Diabetes mellitus (DM) is a complex multifactorial disease, often accompanied by progressive retinopathy and vision loss. With the development of social conditions and improvement of the living standard DM has become the main growing health problem in Europe, a problem of all ages in all countries that puts in danger at least ten milion European citizens. Diabetic retinopathy (DR), as one of the worst DM complications, is leading cause of blindness in fit for work adults of the developed western world. Applying retinal laser photocoagulation (LP) it is posible to prevent blindness, which has been proved, beyond doubt, by several multicentered randomized studies. A favourable impact of retinal lp in dm has been known for approximately 30 years. However, along with this favourable impact, retinal LP involves a number of side-effects complications. One of the most significant of them is development, or deterioration of the existing macular oedema, leading to temporary or permanent impairment of visual acuity. The role of the oxidant stress in the mementioned complications is quite certain. This study aims at determining the state of antioxidant defense in diabetic patients, as well as assesing the oxidant stress role in the macular oedema development after "scatter" LP. This prospective clinical study ivolves 90 subjects dividet into three groups: - 7 male and 23 female healthy subjects aged between 40 and 60 ( control group C1), - 15 men and 15 women suffering from DM type 1 and type 2, aged bettween 40 and 60, with no DR clinical symptoms, having HbA1c to 8% (control group C2), - 16 men and 14 women suffering from typ1 15 (50%) and type 2 15 (50%), with average DM duration of 12,7±2,05 years, aged between 40 and 60. All subjcts had clinical picture of severe nonproliferative diabetic retinopathy (NPDR), and are scheduled for "scatter" LP. "Full-scatter" retinal LP was applied with the number of burns N= 600-700, using 200-500μm size, with the power of 200-300 mW for 0,2 second duration. Widw-angle Mainster's WF panfundoscope was used. Visual acuity was tested just prior to, one day after, 7 days after and 30 days after retinal LP, using international tables at 5m. Optic fundus examination in mydriasis was carried out by Wide-angle Mainster's panfundoscope: just prior to, one day after, 7 days after and 30 days after retinal LP. Fluorescein angiography was applide, when needed, as supporting diagnostic test. Intraocular pressure (IOP) was taken prior to and one day after retinal LP using the applanation method. Venous blood was taken from the subjects suffering from DM with DR treated by LP, just before and 2 hours after standard LP. Venous blood was taken from subjects belonging to the control groups C1 and C2. The following antioxidans from plasma samples and erythrocyte lisate samples were tested: superoxide dismutase (SOD), glutation peroxidase (GPOD), total antioxidant status (TAS), catalase, transferrin, ceruloplasmin, hemopexin and haptoglobin. After applying the "scatter" retinal LP, 13 or 43,3% of the subjects either developed macular oedema or suffered from deterioration of the existing macular oedema; the differnce is significant (χ2=21,8; p=0,001). Immediately one day after LP tretment the mean value of the subjects' visula acuity worsened (0,40), as compared to the visual acuity prior to LP (0,47), the diferenc being significant (p=0,001). Seven days after LP the subjects' visual acuity mean value is firter worsened (0,41) as compared to the visual acuity prior to LP, with significant diference (p=0,002), that represents a direct consequence of a developed, or deterioration of the existing macular oedema. 30 days after LP there is a slight improvement of the subjects' visual acuity mean value (0,48), as compared to the visual acuity prior to LP, the difference not being significant (p>0,448). IOP mean values prior to and after LP show substantial differences (p=0,003) but not exceeding the limits. Concentrations of the tested antioxidans from plasma samples and erythrocytes lisate samples are significantly lowered in C2 subjects as compared to C1 subjects: SOD (p<0,001), GPOD (p=0,030), TAS (p<0,001), catalase (p=0,001), transferrin (p<0,001), ceruloplasmin (p<0.001), hemopexin (p=0,003), haptoglobin (p=0,173). Values in subjects with DR are also significantly lowered as compared to C1 subjects: SOD (p<0,001), GPOD (p=0,001), TAS (p<0,001), catalase (p<0,001), transferrin (p<0,001), ceruloplasmin (p<0,001), hempexin (p=0,002), haptoglobin (p=0,019). Values in subjects with DR were no significantly lowered when compared to C2 subjects. The difference in antioxidant values from plasma samples and erthrocyte lisate samples in subjects with severe DR was tested prior and after the "scatter" LP. Values of all tested antioxidants were lowered after LP in: ceruloplasmin (p=0.458), hemopexin (p=0.075) and haptoglobin (p=0470), and were significantly lowered in SOD (p=0,001), GPOD (p=0,001), TAS (p=0,001), catalase (p=0,001) and transferrin (p=0,001). Antioxidants values in C2 subjects, as well ac in diabetic patients with DR as a complication, were significantly lowered as compared to C1 subjects, indicating weakened antioxidant defence in patients with DM. Values in diabetic patients with DR as a complication, were not significantly lowered as compared to C2 subjects. Macular oedema represents a significant complication of "scatter" LP. Subjects' mean visual acuity on the first and seventh day after LP were significantly lowered as compared to the visula acuity prior to LP, as a direst result of aa developed, or deterioration of the existing macular oedema, with a slight improvement after 30 days. Antioxidant values in diabetic patients with DR were significantly lowered after "scatter" LP, as a direct consequence of the retinal oxidant stress caused by thermal treatment. Oxidant stress caused by produstion of free radicals (FR) and reactive oxidant species (ROS), most often by lipd peroxidation, directly or idirectly damages microvascular endote. Endotel damages necessarily lad to increased vascular permeability, finally resulting in macular oedema development. Assessing antioxidant reserves of the patient scheduled for "scatter" LP, it is possible to predict LP tretment inefficiency or risk factor, regarding macular oedema developments as a complication, possible therapeutic intervention with simple and safe antioxidants, such as vitamins C and E, would enable these susceptible patients to undergo to scheduled laser photocoagulation more effectively, simultaneosly suggested manifold LF procedure to these susceptible patients, but with less numbers of spots and decrease of power.