Testing

If you are at risk of diabetic retinopathy or have the symptoms, your eye specialist may undertake one or more of the following tests to detect and diagnose the disease.

Visual acuity testing

The visual acuity chart measures sight at various distances. From a specified distance, the eye specialist or the optometrist will ask that progressively smaller rows of capital letters be read aloud.

Ophthalmoscopy and slit-lamp examination

Microscope-like viewing instruments will be used to view the retina for the following signs of diabetic retinopathy:

• Leaking blood vessels with small haemorrhages on the retina
• Swelling and inflammation (edema)
• Fatty yellow deposits (exudates)
• Fuzzy white ‘cotton-wool spots’ that indicate areas where tissue has died and become opaque

Before this examination, the eye care professional should dilate (enlarge) the pupils using eye drops. This gives a better view of the retina at the back of the eye but may cause vision to be blurry for a few hours. It is unwise to drive while the vision is blurry, so arrange how to get home before the appointment. In some patients a photograph of the retina may be taken without pupil dilation.

Tonometry

After the use of some anaesthetic drops, the eye care professional may use a tonometer to measure intraocular pressure which is the pressure of fluids inside the eye.

Supplemental testing

Additional testing may be undertaken, if appropriate, including:

• Optical coherence tomography (OCT) scan: a non-invasive procedure that produces high-resolution images of cross-sections of the retina, allowing its thickness to be measured. This test can also show abnormal fluid build-up in and under the retina.
• Fluorescein angiogram: for people with leaking blood vessels or macular edema, an eye specialist may perform a fluorescein angiogram. Fluorescein dye is injected into a vein in the arm and is taken up by vessels of the eye. This identifies any leaking vessels in the retina.