Ординатура / Офтальмология / Английские материалы / Eye Essentials Diabetes and the Eye_Steele, Steel_2008

Type 1 diabetes

This is by far the commonest form of diabetes in the UK and indeed worldwide.

The risk factors for developing type 2 diabetes are:

●family history;

●obesity defined as BMI >/= 30 kg/m2;

●increasing age;

●physical inactivity;

●high fat, energy dense diet;

●ethnicity — especially in the UK in people of Asian and Afro-Caribbean descent.

Type 1 diabetes

Genetic susceptibility may well play a part in the difference of prevalence in different parts of the world. It is highest in

Scandinavia and lowest in Japan. Its prevalence rises with distance from the equator. Even in the British Isles, there is a marked variation.This varies from 6.8 per 100 000 in the Republic of Ireland to 19.8 per 100 000 in Scotland.

The incidence of type 1 diabetes has been increasing quite rapidly over the past 20 years for reasons which have not yet been adequately explained (Fig. 1.2). However, it does appear that ethnic groups emigrating to westernized societies assume the prevalence of type 1 diabetes of the indigenous population (Figs. 1.3 and 1.4).This suggests an environmental influence.The peak incidence of type 1 diabetes is in the early teenage years for both girls and boys with a small male excess.

There is a seasonal variation in the incidence of type 1 diabetes; it is more common in the autumn and winter.

Epidemiology, classification and diagnostic criteria

‘Adults with diabetes have an annual mortality of about 5.4%, double the rate for non-diabetic adults. Life expectancy is decreased by 5–10 years’

Fig. 1.2 Life expectancy and diabetes.

The economic costs of diabetes (year 2000)

NHS diabetes expenditure £4 878 000 000 (9% of NHS budget)

The major costs associated with diabetes relate to expenditure on the micro and macro-vascular complications affecting the eye, the kidney, the nervous system and the cardiovascular system.

Classification and diagnostic criteria

Diabetes mellitus is really a complex metabolic disorder in which there is persistent hyperglycaemia. Its manifestations impact on virtually every system in the body.

Classification and diagnostic criteria

Fig. 1.3 Prevalence of diabetes in the UK Asian population.

Fig. 1.4 Prevalence of diabetes in the UK African-Caribbean population.

Classification

Diabetes can be classified into the following types:

●Type 1 diabetes, formerly known as insulin-dependent diabetes mellitus (IDDM) or juvenile onset diabetes.

Epidemiology, classification and diagnostic criteria

● Type 2 diabetes, formerly known as non-insulin

6dependent diabetes mellitus (NIDDM) or maturity onset diabetes (MOD).

Other types include:

●maturity onset diabetes in the young (MODY);

●genetic defects of insulin secretion which are quite rare;

●diseases of the exocrine pancreas, e.g. pancreatitis or carcinoma;

●drugor chemical-induced diabetes — Alloxan;

●gestational diabetes mellitus (GDM).

Type 1 diabetes

In this condition there is an immune-mediated destruction of the pancreatic beta cells which produce insulin. It is characterized by an absolute deficiency of insulin and is normally of rapid onset with the characteristic symptoms of:

●thirst;

●polyuria;

●weight loss.

In the absence of effective treatment (exogenous insulin) it can rapidly progress to dehydration, diabetic keto-acidosis, coma and death. People with type 1 diabetes require insulin for their survival.They make up about 15% of the total diabetic population.

Type 2 diabetes

In this form of diabetes the main problems are insulin resistance and beta cell dysfunction. It is usually of insidious onset and people can have complications at diagnosis.Type 2 diabetes makes up about 85% of the total diabetic population so that it is by far the commonest form of diabetes. It is frequently associated with the overweight and obesity. In fact about 85% of people with type 2 diabetes are overweight

or obese.

Classification and diagnostic criteria

Gestational diabetes mellitus (GDM)

after delivery but can recur in subsequent pregnancies.

Risk factors for developing GDM are obesity, previous history of still-birth or big babies and having previously had GDM. People who develop GDM are at increased risk of developing type 2 diabetes in later life.They are also at increased risk of developing hypertension. Asians and African-Caribbeans are particularly at risk.

Regarding the other forms of diabetes, genetic defects of insulin secretion are very rare. Of all diseases of the exocrine pancreas — the commonest is cystic fibrosis, others are carcinoma of the pancreas and pancreatitis.

Of the endocrinopathies, Cushing’s disease and acromegally are examples.

Drugor chemical-induced hypoglycaemia

Corticosteroids have by far the greatest impact on glucose tolerance of any groups of drugs.They act by increasing gluconeogenesis (the manufacture of glucose in the liver) and by increasing insulin resistance.The thiazide diuretics, commonly used in the treatment of hypertension and congestive heart failure, act by impairing insulin

secretion.

Beta-blockers can impair glucose tolerance and thus exacerbate hyperglycaemia.

MODY clusters in families.There is a strong genetic component.The genetic components are complex and still being unravelled. Some forms seem to have an immunity to complications. In terms of everyday clinical practice, it is comparatively rare.

Diagnostic criteria

These are defined in Table 1.1. In asymptomatic patients two abnormal fasting values are required for diagnosis.There are two other important conditions:

Epidemiology, classification and diagnostic criteria

● impaired fasting glucose (IFG);

8● impaired glucose tolerance (IGT).

These are precursors of frank diabetes mellitus and people with them are at risk of developing type 2 diabetes.They are important not only because they are risk factors, but also because people with these conditions are at risk of developing the vascular complications associated with fully developed type 2 diabetes.

The World Health Organization criteria for these conditions are shown in Tables 1.2 and 1.3.

Table 1.1 WHO diagnostic criteria: diabetes mellitus

aIn asymptomatic patients two abnormal fasting values are required for diagnosis.World Health Organization. Report of a WHO consultation, 1999.

Classification and diagnostic criteria

Table 1.2 WHO diagnostic criteria: impaired glucose

World Health Organization. Report of a WHO consultation, 1999.

Table 1.3 WHO diagnostic criteria: impaired fasting glucose (IFG)

World Health Organization. Report of a WHO consultation, 1999.

Epidemiology, classification and diagnostic criteria

Diabetes UK fact sheet May 2000

The Expert Committee on the Diagnosis and classification of diabetes Mellitus 1997. Diabetes Care 20: 1183–1203

Pickup J C,Williams G 2003 Textbook of Diabetes, 3rd edn. Oxford:

Blackwell Science.

Watkins P J, Amiel S A, Howell S L et al 2003 Diabetes and its management, 6th edn. Oxford: Blackwell Publishing

Williams G, Pickup J C 1999 Handbook of diabetes, 2nd edn. Oxford:

Blackwell Science

World Health Organization 1999 Report of a WHO consultation. Geneva

Clinical presentation of diabetes mellitus

12 Type 1 diabetes

The clinical features of type 1 diabetes tend to present more acutely than those of type 2 diabetes.

Young patients typically have a short history (a few days or weeks) of the classic symptoms of:

●thirst, which is often intense;

●polyuria — the passage of large amounts of urine (perhaps several litres per day) due to the osmotic diuresis caused by high glucose and ketone body concentrations in urine;

●rapid weight loss due to the absence of the anabolic actions of insulin and the virtually unopposed actions of glucagon and the counter-regulatory hormones.

The effect is increased appetite but also increased dehydration and catabolism of muscle and fat;

●some patients present in the dangerous state of keto-acidosis;

●blurring of vision can also be a presenting symptom due to osmotic disturbances in the crystalline lens;

●sleep is disturbed by nocturia and previously continent children may develop enuresis.

The symptoms of thirst, polyuria and weight loss should always point to a diagnosis of type 1 diabetes mellitus until proven otherwise.

In children these symptoms in combination with a positive urine test for glucose demand immediate referral to a paediatrician.