Effect of age on the morphology and optical quality of the avian crystalline lens

The effect of age on the avian lens was examined using White Leghorn chicke ns of Eve age groups: hatchling (n = 19), 7 day (n = 15), 34 week (n = 10), 2 year (n = 24), and 5 year (n = 25). The chick lens grows steadily up to 34 weeks of age, after which, the rate of growth slows down. During growth, average focal length of the lens becomes longer. However, no significant c hanges were noted between 2 and 5 year old lenses. An age related increase in average lenticular focal length variability (FLV) was observed, revealin g that the optical quality of the lens decreases with age. Scanning electro n microscopy demonstrated that: (1) the suture region of the lens becomes m ore diffuse and less precise with age: (2) the central regions of younger l enses are oblate spheroids, while order lenses become more apple-shaped; (3 ) individual lens fibres in the young lens are crescent-shaped, while older lens fibres are square-bracket-like in shape; (4) the edges of individual lens fibres become more jagged and irregular with age; and (5) the layering of lens fibres is more disorderly in older lenses, in contrast to the para llel and organized layering of fibres in young lenses. (C) 1999 Academic Pr ess.