Proliferative diabetic retinopathy
 

Proliferative diabetic retinopathy showing severe ischaemia (extensive multiple cotton wool spots) and new vessels in the superotemporal arcade. Subhyaloid haemorrhage (note the fluid level) in an eye with old pan-photocoagulation scar.

The retina shows ischaemic changes as described in preproliferative diabetic retinopathy. The optic disc  or the retinal vein(s) contains new vessels. There may be associated pre-retinal haemorrhages. Look for features of high risk of proliferative diabetic retinopathy (ie. those which may lead to severe  visual loss unless treated with laser): disc vessels which are 1/4 or more of the disc area any disc vessels associated with pre-retinal or vitreous haemorrhage peripheral new vessels associated with pre-retinal or vitreous haemorrhages Look at the peripheral retina for pan-photocoagulation scars. New scars are white whereas old ones  contain pigment due to retinal pigment epithelium hyperplasia.

Questions:

1. What does the Diabetic Control and Complications Trial (DCCT) show ?

Answer
It is a 10 year study of the effects of tight glucose control in Type I diabetic patients. Patients had three to four daily insulin injections with mean glycosylated haemoglobin 7.2%. The trial shows the following:
reduction of diabetic retinopathy by 76%
reduction of diabetic nephropathy by 35 -56
reduction of diabetic neuropathy by 60%

2. How many laser burns are required in proliferative diabetic retinopathy?

Answer
This would depend if the new vessels are early, established or florid. Early vessels are those which are flat and wispy and usually responds to 1500-2000 200-500 micron laser burns which can be applied over more than one session. Whereas established new vessels in which the vessels show mature branching and/or arcade formation but are still flat will require more than 2000 burns applied over more than one session. In florid neovascularization, in which there are extensive sheets of vessels covering a wide region of the retina, aggressive laser treatment is needed and ideally with more than 2000 burns in one session.

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