2008 Clinical Practice Guidelines - Canadian Diabetes Association

2008 CLINICAL PRACTICE GUIDELINES
S134
Retinopathy
Canadian Diabetes Association Clinical Practice Guidelines Expert Committee
The initial draft of this chapter was prepared by Shelley R. Boyd MD FRCSC DABO and
Filiberto Altomare MD FRCSC
KEY MESSAGES
• Screening is important for early detection of treatable
disease. Screening intervals for diabetic retinopathy vary
according to the individual’s age and type of diabetes.
• Tight glycemic control reduces the onset and progression
of sight-threatening diabetic retinopathy.
• Laser therapy reduces the risk of significant visual loss.
INTRODUCTION
Diabetic retinopathy is the most common cause of new cases
of legal blindness in people of working age (1). The Eye
Diseases Prevalence Research Group determined the crude
prevalence rate of retinopathy in the adult diabetic population
of the United States to be 40.3%; sight-threatening retinopathy
occurred at a rate of 8.2% (2). Previous data showed the
prevalence rate of proliferative retinopathy to be 23% in people
with type 1 diabetes, 14% in people with type 2 diabetes
and on insulin therapy, and 3% in people receiving oral antihyperglycemic
therapies (3). Macular edema occurs in 11, 15
and 4% of these groups, respectively (4). First Nations populations
in Canada have high rates of diabetes and its complications
(5,6). It is estimated that approximately 2 million
individuals in Canada (i.e. almost all people with diagnosed
diabetes) have some form of diabetic retinopathy (7).
Visual loss is associated with significant morbidity, including
increased falls, hip fractures and a 4-fold increase in
mortality (8). Among individuals with type 1 diabetes, limb
amputation and visual loss due to diabetic retinopathy are the
2 independent predictors of early death (9).
DEFINITION AND PATHOGENESIS
Diabetic retinopathy is clinically exclusively defined, diagnosed
and treated based on the extent of retinal vascular disease.
Three distinct forms of diabetic retinopathy are
described: 1) macular edema, which includes diffuse or focal
vascular leakage at the macula; 2) progressive accumulation of
blood vessel change that includes microaneurysms, intraretinal
hemorrhage, vascular tortuosity and vascular malformation
(together known as nonproliferative diabetic retinopathy)
that ultimately leads to abnormal vessel growth (proliferative
diabetic retinopathy); and 3) retinal capillary closure, a form
of vascular change detected by fluorescein angiography, which
is also well recognized as a potentially blinding complication
of diabetes, but currently has no treatment options.
SCREENING AND DIAGNOSIS
Since laser therapy for sight-threatening diabetic retinopathy
reduces the risk of blindness (10-13), ophthalmic screening
strategies are intended to detect treatable disease. Sightthreatening
diabetic retinopathy includes severe nonproliferative
diabetic retinopathy, proliferative diabetic retinopathy or
clinically significant macular edema. Screening programs consider
the differences in incidence and prevalence of retinopathy
observed in type 1 and type 2 diabetes, and distinguish
between children and adults (see Table 1) (14-19).
Diabetic retinopathy rarely develops in children with
type 1 diabetes