The diagnosis of diabetic retinopathy is closely associated with its stage. The disease is diagnosed and classified when initial signs of the condition are observed in the fundus of the eye, normally using photography. When fluid is also detected in the inner retina, diabetic macular oedema is diagnosed in association with the retinopathy.
Tests used to diagnose Diabetic Retinopathy
The diagnosis of diabetic retinopathy requires a series of complementary tests, because the condition cannot be observed externally as it affects the very back of the eye (the eye fundus). Of all these tests, only fluorescein angiography causes side effects and requires any special care. The main techniques used are:
Indirect biomicroscopy of the eye fundus. This technique uses a slit lamp and condenser lens to provide a view of the eye fundus. Only the person carrying out the examination, normally the ophthalmologist, can see the image in the eyepiece.
Retinography. Photography of the eye fundus using a camera, hence the results can be saved. Depending on the model type, the patient’s pupils may need to be dilated. The field of view can range from 30–45° (conventional models) up to 210° (ultra-wide field systems). This is the main technique used to screen for retinopathies in people with diabetes.
Fluorescein retinal angiography. This method is similar to retinography, but the contrast agent fluorescein is injected into a vein. When this dye reaches the fundus of the eye it highlights any changes in retinal blood flow and, chiefly, the presence of neovascularisation and haemorrhages. This test cannot be performed on people with a fluorescein allergy and must be conducted with special care in patients with kidney problems. Patients who undergo this test may produce yellow urine for the next 24 hours.
Optical coherence tomography. This technique uses a light beam to scan the inner retina (macula). It produces cross-sectional images of the different layers in the retina. It is particularly useful for examining diabetic macular oedema.
Optical coherence tomography angiography. This recently developed test involves processing the images obtained by scanning the retina’s layers. Blood circulation in the retina can be characterised without having to inject a dye.
Optical coherence tomography angiography
A novel imaging technique, known as optical coherence tomography angiography, has recently been developed for examining patients with abnormal retinal blood circulation. Over the last 10 years, optical coherence tomography has revolutionised the field of ophthalmology, since it provides highly detailed images of the retina’s anatomy and without any side effects.
Nevertheless, until recently, it only produced information about tissues rather than blood vessels, which could be used to diagnose and monitor accumulations of fluid in the macula (diabetic macular oedema). Building on this technique, new computer processing technology means we can now obtain images of the retinal circulation (angiography). Therefore, ophthalmologists now capture images like those produced by traditional fluorescein angiography but without having to inject a dye that can cause side effects.
With this test, patients can undergo detailed examinations on a regular basis and without additional risks. The new information gathered by this technique is very important in a lot of fields researching the disease. The availability of optical coherence tomography angiography is therefore expected to increase in ophthalmology departments over the coming years.