Retinopathy with and without diabetes: Risk factors and visual impairment.

Transkript

1 FACULTY OF HEALTH SCIENCES DEPARTMENT OF COMMUNITY MEDICINE Retinopathy with and without diabetes: Risk fators and visual impairment. The Tromsø Eye Study and a Norwegian sreening study Geir Bertelsen A dissertation for the degree of Philosophiae Dotor January 2013

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3 Retinopathy with and without diabetes: Risk fators and visual impairment. The Tromsø Eye Study and a Norwegian sreening study Geir Bertelsen Department of Ophthalmology and Neurosurgery, University Hospital of North Norway. Department of Community Mediine, Faulty of Health Sienes, University of Tromsø. 1

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5 Table of Contents Figures and tables... 5 Aknowledgements... 6 Norsk populærvitenskapelig sammendrag... 8 Summary... 9 List of papers Abbreviations Introdution Diabetes Diagnosti riteria of diabetes Compliations of diabetes The eye Diabeti retinopathy Diabeti maular oedema Prevalene of diabeti retinopathy Risk fators for diabeti retinopathy Retinopathy without diabetes Prevalene of retinopathy without diabetes Risk fators for retinopathy without diabetes Aim of the thesis Methods paper I-III, Tromsø Eye Study The Tromsø Study and Tromsø Eye Study Study sample Data olletion and definitions Laboratory measurements Eye examinations Visual auity Retinal imaging and interview Grading of images Retinopathy Statistial analyses Methods paper IV Study sample Retinal imaging Retinopathy grading Visual auity Interview

6 The author ontribution Main results Paper I: The Tromsø Eye Study: Study design, methodology and results on visual auity and refrative errors Paper II: Tromsø Eye Study: Prevalene and risk fators of diabeti retinopathy Paper III: Sex differenes in risk fators for retinopathy in non-diabeti men and women. The Tromsø Eye Study Paper IV: Prevalene of diabeti retinopathy in Norway: report from a sreening study General disussion Methodology onsiderations paper I-III, Tromsø Eye Study Study design Internal validity Seletion bias Information bias and mislassifiation Confounding External validity Statistial onsiderations Methodologial onsiderations paper IV Conlusions Impliations for publi health Risk fators for retinopathy Sreening Further researh Referenes

7 Figures and tables Figure 1: The shemati eye Figure 2: The normal human retina. (Photo: Tromsø Eye Study ) Figure 3: Diabeti maular oedema. (Photo: Tromsø Eye Study ) Figure 4: Flow hart illustrating the study sample. Tromsø Study Figure 5: Age distribution of partiipants. Tromsø Eye Study Figure 6: Confounding illustrated by offee, smoking and lung aner Table 1: Age distribution in invitees and partiipants in the sixth Tromsø Study Table 2: The International Clinial Diabeti Retinopathy Severity Sales Table 3: The International Clinial Diabeti Maular Edema Severity Sales

8 Aknowledgements The studies inluded in this thesis were funded by the Norwegian Extra Foundation for Health and Rehabilitation through EXTRA funds, the Norwegian Diabetes Assoiation, the Researh Counil of Norway, University of Tromsø, the North Norway Regional Health Authority and Simon Fougner Hartmanns Familiefond. My interest in researh started as a medial student when I was given the opportunity to work part time at the Cardiovasular Researh Group, Department of Medial Biology, University of Tromsø. I would like to thank Rune Sundset, Laila Arvola, Knut Steinnes and all the other olleagues for giving me a positive and stimulating introdution to researh. By hoosing a linial areer in ophthalmology it beame diffiult to ontinue the ardiovasular researh. The researh at the Ophthalmology Department was limited without any possibilities for supervising a PhD-projet and we had to find other alternatives. At the same time the sixth survey of the Tromsø Study was under planning. Inger Njølstad at the Department of Community Mediine, University of Tromsø, agreed to supervise a PhDprojet in the Tromsø Study and has been important for all parts of the study from beginning until end. This thesis and the Tromsø Eye Study would not have happened without you. I sinerely thank Anne Katrin (Anka) Sjølie for o-supervising the study. Anka s long experiene in ophthalmologial researh has been invaluable, and I m very grateful for all the effort Anka has put in to the study. I greatly aknowledge Tunde Peto for reviewing and helping out on all the Tromsø Eye Study papers, the thesis and for introduing the Tromsø Eye Study to international onsortia. I owe you a bottle of Champagne. I am thankful for the work all the o-authors have done on ritial review of the papers, and all the members of the Tromsø Eye Study group for interesting disussions, espeially Maja who was the first to join in on the Tromsø Eye Study, sharing many frustrations and solving problems. 6

9 The tehnial and administrative staffs at the Tromsø Study have been important for the study, and espeially Ann-Kristin, Bente and Unni who worked hard on the eye examinations, and Elise, Kristin and Merete who made the Tromsø Study possible. I also appreiate the support from all the good olleagues at the Department of Ophthalmology and Neurosurgery, University Hospital of North Norway, and thanks to Oleg and Kjell Arne for making offee breaks interesting. Without the enthusiasm of the partiipants the Tromsø Study would not have happened. The inhabitants of Tromsø deserve my warmest thanks for partiipating in the Tromsø Study. I also thank those I have not mentioned and who deserve a thank you. Finally, I would like to thank the family, my wife Eirin and my two little prinesses Marie and Sofie for ontinuous support and most important of all; making life meaningful. 7

10 Norsk populærvitenskapelig sammendrag Diabetes retinopati er en av mange komplikasjoner knyttet til diabetes. I den vestlige verden er dette den viktigste årsak til nedsatt syn og blindhet i arbeidsfør alder. Vi gjennomførte øyeundersøkelser av deltagere i den sjette Tromsøundersøkelsen. Forekomsten av diabetes retinopati var 26,9% blant deltakere med diabetes, og varigheten av diabetes, blodsukker nivå, blodtrykk og mikroalbuminuri var risikofaktorer. Det var en lav andel med redusert syn. Vi undersøkte også forekomsten av diabetes retinopati blant diabetikere rekruttert fra allmennpraktikere i Tromsø, Tønsberg og Stavanger og fant en forekomst på 28,2%. Denne studien viste også at omtrent en tredjedel av deltagerne ikke hadde vært undersøkt av øyelege i løpet at de siste to år slik de nasjonale retningslinjer anbefaler. Videre undersøkte vi forekomsten av retinopati hos deltakere i Tromsøundersøkelsen uten diabetes og fant at det var forskjeller mellom menn og kvinner. Forekomsten hos menn var 15,9% og hos kvinner 14,0%. Risikofaktorer for kvinner var blodtrykk, alder og mikroalbuminuri og for menn blodtrykk og blodsukkernivå målt ved forsukret hemoglobin (HbA1). 8

11 Summary Diabeti retinopathy is a well-known ompliation of diabetes and a major ause of visual impairment and blindness in developed ountries. We explored visual impairment and diabeti retinopathy among partiipants with diabetes in the Tromsø Eye Study. The prevalene of visual impairment (orreted Snellen visual auity < 20/40) was 4.1% in the better-seeing eye. We found no legally blind partiipants. The prevalene of diabeti retinopathy was 26.9% and maular edema 3.9%. In a multivariable logisti regression model, retinopathy was assoiated with longer diabetes duration, insulin use, non-fasting gluose and urinary albumin exretion. We found a very low miroalbuminuria ut-off level for inreased risk of diabeti retinopathy (urinary albuminreatinine ratio > 1.16 mg/mmol). Visual impairment and diabeti retinopathy were also explored in diabetes patients reruited from general pratitioners in a multi-entre study onduted in Tromsø, Tønsberg and Stavanger. In this study the prevalene of visual impairment (orreted Snellen visual auity < 20/40) was 5.4% and one partiipant was legally blind. The prevalene of diabeti retinopathy was 28.2%. This study also showed that about one third of the diabetes patients did not attend at least biannual eye examination as reommended by the national guidelines. Retinopathy lesions, suh as miroaneurysms and retinal haemorrhages, are also ommon in subjets without diabetes. We explored retinopathy in subjets without diabetes in the Tromsø Eye Study, and the overall prevalene of retinopathy was 14.8%. Men had a higher prevalene of retinopathy ompared to women (15.9% vs. 14.0%, p=0.04). In men retinopathy was assoiated with hypertension and HbA1. In women retinopathy was assoiated with age, hypertension and urinary albumin exretion. In women, the miroalbuminuria ut-off level for inreased risk of retinopathy was very low (urinary albumin-reatinine ratio > 0.43 mg/mmol). 9

12 Visual impairment was also explored in a general population using data from both diabeti and non-diabeti partiipants in the Tromsø Eye Study and the overall prevalene of visual auity < 20/60 was 1.2%. 10

13 List of papers I. Bertelsen G, Erke MG, von Hanno T, Mathiesen EB, Peto T, Sjølie AK, Njølstad I. The Tromsø Eye Study: study design, methodology and results on visual auity and refrative errors. Ata Ophthalmol. 2012; [Epub ahead of print]. II. Bertelsen G, Peto T, Lindekleiv H, Shirmer H, Solbu MD, Toft I, Sjølie AK, Njølstad I. Tromsø Eye Study: prevalene and risk fators of diabeti retinopathy. Ata Ophthalmol. 2012; [Epub ahead of print]. III. Bertelsen G, Peto T, Lindekleiv H, Shirmer H, Solbu MD, Toft I, Sjølie AK, Njølstad I. Sex differenes in risk fators for retinopathy in non-diabeti men and women. The Tromsø Eye Study. [Submitted]. IV. Kilstad HN, Sjølie AK, Gøransson L, Hapnes R, Henshien HJ, Alsbirk KE, Fossen K, Bertelsen G, Holstad G, Bergrem H. Prevalene of diabeti retinopathy in Norway: report from a sreening study. Ata Ophthalmol 2012; 90:

14 Abbreviations ACR: Urinary Albumin/Creatinine Ratio AGE: Advaned Glyation End-produts BMI: Body Mass Index DCCT: Diabetes Control and Compliations Trial EDIC: Epidemiology of Diabetes Interventions and Compliations ETDRS: Early Treatment Diabeti Retinopathy Study egfr: Estimated Glomerular Filtration Rate GP: General Pratitioner HbA1: Glyosylated Haemoglobin HPLC: High Performane Liquid Chromatography ICPC-2: International Classifiation of Primary Care, Seond edition IRMA: Intra Retinal Mirovasular Abnormalities PKC: Protein Kinase C UKPDS: UK Prospetive Diabetes Study WESDR: Wisonsin Epidemiologi Study of Diabeti Retinopathy WHO: World Health Organization 12

15 Introdution Diabetes Diabetes Mellitus is a hroni metaboli disorder haraterized by hyperglyaemia and disturbanes in arbohydrate, fat and protein metabolism aused by defets in insulin seretion, ation or both [1]. The global prevalene among adults is inreasing and has been estimated to 6.4% in 2010 and 7.7% in 2030 [2]. The prevalene inreases with age and a Norwegian study using data from 9 population based studies onduted from 1996 to 2001 reported an overall prevalene of 3.4% in adults 30 years and older. In subjets aged 80 years and older the prevalene was 12.4% in women and 11.5% in men [3]. Type 1 diabetes is haraterised by an autoimmune destrution of insulin produing beta-ells usually leading to absolute insulin defiieny and aounts for 5-10% of the diabetes ases [4]. Type 2 diabetes is haraterised by insulin resistane and usually a relative insulin defiieny, and aounts for 90-95% of diabetes ases [4]. The aetiology is multifatorial and assoiated with both geneti and environmental fators as inativity and over-nutrition, ausing a slowly progressing hyperglyaemia and altered lipid metabolism [5]. The gradual onset of symptoms may result in several years of undiagnosed type 2 diabetes [3]. Diagnosti riteria of diabetes In 1965, the World Health Organization (WHO) published guidelines for diabetes, and sine then the diagnosti riteria have been revised several times. The urrent WHO riteria is based on the presene of diabeti retinopathy and uses fasting plasma gluose 7.0 mmol/l and two hour plasma gluose 11.1 mmol/l [6]. Reently a WHO report from 2011 reommended glyosylated haemoglobin (HbA1) 6.5% as an alternative diagnosti riterion for diabetes [7]. Compliations of diabetes Diabetes inreases the risk of many different ompliations that in general an be divided into maro- and mirovasular disease [8]. The marovasular ompliations inlude oronary heart disease and erebrovasular disease. The mirovasular ompliations inlude 13

16 neuropathy, nephropathy and diabeti retinopathy. Diabeti retinopathy is a major long-term ompliation of diabetes and the major ause of visual impairment and blindness below 75 years of age in developed ountries [9-12]. In addition, diabetes inreases the risk for atarat and glauoma [13]. Due to the risk of visual impairment and blindness aused by diabeti retinopathy, national guidelines reommend annual or biannual eye examination for diabetes patients without retinopathy. In ase of retinopathy more frequent examination is reommended [14]. Figure 1: The shemati eye The eye A shemati eye is illustrated in figure 1. The eye is often ompared to a amera. The ornea, lens and pupil orrespond to the amera lens and aperture to reate a foused image with adequate amount of light on the neurosensory retina lining the inside posterior 2/3 of the eye (Figure 2). In the retina, rods and ones onverts the photons into eletrial signals by photo transdution. This proess orresponds to the image sensor in a modern amera. 14

17 Figure 2: The normal human retina. (Photo: Tromsø Eye Study ) Diabeti retinopathy Diabeti retinopathy is a multifatorial disease of the retina, and the underlying pathologial mehanisms are omplex. Several biohemial pathways leading to the hyperglyaemia indued abnormalities seen in diabeti retinopathy have been identified and probably interat. Pathologial biohemial mehanisms inluding Advaned Glyation End-produts (AGEs), Protein Kinase C (PKC), the polyol pathway, the hexosamine pathway, angiogeni fator expression and oxidative stress probably ause damage to all major retinal ells leading to neuroglial and mirovasular damage [15]. The relative ontribution of the different biohemial abnormalities is unlear. The progressive neuroglial and mirovasular damage are also affeted by an interplay of fators suh as blood pressure, impaired retinal autoregulation and hormones to develop the linial manifestation of diabeti retinopathy where inflammation, leuostasis, ishemia and strutural alterations are important features [15-17]. Histopathology studies of diabeti retinopathy show thikening of the apillary basement membrane, loss of periytes, miroaneurysms, endothelial ell death and apillary loss [16]. 15

18 Retinopathy is linially haraterised by miroaneurysms, haemorrhages, venous beading, otton wool spots, intra retinal mirovasular abnormalities and new proliferative vessels. The retinal abnormalities range from hanges not visible on a retinal photo to severe proliferative retinopathy with pathologial angiogenesis resulting in fibrovasular proliferation on top of the retina or into the vitreous, and eventually vitreous haemorrhage and trational retinal detahment. Diabeti maular oedema The retina laks lymphati drainage, and fluid transportation aross the apillaries must be Figure 3: Diabeti maular oedema. (Photo: Tromsø Eye Study ) balaned by apillary reuptake and transportation aross the pigment epithelium separating the retina and underlying horoid. In diabeti maular oedema hyperglyaemia indued apillary dysfuntion and damage auses exess vasopermeability, hypoxia and retinal oedema resulting in dereased visual auity. Key omponents in the pathophysiology inlude altered hemodynamis, breakdown of blood retina barrier, angiogeni fator expression, inflammation and oxidative stress [18]. The entre of the maula is prone to oedema due to the high metaboli turnover and the foveal avasular zone limiting both the blood supply and apillary reuptake of extraellular fluid. In a retinal image, maular oedema is haraterised by hard exudates onsisting of lipid and protein deposits. Figure 3 illustrates maular oedema with hard exudates, miroaneurysms and haemorrhages. Prevalene of diabeti retinopathy There are inonsistenies between epidemiologial studies and differenes in study methods ontribute to onfliting reports on prevalene of diabeti retinopathy [12, 19]. A reent study used pooled data from 35 studies using similar methodology and estimated the world 16

19 prevalene (age-standardized) of any diabeti retinopathy to 34.6%, proliferative retinopathy to 7.0% and diabeti maular oedema to 6.8% in subjets aged years with diabetes [20]. Risk fators for diabeti retinopathy Diabetes duration The most important and onsistent risk fator for retinopathy in observational studies is diabetes duration [21-24]. Type 1 diabetes has a higher prevalene of retinopathy ompared to type 2 diabetes [20]. In the Wisonsin Epidemiologi Study of Diabeti Retinopathy (WESDR) the prevalene of diabeti retinopathy was 98% for diabetes duration > 14 years in type 1 diabetes. In type 2 diabetes the prevalene of diabeti retinopathy was 85% for insulin users and 58% for non-insulin users for diabetes duration > 14 years [25]. Hyperglyaemia Hyperglyaemia is an important risk fator for diabeti retinopathy. Clinial trials as the Diabetes Control and Compliations Trial (DCCT) and UK Prospetive Diabetes Study (UKPDS) have demonstrated the benefiial effet of tight glyaemi ontrol on development and progression of diabeti retinopathy [26, 27]. Longitudinal observational studies as WESDR, the Blue Mountains eye study and others have also doumented the relationship between elevated gluose and diabeti retinopathy [28-30]. Blood pressure In most studies, blood pressure is orrelated to retinopathy [31]. Clinial trials as the UKPDS, DCCT, Epidemiology of Diabetes Interventions and Compliations (EDIC) and EuroDIAB studies have demonstrated the importane of blood pressure, but the initial blood pressure was relatively high in some studies [32-34]. The ACCORD study failed to demonstrate any effet of intensive blood pressure ontrol in type 2 diabetes suggesting that there might be a lower limit for the benefiial effet of blood pressure ontrol [35]. In observational studies the results are less onsistent, but may be onfounded by blood pressure treatment [29, 30, 36-39]. 17

20 Hyperlipidaemia Observational studies have investigated the relationship between hyperlipidaemia and retinopathy reporting both positive, negative and no assoiations [36, 40-42]. The ACCORD Lipid study showed that intensive lipid lowering therapy with fenofibrate slowed the progression of retinopathy at four years ompared to plaebo, indiating an effet of hyperlipidaemia on retinopathy [35]. Renal disease Kidney disease is a well-known ompliation of diabetes, and about 50% of diabetes patients will develop miroalbuminuria, and 1/3 of the miroalbuminuria ases will progress to proteinuria eventually leading to end stage renal disease in many ases [8]. Miroalbuminuria and proteinuria are assoiated with retinopathy in several studies [39, 43, 44]. In addition diabeti retinopathy have been reported to be assoiated with pregnany, ardiovasular disease, stroke and ognitive funtion [45-49] Retinopathy without diabetes The knowledge about the pathogenesis leading to retinopathy without diabetes in a general population is limited and mostly derived from observational studies. The onept of retinopathy ourring in a presumably healthy individual makes it diffiult to explore the pathogenesis in detail. The retinal lesions found in a retinal image inlude the same as in diabeti retinopathy, although usually more disrete and limited to a few haemorrhages, miroaneurysms or otton wool spots. Although hypertension and diabetes are seemingly well defined linial entities, in reality they both probably represent parts of a ontinuum with progressive dysfuntion. Studies of diabeti retinopathy and hypertensive retinopathy may therefore provide important lues about the pathogenesis of retinopathy without diabetes whih probably is a mixture of several pathologial mehanisms when studied in a general population. 18

21 Prevalene of retinopathy without diabetes Retinopathy lesions are relatively ommon in subjets without diabetes. Several studies have reported the prevalene in non-diabeti populations ranging from % in different ethni populations, but the results are onfounded by differenes in age distribution, methodology and number of images used in the retinopathy grading [43, 50-54]. Risk fators for retinopathy without diabetes Studies have found assoiations between several risk fators and non-diabeti retinopathy inluding blood pressure, age, miroalbuminuria, body mass index, arotid artery intimamedia thikness, smoking, ardiovasular disease, stroke, ognitive impairment and impaired gluose metabolism below the urrent diagnosti threshold for diabetes [43, 50, 52-61]. Even though the results differ between the studies, hypertension seems to be the most onsistent risk fator in the non-diabeti population. In general the risk fators for retinopathy are similar in diabeti and non-diabeti populations although diabetes duration and severity are obviously not relevant in non-diabeti populations. The wide range of assoiations between retinopathy and vasular disease in various organ systems suggests that retinopathy is a result of systemi proesses. 19

22 Aim of the thesis To investigate the prevalene of visual impairment in diabetes Estimate prevalene of diabeti retinopathy Assess risk fators for diabeti retinopathy Estimate prevalene of retinopathy in a non-diabeti population Assess risk fators for retinopathy without diabetes Determine the proportion of diabetes patients following the national guidelines on regular eye examination 20

23 Methods paper I-III, Tromsø Eye Study The Tromsø Study and Tromsø Eye Study The Tromsø Eye Study is a substudy of the Tromsø Study. The Tromsø Study is a large omprehensive longitudinal population-based study started in The Tromsø Study and the ohort profile has been desribed elsewhere [62]. A total of 40,051 subjets have partiipated in at least one of the six surveys. A desription of the large amount of variables olleted is presented at: Serum samples from eah survey and DNA samples from the 4 th survey and onwards are stored in a biobank. The Tromsø Study holds several endpoint registers with registration of inident myoardial infartion, stroke, atrial fibrillation, diabetes and non-vertebral fratures from ase note reviews at the only loal hospital in the region. The 6 th Tromsø Study survey was onduted from Otober 2007 through Deember 2008 and onsisted of two separate visits [63]. All partiipants were invited to a 1 st visit where they answered a questionnaire (Appendix I) and underwent a physial examination omprising the measurement of blood pressure, height, weight, waist and hip irumferene. Blood sampling, bone mineral density and pain threshold tests were also performed. A large subgroup was invited to a 2 nd visit a few weeks later. The eye examinations of the Tromsø Eye Study were performed at the 2 nd visit. In addition, the 2nd visit omprised a seond questionnaire (Appendix II), blood samples, ognitive tests, ultrasound of the arotid artery, 12-lead eletroardiogram, ehoardiography, spirometry, and bone mineral densitometry. The Tromsø Study and Tromsø Eye Study followed the tenets of the Delaration of Helsinki for researh involving humans and were approved by the Regional Committee for Medial and Health Researh Ethis. All partiipants gave an informed written onsent. Study sample The study sample was based upon the offiial population registry and all subjets were residents of the muniipality of Tromsø. The sampling strategy for the 6 th Tromsø Study survey was omplex and a balane between the need for inluding the partiipants from 21

24 previous visits for longitudinal analyses and the different needs in all substudies for new partiipants. Therefore the sample onsists of a mix of whole birth ohorts, random samples and previous partiipants. First visit A total of 19,762 subjets were invited to the 1 st visit. Subjets invited to the 1 st visit of the 6 th Tromsø Study survey were: 1. All Tromsø residents aged or years (n=12,578). 2. A 10% random sample of individuals aged years (n=1056). 3. A 40% random sample of individuals aged years (n= 5787). 4. Subjets who had attended the 2 nd visit of the 4 th survey, if not already inluded in the three groups above (n=341). A total of 12,984 subjets (65.7%) partiipated. Seond visit The 2 nd visit study sample was preseleted before the start of the survey, and inluded: 1. All subjets eligible for the 1 st visit aged years or aged years (n=7657). 2. A 20% random sample of subjets eligible for the 1 st visit aged years (n=942). 3. Subjets, if not already inluded in the two groups above, who had attended the 2 nd visit of the 4 th survey (n=2885). In addition, partiipation in the 1 st visit was a prerequisite to be reinvited to the 2 nd visit [62]. A total of 7958 were invited and 7307 (91.8%) attended the 2 nd visit. A total of 6540 attended retinal photography (82.2%). Figure 4, 5 and Table 1 illustrates the study sample and seletion proess. The partiipants in the 2 nd visit were mainly Cauasians with 91% reporting Norwegian ethniity and 1.5% reporting Sami ethniity. 22

25 Figure 4: Flow hart illustrating the study sample. Tromsø Study Invited 1 st visit n = 19,762 All aged and % random sample aged % random sample aged Previously attended seond visit of T4* Attended 1 st visit n = 12,984 Not attending 1 st visit n = 6778 Not invited 2 nd visit n = 5026 Invited 2 nd visit n = 7958 All aged and % random sample aged Previously attended seond visit of T4* Not attending 2 nd visit n = 651 Attended 2 nd visit n = 7307 Not attending retinal photographi examination n = 767 Tromsø Eye Study n = 6540 (Attended retinal photographi examination) *T4: The 2 nd visit of the 4 th Tromsø Study survey. 23

26 Table 1: Age distribution in invitees and partiipants in the sixth Tromsø Study First visit Seond visit Tromsø Eye Study* Age, years Invited (n) Attended n (%) Invited (n) Attended n (%) Attended n (%) (46.9) (91.3) 20 (87.0) (68.0) (95.3) 183 (85.1) (71.5) (93.6) 1927 (84.6) (76.9) (94.0) 2736 (85.3) (68.9) (89.6) 1344 (78.4) (40.1) (76.2) 330 (63.3) Total (65.7) (91.8) 6540 (82.2) * Partiipated in retinal photographi examination Figure 5: Age distribution of partiipants. Tromsø Eye Study Partiipants (n) Invited seond visit Attended seond visit Attended photographi examination Age, Years 24

27 Data olletion and definitions Anthropometri measurements, blood pressure, blood and urine samples were obtained by physial examination. Blood pressure was measured by trained tehniians, using an automated devie (Dinamap Vital Signs Monitor, Tampa, FL, USA). Three onseutive measurements were done with one minute intervals and the mean of the two last measurements were used in the analyses. Hypertension was defined as systoli blood pressure > 140 mmhg, diastoli blood pressure > 90mmHg, or use of antihypertensive treatment. Pulse pressure was defined as the differene between systoli and diastoli blood pressure and mean arterial pressure as: 2/3(diastoli blood pressure) + 1/3(systoli blood pressure). Body mass index (BMI) was alulated by dividing body weight (kilograms) with the square of height (meters). Diabetes was defined as self-reported diabetes, non-fasting blood gluose 11.1 mmol/l, Hb1A > 6.5% or a diabetes diagnosis in the Tromsø Study diabetes registry. Estimated glomerular filtration rate (egfr) was alulated using the CKD-EPI formula [64]. Smoking habits and medial history were obtained by questionnaires. Laboratory measurements All laboratory measurements were performed at the University Hospital of North Norway. Urinary albumin exretion was assessed as urinary Albumin/Creatinine Ratio (ACR). Three separate urine samples of morning spot urine from three onseutive days were olleted and analysed within 20 hours. Urine reatinine was measured using olorimetri methods (Jaffes reation) with an autoanalyzer (ABX PENTRA, Horiba ABX, Montpellier, Frane). Urine albumin onentration was measured with immunoturbidimetri method, on an ABX PENTRA autoanalyzer (Horiba ABX, Montpellier, Frane). ACR was alulated by dividing albumin onentration (mg/l) by reatinine (mmol/l). Mean of the three ACRs from three different days, was defined as ACR. In paper II miroalbuminuria was defined as: ACR > 3.4 mg/mmol. Paper III used two alternative miroalbuminuria ut-off levels defined as: ACR > 25

28 3.4 mg/mmol or ACR > 1.13 mg/mmol (aording to KDIGO) [65]. Due to the extremely skewed distribution of ACR, we also analysed log-transformed ACR in paper II and III. Serum reatinine was analysed on a Hitahi Modular model using an enzymati method that has been standardized against isotope dilution mass spetrosopy (CREA Plus, Rohe Diagnostis, GmbH, Mannheim, Germany). HbA1 was measured in EDTA whole blood by high performane liquid hromatography (HPLC) using an automated analyser (Variant II, Bio-Rad Laboratories In., Herules, CA, USA). Non-fasting serum holesterol, triglyerides and gluose were analysed using an automated linial hemistry analyser (Modular P, Rohe Diagnostis, Mannheim, Germany). Standard enzymati olorimetri assays were used for holesterol and triglyerides, and UV test (hexokinase) for gluose. Eye examinations The eye examination was divided in two parts and visual auity was measured in the first part. Visual auity Visual auity was measured by a Nidek AR 660A auto refrator (Nidek CO., LTD., Gamagori, Japan). Auto-Shot and Auto eye traking were enabled and visual auity reorded using the built in Snellen harts ranging from 20/200 20/20 after obtaining stable refration measurements. In ase of visual auity below 20/200, no attempt on further testing was performed. The visual auity results were ategorized and adapted to WHO riteria as visual impairment (< 20/60) or blindness (< 20/200). For omparison to other studies visual impairment defined as visual auity < 20/40 was also analysed. Spherial equivalent was alulated as spherial power plus half the ylindrial power in dioptres (D) and presented as the mean value of left and right eye. Visual auity results and refrative measures were printed on paper, stored and entered in the Tromsø Study database at a later date. 26