Diabetes can lead to damage of the small blood vessels in the retina, the nerve layer for the eye that allows us to see. In the early and moderate stages these changes do not cause symptoms or changes in vision, so it is important to get yearly screening eye examinations with an optometrist.
Diabetic retinopathy is classified into categories based on the severity of the disease. Most patients have non-proliferative diabetic retinopathy (NPDR). The earliest finding in NPDR is microaneurysms, a subtle weakening of the retina’s tiny blood vessels. As the disease progresses into moderate and severe forms, dot and blot haemorrhages accumulate within the retina, and blood vessels can leak fluid and exudate, lipid and protein deposits. Patients with NPDR usually have good vision but are at risk of progressing to more severe forms of retinopathy.
Patient with diabetes are also at risk of developing cataracts, a clouding of the natural lens of the eye, at an earlier age.
The best way to protect the eye health of patients with diabetes is by improving blood sugar control and having regular screening eye examinations to monitor for disease. The longer you have diabetes the more likely you are to develop severe stages of retinopathy.
Vision-threatening diabetic retinopathy
Patients with diabetes are at risk of two types of vision-threatening changes: diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR).
Diabetic macular edema
In diabetic macular edema (DME) the damaged blood vessels in the eye start to leak fluid into the central retina, causing painless blurry vision. DME can happen with any stage of diabetic retinopathy and requires prompt referral to an ophthalmologist for a detailed eye exam. Treatment with anti-VEGF intravitreal injections may be required or rarely specialised laser macular photocoagulation. Your eye surgeon will discuss options with you based on the status of your retinopathy.
Proliferative diabetic retinopathy
Patients with severe NPDR are at risk of progressing to a more vision threatening condition called proliferative diabetic retinopathy (PDR). In PDR the damaged retinal tissues release signals that trigger the growth of new abnormal blood vessels.
The abnormal blood vessels in PDR tend to grow in abnormal locations:
- on the surface of the retina
- in the front segment of the eye on the iris
- in the drainage pathway
The abnormal blood vessels in PDR do not cause symptoms until they leak blood or start to form into a membrane that pulls on the underlying tissues. If a patient is identified as having PDR, they are promptly referred to an eye surgeon for treatment with panretinal photocoagulation laser (PRP) to the peripheral retina. PRP laser reduces the tendency for damaged retinal tissues to release the growth factors that cause new blood vessels to form.
Patients with PDR can develop a vitreous hemorrhage, bleeding into the vitreous gel of the eye from the abnormal vessels growing on the retina. Patients with vitreous hemorrhage often describe sudden onset of multiple floaters, or a stream of floaters that progressively blurs the vision. Vision can be severely reduced from vitreous hemorrhage. Patients are urgently referred for an assessment and management by an eye surgeon. The blood sometimes settles over the course of weeks and then PRP laser treatment is completed. In other cases, patients require surgery to remove the blood and then have the PRP laser treatment.
Patients with PDR can develop retinal detachment if the membrane formed by the abnormal new blood vessels starts to pull on the underlying retina. This is a severe problem that requires complex retina surgery for tractional retinal detachment to remove the membrane from the delicate underlying retina.
Patients with PDR can develop a rare form of glaucoma, neovascular glaucoma, when the abnormal blood vessels grow over the drainage pathway. The membrane of blood vessels can contract and close off the drainage pathway. The eye continues to produce fluid and the eye pressure rises, risking damage to the optic nerve, the cable that transmit light signals from the eye to the brain. Neovascular glaucoma is a severe problem that is difficult to treat—often requiring eye injections, laser, medications and surgery— and carries a high risk of blindness and chronic eye pain. It requires urgent referral to an ophthalmologist.