Large doses of vitamin A, more than 33,000 IU or 10 mg retinol, can cause hair to fall out. Check for the dose of the vitamin A preparation you are taking. If you are not taking so much, then the hair loss is probably from another cause and you should see a physician about it. Weak eyesight can result from severe deficiency in vitamin A. If you eat a reasonably balanced diet, vitamin deficiency is unlikely to be the cause of your weak eyesight and that too should be evaluated by a doctor.