Studies on the relationship between vitamin B12 and cyanide in the aetiology of tobacco amblyopia and related conditions

Epidemiology

Chisholm, Ian A

University:University of Glasgow

关键词: Epidemiology;   

Others  :  http://theses.gla.ac.uk/72966/1/10647294.pdf

来源: University of Glasgow

【 摘 要 】

The association between tobacco smoking and a form of amblyopia has been recognised for over one hundred years. The disease characteristically affects elderly men affects both eyes unequaly and does not progress to complete blindness. The patient typically has poor vision both for near and distance, centro-caecal scotomas larger for colour than white targets in the field of vision and an acquired colour blindness of each eye. Recent additions to the world literature on the subject have postulated an abnormality of the vitamin B12 cyanide relationship as being the underlying aetiological feature and that tobacco amblyopia is a member of a group of diseases which includes Leber's hereditary optic atrophy, the optic neuropathy of pernicious anaemia, the optic neuropathy of diabetes and some forms of tropical nutritional amblyopia, This study reports the findings in 65 patients diagnosed as suffering from tobacco amblyopia which have been collected over a period of three years in the Western Regional Hospital Board area. The patients showed a marked reduction in visual acuity by the time they have reported for treatment. It was found that the duration of symptoms did not influence the initial visual acuity but those patients who came under treatment early had the greatest improvement in visual acuity. The Farnsworth Munsell Hundred Hue test was chosen as one of the major parameters evaluating new patients prior to and whilst on therapy. As the Hundred Hue test error scores obtained in the untreated tobacco amblyopes were higher than previously recorded analyses, an investigation to establish the validity of such error scores was carried out. It was found that with error scores above 600 it was better to take the average of several readings rather than the result of one test. In untreated tobacco amblyopia the Farnsworth Munsell Hundred Hue test result correlated well with visual acuity, and tended to do so with patient ago. There was no significant correlation between the Farnsworth Munsell Hundred Hue test result and duration of symptoms, serum vitamin B12 concentration, or serum folate concentration. The incidence of the disease increases in a positive manner with age, reaching a peak in the 70-80 years age group. The mean duration of symptoms prior to seeking advice was 6 months and it was found that age played no part in determining when a patient presented for treatment. Patients were examined for evidence of avitaminosis B12 by having serological estimations of vitamin B12 and estimations of vitamin B12 absorption carried out. Serum vitamin B12 concentrations were found to be lower in tobacco amblyopia than in the general smoking and non-smoking populations. The serum vitamin B12 concentration correlated well with tobacco consumption, the Schilling test less well so, and the Xylose absorption test poorly so. In the untreated tobacco amblyope the serum folate concentration tended to correlate with tobacco consumption. Patients with tobacco amblyopia in the presence of frank Addisonian Pernicious Anaemia exhibited higher serum folate concentrations than those patients without pernicious anaemia. As cyanide is volatile investigations into its metabolism is to be directed to its detoxication products namely thiocyanate. Although tobacco amblyopes smoke more tobacoo than non-amblyopic subjects, their serum thiocyanate concentrations are lower than those of non-amblyopic smokers and tend to resemble the concentrations found in non-smokers. These reduced concentrations, on treatment with hydroxocobalamin, tend to revert towards the higher concentrations found in the non-amblyopic smokers. Associated with this rise in the blood there is an increased excretion of thiocyanate in the urine. A significant negative correlation was found to esixt between the plasma cyanide and the serum vitamin B12 concentrations and between the plasma thiocyanate and the renal clearance of thioeyanate in untreated tobacco amblyopia.(Abstract shortened by ProQuest.).