Diabetic eye disease basically affects the retinal vasculature. It also affects other structures including iris and lens. Most patients with diabetes will exhibit signs of retinopathy after the duration of 25 years. Diabetic retinopathy develops to severe or complicated condition only in a minority among diabetic patients. Although Photocoagulation has revolutionized the treatment of retinopathy diabetes remains a central cause of visual damage.
Pathological features of diabetic retinopathy
Diabetic retinopathy can essentially categorized as non-proliferative and proliferative. An increase in retinal blood flow is the basic physiological feature of diabetes. The increase in retinal blood flow creates mechanical stress that leads to endothelial separation and pericyte loss. The earliest pathological features of diabetic retinopathy include thickening of the retinal capillary basement membrane and loss of tight junctions in the retinal endothelium. and loss of Pericytes are the contractile cells enveloping the capillaries and which control vessel calibre and hence perfusion. Diabetic retinopathy causes the loss of pericytes.
Causes of Diabetic Retinopathy
The most common cause of diabetic retinopathy is maculopathy. Maculopathy is the outcome of ischaemia and subsequent oedema of the central retina. Focal maculopathy is generally connected with areas of circinate or star – shaped exudates within one optic disc diameter of the macula. Diffuse macular oedema occurs with ischaemia and generate thickening of the retina. The thickening of the retina is very complicate to detect clinically. It requires either stereo ophthalmoscopy or optical coherence tomography (OCT) which can produce clear images of the retina and accurate estimates of thickness.
Ischaemia causes new vessel growth on the iris or trubeosis iridis. This vessel growth can close the drainage angle and leads to acute glaucoma. This acutely painful condition is called rubeotic glaucoma. It frequently occurs following cataract surgery or vitrectomy. Treatment is unsatisfactory in patients with active proliferative retinopathy and the outcome is often a painful blind eye.
Cataract is the most common diabetic eye disease. It usually occurs acutely and diffusely with newly diagnosed diabetes. (so – The so called snowstorm cataract or the usual posterior subcapsular and cortical cataracts occur after the duration of several years. acute fluid shift due to hyperglycaemia and hyperosmolality is fundamental cause for snowstorm cataract. Linear or central cataract is probably the outcome of non – enzymatic glycation and subsequent cross – linkage of lens crystallins. Sorbitol accumulation secondary to activation of the polyol pathway may also generate linear cataract. Extraction and replacement with a plastic implant is the most effective method of treatment
Anterior ischaemic optic neuropathy-Optic disc
Microvascular disease of the anterior optic nerve causes anterior ischaemic optic neuropathy. Patients appear with painless loss of vision upon wakening. This condition of vision loss generally remains stable. There is no known effective treatment.for anterior ischaemic optic neuropathy. Diabetic papillopathy is an associated problem of anterior ischaemic optic neuropathy. It is marked by acute disc oedema and moderate visual loss. Diabetic papillopathy is generally improved spontaneously but it may persist up to twelvemonths. Papillopathy is often confused with papilloedema. There are certain other ocular conditions also associated with diabetic retinopathy.