Diabetic retinopathy
is the leading cause of blindness world over. Neurovascular degeneration of the
retina is considered presently as the cause as against the vascular changes
which are believed to be causative previously. In fact the neuronal changes are
shown to ante-date the vascular changes. There is complex interaction of many
cells like pericytes, mullers cells, astrocytes, vascular endothelial cells as
well as factors like advanced glycation products, Oxidative and metabolic
stress, inflammatory cytokines, leukotrienes, various growth factors and
glycoproteins etc. in the pathogenesis of DR. Various biochemical pathways like
Polyol pathway, glucosamine pathway, AGE pathway and PKC pathways interacting
with one another is also recognised as having a role in the pathogenesis of DR.
But the common link responsible for all these factors involvement linking to
DM2 is still not clear. The mechanism explaining Benfotiamine, a thiamine
analogue found to be useful in treating DR , though attractive in integrating
the various biochemical pathways cited above, is not comprehensive. The concept
of reactive oxygen species (ROS) is a better alternative explanations linking
up all pathogenic factors concerned to chronic hyperglycaemia of DzM2. But
antioxidants proved futile in treating DR. It may be useful to remember that
extensive ROS production in DM2 is consequent to shift of energy metabolism
from glycolysis to B-oxidation of fats. Unless this is reversed, ROS production
continues. The Diabetes Control and Complications Trial (DCCT) and UKPDS are
the two landmark clinical trials that clearly showed the relationship between
chronic hyperglycaemia and genesis of DR. Progression in T1DM and T2DM
patients, respectively. Randomized controlled trials have shown that early
treatment of DM2 can reduce an individual’s risk of severe visual loss by 57%.
Intensive glycaemic control appeared long lasting because of the metabolic
memory, also known as ‘legacy effect’. A term which explains the beneficial
effects of immediate intensive treatment of hyperglycaemia with a sustained
benefit with respect to the outcomes for many years, regardless of glycaemia in
the later course of diabetes. Hence the current emphasis is prevention of DR
with strict glycaemic control in DM2 ab initio.
Biography
of author(s)
A. S. V. Prasad
Department of Internal Medicine, GITAM Dental College, Rishikonda, Visakhapatnam, Andhra Pradesh, India.
Department of Internal Medicine, GITAM Dental College, Rishikonda, Visakhapatnam, Andhra Pradesh, India.
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