| Objective: Diabetic macular edema (DME) is the major cause of visual impairment and visual loss among diabetic patients. The beneficial effects of laser photocoagulation for DME have been demonstrated. Visual is improved and the macular edema is reduced. However, the exact physiologic mechanism of laser photocoagulation is still unknown. A series clinical trials have shown the major mechanism is that laser photocoagulation improves retinal oxygenation. This study was designed to analyse the change of retinal vessel diameter, aimed to investigate retinal oxygenation after laser photocoagulation . On the other hand ,we measure changes in retinal function before and after laser photocoagulation ,especiall in the macular, to assess the effects of photocoagulation, in order to provide valuable theories for laser photocoagulation for DME. Methods: 1 48 eyes of 30 patients meet eligility criteria were enrolled in the study, and were test for the most accurate corrected visual. 2 Fundus fluorescein angiography (FFA): As the standard of angiography at the 5th minutes, observed the retina pathological changes and extent of macular edema. The DME was confirmed by fluorescein angiography. On the basis of fluorescein angiography, all cases with DME were classified into 3 group: local macular edema, diffuse macular edema and cystoid macular edema. 3 we selected 30 eyes of 18 patients with macular grid photocoagulation treatment. The diameter of retinal arterioles, venules, and their macular branches was measured before and after macular grid photocoagulation by Heidelberg retinal angiograph(HRA). 4 Multifocal electroretinogram (mfERG) test: RETI Scan multifocal ERG version 3.15 system was used. 61 equal-size hexagonal black were used and the recordings were evaluated. The elements were flashed on and off accordings to a pseudorandom sequence (m-sequence). Eight segments were recorded, with each segment lasting 47 seconds in duration. The first-order kernel (FOK) reponses were used to calculate amplitude densities (nv/deg2) and latencies (ms) in 61 retinal locations on a central visual field of about 31 degree. The first negative wave (a-wave) and first positive wave (b-wave) were measured. The 61 traces were grouped into 3 areas: fovea, macular, perimacula from center to periphery. 5 Laser photocoagulation treatment: Multiple wave length Krypton laser was used. Krypton yellow laser was used for macular focal photocoagulation. The patients with focal macular edema were treated in focal treatment and the patients with diffuse leakage were treated in the grid pattern.6 Follow-up: Follow up were performed at 1st, 3rd, and 6th month respectively after laser treatment. Visual acuity and fundus examination were tested each time. Fundus fluorescein angiography and mutifocal electroretinogram should be performed at the 3rd month. Rsults: 1 Compared with pre-treatment visual acuity improved at the 1st,3rd and 6th month after laster treatment , and macular edema absorbed in most cases at 3rd month after laser treatment. 2 After macular grid photocoagulation for DME, the diameter of the superotemporal and inferotemporal arteriolar and venular showed a significant constriction. And A significant constriction of superotemporal and inferotemporal arteriolar and venular branches was observed. 3 Compared with the control group, a-wave and b-wave amplitude densities at the fovea, the macula ,and paramacular of DME retina attenuated(p<0.01). The latency of a-wave at fevea and macula were longer(p<0.05). the latecy of a-wave and b-wave at paramacular were longer.(p<0.01) 4 The amplitude density of a-wave at fovea of local macular edema was statistically larger than that of diffuse macular edema(p<0.01) and cystoid macular edema (p<0.01). There were statistical difference in b-ware amplitude density of a-ware and b-ware at macular of local macular edema (p<0.05,p<0.01) and cystoid macular edema(p<0.01, p<0.01). There was statistical difference in a-ware amplitude dencity atparamacular in focal macular edema and cystoid macular edema (p<0.05), and there was statistical difference in b-ware amplitude density at paramacular among three groups. There were no statistical difference in a-ware latency and b-ware latency among three groups. 5 The amplitude density of a-ware and b-ware at fovea were statistically larger than that before macular grid photocoagulation treatment.(p<0.01,p<0.05) The latency of a-ware at fovea were statistically decreased(p<0.05) There was no statistical difference in the latency of b-ware at fovea between before and after laser treatment.(p>0.05). Compared with pretreatment, a-ware amplitude density of fevea was larger.(p<0.01).and b-ware amplitude density of fovea was no statistical change. The latency of a-wave and b-wave at macular were statistically longer after laser photocoagulation.(p<0.01). There were statistically longer in the latency of a-wave and b-wave at paramacular after laser photocoagulation treatment(p<0.05). 6 A statistically significant correlation was founded between the most accurate corrected visual and amplitude dencity of a-wave and b-wave at fovea.(r=0.612 p<0.01,r=0.489 p<0.05) Conclusions: 1 The macular grid photocoagulation for DME improves oxygenation of the inner retina. Increased oxygenatior causes retnal vessel constriction, especially the...
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