The Facility of Aqueous Outflow Calculated From the Rate of Fall in Applanation Pressure After Intravenous Acetazolamide in Man

Abstract

The fall in applanation pressure after intravenous acetazolamide was followed in seven patients with normal intraocular pressures and in five patients with monolateral glaucoma. The experimental pressure decay curves were compared with similar curves calculated on the basis of different values for the facility of outflow of aqueous humour, and on the assumption of a prompt shift in the rate of aqueous secretion from the preinjectional level to a stable acetazolamide dominated level. The experimental decay curves resembled the matching, calculated curves. The outflow facilities read from the latter averaged 0.4 (range 0.2-1.0) in the normal eyes, and 0.1 (range 0.05-0.15) in the glaucomatous eyes. These results strongly indicate that the above-mentioned assumptions are justified, and that the method allows a simultaneous estimation of outflow facilities in the right and left eye at pressures below the usual. W e find that a study of the shape of the decay curves in glaucomatous eyes might give a clue to the problem of whether the hindrance to the drainage of aqueous humour in the diseased Schlemm system shows reversibility under the decompressing effect of the falling intraocular pressure.

The Immediate Response in Applanation Pressure to Intravenous Acetazolamide in Primary Glaucomas and Glaucoma Suspects

“…This is an acceptable value for sitting persons which, furthermore, harmonizes well with an average inhibitory effect of acetazolamide on the aqueous secretion of 50"/0 in a series of normal eyes (Nissen & Hoppe 1974).…”

“…Another point which tends to make the estimate of the facility of outflow inaccurate is that the reference curves are calculated on the basis of a single, 'normal' ocular rigidity (0.0215); in spite of the fact that it is well known that this parameter varies somewhat from eye to eye, and in the same eye changes with the intraocular pressure and volume (Duke-Elder 1968, Thorburn 1973). Nor has 'pseudofacility' (BBr6ny 1963, Kupfer 1973) been taken into account in the reference curvesthese were calculated on the assumption that the rate of the (acetazolamidedominated) secretion of aqueous humour was constant during the pressure decay (Nissen & Hoppe 1974). In one case (Fig.…”

“…Generally, the test was carried out on untreated eyes, in principle as described by Nissen & Hoppe (1974), and was combined with a routine examination including visual acuity, gonioscopy, ophthalmoscopy, slit lamp examination, and examination of the visual fields on the tangent screen.…”

“…The material consists of four patients with narrow-angle glaucoma and 20 patients with open angles, pressures above 22 mmHg (measured on several occasions), and in some of the cases, glaucomatous optic discs and visual field defects (see Results). Generally, the test was carried out on untreated eyes, in principle as described by Nissen & Hoppe (1974), and was combined with a routine examination including visual acuity, gonioscopy, ophthalmoscopy, slit lamp examination, and examination of the visual fields on the tangent screen.…”

“…In the present studies the intraocular pressure of both eyes of the sitting patient are followed by alternating measurements with a Goldmann applanation tonometer, and it seems that the shape and steepness of the acetazolamide-induced 'deflation curves' obtained in this way relate various parameters from which a picture of the state of the aqueous circulation appears (Nissen & Hoppe 1974). In the following, a general description of how the pressure curves have been evaluated is combined with a presentation of the results obtained so far, in primary glaucomas and glaucoma suspects.…”