What is Diabetic Retinopathy?
Diabetic retinopathy is a complication of diabetes mellitus (sugar diabetes) that affects the retina of the eye. This is the inner lining of the eyeball which is light sensitive and converts incoming light into electrical impulses. The signals then travel to the brain where it is deciphered and results in the sense of sight.
When the retina is diseased, vision is impaired to varying degrees. With diabetic retinopathy, the changes are gradual and progressive. The tiny blood vessels thats supply oxygen to the retina (retinal capillaries) are compromised and results in a number of changes that eventually damage the retina irreversibly.
Regular monitoring of the vision and opthalmalogical examinations will help to identify diabetic retinopathy in the early stages. However, many diabetics only seek treatment once the visual disturbance is significant and affecting daily functioning. Blurred vision is more commonly reported as a reason for seeking medical attention than the other diabetic retinopathy symptoms. If left untreated, diabetic retinopathy can lead to blindness.
Causes of Diabetic Retinopathy
Prolonged hyperglycemia (high blood glucose levels) affects the anatomy and function of retinal capillaries. The excess glucose is converted into sorbitol when it is diverted to alternative metabolic pathways. Sorbitol leads to death or dysfunction of the pericytes of the retinal capillaries. This weakens the capillary walls allowing for the formation of microaneurysms, which are the earliest signs of diabetic retinopathy. The weak capillary walls can also be responsible for increased permeability and the exudates.
Due to the predisposition to increased platelet aggregration and adhesion (blood clot formation) as a result of diabetes, the capillary circulation becomes sluggish or even totally impaired by an occlusion. This can also contribute to the development of diabetic retinopathy.
These changes and the progression of the disease can be categorized into two clinical stages :
- Non-proliferative diabetic retinopathy
- Proliferative diabetic retinopathy
Risk Factors for Diabetic Retinopathy
Both type 1 and type 2 diabetics are at risk of developing retinopathy. Long term diabetes and poorly controlled diabetes increases the risk significantly, irrespective of the types of diabetes. In addition, diabetics with hypertension, who are pregnant or have high cholesterol levels (hypercholesterolemia) are at a greater risk.
Symptoms of Diabetic Retinopathy
It is not uncommon for there to be no symptoms in the early stages of diabetic retinopathy (mild non-proliferative stage). Due to the gradual onset of symptoms, many diabetics ignore the early symptoms until it has significantly affected the vision or been diagnosed upon opthalmoscopic examination (fundoscopy).
Many of the symptoms of diabetic retinopathy could also be attributed to other opthalmic complications of diabetes, like glaucoma, cataracts, corneal abnormalities or neuropathy.
Symptoms may vary but the most commonly reported visual disturbances include :
- Blurred vision
- Poor night vision
These visual disturbance should not be mistaken for age-related changes and other causes of problems with visual acuity. Other reported symptoms of diabetic retinopathy include fluctuating and progressive deterioration of vision, dark spots, impairment of color vision and/or reduced peripheral vision. Eventually significant or total loss of vision (blindness) will occur.
Screening for Diabetic Retinopathy
The most widespread method of screening is via opthalmoscopy. This involves examination of the retina with an opthalmoscope and is described in detail below. In the hands of an experienced practitioner, non-proliferative diabetic retinopathy can be detected at an early stage. Retinal imaging through measures like fluoroscein angiography and digital photography depends on the availability of facilities. If available, these screening measures should be considered. Both type 1 and type 2 diabetics should be screened annually even if the diabetes is well controlled.
Diabetic patients should be made aware of the seriousness of diabetic retinopathy and the possibility of blindness. Tight diabetic control with medication, dietary and lifestyle measures are essential for life in order to limit or prevent diabetic complications. Patients should report to the supervising doctor immediately if any change of vision is noticed despite the routine annual screening.
Diagnosing Diabetic Retinopathy
The most important tests employed in ophthalmologic evaluations are ophthalmoscopy (fundoscopy), and fluorescein angiography. Other tests that may also be considered slit-lamp biomicroscopy, B scan ultrasonography, optical coherence tomography, tonometry and digital retinal screening.
Glucose testing with fasting glucose and hemoglobin A1c (HbA1c) are other lab investigations that are also essential in diagnosis, management and follow up of diabetes mellitus as a whole as well as complications like diabetic retinopathy.
Examination of the eye with an ophthalmoscope is the most important clinical examination which is necessary for screening. Ophthalmoscopy involves visualizing the retina through a magnifying lens which a provides clear view of the retinal surface and capillaries. The findings of ophthalmoscopy can be confirmed with a slit-lamp biomicroscopy.
Ophthalmoscopic examination of the eye (fundoscopy) may show :
- microaneurysms (seen as small red dots in retina)
- dot and blot hemorrhages (round shaped with blurred edges)
- splinter hemorrhages (flame shaped hemorrhages)
- hard exudates (yellowish and sharply edges)
- cotton-wool spots (round whitish or grayish swellings)
- venous beading
- retinal edema
- intraretinal microvascular abnormalities (non-leaky collateral vessels found along the borders of the ischemic retina)
- macular edema
- neovascularization (usually seen near the optic disc) – new capillaries and extensive capillary network
- vitreous hemorrhage (may appear as a haze or as clumps of blood clots
- retinal detachment
Fluorescein angiography is another important diagnostic test that is useful in identifying and managing diabetic retinopathy. It will help the practitioner to conclusively identify and distinguish between the different defects mentioned above.
Treatment of Diabetic Retinopathy
The treatment options currently available are effective in halting or delaying further vision loss but will not reverse changes. The approach to the treatment of diabetic retinopathy depends on the stage of retinopathy, presence and extent of clinically significant macular edema, type of diabetes, general condition of the patient, and status of the opposite eye.
The treatment options for diabetic retinopathy include :
- surgical management (laser surgery, vitrectomy)
- medical treatment (drug)
The specific treatment for diabetic retinopathy should not be seen as a means of undoing the effects of prolonged and poorly controlled diabetes mellitus (sugar diabetes). Proper management of diabetes through medication, diet and lifestyles are essential.
Surgical Management for Diabetic Retinopathy
Laser surgery or laser photocoagulation is the standard treatment approach for diabetic retinopathy that aims to slow the disease progression. Laser photocoagulation is a noninvasive treatment with a high success rate and low complication rate. A highly focused laser beam is directed at the target tissue to produce a coagulation response. Focal photocoagulation is recommended for nonproliferative diabetic retinopathy while panretinal photocoagulation is considered for proliferative diabetic retinopathy.
Vitrectomy is another surgical option available for diabetic retinopathy. The surgery involves the removal of vitreous humor, usually under local anesthesia. Vitrectomy is usually required in long standing vitreous hemorrhage (unresolved for more than 6 months) and retinal detachment. The surgery aims to repair or prevent retinal detachment and to remove the blood in the vitreous hemorrhage.
Cryotherapy may be occasionally used to treat retinopathy in presence of cataract or vitreous hemorrhage.
Medication for Diabetic Retinopathy
The treatment of diabetic retinopathy with medication has limited use if good glucose control is not undertaken. Intravitreal injections (injecting the drug into the vitreous humor) of triamcinolone (corticosteroid) is used for the treatment of diabetic macular edema but focal photocoagulation (mentioned above) is still a more effective option in the long term. The effect of single injection of triamcinolone lasts for only about 3 months and repeated injections are necessary to sustain the beneficial effects.
Intravitreal bevacizumab and ranibizumab are anti-VEGF agents which are used for macular edema, vitreous hemorrhage, and neovascularization. These medications have shown encouraging results. A combined approach with focal laser therapy and anti-VEGF drugs may yield better results. Other drugs under evaluation for diabetic retinopathy include ruboxistaurin for delaying progression of proliferative diabetic retinopathy and ovine hyaluronidase for the clearance of a vitreous hemorrhage.
Complications of Diabetic Retinopathy Treatment
Laser photocoagulation may result in a loss of some peripheral vision and some reduction in color vision and nocturnal vision. This is of less consequence when the benefits are weighed against the long term impact of diabetic retinopathy. Other complications may include decreased central vision, areas of reduced vision (scotoma), neovascularization in choroid and an occasional increase in macular edema.
Intravitreal injections of triamcinolone can result in cataract, glaucoma, and serious eye infections (like endophthalimitis).
Last updated on March 30, 2019.