This site is intended for health professionals only

Diabetic retinopathy: all the facts

Margaret Spencer
RGN Ophthalmic Nursing Diploma (London)
Ophthalmic Outpatients
Worthing Hospital
Worthing
West Sussex

Diabetic retinopathy is the most common cause of blindness in the working age group, accounting for approximately 12% of blind registrations among those under 65 years of age. Patients with both type 1 and type 2 diabetes are at risk of developing diabetic eye disease, with up to 38% of patients with type 2 diabetes presenting with eye disease on diagnosis.(1)

Background retinopathy
Background retinopathy is the most common form of retinopathy and is a microvascular complication of diabetes. Microaneurysms are thought to be outpouchings of the capillary walls and are the earliest signs of retinopathy. These appear as small, red, round dots on the surface of the retina (see Figure 1).

[[NIP30_fig1_58]]

Haemorrhages, unlike microaneurysms, are not necessarily round. Those arising in the compact middle layer of the retina are known as "dot and blot" haemorrhages, and those that occur in the nerve fibre layer are "flame-shaped"
Exudates are small collections of lipoprotein that accumulate within the retina due to abnormal vascular leakage. These may be as individual deposits or as circinate rings with microaneurysms in the centre.(2,3) Background retinopathy does not usually affect the vision unless maculopathy occurs. Macular oedema is the swelling of the macular caused by fluid leaking from the retinal blood vessels, endangering central vision, but leaving peripheral vision unchanged. This is the most common cause of visual loss in patients with type 2 diabetes.
The best treatment that has been proven to delay the onset and reduce the progression of background retinopathy is strict control of the diabetes.
Maculopathy can be treated with laser therapy, with the laser being applied directly to the areas of leakage, in order to prevent further leakage and absorption of fluid. Unfortunately, laser treatment for diabetic maculopathy is not always successful and may only maintain the current level of vision, or slow the rate of progression, rather than improve vision. It is most effective if given early in the disease before there is significant visual loss.(4) The use of intravitreal triamcinolone is currently under trial. It is given under topical anaesthetic and  has been found to reduce macular oedema.

Preproliferative retinopathy
Preproliferative retinopathy is a severe form of background retinopathy and indicates the development of new vessels. It may occur in 50% of patients within a year but is not usually associated with sight loss.(2,4)
Venous beading is the most common and important lesion. It is associated with widespread capillary occlusion. Venous loops occasionally occur due to local occlusion of the veins and are specific to diabetes.(2) Cottonwool spots are also indicative of retinal ischaemia and have a pale "fluffy" appearance. These spots are caused by an infarction in the nerve fibre layer that causes swelling on the nerve axon.(5)

Proliferative retinopathy
Proliferative retinopathy, or neovascularisation, occurs when abnormal blood vessels develop on the surface of the retina, most commonly at the optic disc, but they may appear anywhere on the surface of the retina. These are due to severe hypoxia of the peripheral retina caused by occlusion of the capillaries. Those arising from the disc have a more rapid course and bleed easily, resulting in vitreous haemorrhage. The vessels proliferate onto the posterior face of the vitreous, and the relative movement of the vitreous gel leads to traction on the vessels, which results in rupture. Blood leaking into the space vacated by the gel cause sudden loss of vision. Fibrous tissue also proliferates alongside the vessels and adheres to points along the surface of the retina. This tissue shrinks, pulling on the points of attachment and causing tractional retinal detachment.(2,4,6)
Panretinal laser photocoagulation of the retina involves the scattering of thousands of regularly spaced laser burns throughout the retina, sparing the area around the macular and disc. This is believed to reduce the hypoxic state of the retina that leads to the absorption of the proliferative vessels.(4)
If vitreous haemorrhage occurs, the blood may  absorb over time and vision may return to near normal levels. If the haemorrhage does not clear, then vitrectomy surgery may be advised. This involves removal of the vitreous gel and replacing it with gas or oil.

[[NIP30_fig2_60]]

[[NIP30_fig3_60]]

[[NIP30_fig4_60]]

Risk factors

Hyperglycaemia
Hyperglycaemia is by far the biggest contributing factor in the development of diabetic eye disease. In 1993, the Diabetes Control and Complications Trial Research Group found that good glycaemic control slowed the onset of microvascular complications and also delayed the progression of those already present.(7) Hypertension control has been found to result in a 34% reduction in the progression of retinopathy.(8)

Hyperlipdaemia
People with diabetes who have a raised cholesterol at diagnosis were found to be twice as likely to have retinal hard exudates as those with normal levels. Therefore, lowering lipid levels may reduce the risk of further developments of hard exudates and the progression of macular oedema.(9)

Puberty
Diabetic retinopathy is rare before puberty, but the incidence increases steadily during puberty. Good diabetic control throughout puberty is essential to lower the incidence.

Pregnancy
Evidence shows that pregnancy advances the progression of diabetic retinopathy, with progression related to pregestational control as well as improved glycaemic control during pregnancy. During the first trimester, diabetics with pre-existing retinopathy, may develop an increase of retinopathy, with progression to proliferative retinopathy.(10)

Recommendations
In 2001, the National Service Framework for Diabetes (NSF) published its standard document.(11) In Standard 10, it recommended that all young people and adults with diabetes receive regular surveillance for the long-term complications of diabetes. The rationale stated that early detection of sight-threatening diabetic retinopathy and treatment with laser therapy can prevent visual impairment.(11)
In 2002, the NSF published a delivery document which recommended that a systematic eye screening programme be implemented within three years to national standard.(12) In 2006, it is expected that 80% of diabetic patients will be offered screening for the detection and treatment of diabetic retinopathy, as part of a systematic programme that meets national standards, rising to 100% coverage by 2007.(12) The method used for retinal screening may be retinal photography (either static or mobile units) or direct ophthalmoscopy by a doctor or an optometrist.

Conclusion
The incidence of diabetic retinopathy can be reduced by annual retinal screening of all diabetic patients, early detection of diabetes, especially in the elderly, and tight control of glycaemic levels, blood pressure and cholesterol. Patients' understanding of the importance of these is essential in the prevention of diabetic eye disease.

References

  1. University of York. Complications of diabetes - screening for retinopathy. London: RSM Press; 1995. 
  2. Kohner E. Diabetes and the eye. Oxford textbook of ophthalmology. Oxford: Oxford Medical Publications; 1999.
  3. Perry J, Tullo A. Care of the ophthalmic patient - a guide for nurses and healthcare professionals. London: Chapman and Hall; 1990.
  4. Hean-Choon C. Vascular complications of diabetes. Current issues in pathogenesis and treatment. Oxford: Blackwell Science; 2002.
  5. Kanski J. Clinical ophthalmology. A systematic approach. Oxford: Butterworth Heinemann; 1994.
  6. Vaughan D,  Asbury T. General ophthalmology. California: Large Medical Publications; 1989.
  7. Diabetes Control and Complications Trial Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependant diabetes. N Engl J Med 1993;329:977-86.
  8. UK Prospective Diabetes Study Group. Tight blood pressure control and risk of macrovascular and microvascular complications in type 2 diabetes. UKPDS 38. BMJ 1998;317:703-13.
  9. Emily Y, Chew M.  Diabetic retinopathy and lipid abnormalities.Curr Opin Ophthalmol 1997;8:59-62.
  10. Kohner E. Report of the visual handicap group. Diabet Med 1996;13 Suppl 4:13-26.
  11. Department of Health. National Service Framework for diabetes: standards. London: HMSO: 2001.
  12. Department of Health. National Service Framework for diabetes: delivery strategy. London: HMSO: 2002.