How diabetic retinopathy develops?
Occlusion of small vessels leads to loss of blood supply (ischaemia) of corresponding part of retina and further complications. It can be compared with the situation of road accident on the highway leading to traffic stand still. While waiting for the accident site to clear up , the traffic tries to negotiate through the sides of road, even running into the unconstructed stretches to bypass the blockage in the traffic. Seepage of the traffic from the main road into the cellular surroundings is what constitutes the oedema in the areas where the capillary is blocked. The thickened areas of retina due to seepage of plasma invites hard exudates around them. Some of the formed blood also comes out as spots of bleeding. These diversionary channels formed in hurry, are uneven, fragile and more liable to breakdown and blockage than the original highway.
The blockage of blood supply, ischaemia, may be partial or complete. Complete ischaemia leads to death of tissue . But partial ischaemia may be more harmful. The dying tissue because of partial ischaemia create a cry of hunger in the form of Neovascular growth factor and lead to formation of new channels to support their nutrition. These new vessels have increased permeability in their walls to allow seepage of proteins and other nutrients for direct consumption by cells in the ischaemic sectors. The new vessels may come from disc
(NVD ) or from a peripheral retina (NVE). Because of fragile nature these blood vessels may bleed by any strain leading to preretinal and vitreous
haemorrhage. Laying down of fibrous tissue around these vessels in an attempt to heal it , further aggravates the problem. These fibrous proliferation may cause pull on retina and lead to retinal detachment.
How does laser work ;
Laser causes death of retinal tissue and so:
Reduces the demand of oxygen and nutrients for remaining retina.
Reduces formation of neo vascular growth factors.
Reduces new vessels and so bleeding and related complications.