The retina is a light-sensitive layer of tissue at the back of your eye. When light comes through the cornea and lens to the retina, chemical and electrical events send nerve impulses to visual centers of the brain through the fibers of the optic nerve.
The retina is an extremely complex, thin, and delicate multilayer structure, consisting mainly of nerve cells. A variety of damage to the retina can result in a broad spectrum of retinal diseases.
Retinal tissue’s capacity to respond to such injuries depends mainly on the specific cells and tissue involved and the type, duration, and severity of the injury. In the vernacular of ophthalmology, retina disease is called retinopathy.
Retinopathy is one of the leading causes of blindness. Risk factors include age, family history, or pre-existing health conditions. Having a complete examination of the retina is something everyone should have, especially those who are 40 and older and have diabetes.
How does your eye doctor diagnose retinal diseases? Following are some of the prevalent diseases common to the retina and diagnostic methods an ophthalmologist may use.
Non-Proliferative Diabetic Retinopathy
Diabetic retinopathy (DR) is the most frequent problem of the eyes in patients with diabetes. In its early and moderate stages, it is called non-proliferative diabetic retinopathy (NPDR).
To diagnose diabetic retinopathy, an ophthalmologist or retinal specialist commonly uses a dilated eye exam. Drops are placed in the eyes to dilate the pupils (open widely), allowing a better view of the eye’s inside, especially the retinal tissue.
A retinal specialist, when undertaking an examination of a patient who has been diagnosed with diabetes, will look for one or more of the following signs:
- intraretinal hemorrhages
- cotton-wool spots (CWS)
- hard exudates
- intraretinal microvascular anomalies (IRMA)
- venous beading
The hallmark of DR is the development of microaneurysms, which are small dilations of the capillaries due to their weakening walls. Microaneurysms appear as tiny red dots on the outer surface of the retina. Eventually, they may break, leading to the formation of intraretinal hemorrhages.
When the broken microaneurysms are located in the retina’s most superficial layers, the hemorrhage will take a flame or splinter-like appearance, oriented along with the nerve fiber layer. When they are located in the deeper layers, the hemorrhage will look like a red dot or blot.
Often microaneurysms and dot hemorrhages are indistinguishable. The ophthalmologist can use a Fluorescein angiography (FA) to get a better view. In FA, a fluorescent dye is injected into the bloodstream, and the microaneurysms will show as fluorescent points. Photographs are taken for closer examination.
Your retinal specialist may also use a non-invasive diagnostic tool called Optical coherence tomography (OCT). OCT uses light waves to take cross-section pictures of your retina. The largest intraretinal hemorrhages may be seen in an OCT as moderately reflective masses located in the inner retinal layers.
Capillary wall damage will lead to leakage of fluids that accumulate in the retina producing macular edema, which are thickening areas of the retina.
Lipoproteins spreading from microaneurysms or weakened capillaries will be trapped at the outer retinal layer, forming what are called hard exudates. These irregularly shaped yellow-white spots located slightly deeper in the retina may coalesce, forming streaks, clusters, or a form circular pattern centered on the leaking capillary.
They may accumulate in the center of the fovea, forming a dense plaque, which may initiate an inflammatory response, leading to a retinal detachment. They are not usually seen on a Fluorescein angiography, except when too dense, causing minimum blockage of the dye. On the OCT, they appear as reflective and irregular images.
As diabetic retinopathy progresses, there will be further damage to the capillaries, leading to progressive ischemia (restriction in blood supply). Ischemia in the inner retinal layers will dilate the nerve fiber creating superficial grey-white fluffy spots with feathery borders called cotton-wool spots (CWS).
In some cases, tiny tortuous vessels (twisted) may develop in the proximity of previous CWS or other ischemic areas that are very difficult, called intraretinal microvascular anomalies (IRMA).
The last sign of non-proliferative diabetic retinopathy is venous beading, a succession of constrictions and thickenings of the vein walls and causing significant ischemia.
This sign is most strongly associated with progression to proliferative diabetic retinopathy.
Proliferative Diabetic Retinopathy
Proliferative diabetic retinopathy (PDR) occurs as a progression of severe diabetic vascular damage. It includes intra-retinal capillary closure with resultant ischemia (restriction in blood supply) and the formation of new vessels, a process called neovascularization. The new fragile vessels can bleed, creating vision-impairing hemorrhages, scar tissue, retinal detachment.
Severe non-proliferative diabetic retinopathy is the precursor of proliferative diabetic retinopathy. It includes diffuse intra-retinal hemorrhages, venous beading, and intra-retinal microvascular abnormalities (IRMA). The chance of progression from NPDR to PDR in 1 year is between 15% and 45%.
Severe NPDR can be confused with PDR. Fluorescein angiography is the best way to differentiate IRMA from neovascularization, as the latter shows significant leakage throughout the examination.
The evolution of new vessels starts with fine vessels with minimal fibrosis, then an increase in vessel size and fibrous tissue, and then the end stage of PDR, which includes regressed vessels and significant fibrovascular proliferation on the posterior hyaloid (layer of collagen separating the vitreous humour from the rest of the eye).
Diabetic Macular Edema
Diabetic macular edema (DME) is the leading cause of visual loss in diabetic patients. It may present at every stage of diabetic retinopathy. DME manifest when fluid and protein deposits collect on or under the macula, the center of the retina needed to see clearly, it can thicken and swell. The swelling can distort a person’s central vision.
Diabetic macular edema is diagnosed with a detailed bio-microscopic examination with the slit lamp and indirect ophthalmoscopy (a view of the eye’s back through a lens held close to the eye).
Contact Arizona Retinal Specialist
Schedule a comprehensive eye exam today as early diagnosis can save you from complications of retinopathy. Call us at 623-474-3937 (EYES) to schedule a comprehensive eye exam at a location near you.