الفهرس | Only 14 pages are availabe for public view |
Abstract Diabetic retinopathy is one of the leading causes of blindness worldwide. It has long been considered as a microvascular disease but recent animal and human studies have demonstrated that neurodegeneration precedes the microvascular changes. Several factors have been reported to contribute to the neurodegenerative process in diabetic patients. The major contributor reported in the past few decades was hyperglycemia. Recent studies implemented to assess the pathophysiology of diabetic neurodegeneration in the retina have shown that other factors contribute to this neurodegenerative process. These include glutamate excitotoxicity, hyperhomocysteinemia, RAS overexpression and finally dysregulation of the release of growth factors including VEGF and insulin. The two hallmarks of this neurodegenerative process reported in animal models are glial activation and apoptosis mainly of the ganglion cells. Optical coherence tomography has been used to assess the retinal layers. There is no built in method in the OCT machines to measure the ganglion cell layer thickness and all the attempts are manual ones. On the other hand, the retinal nerve fiber layer, formed of the axons of ganglion cells, can be measured by the machine in the peripapillary region where it is most thick. So peripapillary RNFL thickness assessment by OCT can be used for in vivo measurement of RGC layer loss and thus diabetic neurodegeneration. Several studies have been implimented to assess RNFL thickness in diabetic patients but the results were controversial. Some reported a reduction in the peripapillary RNFL thickness while others found no difference in the RNFL thickness in diabetics versus age matched controls. On the other extreme some reported an increase in the peripapillary RNFL thickness. Another point of controverse in the studies which reported reduction in the RNFL thickness was the affected quadrants. Again the relation between the RNFL thickness and several parameters including HbA1c level, duration of diabetes mellitus and severity of diabetes were a matter of controverse. No previous study assessed the relation between RNFL thickness and insulin therapy. So in this study we included ninety eyes of 60 diabetic Egyptian patients who met the inclusion criteria. Thirty eyes of 23 healthy subjects acted as age matched controls. All patients were recruited from the ophthalmic outpatient clinic in Ain Shams university hospitals in the period between March 2011 and January 2013. Diabetic eyes were further divided as follows: Group 1: Thirty eyes of 17 diabetic patients with no or mild non-proliferative diabetic retinopathy. Group 2: Thirty eyes of 21 diabetic patients with moderate non-proliferative diabetic retinopathy. Group 3: Thirty eyes of 22 diabetic patients with severe non-proliferative diabetic retinopathy. Group 4: Thirty eyes of 23 normal healthy subjects were included as age matched control eyes. And as we analyzed the results we found: A statistically significant reduction in the mean nasal RNFL thickness in eyes with no diabetic retinopathy and eyes with mild non-proliferative diabetic retinopathy in comparison to the age matched controls. The mean inferior RNFL was statistically significantly thinner in eyes with moderate nonproliferative diabetic retinopathy in comparison to the age matched controls. No statistically significantly difference between the RNFL thickness in eyes with severe nonproliferative diabetic retinopathy and age matched controls and that was related to edema in the RNFL in late stages of diabetic retinopathy. In the early stages of diabetic retinopathy, the RNFL thickness is not related to the severity of diabetic retinopathy. On the other hand the RNFL thickness in the nasal quadrant was statistically significantly higher in eyes with severe non-proliferative diabetic retinopathy in comparison to eyes with mild non-proliferative diabetic retinopathy.There was only a weak negative correlation between Hb A1c and both the average RNFL thickness and the RNFL thickness in the inferior quadrant. There was no statistically significant correlation between the RNFL thickness and sex, the duration of diabetes mellitus, insulin use and macular edema not reaching the disc. So we can conclude from this: 1. That retinal neurodegeneration occurs in the early stages of diabetic retinopathy even before micovascular abnormalities are visible. 2. This neurodegeneration can be assessed by peripapillary RNFL assessment even before diabetic changes appear. 3. This effect may be masked in the late stages of diabetic retinopathy due to subclinical edema in the retinal nerve fiber layer. |