To determine the visual results of conservative (non- surgical) therapy, we reviewed all our patients with genetic ectopia lentis, with and without Marfan's Syndrome. Of these patients, 50% had significant permanent (or potentially so) ametropic functional amblyopia (visual acuity 20/50 to 20/200) in spite of good conservative management. This was especially true (100%) if the amount of lens dislocation was such that the lens edge was approaching the center of the pupil (vision still primarily phakic). The worst amblyopia was noted when the lens was still covering the visual axis and the lens edge was 1.3 mm from the center of the pupil (range of 0.3 to 2.3 mm). With regard to the most serious complication of ectopia lentis and its treatment, retinal detachment, when it occurred in our patients it was more strongly related to axial high myopia than surgery, per se. Since the axial high myopia which characteristically develops in ectopia lentis is probably the result of the amblyopia or the amblyopiagenic optics of ectopia lentis, lentectomy may be indicated early in this condition, before the axial high myopia develops, to prevent both axial high myopia and the attendant risks of retinal detachment as well as functional amblyopia. If the refractive error cannot be corrected well and the resultant ametropic amblyopia does not respond to conservative management, early surgery should be considered. If the lens is subluxated so that the edge of the lens approaches to within 0.3 to 2.3 mm of the center of the pupil (with best correctable vision still phakic), this is highly probable.