Thursday 14th October 1993 Morning coffee break 11:35
“What do you think, Dilys?”
“I don’t know, Dr Lewis. I have been over this so many times. I never remember it for long.”
“Perhaps you need to think about it slightly differently,” said Dr Lewis. “I will tell you how I look at it. We know that most of the long term complications of diabetes are due to bad circulation. The circulatory changes that we see in people with diabetes are different to the normal circulatory changes that occur as we get older. Can you remember what those differences are?”
“Yes,” said Dilys. “The changes occur more quickly in diabetes and, as well as affecting the large blood vessels, they also effect the small vessels like the blood vessels in the eyes and the kidneys.”
“Good,” said Dr Lewis. “Now the retina at the back of the eye is usually a nice pink colour because it has a very rich blood supply. The rods and cones use up a lot of energy. They need plenty of oxygen and nutrients.”
Dilys knew the retina was pink but had not really thought about why.
Dr Lewis continued: “The first important changes we see in patients with diabetic retinopathy are ischaemic areas.”
“Are they cotton wool spots?
“Yes, they are . They’re pale patches called cotton wool spots which is exactly what they look like. Another name for them is soft exudates.”
“The retina compensates for these tiny, blocked blood vessels by producing new blood vessels. These new vessels are not as good as the originals so what do you think happens?”
“They can leak or burst. You can get haemorrhages,” said Dilys.
“Excellent! Now the retina is very sensitive. The leaks and haemorrhages are irritant. The affected areas of retina become inflamed.”
“Do you get scarring or fibrosis?” Dilys asked.
“You do. The inflammation leads to fibrosis. The fibrosis causes traction and distorts the back of the retina. It can pull on a blood vessel and cause a large haemorrhage or even cause a retinal detachment. This would have a severe effect on the patient’s vision. Do you know how diabetic retinopathy is treated?”
“They burn the new blood vessels with a laser.”
“Good. This blocks the vessels but it stops the leaking and haemorrhage. It means there will be less inflammation or fibrosis.” Dr Lewis paused and took a breath. “To sum up, then: circulatory damage affecting the small retinal vessels causes pale areas of ischaemia, new blood vessels are formed to help mitigate this, the new vessels leak or burst and this causes inflammation and fibrosis. The ischaemic areas, the haemorrhages and the scar formation all damage the patient’s vision.”
Dilys smiled. “Thanks, Dr Lewis. It seems to make sense but I am not sure I will remember it.”