Diabetic Retinopathy

Examination of the optic fundus is a different thing for family physicians than it is for ophthalmologists due to technical and equipment differences.

Most family physicians are using a hand direct held ophthalmoscope in the office with patients who have not had their pupils dilated. While this may not be the optimal situation, there is still important information that can be gathered and which may prompt a referral to the ophthalmologist.

Fundoscopic exam does give you a unique opportunity to directly evaluate the state of your patientŐs vaculature. This is particularly important with diabetics, given that diabetes mellitus is the most common cause of blindness among individuals of working-age (20-65 years) and 10.2% of Type 2 diabetics have signs of diabetic retinopathy already present when their diabetes is discovered.

Another thing that it is useful for family physicians to know is how such terms as Proliferative and Non-proliferative retinopathy are defined, so that they are better able to interpret these findings for their patients.

This article will attempt to address some of these issues. An excellent review of this topic can be found at: http://medweb.bham.ac.uk/easdec/eyetextbook/dminternet.htm

Technique: While most FPs don't dilate the patient's pupils in the office, having the patient sit in a dark room for a few minutes prior to the exam can be helpful. Advise the patient to look at a specific spot on the wall and tell them to continue looking there, even after you have moved your head into the way. Ask them not to look at the light. Find the optic disc, evaluate the vessels and margins and then move temporally to the macula and an examination of the retinal vessels. Check for signs of hemorrhage and for exudates.

The following a quick, (but not complete), primer on fundoscopic examination:

RED REFLEX:
Its absence indicates a cataract or something else blocking light transmission to the retina.

VESSELS:
The veins are normally slightly bigger than the arteries. Arterio-venous nicking occurs when hypertension narrows the arteries and creates indentations in the veins where arteries cross the veins.

MACULA:
The darker area lateral to the optic disc, containing the fovea.

OPTIC DISC:
Out of which the vessels travel. It is the brightest area on the fundoscopic exam and the easiest landmark to find.

RETINOPATHOLOGIES:

DIABETIC RETINOPATHY:
Shows microaneurysms, areas of hemorrhage, cotton wool spots, hard exudates, venous beading, neovascularization, retinal detachment, vitreous detachment, pre retinal hemorrhage.

PAPILLEDEMA:
Swelling of retinal vessels, from impaired venous return in the eye leads to venous distension. Papilledema is caused by increased intracranial pressure (Brain tumors, malignant hypertension, hydrocephalus)

With Papilledema, as opposed to Pappilitis, there is no loss of vision.

HYPERTENSION:
Changes in retina are graded 1 thru 4. An abnormally high V/A ratio can be found, indicating venous distension.

Classification of Diabetic Retinopathy

A useful clinical classification according to the types of lesions detected on fundoscopy is as follows:

Non-proliferative diabetic retinopathy (NPDR)

• Microaneurysms
• Dot and blot hemorrhages
• Hard (intra-retinal) exudates

Moderate-to-severe non-proliferative diabetic retinopathy

• The above lesions, usually with exacerbation, plus:
• Cotton-wool spots
• Venous beading and loops
• Intraretinal microvascular abnormalities (IRMA)

Proliferative diabetic retinopathy

• Neovascularization of the retina, optic disc or iris
• Fibrous tissue adherent to vitreous face of retina
• Retinal detachment
• Vitreous hemorrhage
• Pre retinal hemorrhage

Maculopathy

• Clinically significant macular edema (CSME)
• Ischemic Maculopathy

Progression of Diabetic Retinopathy

Retinal microaneurysms are focal dilatations of retinal capillaries, 10 to 100 microns in diameter, and appear as red dots. They are usually seen at the posterior pole, especially temporal to the fovea . Microaneurysms are often the first ophthalmoscopically detectable change in diabetic retinopathy.

When the wall of a capillary or microaneurysm is sufficiently weakened, it may rupture, giving rise to an intraretinal hemorrhage. Dot hemorrhages appear as bright red dots and are the same size as large microaneurysms. Blot hemorrhages are larger lesions located within the mid retina, often within or surrounding areas of ischemia.

If the hemorrhage is more superficial and in the nerve fiber layer, it takes a flame or splinter shape, which is indistinguishable from a hemorrhage seen in hypertensive retinopathy. The presence of flame hemorrhage strongly suggests the co-existence of systemic hypertension.

Cotton wool spots result from occlusion of retinal pre-capillary arterioles supplying the nerve fibre layer, with concomitant swelling of local nerve fibre axons. They are white, fluffy lesions in the nerve fibre layer. Fluorescein angiography shows no capillary perfusion in the area of the soft exudate. They are very common in DR, especially if the patient is also hypertensive.

Hard exudates (Intra-retinal lipid exudates) are yellow deposits of lipid and protein within the sensory retina that leak from surrounding capillaries and microaneuryisms.

Venous beading has an appearance resembling sausage-shaped dilatation of the retinal veins. It is a sign of severe non-proliferative diabetic retinopathy. Intra-retinal microvascular abnormalities (IRMA) are abnormal, dilated retinal capillaries that indicate severe non-proliferative diabetic retinopathy that may rapidly progress to proliferative retinopathy.

Proliferative diabetic retinopathy

Retinal ischemia due to widespread capillary non perfusion results in the production of vasoproliferative substances and to the development of neovascularization. Neovascularization can involve the retina, optic disc or the iris.

Rubeosis iridis is a sign of severe proliferative disease, it may cause intractable glaucoma.

Bleeding from fragile new vessels involving the retina or optic disc can result in vitreous or retinal hemorrhage. Retinal damage can result from persistent vitreous hemorrhage.

Pre-retinal hemorrhages are often associated with retinal neovascularization and they may dramatically reduce vision within a few minutes.

Diabetic Maculopathies

Macular edema is an important manifestation of DR because it is now the leading cause of legal blindness in diabetics. The intercellular fluid comes from leaking microaneurysms or from diffuse capillary leakage.

Maculopathy in Type 1 diabetics is often due to drop out of the perifoveal capillaries with non perfusion and the consequent development of an ischemic maculopathy. Enlargement of the foveal avascular zone is frequently seen on fluorescein angiography. Ischemic maculopathy is not uncommon in type 2 diabetics.

Screening

Because of the significance of Diabetic Retinopathy, screening is of the utmost importance. This screening should be done by opthalmologists, or optometrists trained to evaluate the eye for signs of DR. Screening should be done on a regular basis, annually for patients with little or no signs of DR and more frequently for those with existing DR.

- John Hickey

Thanks to Dr. John Hamilton, Chairman of the Department of Ophthalmology, St. Martha's Regional Hospital, Antigonish, Nova Scotia, for reviewing the draft copy of this article.