Cataract is considered a major cause of visual impairment in diabetic patients as the incidence and progression of cataract is elevated. Cataracts are among the earliest complications of diabetes. Remarkably, impaired fasting glucose (IFG), a pre-diabetic condition, has been considered as a risk factor for the development of cortical cataracts 2. While in the older-onset diabetic population cataracts are the most common cause of visual impairments3.
Several clinical studies have shown that cataract development occurs more frequently and at an earlier age in diabetic compared to nondiabetic patients. Patients with diabetes are 2–5 times more likely to develop cataracts than their nondiabetic counterparts; this risk may reach 15–25 times in diabetics less than 40 years of age. There is a three to fourfold increased prevalence of cataract in patients with diabetes under the age of 65, and up to a twofold increase in prevalence in patients above 65 1.
Cataracts may develop at an earlier age and may have a higher prevalence rate in patients with diabetes due to hyperglycaemia 4,5 and the compromised blood–aqueous or blood–retina barriers . Breakdown of these barriers may also worsen postoperative inflammation after cataract surgery, and may initiate DR progression6. Up to 20 % of cataract surgeries are performed on diabetic patients 3 .Per million diabetic patients 440 eyes will require cataract surgery annually 4.
The Wisconsin Epidemiologic Study of Diabetic Retinopathy investigated the incidence of cataract extraction in people with diabetes. Cataract surgery was 8.3% in patients suffering from type 1 diabetes and 24.9% in those from type 2 diabetes. Predictors of cataract surgery included age, severity of diabetic retinopathy and proteinuria in type 1 diabetics whereas age and use of insulin were associated with increased risk in type 2 diabetics 1.
Several studies have compared different types of cataracts in diabetics versus non-diabetics.
An uncommon type of lens opacity, referred to as a true diabetic cataract or snowflake cataract, consists of widespread subcapsular lens opacities of abrupt onset and acute progression, typically in young people with uncontrolled diabetes. This is rare and some suggest this may be the initial presentation of diabetes 3.
In a Beaver Dam Eye study 5, the incidence and progression of cortical and posterior subcapsular cataract was associated with diabetes, with longer duration of diabetes associated with an increased frequency of cortical cataract as well as an increased frequency of cataract surgery. In a Blue Mountains Eye Study, posterior subcapsular cataract was shown to be statistically significantly associated with diabetes 1. Additional studies also support a higher percentage of cortical cataracts in diabetics 7, 2.
Other risks for cataract formation in the diabetic eye include untreated uveitis and prolonged corticosteroid treatment of ocular surface complications or of diabetic macular edema (DME) 8.
Incidence rates of cataracts in the diabetic community has been investigated for some countries for example:
- In the UK diabetic population the incidence of cataract is 20.4 per 1000 person-years compared to 10.8 per 1000 person-years in the non-diabetic population 9
- In the Russian Federation a study of 7,186 diabetic patients reported the presence of cataracts in 30.6% of diabetics 10.