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The purpose of this study was to investigate choroidal perfusion in glaucoma, using histological and angiographic techniques.We examined the choroidal vasculature in clinicopathological slides from 25 cases of primary open-angle glaucoma, five cases of optic atrophy, and 18 normal eyes. We measured choroidal thickness at fixed distances from the disk margin with light microscopy. Using a quantitative computer image analysis system, we established the depth of all vessels and the best fitting diameter and width-to-length ratio for each vessel in three pairs of eyes. Separate statistical analyses were done on the parapapillary area and the whole choroid. We compared standard fluorescein angiographic measures to peak choroidal filling time in a further 78 glaucoma and 84 normal eyes.Choroids were significantly (∼50 μm) thinner in glaucoma than in normal or optic atrophy irrespective of fundal position. Vessel frequency and mean diameter, relative to normal, showed greatest decrease near the choriocapillaris. Peak choroidal filling was the only fluorescein angiographic measure that was significantly delayed in glaucoma irrespective of age.Reduced choroidal thickness in primary open-angle glaucoma is primarily due to loss of the innermost choroidal vessels. Overall size decreases without significant flattening. These changes are not seen with optic atrophy alone and may be correlated with the delayed choroidal perfusion seen in fluorescein angiography.