Computational Modeling of Ophthalmic Procedures: Computational Modeling of Ophthalmic Procedures.

PURPOSE: To explore how finite-element calculations can continue to contribute to diverse problems in ophthalmology and vision science, we describe our recent work on modeling the force on the peripheral retina in intravitreal injections and how that force increases with shorter, smaller gauge needles. We also present a calculation that determines the location and stress on a retinal pigment epithelial detachment during an intravitreal injection, the possibility that stress induced by the injection can lead to a tear of the retinal pigment epithelium. BACKGROUND: Advanced computational models can provide a critical insight into the underlying physics in many surgical procedures, which may not be intuitive. METHODS: The simulations were implemented using COMSOL Multiphysics. We compared the monkey retinal adhesive force of 18 Pa with the results of this study to quantify the maximum retinal stress that occurs during intravitreal injections. CONCLUSIONS: Currently used 30-gauge needles produce stress on the retina during intravitreal injections that is only slightly below the limit that can create retinal tears. As retina specialists attempt to use smaller needles, the risk of complications may increase. In addition, we find that during an intravitreal injection, the stress on the retina in a pigment epithelial detachment occurs at the edge of the detachment (found clinically), and the stress is sufficient to tear the retina. These findings may guide physicians in future clinical research. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

A novel 3D segmentation approach for extracting retinal layers from optical coherence tomography images.

PURPOSE: Accurate segmentation of retinal layers of the eye in 3D Optical Coherence Tomography (OCT) data provides relevant information for clinical diagnosis. This manuscript describes a 3D segmentation approach that uses an adaptive patient-specific retinal atlas, as well as an appearance model for 3D OCT data. METHODS: To reconstruct the atlas of 3D retinal scan, the central area of the macula (macula mid-area) where the fovea could be clearly identified, was segmented initially. Markov Gibbs Random Field (MGRF) including intensity, spatial information, and shape of 12 retinal layers were used to segment the selected area of retinal fovea. A set of coregistered OCT scans that were gathered from 200 different individuals were used to build a 2D shape prior. This shape prior was adapted subsequently to the first order appearance and second order spatial interaction MGRF model. After segmenting the center of the macula "foveal area", the labels and appearances of the layers that were segmented were utilized to segment the adjacent slices. The final step was repeated recursively until a 3D OCT scan of the patient was segmented. RESULTS: This approach was tested in 50 patients with normal and with ocular pathological conditions. The segmentation was compared to a manually segmented ground truth. The results were verified by clinical retinal experts. Dice Similarity Coefficient (DSC), 95% bidirectional modified Hausdorff Distance (HD), Unsigned Mean Surface Position Error (MSPE), and Average Volume Difference (AVD) metrics were used to quantify the performance of the proposed approach. The proposed approach was proved to be more accurate than the current state-of-the-art 3D OCT approaches. CONCLUSIONS: The proposed approach has the advantage of segmenting all the 12 retinal layers rapidly and more accurately than current state-of-the-art 3D OCT approaches.

PENETRATING OCULAR INJURY WITH RETAINED INTRAOCULAR FOREIGN BODY FROM DRYWALL.

PURPOSE: To present a case of open globe injury and retained intraocular foreign body secondary to drywall. METHODS: Interventional case report. RESULTS: A 21-year-old man presented with corneal laceration, iris defect, and vitreous hemorrhage after hammering drywall. Computed tomography scan was negative for intraocular foreign body, but a drywall intraretinal foreign body was found on 25-gauge vitrectomy. Intraoperative findings and 6-month follow-up are presented. CONCLUSION: Intraocular foreign body must always be suspected in all cases of penetrating ocular trauma. Although magnetic resonance imaging is ideal in diagnosing nonmetallic foreign bodies, computed tomography scan with Hounsfield units should be used in an emergency setting.

International multi-center study of iatrogenic retinal tears in pars plana vitrectomy.

AIM: To study and compare the effect of different surgical settings on the development of iatrogenic retinal tears (IRT) in conventional (20-gauge) and microincisional vitrectomy. METHODS: An international retrospective comparative study of 394 patients who had simple vitrectomy at three tertiary centers. Surgeries were performed by four retina surgeons using different viewing systems. Two groups of eyes were compared: microincisional vitrectomy (327 eyes) and conventional (67 eyes) vitrectomy. An iatrogenic tear was defined as the occurrence of one or more peripheral retinal tears during surgery or at any visit in the first 6wk postoperatively. RESULTS: Mean age was 67±12y and 55% were female. Iatrogenic tears occurred in 11/394 (2.8%) of eyes. The rate of tears was similar among different surgeons and viewing systems (P=0.93 and P=0.76, respectively). Surgical indication, preexisting pseudophakia/aphakia, induction of posterior vitreous detachment (PVD) during surgery, and the use triamcinolone acetonide didn't significantly affect the rate of tears (P>0.1 for all factors). A higher rate of tears was found in the conventional group compared to the microincisional group (respectively, 7.5%, 1.8%, P=0.02). CONCLUSION: The rate of IRT in vitrectomy is not significantly affected by surgical indication, preexisting PVD or pseudophakia, or use of triamcinolone or different viewing systems but is significantly higher in conventional vitrectomy. Microincisional platforms improve the safety of vitrectomy regardless of the viewing system used.

Early diabetic retinopathy diagnosis based on local retinal blood vessel analysis in optical coherence tomography angiography (OCTA) images.

PURPOSE: This paper introduces a new computer-aided diagnosis (CAD) system for detecting early-stage diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA) images. METHODS: The proposed DR-CAD system is based on the analysis of new local features that describe both the appearance and retinal structure in OCTA images. It starts with a new segmentation approach that has the ability to extract the blood vessels from superficial and deep retinal OCTA maps. The high capability of our segmentation approach stems from using a joint Markov-Gibbs random field stochastic model integrating a 3D spatial statistical model with a first-order appearance model of the blood vessels. Following the segmentation step, three new local features are estimated from the segmented vessels and the foveal avascular zone (FAZ): (a) vessels density, (b) blood vessel calibre, and (c) width of the FAZ. To distinguish mild DR patients from normal cases, the estimated three features are used to train and test a support vector machine (SVM) classifier with the radial basis function (RBF) kernel. RESULTS: On a cohort of 105 subjects, the presented DR-CAD system demonstrated an overall accuracy (ACC) of 94.3%, a sensitivity of 97.9%, a specificity of 87.0%, the area under the curve (AUC) of 92.4%, and a Dice similarity coefficient (DSC) of 95.8%. This in turn demonstrates the promise of the proposed CAD system as a supplemental tool for early detection of DR. CONCLUSION: We developed a new DR-CAD system that is capable of diagnosing DR in its early stage. The proposed system is based on extracting three different features from the segmented OCTA images, which reflect the changes in the retinal vasculature network.

Retracted: Early diabetic retinopathy diagnosis based on local retinal blood vessels analysis in optical coherence tomography angiography (OCTA) images.

The above article from Medical Physics, published online on 22 February 2018 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the authors, the journal Editor in Chief and John Wiley & Sons Ltd. The retraction has been agreed following an investigation carried out by the editors due to major overlap with a previously published article: British Journal of Ophthalmology (BJO) (Sandhu HS, Eladawi N, Elmogy M, et al Automated diabetic retinopathy detection using optical coherence tomography angiography: a pilot study, British Journal of Ophthalmology Published Online First: 23 January 2018. doi:10.1136/bjophthalmol-2017-311489.

Automated diabetic retinopathy detection using optical coherence tomography angiography: a pilot study.

BACKGROUND: Optical coherence tomography angiography (OCTA) is increasingly being used to evaluate diabetic retinopathy, but the interpretation of OCTA remains largely subjective. The purpose of this study was to design a computer-aided diagnostic (CAD) system to diagnose non-proliferative diabetic retinopathy (NPDR) in an automated fashion using OCTA images. METHODS: This was a two-centre, cross-sectional study. Adults with type II diabetes mellitus (DMII) were eligible for inclusion. OCTA scans of the macula were taken, and the five vascular maps generated per eye were analysed by a novel CAD system. For the purpose of classification/diagnosis, three different local features-blood vessel density, blood vessel calibre and the size of the foveal avascular zone (FAZ)-were segmented from these images and used to train a new, automated classifier. RESULTS: One hundred and six patients with DMII were included in the study, 23 with no DR and 83 with mild NPDR. When using features of the superficial retinal map alone, the system demonstrated an accuracy of 80.0% and area under the curve (AUC) of 76.2%. Using the features of the deep retinal map alone, accuracy was 91.4% and AUC 89.2%. When data from both maps were combined, the presented CAD system demonstrated overall accuracy of 94.3%, sensitivity of 97.9%, specificity of 87.0%, area under curve (AUC) of 92.4% and dice similarity coefficient of 95.8%. CONCLUSION: Automated diagnosis of NPDR using OCTA images is feasible and accurate. Combining this system with OCT data is a plausible next step that would likely improve its robustness.

Association of Red Cell Distribution Width Values with Vision Potential in Retinal Vein Occlusion.

PURPOSE: To explore a possible association of red cell distribution width (RDW), a parameter that measures variation in red blood cell size or red blood cell volume and is an index of erythrocyte heterogeneity, with vision in patients with retinal vein occlusion (RVO). DESIGN: Cross-sectional study. PARTICIPANTS: Patients with either branch RVO (n = 70) or central RVO (n = 56) and gender-matched controls (n = 67) were included. METHODS: All participants underwent a comprehensive ophthalmologic examination, including fundus fluorescein angiography and macular OCT (Heidelberg Spectralis; Heidelberg Engineering, Heidelberg, Germany). Exclusion criteria included RVO not confirmed by fluorescein angiography, history of malignancy, anemia, follow-up of less than 6 months, and unavailability of RDW value within 3 months of first presentation of RVO. Retinal vein occlusion patients were divided into 4 quartiles according to RDW value: quartile 1 (RDW ≤ 13.8%), quartile 2 (13.8% < RDW ≤ 14.8%), quartile 3 (14.8% < RDW ≤ 16.0%), and quartile 4 (RDW > 16.0%). Unpaired samples t tests, Pearson correlation tests, chi-square tests, analyses of variance, and multiple regression analyses were used for statistical evaluation. MAIN OUTCOME MEASURES: Red cell distribution width value and best-corrected visual acuity (BCVA). RESULTS: There was no significant difference in the demographics of participants in all 3 groups with respect to age, gender, and associated systemic diseases. Red cell distribution width was significantly higher in RVO patients (14.9±1.6 µm) compared with control participants (12.5±1.4 µm; P<0.0001). There was a statistically significant correlation between RDW value and both initial BCVA (r = 0.443; P<0.0001) and final BCVA (r = 0.379; P<0.0001) in RVO patients. Both initial and final BCVA were better in RDW quartiles 1 and 2 compared with RDW quartiles 3 and 4. CONCLUSIONS: Red cell distribution width was significantly higher in RVO patients compared with control participants. Furthermore, higher RDW value was associated with lower initial and final BCVA. Red cell distribution width merits further studies related to being a potential prognostic factor for vision in RVO patients.

COMPARISON OF 2D AND 3D VIDEO DISPLAYS FOR TEACHING VITREORETINAL SURGERY.

PURPOSE: To compare medical students' learning uptake and understanding of vitreoretinal surgeries by watching either 2D or 3D video recordings. METHODS: Three vitreoretinal procedures (tractional retinal detachment, exposed scleral buckle removal, and four-point scleral fixation of an intraocular lens [TSS]) were recorded simultaneously with a conventional recorder for two-dimensional viewing and a VERION 3D HD system using Sony HVO-1000MD for three-dimensional viewing. Two videos of each surgery, one 2D and the other 3D, were edited to have the same content side by side. One hundred UMass medical students randomly assigned to a 2D group or 3D, then watched corresponding videos on a MacBook. All groups wore BiAL Red-blue 3D glasses and were appropriately randomized. Students filled out questionnaires about surgical steps or anatomical relationships of the pathologies or tissues, and their answers were compared. RESULTS: There was no significant difference in comprehension between the two groups for the extraocular scleral buckle procedure. However, for the intraocular TSS and tractional retinal detachment videos, the 3D group performed better than 2D (P < 0.05) on anatomy comprehension questions. CONCLUSION: Three-dimensional videos may have value in teaching intraocular ophthalmic surgeries. Surgical procedure steps and basic ocular anatomy may have to be reviewed to ensure maximal teaching efficacy.

Classification of retinal diseases based on OCT Images.

Optical Coherence Topography (OCT) is an emerging biomedical imaging technology that offers non-invasive real-time, high-resolution imaging of highly scattering tissues. It is widely used in ophthalmology to perform diagnostic imaging on the structure of the anterior eye and the retina. Clinical studies are carried out to assess the application of OCT for some retinal diseases. OCT can provide means for early detection for various types of diseases because morphological changes often occur before the physical symptoms of these diseases. In addition, follow-up imaging can assess treatment effectiveness and recurrence of a disease. A review in this area is needed to identify the results and the findings from OCT images in the field of retinal diseases and how to use these findings to help in clinical applications. This paper overviews the current techniques that are developed to determine the ability of OCT images for early detection/diagnosis of retinal diseases. Also, the paper remarks several challenges that face the researchers in the analysis of the OCT retinal images.

An automated approach for early detection of diabetic retinopathy using SD-OCT images.

This study was to demonstrate the feasibility of an automatic approach for early detection of diabetic retinopathy (DR) from SD-OCT images. These scans were prospectively collected from 200 subjects through the fovea then were automatically segmented, into 12 layers. Each layer was characterized by its thickness, tortuosity, and normalized reflectivity. 26 diabetic patients, without DR changes visible by funduscopic examination, were matched with 26 controls, according to age and sex, for purposes of statistical analysis using mixed effects ANOVA. The INL was narrower in diabetes (p = 0.14), while the NFL (p = 0.04) and IZ (p = 0.34) were thicker. Tortuosity of layers NFL through the OPL was greater in diabetes (all p < 0.1), while significantly greater normalized reflectivity was observed in the MZ and OPR (both p < 0.01) as well as ELM and IZ (both p < 0.5). A novel automated method enables to provide quantitative analysis of the changes in each layer of the retina that occur with diabetes. In turn, carries the promise to a reliable non-invasive diagnostic tool for early detection of DR.

Sunlight and ultraviolet radiation-pertinent retinal implications and current management.

Unprotected and prolonged exposure to ultraviolet (UV) light from sunlight, lasers, and arc welding leads to outer retinal damage. The photoreceptors and retinal pigment epithelium located in the posterior pole are particularly susceptible to this radiation. Classically known as solar retinopathy, this disorder frequently affects young individuals who have clear lenses and a propensity toward observing solar eclipses. Various imaging techniques aid the clinician in diagnosis, even if patients cannot recall an exposure event. By far the most utilized technique is optical coherence tomography that, in tandem with fluorescein angiography, and fundus autofluorescence, is crucial in ruling out other conditions. Fortunately, the prognosis of acute UV retinopathy is favorable, as most cases fully recover; however, a significant percentage of patients suffer from chronic sequelae: reduced acuity and lifelong central/paracentral scotomas. Thus, education toward understanding UV exposure risks, coupled with either abstinence or proper eye protection, is critical in preventing macular damage. We outline the various etiologies responsible for UV-induced retinopathy, describe the limited treatments available, and provide recommendations to minimize the potential devastating ophthalmic consequences as our society increases its reliance on UV-emitting technology and further engages in solar eclipse viewing.

Osseous Metaplasia (Cataracta Ossea) of Lens Remnants in Chronic Uveitis-A Clinicopathologic Report.

PURPOSE: To describe clinically and pathologically the rare occurrence of calcification and osseous metaplasia in lens remnants in both eyes of a patient with pseudophakic chronic uveitis. METHODS: We performed 25-gauge pars plana vitrectomy, removal of dislocated intraocular lens (IOL), and secondary IOL fixation in the left eye. A similar procedure was performed in the right eye with 27-gauge pars plana vitrectomy. RESULTS: The postoperative visual acuities were 20/30 OD and 20/125 OS. Hematoxylin and eosin staining demonstrated an abundance of calcified tissue and rare osteoclasts in lacunae, compatible with osseous metaplasia (cataracta ossea). CONCLUSION: To our knowledge this is the first clinicopathologic report demonstrating cellular metaplasia that resulted in osseous transformation of the cortical lens remnants into bone in both eyes of a psuedophakic patient with chronic granulomatous pan uveitis of unknown etiology. The surgical technique described in the supplemental videos demonstrates an effective way of managing this complication.

EX VIVO MODEL FOR THE CHARACTERIZATION AND IDENTIFICATION OF DRYWALL INTRAOCULAR FOREIGN BODIES ON COMPUTED TOMOGRAPHY.

BACKGROUND: The study was inspired after the authors encountered a patient with a penetrating globe injury due to drywall, who had retained intraocular drywall foreign body. Computed tomography (CT) was read as normal in this patient. Open globe injury with drywall has never been reported previously in the literature and there are no previous studies describing its radiographic features. METHODS: The case report is described in detail elsewhere. This was an experimental study. An ex vivo model of 15 porcine eyes with 1 mm to 5 mm fragments of implanted drywall, 2 vitreous only samples with drywall and 3 control eyes were used. Eyes and vitreous samples were CT scanned on Days 0, 1, and 3 postimplantation. Computed ocular images were analyzed by masked observers. Size and radiodensity of intraocular drywall were measured using Hounsfield units (HUs) over time. RESULTS: Intraocular drywall was hyperdense on CT. All sizes studied were detectable on Day 0 of scanning. Mean intraocular drywall foreign body density was 171 ± 52 Hounsfield units (70-237) depending on fragment size. Intraocular drywall foreign body decreased in size whereas Hounsfield unit intensity increased over time. CONCLUSION: Drywall dissolves in the eye and becomes denser over time as air in the drywall is replaced by fluid. This study identified Hounsfield Units specific to intraocular drywall foreign body over time.

Automatic blood vessels segmentation based on different retinal maps from OCTA scans.

The retinal vascular network reflects the health of the retina, which is a useful diagnostic indicator of systemic vascular. Therefore, the segmentation of retinal blood vessels is a powerful method for diagnosing vascular diseases. This paper presents an automatic segmentation system for retinal blood vessels from Optical Coherence Tomography Angiography (OCTA) images. The system segments blood vessels from the superficial and deep retinal maps for normal and diabetic cases. Initially, we reduced the noise and improved the contrast of the OCTA images by using the Generalized Gauss-Markov random field (GGMRF) model. Secondly, we proposed a joint Markov-Gibbs random field (MGRF) model to segment the retinal blood vessels from other background tissues. It integrates both appearance and spatial models in addition to the prior probability model of OCTA images. The higher order MGRF (HO-MGRF) model in addition to the 1st-order intensity model are used to consider the spatial information in order to overcome the low contrast between vessels and other tissues. Finally, we refined the segmentation by extracting connected regions using a 2D connectivity filter. The proposed segmentation system was trained and tested on 47 data sets, which are 23 normal data sets and 24 data sets for diabetic patients. To evaluate the accuracy and robustness of the proposed segmentation framework, we used three different metrics, which are Dice similarity coefficient (DSC), absolute vessels volume difference (VVD), and area under the curve (AUC). The results on OCTA data sets (DSC=95.04±3.75%, VVD=8.51±1.49%, and AUC=95.20±1.52%) show the promise of the proposed segmentation approach.

VITREOMACULAR ADHESION EVOLUTION WITH AGE IN HEALTHY HUMAN EYES.

PURPOSE: To quantify the changes in vitreomacular interactions that occur with normal aging in normal eyes. METHODS: Spectral domain optical coherence tomography (SD-OCT, Spectralis; Heidelberg Engineering, Heidelberg, Germany) foveal scans of subjects with best corrected visual acuity better than 20/40 and no ocular pathology were included in the study. Each scan was analyzed to determine the status of vitreoretinal interface: complete vitreous adhesion, partial posterior vitreous detachment (PVD) with persistent vitreomacular adhesion (VMA), or complete PVD. Area of VMA was delineated using the Spectralis drawing tool and calculated in mm for each scan. Subjects, aged 10 years to 97 years, were divided into 9 age groups according to decade of life. RESULTS: Five hundred and sixty-six SD-OCT scans were analyzed. Area of VMA (mm) decreased sigmoidally (R = 0.99) with each decade of life. With aging, percentage of PVD increased while percentage of complete adhesion decreased. Males were found to have significantly larger area of VMA (mm) compared with females in the fifth through eighth decades of life, P < 0.05. CONCLUSION: Vitreomacular interface interactions throughout life are age and gender dependent. This adds to our current understanding of the normal aging process undergone by the vitreous, thereby providing assistance in the clinical differentiation between normal and pathologic vitreomacular interactions.

Common and Rare Ocular Side-effects of the Dexamethasone Implant.

PURPOSE: Expanding indications for use, and overall increased use of the slow-release dexamethasone (DEX) implant yields an opportunity to study the reported ocular side-effects and adverse events associated with this drug. METHODS: A PubMed.gov (US National Library of Medicine, National Institutes of Health) review of literature for the search terms, "Ozurdex and complication," through December 2015. RESULTS: Ocular hypertension and cataract are the main long-term sequelae identified in large, randomized clinical trials. Case reports have emerged regarding implant migration, complications with implantation, infection, and posterior segment sequelae, including vitreomacular traction. CONCLUSION: DEX implant overall is well-tolerated and, with careful monitoring, can be a useful adjunct to treating macular edema associated with diabetes, retinal vein occlusion, and chronic uveitis.

DIABETES ALTERS THE MAGNITUDE OF VITREOMACULAR ADHESION.

PURPOSE: To quantify the changes in vitreomacular interactions that occur with aging in diabetic eyes in comparison with age-matched control eyes. METHODS: Spectral-domain optical coherence tomography (Spectralis; Heidelberg Engineering) foveal scans of diabetic patients, without evidence of cystoid macular edema, were included. Twenty-five raster foveal scans were performed on every subject. Area of vitreomacular adhesion was delineated using the Spectralis drawing tool and calculated in square millimeter. Data collected included gender, race, best-corrected visual acuity, and posterior vitreous detachment status. Subjects were divided into age groups according to decade of life. RESULTS: Spectral-domain optical coherence tomography scans from 141 diabetic patients were analyzed. Area of vitreomacular adhesion (mm) showed a hyperbolic decline in diabetic patients (35.5 ± 0, 35.0 ± 3, 34.0 ± 3, 33.9 ± 5, 33.7 ± 6, 29.0 ± 11, 23 ± 15, 13 ± 15). With aging, incidence of posterior vitreous detachment increased and incidence of complete attachment decreased. CONCLUSION: Diabetes affects the magnitude of attachment of the vitreous gel to the macula that results in stronger and longer lasting attachment of the gel throughout life. Gender differences were not noticed in diabetic patients, suggesting that vitreomacular adhesion remains robust in both genders in diabetes despite aging.