published_or_final_version / Molecular Biology / Doctoral / Doctor of Philosophy

PURPOSE: Diabetic macular edema (DME) is the most common cause of vision loss in patients with diabetic retinopathy. This study aims to approach diabetic macular edema and diabetic retinopathy as ischemic conditions and explores a potential treatment through hyperoxia. The study measured changes in retinal thickness, visual acuity, and contrast sensitivity in subjects receiving normobaric oxygen. METHODS: Fifty-one patients with diabetic macular edema at Beth Israel Deaconess Medical Center Eye Clinic (Boston, MA) received oxygen via a face mask at 5 liters per minute for 3 hours. Retinal thickness at the central subfield and maximal retinal thickness were measured using optical coherence tomography. Contrast sensitivity, best corrected visual acuity, and intraocular pressure were measured before and after oxygen as well. RESULTS: Macular thickness from diabetic macular edema decreased by an average of 2.09% (p < .05) at the point of maximal thickness, and by 0.88% (p < .05) at the central subfield. Vision also improved by an average of 0.043 LogMAR units (p < .05). Changes in macular thickness and visual acuity were non-significant in healthy control eyes that received oxygen. The results of hyperoxia on contrast sensitivity were indeterminate. CONCLUSIONS: We found that normobaric hyperoxia for 3 hours reduces macular thickness from diabetic macular edema and improves visual acuity. This study offers additional evidence that diabetic macular edema is an ischemic disorder and suggests that oxygen therapy may serve as an alternate or complimentary treatment of DME. / 2020-06-17T00:00:00Z

In this dissertation, I investigated computing algorithms for automated retinal blood vessel detection. Changes in blood vessel structures are important indicators of many diseases such as diabetes, hypertension, etc. Blood vessel is also very useful in tracking of disease progression, and for biometric authentication. In this dissertation, I proposed two algorithms to detect blood vessel maps in retina. The first algorithm is based on integration of a Gaussian tracing scheme and a Gabor-variance filter. This algorithm traces the large blood vessel in retinal images enhanced with adaptive histogram equalization. Small vessels are traced on further enhanced images by a Gabor-variance filter. The second algorithm is called a radial contrast transform (RCT) algorithm, which converts the intensity information in spatial domain to a high dimensional radial contrast domain. Different feature descriptors are designed to improve the speed, sensitivity, and expandability of the vessel detection system. Performances comparison of the two algorithms with those in the literature shows favorable and robust results. Furthermore, a new performance measure based on central line of blood vessels is proposed as an alternative to more reliable assessment of detection schemes for small vessels, because the significant variations at the edges of small vessels need not be considered. The proposed algorithms were successfully tested in the field for early diabetic retinopathy (DR) screening. A highly modular code library to take advantage of the parallel processing power of multi-core computer architecture was tested in a clinical trial. Performance results showed that our scheme can achieve similar or even better performance than human expert readers for detection of micro-aneurysms on difficult images.

Previous in vitro studies showed that exchange protein directly activated by cyclic AMP 1 (Epac1), which is a cAMP mediator, plays an important role in maintenance of endothelial barrier function. Diabetic retinopathy is characterized by impairment of retinal blood vessel integrity leading to breakdown of blood retinal barrier, retinal hypoxia, and neuronal damage. Here, we hypothesize that Epac1 regulates endothelial permeability and protects retina from the retinal damage associated with diabetes. To test such hypothesis, we first demonstrated that human retinal microvascular endothelial cells (HRMECs) exposed to high glucose concentration at 25 mM or 35 mM showed the decreased Epac1 expression level. Our preliminary data also showed that Epac1-downstream activator, Rap1, a member of Ras GTPase, was also altered by different glucose levels. In addition, retina from type 2 diabetic, db/db, mice also showed the decreased Epac1 expression compared to that of non-diabetic, db/m, mice. To further determine the role of Epac1 in diabetic retinopathy, we made use of Epac1-deficient mice. The pathogenesis of diabetic retinopathy share similar characteristics to that of ischemic retinopathy, such as neuronal cell death, glial reactivity, and glutamate toxicity. Therefore, we used our previous retinal ischemic model, i.e., transient middle cerebral artery occlusion (tMCAO). Firstly, we determined the retinal morphology of Epac1-/- mice under normal condition at 3wks. At 3 wks old, the Epac1-/- retinae showed a significantly decreased thickness of outer plexiform layer (OPL) with a trend of increase in inner nuclear layer (INL) thickness. Interestingly, there were obviously more glutamine synthetase (GS)-positive M?ller cells and protein kinase C (PKC)-α positive rod bipolar cells in INL. In addition, there were more IgG-positive blood vessels in OPL. To further determine whether these phenotypes will lead to more severe retinal damage, Epac1-/- mice were exposed to 2 hours of MCAO followed by 22 hours of reperfusion, which we have previously shown to induce retinal ischemia. There was no obvious difference in retinal thickness and expressions of glial fibrillary acidic protein (GFAP) and GS in the contralateral sides of Epac1+/+ and Epac1-/- retina after tMCAO suggesting that the Epac1-deficiency may be compensated by either protein kinase A (PKA) or Epac2. However, Epac2 level was not altered by Epac1-deficiency by Western blot analysis. The ipsilateral sides of the retina of Epac1+/+ and Epac1-/- after tMCAO also did not show obvious difference in swelling and cell death in inner retina, GFAP, glutamate, GS, nitrotyrosine (NT), and peroxiredoxin 6 (Prx6), suggesting that Epac1-deficiency may have been compensated by other cAMP mediators, such as Epac2. However, Epac2 expression in the ipsilateral side of Epac1+/+ and Epac1-/- retinae was not significantly different, although the activities of Epac and PKA were not determined. Taken together, the Epac1-deficient mice would serve as a useful model to determine the role of Epac1 in retinal development, and to determine the detail mechanisms of pathogenesis of diabetic and ischemic retinopathy. / published_or_final_version / Anatomy / Master / Master of Philosophy

Objective The main objective is to evaluate the current diabetic retinopathy (DR) screening by optometrists under Risk Assessment and Management Programme (RAMP) in general outpatient clinics (GOPC), and to compare it to conventional screening by clinical examination. The secondary objective is to predict the prevalence of DR and maculopathy (DMac) in the study cohort, and identify risk factors especially the role of nephropathy. Methodology Ophthalmologist’s re-grading of the digital fundus photos previously screened by optometrists according to RAMP protocol was used as the gold standard to evaluate the current screening programme. Accuracy of optometrist screening was calculated by percentage of agreement and Kappa coefficient. Fundus photo grading by ophthalmologist and optometrist was compared to clinical examination findings in eye clinics. Sensitivities and specificities were calculated, and plotted on ROC curve for comparison of the two methods of screening. Prevalences of DR and DMac were estimated from the gold standard grading, and their correlation with other factors also screened by RAMP was identified using chi-square test and logistic regression. Results There was an overall over-grading of disease by optometrists. The overall inter-observer agreement in diagnosis was 81.2%, and the overall kappa coefficient was 0.65 (p<0.001), which reached substantial strength of agreement. Use of mydriatics reduced the percentage of ungradable photos by at least 4 times. The overall agreement of clinical examination with ophthalmologist-photo-grading was 69.2%, and that with optometrist was 60.9%, and the respective Kappa coefficients were 0.31 (p<0.001) and 0.25 (p<0.001). The areas under curve (AUC) on ROC curve were larger for optometrist photo screening (DR=0.85 and DMac=0.80) than clinical examination (DR=0.52 and DMac=0.54). The prevalences of DR and DMac were 19.4% and 3.3% respectively. Duration of DM was the only common significant predictor of referable DR and DMac by chi-square test. 15-year of disease significantly increased the risk of more advanced DR and DMac. Nephropathy was only significant for DR but not DMac. Moderate renal dysfunction as indicated by decreased excretory glomerular filtration rate (eGFR) < 60 mL/min/1.73m2 and presence of macroalbuminuria significantly worsened DR staging, by over 5 times (p=0.02). Family history of diabetes mellitus (DM), on the other hand, increased the risk of DMac only, by 5 times (p=0.01). Conclusion The current optometrists’ screening is reasonably valid and reliable, although there is room for improvement. None-the-less, the higher false-positive rates than false-negative rates for referable disease suggests that it is safer than otherwise. It is a better method than clinical examination. Duration of DM and presence of nephropathy, especially macroalbuminuria which predates decrease in eGFR, and family history of DM can predict more advanced DR and/or DMac development. / published_or_final_version / Public Health / Master / Master of Public Health

Thesis (Ph.D.)--University of Adelaide, Dept. of Public Health, 2003. / "January 2003." Bibliography: 10.1-10.11 leaves.

Thesis (Ph. D.)--University of Sydney, 2006. / Title from title screen (viewed Oct. 7, 2009) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Discipline of Clinical Ophthalmology and Eye Health, Faculty of Medicine. Includes bibliography. Also available in print form.

BACKGROUND: Diabetic retinopathy (DR) is the leading cause of vision loss in the world. The Center for Disease Control and Prevention categorizes those with diabetes into three age groups, including a young adult group, ages 18-44. In the Boston metropolitan area, around 4.6% of this age population has diabetes. EYESPOT is a private eye care practice in Boston. Of the few diabetic patients seen, most do not fall within the young adult age range. Several studies have demonstrated the effectiveness of social media to promote awareness of healthy behaviors. OBJECTIVE: The goal of this study is to utilize social media in order to raise awareness of DR in the young adult population and encourage preventative behavior. METHODS: A Facebook page for EYESPOT Diabetes was created to engage the young adult patient population and was monitored over a four-month period. Four categories of Facebook posts, differentiated by type, were disseminated. Posts were targeted to different audiences during each month, creating three unique time blocks. Posts were analyzed for their Engagement (total number of people who interacted with the post via a “like”, click, or “share”) and their Reach (total number of people that saw the post). Preliminary Engagement measures of each post were standardized to account for measures of Reach, creating an additional measure of standardized engagement scores (SES). A 4x3 ANOVA was conducted using SPSS to evaluate the effects of post type and time block on SES. RESULTS: Main effects were found for both post type and time block. Posts of the “Advertising” type had a significantly lower SES than all other posts (p<.01). Posts in the “Promotional College Student” time block had a significantly higher SES (p<.01) than posts in other blocks. There was a significant type-by-block interaction for SES (p<.01). Post hoc analysis revealed that posts of the “Technological” type had higher SES when posted in the block aimed at College Students (p<.01). Of note, 96% of the Facebook users who saw our posts (n = 4050) fell in the young adult bracket. After the conclusion of the study, two new patients in the young adult range contacted EYESPOT with intent to make future appointments, citing our Facebook page as reference. CONCLUSION: Our study suggests that Facebook may be an effective tool to encourage the young adult population to be aware of and engage in beneficial health behaviors. Future studies will investigate how to utilize social media further to increase physical appointments and patient-clinician interactions.

M.Phil. (Optometry) / Despite many years of research, diabetic retinopathy (DR), and diabetic macular edema (DME) remain difficult to diagnose, prevent, and treat. The complicated nature of the disease, the limited information on DR and DME and the increasing prevalence of diabetes mellitus (DM) in South Africa, provided motivation for this study. To the best of my knowledge, this is the first study in our country to identify demographic, medical and visual aspects ofDR and DME collectively. A further incentive was the availability in optometry of recently developed computer software based upon multivariate statistics, which provided a unique opportunity to analyze, for example, tri-variate contrast sensitivity acuities using stereo-pair scatter plots. All refractive status measurements were also analyzed and compared with the same method. Together, the results from this study provide a broader clinical and research perceptive on DR and DME. In this cross-sectional study, 202 diabetic patients at the Helen Joseph Hospital in Johannesburg were recruited. Demographic variables included age, gender, race, age of diagnosis, duration of DM, and social habits. Medical variables included systemic conditions present, blood pressures, body mass index (BMI), lipid profiles, glycerated haemoglobin (HbAlc), and other available biochemical data (for example cholesterol, urea and creatinine levels). Visual variables included, distance, pinhole and near visual acuities, contrast sensitivity acuities, refractive status measured with autorefraction, colour vision, Amsler grid, intraocular pressures (lOP), and fundus photography. Administration of the Impact of Visuallmpainnent (IVI) questionnaire provided new information concerning the restrictions in daily living participation caused by DR or DME. The predominant characteristics of the study population consisted of Type 1DM among female Coloured subjects. Approximately 66% of all subjects had also been diagnosed with hypertension. The mean age ofthe subjects was 52 (± 14) years, age of diagnosis 41 (± 13) years, and duration ofDM 10.8 (± 9.7) years. Mean blood pressures (136/81 ± 20.5/11 mmHg) and glycated haemoglobin (HbAlc, 9.9 ± 3.4%) values were slightly higher than the recommended control levels (BP= 120/80 mmHg and HbAlc = 6 to 7%).

Indiana University-Purdue University Indianapolis (IUPUI) / Transforming growth factor β-activated kinase 1 (TAK1), a hub kinase at the convergence of multiple signaling pathways, is critical to the development of the central nervous system and has been found to play a role in cell death and apoptosis. TAK1 may have the potential to elucidate mechanisms of cell cycle and neurodegeneration. The Belecky-Adams laboratory has aimed to study TAK1 and its potential roles in cell cycle by studying its role in chick retinal development as well as its possible implication in the progression of diabetic retinopathy (DR). Chapter 3 includes studies that explore TAK1 in a study in chick retinal development and TAK1 in in vitro studies in retinal microglia. Using the embryonic chick, immunohistochemistry for the activated form of TAK1 (pTAK1) showed localization of pTAK1 in differentiated and progenitor cells of the retina. Using an inhibitor or TAK1 activite, (5Z)-7-Oxozeaenol, in chick eye development showed an increase in progenitor cells and a decrease in differentiated cells. This study in chick suggests TAK1 may be a critical player in the regulation of the cell cycle during retinal development. Results from experimentation in chick led to studying the potential role of TAK1 in inflammation and neurodegeneration. TAK1 has previously been implicated in cell death and apoptosis suggesting that TAK1 may be a critical player in inflammatory pathways. TAK1 has been implicated in the regulation of inflammatory factors in different parts of the CNS but has not yet been studied specifically in retina or in specific retinal cells. Chapter 2 includes studies from the Belecky-Adams laboratory of in vitro work with retinal microglia. Retinal microglia were treated with activators and the translocation to the nucleus of a downstream factor of TAK1 was determined: NF-kB. Treatment of retinal microglia in the presence of activators with TAKinib, an inhibitor of TAK1 activation, revealed that TAK1 inhibition reduces the activation of downstream NF-kB. Together this data suggests that TAK1 may be implicated in various systems of the body and further studies on its mechanisms may help elucidate potential therapeutic roles of the kinase.