hereabove as illustrated in fig1 the diffusion chamber 20 s of this device 10 s is specifically sized and shaped such that it may be positioned within a subconjuntival pocket which has been surgically formed in one superior quadrant of the eye between the locations at which two 2 adjacent rectus muscles rm attach to the ocular bulb ob e g between the attachment point ap of the lateral rectus muscle and the attachment point ap of the superior or inferior rectus muscle the width w 1 of that portion of the diffusion chamber 20 s which resides posterior to the attachment points ap of the adjacent rectus muscles rm between which the device 10 s is implanted is wider than the distance d between those muscle attachment points ap preferably the width w 3 of that portion of the diffusion chamber 20 s which resides anterior to those attachment points ap of the adjacent rectus muscles rm is also wider than the distance d between those muscle attachment points ap the portion i e the u201c inter muscular u201d portion of the diffusion chamber 20 s which resides between the attachment points ap of the adjacent rectus muscles rm has a width w 2 which is at least slightly narrower than the distance d between those muscle attachment points ap as a result when the device 10 s is implanted in the position shown in fig1 it will be prevented from migrating in either lateral direction ld 1 ld 2 by the.