The document discusses several common eye defects: myopia (nearsightedness) which causes light to focus in front of the retina, hypermetropia (farsightedness) which causes light to focus behind the retina, presbyopia which causes blurred near vision due to a thickening and loss of flexibility of the lens usually beginning at age 40, and cataracts where the lens becomes progressively cloudy resulting in blurred vision and potentially total vision loss if not corrected through surgery.