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Rosina Zakri, Chloe Angwin, Susan Walker, Nishal Patel, East Kent NHS Trust medical retina team.; Oxygenation of retinal vessels before and after laser therapy in sight threatening diabetic macular edema.. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2368. doi: https://doi.org/.
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Laser therapy for macular edema is used to stabilise visual acuity, a direct indicator of retinal function. We aim to identify the short term effects of macular laser therapy on oxygenation of retinal vessels in diabetic macular edema (DME). To assess if a reduction of maculopathy affects oxygenation at the centre of the retina.
Patients were recruited to a single centre, open label, prospective, cohort study, to measure retinal oxygen levels in sight threatening diabetic maculopathy. Ethical approval was obtained by an independent committee and consent was obtained from recruited patients. Retinal images of the macula in 22 patients with unilateral DME was obtained using Oxymap technology. The patients were treated with retinal laser photocoagulation in the affected eye. Oxygenation levels of the retina in the affected eye was compared to the concurrent eye before and after laser. Patients were followed up monthly with repeat Oxymap scans for a period of 4 months, when final images were taken. These were analysed and set against parameters such as visual acuity and retinal thickness. Patients with bilateral DME and other co-morbidities were excluded from the study.
Data was collected from 22 patients at baseline, 16 male and 6 female. In 60% of cases the left eye had laser therapy, and in 40% the right eye. Age of cohort ranged between 29 to 81years. Average central retinal thickness (CRT) in the affected eye at baseline was 302μm, with average normal thickness of 259μm. After 4 months CRT in the treated eye reduced to 260μm. Macular arteriole oxygen (MAO) saturation of the healthy eye was 92.4±3%, with mean venous oxygenation (MVO) of 57±6%. Whereas the eye with DME had average baseline MAO of 93%±4 and MVO of 65%±4 pre-laser. Post laser MAO increased 96%±3 and MVO to 66±3%.
Results show that that initially MVO increases greatly due to DME, but post laser CRT reduced over the 4 months in the effected eye. We also found MAO improved post laser. It is postulated that diabetic retinopathy affects oxygen metabolism. Due to an auto regulatory response the eye shunts oxygen away from ischemic areas of the retina to larger vessels, thus in DME oxygenation increases in venous circulation. Laser therapy reserves this change and increased oxygenation causes vessel constriction, lower intravascular pressure and reduced edema by sterlings law.
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