Diabetic retinopathy is a complication of diabetes that damages blood vessels in the retina, the light-sensitive tissue at the back of the eye. Over time, this damage can lead to vision loss. Medical imaging provides a direct view of the retina, allowing doctors to detect and monitor the condition, often before a person notices any changes in their vision. Understanding what these images show can help clarify how diabetes affects the eye and why regular screenings are important for preserving sight.
Visualizing a Healthy Retina
To understand diabetic retinopathy, it is helpful to first see what a healthy retina looks like. Imaging reveals a clear view of the fundus, the interior back surface of the eye. A prominent feature is the optic disc, a bright, yellowish, oval-shaped area where the optic nerve connects to the retina. In a healthy eye, the optic disc has sharp, well-defined margins.
Radiating from the optic disc are the retinal blood vessels, including arteries and veins that supply blood to the retina. These vessels appear smooth with a consistent caliber. Another area is the macula, responsible for sharp, detailed central vision. The macula appears as a dusky, uniform area darker than the surrounding retina, with a small light reflex at its center, known as the fovea.
Images of Non-Proliferative Diabetic Retinopathy (NPDR)
Non-proliferative diabetic retinopathy (NPDR) is the early stage of the disease where damage to retinal blood vessels becomes visible. One of the earliest signs are microaneurysms, which appear as tiny, red dots on a retinal image. These are small bulges in the capillary walls caused by the weakening of the vessel structure. As these weakened vessels leak, they can cause small hemorrhages within the retinal layers.
These hemorrhages are classified by their appearance. “Dot” hemorrhages are small and circular, while “blot” hemorrhages are larger and more irregular. Both indicate bleeding in the deeper layers of the retina. Another common feature are hard exudates, which are yellowish, waxy deposits of lipids and proteins leaked from damaged blood vessels.
A different lesion, a cotton wool spot, may also appear as a fluffy, white patch on the retinal surface. Unlike hard exudates, cotton wool spots are not deposits but represent areas where nerve fibers have been damaged from a lack of blood flow. The presence and quantity of these signs help ophthalmologists classify the severity of NPDR.
Images of Proliferative Diabetic Retinopathy (PDR)
Proliferative diabetic retinopathy (PDR) represents a more advanced stage of the disease, characterized by a process called neovascularization. In response to widespread capillary closure and lack of oxygen, the retina grows new, abnormal blood vessels. These vessels appear on an image as fine, tangled networks on the surface of the retina or the optic disc and are fragile and structurally unsound.
The primary danger of neovascularization is their tendency to bleed into the vitreous, the clear, gel-like substance that fills the eye. This event, called a vitreous hemorrhage, can appear in an image as a diffuse haze or large pockets of blood that obscure the view of the retina. A small hemorrhage might cause a patient to see a few dark floaters, while a severe bleed can block vision entirely.
These abnormal vessels can also form scar tissue. As this scar tissue contracts, it can pull on the retina, leading to a tractional retinal detachment, which appears as a tented-up, immobile section of the retina on an image. The presence of neovascularization signals a high risk of significant vision loss.
Imaging Diabetic Macular Edema
Diabetic macular edema (DME) is swelling in the macula caused by fluid leaking from damaged blood vessels. It is a major cause of vision loss in people with diabetes and can occur at any stage of retinopathy. While a standard fundus photograph may show hard exudates clustered around the macula, it only provides a surface view and may not reveal the full extent of the swelling.
To visualize fluid accumulation directly, doctors use Optical Coherence Tomography (OCT). An OCT scan creates a high-resolution, cross-sectional map of the retina’s layers, much like an ultrasound but using light. In a healthy eye, an OCT image shows distinct, flat retinal layers. With DME, the image reveals these layers are thickened and separated by dark, fluid-filled cysts, allowing doctors to measure retinal thickness and monitor treatment response.
Understanding Retinal Imaging Technology
The most common imaging method is fundus photography, which produces a high-resolution, two-dimensional color picture of the back of the eye. During this procedure, a fundus camera uses a bright flash of light to illuminate the retina through the pupil, capturing a detailed photograph.