Distribution and regulation of the optic nerve head tissue PO2

We investigated the distribution and regulation of the optic nerve head (ONH) tissue partial pressure of oxygen (PO2) under various stimuli and the role of the nitric oxide in the ONH circulation. Tissue PO2, was measured using double-barreled recess microelectrodes in the intact eyes of miniature pigs during normoxia, hyperoxia, hypoxia, variations of systemic blood pressure, and after inhibition of the endothelial nitric oxide synthesis by the administration of nitro-L-arginine. Measurements were performed in front of the ONH at intervascular and juxta-arteriolar areas and at a depth of 50 and 200 mu m within the ONH at the center and tie rim. During normoxia, PO2 was heterogeneously distributed in the ONH, higher close to the arterioles than in intervascular areas. Hyperoxia induced a significant increase of juxta-arteriolar tissue PO2, while ill intervascular-areas no change was noticed. Hypoxia did not modify intervascular tissue PO2 at 200 mu m depth within the ONH. Variations of the systemic blood pressure did not induce any significant change in ONH tissue PO2,. Similarly, no modification was noticed after the administration of nitro-L-arginine. There is a remarkable autoregulatory capacity of the ONH circulation that may compensate for parameters such as hyperoxia, hypoxia, and variations of the systemic blood pressure. Endothelially derived nitric oxide inhibition does not modify tie ONH tissue PO2, probably because the tissue PO2 is stabilized by compensatory regulation. (C) 1997 by Elsevier Science Inc. All rights reserved

Advice against smoking is not effective in patients with Graves' ophthalmopathy

Advice against smoking is one of the means frequently used in the management of patients with Graves’ ophthalmopathy (GO). The objective of this study was to prospectively evaluate the efficacy of such advice. The study was performed at a referral centre. Eighty-five smokers out of 102 consecutive patients with GO, who were examined during a 1-year period, were included in the study. Severity of the disease, smoking history, and the results from a patients’ self-assessment questionnaire were recorded. The behavioural intervention consisted in a standardized 2-min message from the attending ophthalmologist strongly advising each patient to quit. The main outcome measure was smoking cessation during the 1-year follow-up period. None of the 85 smokers reported smoking cessation either during the follow-up visits or at the end point of the study. The results of our study show that advice against smoking is not effective among patients with GO. Specifically designed intervention programmes may be necessary and should be evaluated in a controlled trial

Hypothyroidism and glaucoma. A study of 100 hypothyroid patients

PURPOSE: To determine whether glaucoma is associated with hypothyroidism, as has previously been suggested. METHODS: This is a cross-sectional study and a noncomparative interventional case series, One hundred consecutive patients with newly diagnosed hypothyroidism were referred for complete ophthalmologic examination, including automated perimetry and examination of the optic disks, to identify the presence of glaucoma. After correction of the hypothyroidism, reexamination was performed. RESULTS: No patient had glaucoma and no correlation was found between intraocular pressure and either thyroid stimulating hormone or free tri-iodothyronine. No statistically significant difference was found between intraocular pressure levels before and after treatment of the hypothyroidism. CONCLUSION: This study does not demonstrate an association between hypothyroidism and glaucoma. (Am J Ophthalmol 2001;131:126-128. (C) 2001 by Elsevier Science Inc. All rights reserved.)