Retinal Vascular Changes in Pre-Diabetes and Prehypertension

 
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Retinal Vascular Changes in Pre-Diabetes
and Prehypertension
New findings and their research and clinical implications
THANH TAN NGUYEN, MBBS1                                                                                      therapy may also reduce retinopathy re-
JIE JIN WANG, MMED, PHD1,2                                                                                   quiring laser treatment (7).
TIEN YIN WONG, MD, PHD1,3
                                                                                                             Hypertensive retinopathy
                                                                                                             Like diabetic retinopathy, classic hyper-
                                                      CLASSIC RETINAL

T
       he retinal vasculature can be                                                                         tensive retinopathy is well characterized.
       viewed directly and noninvasively,             VASCULAR CHANGES                                       The clinical signs include generalized and
       offering a unique and easily acces-                                                                   focal arteriolar narrowing, arterio-venous
sible “window” to study the health and                Diabetic retinopathy                                   nicking, increased retinal arteriolar light
disease of the human microcirculation                 In individuals with diabetes, the classic              reflex (copper or silver wiring), flame-
in vivo. In the last decade, advances in              primary retinal vascular complication—                 and blot-shaped retinal hemorrhages,
digital retinal photography and imaging               diabetic retinopathy—is well described                 cotton wool spots, and, in severe cases,
techniques have allowed precise charac-               (1). Diabetic retinopathy signs are                    optic disc swelling (8,9). The association
terization of subtle retinal vascular                 broadly divided into nonproliferative and              of these retinal signs with blood pressure
changes in large populations. These ret-              proliferative retinopathy. The prevalence              is consistent and seen in both adults (10 –
inal changes can be broadly divided into              of diabetic retinopathy increases with                 20) and children (21), even in individuals
four groups: 1) classic retinal vascular              duration of diabetes. The Australian Dia-              without clinical hypertension (13–15,
changes in diabetes and hypertension                  betes, Obesity and Lifestyle Study (Aus-               22–24).
(i.e., diabetic and hypertensive retinop-             Diab) showed that the prevalence of
athy), 2) isolated retinopathy signs in               diabetic retinopathy is less than 10% in               ADVANCES IN ASSESSING
individuals with diabetes or hyperten-                those with diabetes duration of less than 5            RETINAL VASCULAR
sion (e.g., microaneurysm, retinal hem-               years but more than 50% in those with 20               CHANGES — Digital retinal photog-
orrhage, or cotton wool spot), 3)                     years or longer diabetes (2). The two ma-              raphy and new imaging technology have
changes in retinal vascular caliber, and              jor risk factors of diabetic retinopathy are           now allowed more precise assessment of
4) changes in retinal vascular architec-              hyperglycemia and hypertension, with                   the subtle changes seen in the retinal
ture (e.g., retinal tortuosity).                      hyperlipidemia as a possible third major               microvasculature (22,25–28). One key
     New studies in large populations now             risk factor. The importance of hypergly-               development has been methods to objec-
show that retinal vascular changes are                cemia has been confirmed in epidemio-                  tively quantify retinal vascular caliber.
common in the general population and                  logical studies (3), as well as two pivotal            Historically, narrowed retinal arteriolar
may precede the subsequent develop-                   clinical trials: the DCCT (Diabetes Con-               caliber, an early hypertensive retinopathy
ment of overt diabetes and hypertension. A            trol and Complications Trial) in patients              sign, has been difficult to measure using
consistent pattern of associations is also            with type 1 diabetes (4) and the UKPDS                 the clinical ophthalmoscope (29). Parr,
                                                                                                             Hubbard, and colleagues (22,30,31) de-
emerging, showing that specific retinal vas-          (UK Prospective Diabetes Study) in pa-
                                                                                                             veloped techniques to measure retinal
cular changes may be related differently to           tients with type 2 diabetes (5). The UK-
                                                                                                             vascular caliber from photographs and
hyperglycemia and blood pressure.                     PDS also showed that blood pressure                    summarized these as the arterio-venous
     In this review, we summarize recent              control reduces the risk of retinopathy in-            ratio (AVR). These techniques are now
studies on the retinal vascular changes               dependent of glycemia levels (6). New                  used in large epidemiological studies
seen in diabetes and hypertension and                 data from the FIELD (Fenofibrate Inter-                (20,22,25,27,28) and have substantial re-
speculate on potential research and clini-            vention and Event Lowering in Diabetes)                producibility.
cal implications.                                     Study now suggest that lipid-lowering                       Recent studies suggest the interpreta-
                                                                                                             tion of the AVR may be overly simplistic.
● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●            A smaller AVR was thought to reflect gen-
From the 1Centre for Eye Research Australia, University of Melbourne, Victoria, Australia; the 2Centre for   eralized retinal arteriolar narrowing, since
Vision Research, University of Sydney, New South Wales, Australia; and the 3Singapore Eye Research           venular caliber was assumed to be rela-
Institute, National University of Singapore, Singapore.
   Address correspondence and reprint requests to Tien Yin Wong, MD, PhD, Centre for Eye Research
                                                                                                             tively constant (22). Thus, when a low
Australia, University of Melbourne, 32 Gisborne St., Victoria 3002, Australia. E-mail: twong@                AVR was associated with elevated blood
unimelb.edu.au.                                                                                              pressure (18,32) and cardiovascular out-
   Received for publication 15 April 2007 and accepted in revised form 20 June 2007.                         comes such as stroke (33,34) and coro-
   Published ahead of print at http://care.diabetesjournals.org on 26 June 2007. DOI: 10.2337/dc07-0732.     nary heart disease (35), the associations
   Abbreviations: ARIC, Atherosclerosis Risk In Communities; AVR, arterio-venous ratio.
   A table elsewhere in this issue shows conventional and Système International (SI) units and conversion   were initially thought to reflect general-
factors for many substances.                                                                                 ized arteriolar narrowing. Newer analy-
   © 2007 by the American Diabetes Association.                                                              ses, however, suggest a smaller AVR may

2708                                                                                                    DIABETES CARE, VOLUME 30, NUMBER 10, OCTOBER 2007
Nguyen, Wang, and Wong

not only reflect narrower arterioles but
also wider venules (36,37). Furthermore,
arteriolar and venular calibers appear to
reflect different pathophysiological pro-
cesses (37,38).
     Liew et al. (38,39) have suggested the
need to control for venular caliber in sta-
tistical models of arteriolar caliber, and
vice versa, as venular caliber explains
⬃30% of the variability in arteriolar cali-
ber (38)—presumably from shared ge-
netic and ocular factors (22).
     Improvements in imaging software
have also led to quantification of other
architectural changes in the retinal vascu-
lar network (36,37), as well as “batch pro-
cessing” of retinal images (20,22,
25,27,28). There remain technical chal-
lenges. For example, the impact of mag-
nification error (i.e., eyes of different re-
fraction) requires further study (40).

ISOLATED RETINOPATHY
SIGNS
                                                Figure 1—Prevalence of retinopathy in nondiabetic populations (A) and nondiabetic and non-
Epidemiology                                    hypertensive populations (B). AusDiab: Australian Diabetes, Obesity and Lifestyle Study (year
There is increasing evidence that typical       began: 1999 –2000, n ⫽ 2,177, aged ⱖ25 years) (2); ARIC (year began: 1987–1990, n ⫽ 10,954,
lesions of diabetic retinopathy (microan-       aged 48 –73 years) (22); BDES: Beaver Dam Eye Study (year began: 1988 –1990, n ⫽ 4,926, aged
eurysms, hemorrhages, and cotton wool           43– 84 years) (15); BMES: Blue Mountain Eye Study (year began: 1992–1994, n ⫽ 3,654, aged
spots), termed isolated retinopathy signs,      49 –97 years) (13); CHS: Cardiovascular Health Study (year began: 1989 –1990, n ⫽ 2,050, aged
are now recognized to be more common            67–97 years) (14), Hoorn (year began: 1989 –1992, n ⫽ 626, aged 50 –74 years) (23), Rotterdam
than previously thought in people with-         (year began: 1990 –1993, n ⫽ 6,191, aged 55–99 years) (44), and Funagata (year began: 2000 –
out diabetes and hypertension (41– 43).         2002, n ⫽ 1,481, aged ⱖ35 years) (24).
Recent studies using retinal photography
to document these signs suggest preva-          Risk factors and pathophysiology                isolated retinopathy in people without di-
lence rates in the general population of        The underlying risk factors and patho-          abetes (50) supports the hypothesis that
5–10% (2,13–15,22–24,44) (Fig. 1A)              physiology of isolated retinopathy signs        inflammatory processes may also be a
and 2.6 – 8.6% among those without dia-         in nondiabetic and normotensive individ-        possible pathway that underlies early sub-
betes or hypertension (13–15,22–24)             uals are poorly understood. Associations        clinical microvascular disease in the pre-
(Fig. 1B). Prospective study data have fur-     of these retinopathy signs with increasing      diabetes or prehypertension state.
ther shown that up to 10% of individuals        age (15,45), elevated blood pressure
aged ⱖ40 years without diabetes may de-         (8,13–15,44,47– 49), and hyperglycemia          Associations with risk of diabetes,
velop these isolated retinopathy signs          (24,44,47,48) have been found. Other            hypertension, and cardiovascular
within 5 years (16,45).                         possible risk factors include hyperlipid-       diseases
     Two studies have reported on the           emia (17,23,48), higher BMI (23,24), and        A clinically relevant question is whether
prevalence of retinopathy in individuals        systemic inflammation (48,50). We can           signs of isolated retinopathy in individu-
with pre-diabetes. In the AusDiab Study,        speculate that isolated retinopathy signs       als without diabetes are markers of the
retinopathy signs were seen in 6.7% of          in normotensive and nondiabetic individ-        future risk of diabetes (i.e., do these pa-
individuals with impaired glucose toler-        uals may represent early microvascular          tients require monitoring for the develop-
ance or impaired fasting glucose (46),          damage from a combination of risk fac-          ment of diabetes). The evidence here is
whereas in the Diabetes Prevention Pro-         tors, including blood pressure and abnor-       not consistent. While previous studies
gram this was seen in 7.9% of individuals       mal glucose metabolism, which may               suggest that detectable retinopathy pre-
with impaired fasting glucose (5.3– 6.9         reflect an underlying process of develop-       cedes the onset of type 2 diabetes by 4 –7
mmol/l) or impaired glucose tolerance,          ing clinical diabetes or hypertension.          years (54), new prospective data from the
who had no history of diabetes (47).                 Animal models and human studies            Blue Mountains (45,55), the Atheroscle-
     These isolated retinopathy signs may       suggest that chronic inflammation and           rosis Risk In Communities (ARIC) (56),
be transient. Population studies show that      glucose-induced arteriolar endothelial          and Beaver Dam (57) studies reported no
between 40 and 70% of these isolated ret-       dysfunction are related to development of       increased risk of diabetes in nondiabetic
inopathy signs seen at baseline are not         classic diabetic retinopathy (51–53). The       individuals with signs of retinopathy.
present 3–5 years later (45,48).                association of inflammation and signs of        However, there are two notable excep-

DIABETES CARE, VOLUME 30, NUMBER 10, OCTOBER 2007                                                                                      2709
Retinal vascular changes

Table 1—Associations of retinal vascular changes with diabetes, hypertension, and cardiovascular diseases

Retinal vascular signs                           Associations                                  Populations                            References
Retinopathy                           Impaired fasting glucose                    ARIC                                                  (67)
                                      Obesity                                     Hoorn                                                 (23)
                                      Blood pressure                              ARIC, AusDiab, BDES, BMES, CHS,                (2,13–15,22–24,44)
                                                                                  Funagata, Hoorn, Rotterdam
                                      Incident hypertension                       BDES                                                   (57)
                                      Incident diabetes                           ARIC, BDES                                           (56,57)
                                      Heart disease                               BDES, CHS, ARIC                                    (14,59,114)
                                      Nephropathy                                 ARIC, CHS                                            (60,61)
                                      Cerebrovascular disease                     ARIC, CHS, BDES                                (14,33,34,114–117)
Retinal arteriolar narrowing          Blood pressure                              Funagata, BDES, BMES, Rotterdam,               (10,22,24,32,37,87)
                                                                                  ARIC, CHS
                                      Blood pressure in children                  SCES, SCORM                                             (21)
                                      Measures of atherosclerosis                 Rotterdam                                               (37)
                                      Waist-to-hip ratio                          ARIC                                                    (67)
                                      Incident hypertension                       ARIC, BMES, BDES, Rotterdam                         (58,88–90)
                                      Incident diabetes                           ARIC, BDES                                            (64,65)
                                      Coronary heart disease                      CHS                                                     (98)
Retinal venular dilatation            Impaired fasting glucose                    ARIC, MESA                                            (20,67)
                                      Measures of atherosclerosis                 Rotterdam                                               (37)
                                      Obesity in children                         SCORM                                                   (69)
                                      Waist-to-hip ratio                          ARIC                                                    (67)
                                      Hypertriglyceridemia                        ARIC                                                    (67)
                                      Incident obesity                            BMES                                                   (118)
                                      Incident hypertension                       BMES                                                    (39)
                                      Incident impaired fasting glucose           Rotterdam                                               (66)
                                      Cerebrovascular diseases                    Rotterdam, CHS                                        (96–98)
                                      Carotid artery disease                      Rotterdam                                               (37)
AusDiab, Australian Diabetes, Obesity and Lifestyle Study; BDES, Beaver Dam Eye Study; BMES, Blue Mountain Eye Study; CHS, Cardiovascular Health Study;
MESA, Multi-Ethnic Study of Atherosclerosis; SCES, Sydney Childhood Eye Study; SCORM, Singapore Cohort Study of Risk Factors for Myopia.

tions. First, in the Beaver Dam Study,             that isolated microaneurysms, hemor-               sion and prehypertension, are sum-
among individuals aged ⬍65 years at                rhages, and cotton wool spots predict the          marized in Table 1.
baseline, signs of retinopathy were asso-          development of clinical cardiovascular
ciated with an increased 15-year inci-             and cerebrovascular events independent             Associations with diabetes and pre-
dence of diabetes (odds ratio [OR] 3.68            of traditional risk factors (Table 1). Vari-       diabetes
[95% CI 1.23–10.96]) (57). Second, in              ous population-based studies have shown            Consistent associations of retinal venular
the ARIC Study, among participants with            associations of isolated signs of retinopa-        caliber with hyperglycemia, diabetes, and
a family history of diabetes, signs of reti-       thy with the risk of stroke (33), congestive       its complications are now emerging (20).
nopathy were also associated with an in-           heart failure (59), renal dysfunction              Prospective data from three population-
creased 3-year risk of diabetes (2.3 [1.0 –        (60,61), and measures of atherosclerosis           based cohorts have shown that changes in
5.3]) (56). Thus, the literature suggests          (14,62,63). In the ARIC Study, the pres-           retinal vascular caliber may predict the
that isolated signs of retinopathy in indi-        ence of retinopathy was associated with a          development of type 2 diabetes (64,65)
viduals without diabetes are not necessar-         threefold higher risk of congestive heart          and impaired fasting glucose (66). In two
ily markers of future diabetes risk, except        failure in those without previous coro-            early analyses, an association between
possibly in younger individuals and in             nary heart disease (relative risk 2.98 [95%        smaller retinal AVR and incident diabetes
those with a family history of diabetes.           CI 1.50 –5.92]) (59). This later associa-          was found in the ARIC Study (OR 1.71
     Similarly, there is conflicting evi-          tion suggests that microvascular disease           [95% CI 1.13–2.57]; comparing smallest
dence that isolated signs of retinopathy           may be important in the development of             to largest AVR quintile) and the Beaver
are markers of future hypertension risk.           diabetic cardiomyopathy in the absence             Dam Study (1.53 [1.03–2.27]; comparing
Data from the Beaver Dam Study showed              of established coronary artery disease.            smallest to largest AVR quartile) (64,65).
that among nonhypertensive individuals,                                                               Subsequently, the Rotterdam Study dem-
those with signs of retinopathy had a                                                                 onstrated that these associations reflected
higher incidence of hypertension (OR               RETINAL VASCULAR                                   wider retinal venular caliber rather than
1.48 [95% CI 1.05–2.07]) (57), but these           CALIBER — The associations and clin-               narrower arteriolar caliber (1.23 [1.02–
findings are not supported by other stud-          ical significance of early retinal vascular        1.47]; per SD increase in venular caliber)
ies (15,45,58).                                    caliber changes in individuals with diabe-         (66). Reanalysis of the ARIC and Beaver
     There is now substantial evidence             tes and pre-diabetes, as well as hyperten-         Dam studies confirms this finding

2710                                                                                              DIABETES CARE, VOLUME 30, NUMBER 10, OCTOBER 2007
Nguyen, Wang, and Wong

(T.Y.W., unpublished data). Thus, it ap-        ber, there is now substantial evidence that    Associations with cardiovascular
pears that wider retinal venular caliber is a   hypertension preferentially affects retinal    diseases
marker of chronic hyperglycemia and the         arteriolar caliber (83) (Table 1). It has      In addition to their associations with dia-
pre-diabetes state and reflects the early       long been known that generalized retinal       betes and hypertension, changes in retinal
microvascular changes that occur in the         arteriolar narrowing is an early character-    vascular caliber have also been linked to a
development of diabetes.                        istic sign of hypertensive retinopathy         range of cardiovascular diseases (Table 1).
     Wider retinal venular caliber has also     (8,84,85). More recent studies using           Wider retinal venular caliber has been as-
been linked to the metabolic syndrome           quantitative measurements of retinal vas-      sociated with carotid artery disease (37),
and its components (20,37,67). In the           cular caliber have now demonstrated a          magnetic resonance imaging– detected la-
Blue Mountains Study, wider retinal             graded association of narrowed retinal ar-     cunar infarcts and white matter lesions
venular caliber was associated with the         terioles with increasing blood pressure in     (96), and clinical stroke events (97,98). In
5-year incidence of obesity among indi-         different populations of various racial/       the Cardiovascular Health Study, wider
viduals of normal weight at baseline (OR        ethnic groups and age-groups (10,20,           retinal venular caliber was predictive of
1.8 [95% CI 1.0 –3.1]; comparing largest        22,24,32,37,86,87).                            incident coronary heart disease (rate ratio
to lowest venular caliber quintile) (68).                                                      3.0 [95% CI 1.6 –5.7]; comparing largest
                                                     Of greater significance are prospec-
Similarly, in children aged 6 – 8 years,                                                       to smallest venular caliber quartile) and
                                                tive findings from four populations that
wider retinal venular caliber was also as-                                                     incident stroke (2.2 [1.1– 4.3]), whereas
sociated with higher BMI (69), suggesting       show retinal arteriolar narrowing is a pre-
                                                                                               narrower arteriolar caliber was predictive
that retinal venular caliber may be influ-      clinical marker of hypertension risk. The      of incident coronary heart disease (2.0
enced by metabolic disorders early in life.     ARIC Study (OR 1.62 [95% CI 1.21–              [1.1–3.7]; comparing smallest to largest
There is also evidence that wider venular       2.18]; comparing smallest to largest AVR       arteriolar caliber quartile) (98). These
caliber is associated with various micro-       quintile) (58), the Beaver Dam Study           findings suggest that both wider venular
vascular complications of diabetes, not         (1.82 [1.39 –2.40]; comparing smallest to      caliber and narrower arteriolar caliber
only diabetic retinopathy (70,71) but also      largest AVR quartile) (88), the Blue           may be markers of early subclinical car-
diabetic nephropathy (72).                      Mountains Study (2.6 [1.7–3.9]; compar-        diovascular disease.
     Despite these observations, the            ing smallest to largest arteriolar caliber
pathophysiological processes underlying         quintile) (89), and the Rotterdam Study        CHANGES IN RETINAL
the association of wider retinal venular        (1.38 [1.23–1.55]; per SD decrease in ar-      VASCULAR ARCHITECTURE —
caliber with hyperglycemia, diabetes, and       teriolar caliber) (90) all reported that       New imaging methods have allowed the
its complications are unclear. It has been      among individuals without hypertension         measurement of other architectural
speculated that retinal venular widening        at baseline, those with narrowed retinal       changes in the retinal microvasculature.
may be the result of increased blood flow       arterioles had a higher risk of hyperten-      Hypertension, for example, has been as-
associated with hyperglycemia (73) and          sion in the subsequent 3–10 years, inde-       sociated with an increase in the retinal
retinal hypoxia (74). Alternatively, it may     pendent of baseline blood pressure levels,     arteriolar length-to-diameter ratio
also reflect inflammatory processes impli-      BMI, and other known hypertension risk         (99,100), increased retinal venular tortu-
cated in the pathogenesis of impaired glu-      factors.                                       osity (99), reduced branching angle at ar-
cose metabolism (75), supported by                   These observations support the hy-        teriole bifurcations (101), and reduced
epidemiological findings of wider retinal       pothesis that peripheral vascular resis-       microvascular density (99,101,102).
venules with elevated systemic inflamma-        tance, reflected by retinal arteriolar             Some of these retinal changes have
tory markers (17,20,37,76). Experiments         narrowing, is an important contributing        also been shown to be associated with in-
have demonstrated that local inflamma-          factor for hypertension development            creased cardiovascular risk. For example,
tory processes lead to wider retinal venu-      (91). Added support to this hypothesis         the Beaver Dam Study demonstrated that
lar calibers. For example, administration       comes from a recent genome-wide link-          suboptimal arteriolar bifurcation and de-
of lipid hydroperoxide in the vitreous of       age analysis from the Beaver Dam Study,        creased arteriolar tortuosity are associated
rats leads to an increase in the retinal                                                       with coronary heart mortality (103).
                                                which demonstrated that associations of
venular diameter (77). Similarly, admin-
                                                retinal arteriolar diameter to multiple ge-
istration of Escherichia coli endotoxin in                                                     IMPLICATIONS FOR
                                                netic loci are linked to regulation of blood
human eyes has been reported to increase                                                       RESEARCH AND CLINICAL
retinal venular diameter (78). Finally, ret-    pressure, endothelial function, and vas-       MANAGEMENT — It is now well
inal venular dilation may be related to en-     culogenesis (92). Thus, retinal arteriolar     recognized that individuals with impaired
dothelial dysfunction, reflecting an            narrowing may be considered a surrogate        glucose metabolism or pre-diabetes have
increased production of nitric oxide (79)       marker of an individual’s genetic predis-      higher mortality from cardiovascular dis-
secondary to higher levels of cytokines         position to hypertension development           ease (104 –106). Similarly, individuals
(80), seen often in association with im-        (93).                                          with high to normal blood pressure or
paired glucose metabolism (81,82) and                Finally, a recent study has shown that    prehypertension (107) are more likely to
diabetes (81).                                  the association between higher blood           develop cardiovascular events (108,109).
                                                pressure and retinal arteriolar narrowing      To permit appropriate preventative strat-
                                                is detectable in healthy children aged 6 – 8   egies, there is therefore great interest in
Associations with hypertension and              years (21), reinforcing the concept that       early detection of individuals with pre-
prehypertension                                 the effects of higher childhood blood          diabetes and prehypertension.
In distinct contrast to the association of      pressure may have an adverse effect on             This review suggests that retinal im-
hyperglycemia with retinal venular cali-        the microcirculation (94,95).                  age analysis offers a novel noninvasive

DIABETES CARE, VOLUME 30, NUMBER 10, OCTOBER 2007                                                                                    2711
Retinal vascular changes

measurement of early changes in the vas-       nal vascular changes using new imaging                   on cardiovascular events in 9795 people
culature—not detectable on routine clin-       techniques offers great potential to ad-                 with type 2 diabetes mellitus (the FIELD
ical examination—that may allow the            vance our understanding of the early                     study): randomised controlled trial. Lan-
identification of individuals at risk of di-   pathophysiological pathways of diabetes                  cet 366:1849 –1861, 2005
                                                                                                   8.   Wong TY, Mitchell P: Hypertensive ret-
abetes and hypertension and their subse-       and hypertension development. Recent
                                                                                                        inopathy. N Engl J Med 351:2310 –2317,
quent complications. Retinal vascular          studies support the concept that the reti-               2004
imaging might also permit physicians to        nal vasculature provides a summary mea-             9.   Wong T, Mitchell P: The eye in hyper-
optimize management of individuals with        sure of lifetime exposure to various                     tension. Lancet 369:425– 435, 2007
established diabetes and/or hypertension.      processes involved in the development of          10.    Leung H, Wang JJ, Rochtchina E, Tan
For example, retinal vascular imaging          diabetes and hypertension. Furthermore,                  AG, Wong TY, Klein R, Hubbard LD,
may allow monitoring of chronic varia-         these studies suggest that the effects of                Mitchell P: Relationships between age,
tions in glucose and blood pressure, as        glucose and blood pressure on the retinal                blood pressure, and retinal vessel diam-
well as the presence and severity of sub-      microvasculature are graded and contin-                  eters in an older population. Invest Oph-
clinical microvascular damage. However,        uous, and our current definitions of dia-                thalmol Vis Sci 44:2900 –2904, 2003
a number of issues should be resolved be-      betic and hypertensive retinopathy are            11.    Sharp PS, Chaturvedi N, Wormald R,
                                                                                                        McKeigue PM, Marmot MG, Young SM:
fore retinal vascular imaging can be uti-      arbitrary and do not capture early disease.              Hypertensive retinopathy in Afro-Carib-
lized in clinical practice.                    Future research is clearly needed to assess              beans and Europeans: prevalence and
     First, despite a large body of data on    the ability of retinal vascular imaging to               risk factor relationships. Hypertension
the associations and risk prediction of ret-   provide clinically useful information that               25:1322–1325, 1995
inal vascular caliber measurement in dif-      adds to existing risk prediction models of        12.    Wang JJ, Mitchell P, Leung H, Roch-
ferent population-based studies, there is      diabetes and hypertension.                               tchina E, Wong TY, Klein R: Hyperten-
no accepted standardized classification of                                                              sive retinal vessel wall signs in a general
retinal vascular changes, and a lack of                                                                 older population: the Blue Mountains
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DIABETES CARE, VOLUME 30, NUMBER 10, OCTOBER 2007                                                                                                   2715
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