Aqueous humor dynamics in man as studied by oral fluorescein

Araie, M.; Sawa, M.; Nagataki, S.; Mishima, S.

Japanese Journal of Ophthalmology 24(4): 346-362


ISSN/ISBN: 0021-5155
Accession: 004776337

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A new method was developed for computing the transfer coefficient by flow (kfa) and by diffusion (kdpa) of fluorescein in the anterior chamber of an individual after oral administration of fluorescein. Absorption, metabolism and excretion of fluorescein were studied to substantiate this method. After ingestion of 10% fluorescein solution at a dose of 5 mg/kg of body wt under fasting conditions, its concentration in the blood reached the maximum within 1 h and decreased subsequently. Fluorescein was converted rapidly to glucuronide, the glucuronidation ratio in the plasma ultrafiltrate reached a maximum level of 96% in 5 h. Fluorescein was rapidly excreted into urine, the elimination rate constant was 0.18/h from blood and 0.25 hour .alpha.1 from urine. All oral fluorescein apparently was absorbed in a few hours and excreted almost completely in 48 h. The ratio of fluorescein binding to plasma protein averaged 82.5%. To the time courses of the changes in the apparent fluorescein concentrations in the plasma ultrafiltrate and aqueous humor, a transfer equation formulated by Kinsey and Palm was fitted by a weighted least squares method using a computer technique. Assuming the fluorescence ratio of the posterior chamber aqueous to the anterior chamber aqueous was 0.32, calculations were carried out yielding average values for kfa 0.69 .+-. 0.14 .times. 10-2/min (mean .+-. SD) and for kdpa 0.68 .+-. 0.37 .times. 10-3/min in 20 normal eyes. The influence of glucuronidation and the fluorescein exchange with the cornea were considered. kfa was underestimated and kdpa overestimated; the values after correction for these influences were 0.90 .times. 10-2/min for kfa and 0.45 .times. 10-3/min for kdpa. This method is safer than the method of i.v. injection and gives kfa and kdpa separately in an individual with reasonable accuracy. The method seems suitable for comparison of the parameters in both eyes of an individual and to study effects of various drugs.