robust alternative for modeling corneal elevation data than traditionally used Zernike polynomials. Examples of modeling corneal elevation are given for normal corneas and for abnormal corneas with significant distortion.

Optimal modeling of corneal surfaces with Zernike polynomials.

Zernike polynomials are often used as an expansion of corneal height data and for analysis of optical wavefronts. Accurate modeling of corneal surfaces with Zernike polynomials involves selecting the order of the polynomial expansion based on the measured data. We have compared the efficacy of various classical model order selection techniques that can be utilized for this purpose, and propose an approach based on the bootstrap. First, it is shown in simulations that the bootstrap method outperforms the classical model order selection techniques. Then, it is proved that the bootstrap technique is the most appropriate method in the context of fitting Zernike polynomials to corneal elevation data, allowing objective selection of the optimal number of Zernike terms. The process of optimal fitting of Zernike polynomials to corneal elevation data is discussed and examples are given for normal corneas and for abnormal corneas with significant distortion. The optimal model order varies as a function of the diameter of the cornea.

Clinical results of implantation of the Chirila keratoprosthesis in rabbits

AIMS/BACKGROUNDAn ideal keratoprosthesis (KPro) would closely resemble a donor corneal button in terms of its surgical handling, optics, and capacity to heal with host tissue in order to avoid many...