Ophthalmology

Diagnostic Tests and Retinal Imaging

At a Glance

Eye tests for diabetic retinopathy show problems that may not yet affect vision. A dilated exam and retinal photos find visible damage, OCT measures swelling and fluid, and fluorescein angiography reveals leaking or blocked blood vessels to guide monitoring and care.

Diagnostic tests are the “eyes” your medical team uses to see exactly what is happening inside your retina. While you may notice changes in your vision, these imaging tools allow doctors to see microscopic damage—such as leaking fluid or blocked blood vessels—long before they cause permanent sight loss. Understanding these tests helps you track your progress and understand why certain treatments are recommended ^[1]^[2].

The Dilated Fundus Exam

The foundation of every eye check-up is the dilated exam. After using special drops to widen (dilate) your pupils, your doctor uses a high-powered lens to look directly at the back of your eye ^[1]. Be prepared for light sensitivity and blurry vision for a few hours afterward, and consider bringing sunglasses or a driver.

What they look for: Doctors check for visible signs of damage like microaneurysms (tiny bulges), hemorrhages (small bleeds), and hard exudates (fatty deposits from leaky vessels) ^[3].
Color Fundus Photography: Your doctor may take high-resolution color photos of your retina. These photos serve as a permanent record, allowing the team to compare “side-by-side” images over months or years to see if your condition is stable or progressing ^[4]^[5].

Optical Coherence Tomography (OCT)

OCT is one of the most important tools for managing diabetic retinopathy, especially Diabetic Macular Edema (DME). It is a non-invasive, quick test that uses light waves to create a detailed, 3D “cross-section” of your retina ^[2]^[6].

Measuring Thickness: OCT provides a precise measurement of your Central Subfield Thickness (CST). If the retina is thicker than normal, it usually means fluid is leaking into the tissue ^[7]^[8]. Keep in mind there is no single “normal” thickness number; it varies by the machine used and individual anatomy. Your doctor will look at the trend over time.
Identifying Fluid: The scan can show exactly where fluid is trapped—either inside the retina or underneath it ^[9]. It can also show if layers of the retina are disrupted.
Tracking Treatment: If you are receiving injections, your doctor will use repeat OCT scans to see if the fluid is drying up ^[10].

Fluorescein Angiography (FA)

While OCT shows the structure of the retina, Fluorescein Angiography (FA) shows the blood flow. During this test, a synthetic dye called fluorescein is injected into a vein in your arm. As the dye travels through the blood vessels in your eye, a special camera takes a series of photos ^[11]^[12].

Side effects: The dye will temporarily turn your urine and skin slightly yellow. Nausea is also a common side effect. Serious allergic reactions are rare, but you should tell your doctor if you have had a reaction to fluorescein before. (Note: Fluorescein is not an iodine contrast dye).
Identifying Leakage: The dye glows under the camera’s light. If blood vessels are damaged, the dye will “leak” out, showing the doctor exactly where the problem areas are ^[11]^[13].
Checking for Ischemia: FA is the best way to see if any blood vessels are blocked. These “dark zones” of non-perfusion (ischemia) are areas where the retina isn’t getting enough oxygen, which is a major trigger for the growth of abnormal new vessels ^[14]^[15].

Your Diagnostic Checklist

When you receive your results, ensure your records include these key details for both eyes. You can ask your doctor:

Retinopathy Stage: Am I in the mild, moderate, severe (NPDR), or proliferative (PDR) stage? ^[16]
DME Status: Is there any swelling (edema) in the macula? Is it “center-involving”? ^[17]
New Vessel Growth: Are there any signs of neovascularization (abnormal new vessels)? ^[18]

Having these specific data points allows you to be an active partner in your care and monitor your eye health more effectively over time ^[1].

Common questions in this guide

What can an OCT scan show in diabetic retinopathy?

OCT uses light to create detailed cross-sectional images of the retina. It can measure retinal thickness, show fluid inside or beneath the retina, identify disrupted retinal layers, and help track changes during treatment, especially with diabetic macular edema.

What happens during a dilated eye exam for diabetic retinopathy?

An eye professional uses drops to widen your pupils and then examines the back of your eye with a high-powered lens. The exam can reveal tiny bulges in blood vessels, small hemorrhages, and fatty deposits called hard exudates. Light sensitivity and blurry vision can last for a few hours afterward.

What does fluorescein angiography show?

Fluorescein angiography uses a dye injected into a vein in your arm and a special camera to photograph blood flow through the retina. It can show leaking blood vessels and areas where vessels are blocked or the retina is not receiving enough oxygen. Temporary yellow skin or urine and nausea can occur, while serious allergic reactions are rare.

What does retinal ischemia mean in diabetic retinopathy?

Retinal ischemia means that blocked blood vessels are preventing part of the retina from receiving enough oxygen. Fluorescein angiography can help identify these areas, which may stimulate abnormal new blood vessel growth. Ask your eye professional how any ischemia affects your monitoring and care.

What information should be included in my diabetic retinopathy imaging results?

Your records should identify the retinopathy stage in each eye, whether diabetic macular edema is present and involves the center of the macula, and whether abnormal new vessels are present. Keeping these details makes it easier to compare results over time and discuss care decisions.

How often will I need repeat retinal imaging?

The timing depends on your retinopathy stage, whether retinal swelling or leakage is present, and whether you are receiving treatment. Repeat OCT scans and other imaging may be used to monitor changes and treatment response. Your eye professional can set a schedule based on your individual findings.

Curated prompts to bring to your next appointment.

1.What is my Central Subfield Thickness on today's OCT, and how does the trend compare to my last scan?
2.Are there signs of structural damage to the retina layers on my OCT that might explain my vision changes?
3.If you saw leakage on my Fluorescein Angiogram, was it focal or diffuse, and how does that affect my treatment options?
4.Did the imaging show any areas of ischemia (areas not getting enough blood flow) that I should be concerned about?
5.How often will I need repeat imaging (like OCT) to monitor my response to treatment?

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References (18)

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This page is for informational purposes only and does not constitute medical advice. Ask your eye-care professional what your results mean and how often you need follow-up imaging.

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