Human crystalline lenses were dissected from fresh donor eyes provided by the Banco de Ojos para Tratamientos de la Ceguera (Barcelona, Spain), after the removal of the corneas for transplantation (mean postmortem time 46 ± 24 hours). In a few cases, they originated from the Cornea Bank Amsterdam (Amsterdam, The Netherlands). The research adhered to the tenets of the Declaration of Helsinki for research involving human tissue. A total of 26 lenses aged 12 to 103 years were thus obtained, fixed in 3.6% buffered formaldehyde, embedded in paraffin, sagittally sectioned, and stained for collagen with periodic acid-Schiff (PAS). Images of the sections passing approximately through the lens poles were taken through a 25× objective with a digital camera mounted on a photomicroscope (Carl Zeiss, Oberkochen, Germany;
Fig. 2 ).
For each lens, between 80 and 100 serial microscopic images were captured along the section perimeter at a 1200 × 1600-pixel resolution, and printed on A4 paper, resulting in a magnification of approximately 780 times, with a total lens size on paper of approximately 3 × 7.5 m. The actual capsular thickness measured between 12 and 120 pixels in each image, equaling 2 to 20 mm on print. We considered digitally mounting the images for each lens. However, this proved impractical, given the huge size of the resultant files (approximately 980 megapixels). Instead, the complete circumferential series of prints for each lens were registered, aligned, and mounted on the floor of an appropriately sized room. The capsule thickness was measured with a rule on the prints every 20 cm, equaling every 250 μm along the lens perimeter. Care was taken to distinguish the capsule proper from the zonular lamella and zonular remnants and to include only the former in the measurements.
The thickness data thus obtained were normalized to standard positions (p) in the lens perimeter, with p0 conventionally assigned to the anterior lens pole, p100 to the equator, and p200 to the posterior pole
(Fig. 3) . For the anterior and posterior portion of the lens, the data from both lateral halves were averaged independently for each lens and fitted to a sixth-order polynomial equation as a function of position along the perimeter.
For statistical analysis of the influence of age, we considered three groups of equal size (n = 7): group A, still with accommodation and a mean age of 36 years (30, 33, 33, 36, 40, 40, and 42 years); group B, presbyopic and a mean age of 65 years (54, 58, 65, 68, 69, 70, and 74 years); group C, advanced age group with a mean age of 92 years (85, 85, 89, 91, 94, 97, and 103 years). The data were evaluated with two-way ANOVA, followed by orthogonal comparison. The significance level was set at 0.05.