Factors influencing the Natural course of Diabetic Retinopathy and macular oedema

Factors  influencing  the Natural  course  of Diabetic  Retinopathy  and  macular oedema

a)  Duration  of diabetes

All  people with diabetes  mellitus  are at risk - those  withType I  diabetes  and  those  with Type II diabetes. The longer  a person has diabetes, the higher the risk of developing  some  ocular problem. Between  40 to 45 percent of Americians  diagnosed with diabetes have some stage of diabetic retinopathy.  After 20 years of diabetes , nearly 99% of patients with type I and 60% with type2 had some degree of diabetic  retinopathy and 3.6% of younger - onset patients (aged < 30 years at diagnosis, an operational definition of type J diabetes ) and 1.6% of older onset patients ( aged < 30 years at diagnosis , an  operational  definition of type 2 diabetes ) were found to be legally blind. In the younger - onset group, 86% of blindness was attributable to diabetic retinopathy .  In the  older- onset  group, where other eye diseases were  more common , one third of the cases of legal blindness were the result of diabetic  retinopathy.

b)  Glycaemic  Control

There is an  indirect relationship between the glycaemic controls and the development and   progression of DR. DCCT and Early Treatment of Diabetic  Retinopathy Study (ETDRS ) have convincingly shown the reduction  in risk of progression of  DR with intensive treatment. Decrease  in glycosylated  haemoglobin  levels was associated with a significant decrease  in the  progression of DR as well as the incidense of PDR . Intensive  diabetic  control leads to reduction in the development  and progression  of all diabetic complications.

c)  Age and Sex

The prevalence and severity of DR  increases  with  increasing  age  in type I  DM but donot  increase in  type II  DM.

d) Hypertension

Studies, such as WESDR  and  UKPDS , suggest that hypertension  increases the risk and progression of  DR  and  DME.  In  UKPDS , tight control of blood pressure  resulted  in  34% reduction in progression  of retinopathy with 47% reduced risk  of deterioration  in  visual  acuity  of three lines.

e)   Nephropathy

The  presence  of  gross  proteinuria  at  baseline  has  been  reported  to  be associated  with  95% increased  risk  of developing  DME  among  type I  patients  in  the  WESDR .  The  prevalence  of  PDR  was  much  higher  in  patients  with  persistent    microalbuminuria .

f)   Genetics

In  WESDR ,  patients  with  HLA  DR4  and  absent  HLA  DR3  were  found  to be at  a greater  risk  of  having  PDR. Data  from  the  DCCT  also  suggested  genetic  predisposition   diabetes .  However , it  is probable  that  both  genetic  and environmental  factors  play  a role  in  the  expression  of DR .

g )  Serum  Lipid

In  WESDR ,  higher  total  serum  cholesterol  was  associated  with  increased  risk  of having  retinal  

hard  exudates.  ETDRS  has  reported  a positive  correlation  between  serum  lipids  and risk  of  retinal  hard  exudates in  type 2 DM  .  Recently ,  Gupta et al.  have reported  reduction  in  oedema  , severity  of hard  exudates  and  subfoveal  lipid  migration  in patients  with  type 2  diabetes  and dyslipidaemia ,  using  a lipid - lowering  drug , atorvastatin ,  as  an  adjunct  to  macular  photocoagulation.

h )   Anaemia

In  ETDRS ,  low  hematocrit  levels  At  baseline  were  identified  as  independent  risk  factor  for  the  development  of  high - risk PDR  and  severe  visual  loss.  It  showed  an increased  risk  of  retinopathy  in patients  with  the  haemoglobin  level  of less  than  12 g/ dl .  Anaemia  -induced   retinal  hypoxia  is  speculated   as  cause  of   development  of  microaneurysms  and  other  retinopathy  changes.

i )  Puberty

In the  WESDR , younger  on set  subjects who were post-menarchal  stood  a 3.2  times  greater  risk  of developing  DR as  compared  to  pre- menarchal subjects.  Those  who were older than 13 years at the time of diagnosis were  likely  to have retinopathy  than  those who were younger.  The  exact  mechanism  by  which  puberty  might  exert  its effect  on the  development  of early  retinopathy  is  not yet  understood ,  but  a possible  role  of hormonal  factors  is suspected.

j )  Socioeconomic  Status

Although  educational   attainment  was  inversely  associated   with  retinopathy  in women  in  the WESDR , socioeconomic  status  was  not  associated  with  increased  risk  of  worsening  of  retinopathy.  Once  the  level  of  glycaemia  is  accounted  for ,  social  factors  have  little  or  no influence  on this   complication   of  diabetes .

k)  Pregnancy

Pregnant  women  with  type  1  diabetes  have  twice  the  risk  of  developing  PDR  than  non-  pregnant  women .  Ideally , young mothers  should  be  examined  for  retinopathy  before  the  onset  of  pregnancy.  The  cause of  acceleration  of DR  may  be  a  simple  reflection  of  long  duration of  diabetes  or  there  may  be factors ,  both  metabolic  and  hormonal ,  that  contribute   to  the  overall  deterioration  of  DR  in  the  pregnant  patient .

Ocular  conditions  are :  Status  of  posterior  vitreous ,  intraocular   pressure,  Ocular  perfusion  pressure,  Refractive  error ,  intraocular surgery  like  cataract  and  glaucoma ,  intraocular  infection  and  inflammation .