Melatonin is a product of the amino acid tryptophan in the pineal gland. Once synthesized, the specific mechanisms governing the release of melatonin from the pineal gland and its functions are largely unknown. Besides its regulatory role in circadian rhythms in mammals, because of its widespread subcellular distribution, melatonin contributes to the reduction of oxidative damage in both the lipid and the aqueous environments of the cell. This postulate is widely supported by the experimental observations showing that melatonin protects lipids in membranes, proteins in the cytosol, and DNA in the nucleus and mitochondria from free radical damage. Melatonin thus reduces the severity of disease conditions where free radicals are implicated. The direct free radical scavenging effects of melatonin are receptor independent. It has recently been shown that it has an ability to scavenge free radicals, including hydroxyl radicals, hydrogen peroxide, peroxyl radicals, singlet oxygen and nitric oxide (NO) and peroxynitrite anion. An excessive amount of NO, a free radical which is generated by the inducible form of NO synthase, is known to cause cytotoxic changes in cells. Hence, NO synthase is considered a pro-oxidative enzyme, and any factor that reduces its activity would be considered an antioxidant. Recent studies have shown that melatonin inhibits the activity of NO synthase, beside its NO and peroxynitrite scavenging activity. Thus, inhibition of NO production may be another means whereby melatonin reduces oxidative damage under conditions, such as ischemia-reperfusion, sepsis, etc, where NO seems to be important in terms of the resulting damage.

Purpose. To assess the macular, choroid, and peripapillary nerve fiber layer thickness (RNFL) in Behçet's disease (BD) patients with and without ocular involvement by means of optical coherence tomography (OCT) and compare these findings with healthy controls. Design. Eighty patients with BD and 40 healthy controls who were followed up at the Uveitis and Retina Clinic of the Kayseri Research and Education Hospital in Turkey were enrolled in this prospective study. Subjects and Controls. The patients with BD were divided into two groups according to the presence of ocular involvement. Group 1 consisted of 40 eyes of 40 patients with ocular involvement and group 2 consisted of 40 eyes of 40 patients without ocular involvement. Methods. All of the patients and controls underwent macular, choroid, and peripapillary nerve fiber layer thickness analysis with Spectralis domain OCT (Spectralis OCT Heidelberg Engineering, Dossenheim, Germany). Main Outcome Measures. The differences in macular, choroid, and peripapillary nerve fiber layer thicknesses between groups were analyzed statistically. Results. Macular thickness was thinner in patients with BD than in the control group; this result was statistically significant (P = 0.05). There was no statistically significant difference in thickness between RNFL analysis of the patients with BD and control subjects. However, the BD patients with ocular involvement had statistically significant thinning in RNFL compared with BD patients without ocular involvement. Although the choroid was thicker in patients with BD than in the control group, it did not reach a statistically significant level (P = 0.382). Conclusions. BD with ocular involvement may be associated with decreased macular and RNFL thickness measured with spectral-domain OCT.

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The data from our study emphasize that age, but not gender, is the main determinant of ECD.