Regional Blood Flow in the Myopic Chick Eye during and after Form Deprivation: a Study with Radioactively-labelled Microspheres

Abstract

The purpose of the present study was to determine the regional blood flow in the myopic chick eye during and after short-term monocular form deprivation. Chicks were monocularly form-deprived by covering one eye with a translucent occluder for 7–10 days. The anterior chamber–lens distance, the vitreous chamber length and the axial length of the eye were measured by ultrasonography, the equatorial diameter was measured with calipers and the size of the eye was estimated by weighing. The regional blood flow in the eye was determined with radioactively-labelled microspheres in three groups of animals: a group of chicks wearing an occluder (n=10), a group of chicks in which the occluder was removed 7 or 24 hr prior to the blood flow determination (n=9), and a group of age-matched control chicks without occluder (n=9).Monocular form deprivation increased the axial length 0.64±0.06 and 0.56±0.09mm compared to the contralateral control eye in the two groups of chicks wearing an occluder (P<0.001). Both the equatorial diameter and the weight of the eye increased significantly (P<0.001). Removal of the occluder tended to reduce the difference in the vitreous chamber length during the first 24hr. There was no statistically significant difference in the blood flow of the anterior uvea, choroid, pecten or the sclera between the form-deprived and contralateral control eyes (P>0.05, n=10), but when comparing to the control group, the blood flow was significantly (P<0.05) reduced in the choroid of the occluded eye. A similar tendency was found in the anterior uvea. When the blood flow was measured 7–24hr after the removal of the occluder, a marked increase was found in the blood flow of the choroid of both eyes compared to the situation during occlusion (P<0.001), and to the control group (P<0.05). In the pecten a significant (P<0.05) increase of the blood flow in comparison to the situation during occlusion and the control group was detected after removal of the occluder, and a similar change was found in the contralateral control eye, but it did not reach statistical significance. In the anterior uvea and sclera the blood flow was also significantly (P<0.05) or almost significantly increased after removal of the occluder in both eyes. The arterial blood pressure was 79±2, 88±2 and 99±5mmHg in the control group, the group with monocular occlusion, and the group in which the occluder was removed, respectively.Thus, monocular form deprivation in the chick reduced the choroidal blood flow, and a similar tendency was found in the anterior uvea. However, there was no statistically significant difference in blood flow between the form-deprived and contralateral control eyes. Removal of the occluder increased the blood flow in all tissues, notably the choroid and pecten. Generally the changes in blood flow seemed to be bilateral, despite monocular occlusion.