AXIAL DIMENSION OF THE HUMAN CATARACTOUS LENS

Objective: To determine the axial thickness of the human cataractous lens and analyze the effect of age and axial length on its thickness. Method: The axial thickness of the human lens was measured ultrasonically with immersion technique A-scan at 1641 m/s in 600 cataractous eyes immediately before cataract surgery for visual rehabilitation. The axial length was similarly measured but at 1555 m/s. Results: The mean (+/- SD) thickness for all eyes in patients aged from 19 to 97 years was 4.63 (+/- 0.68) mm, with a mean age of 69 (+/- 12) years and a mean axial length of 23.65 (+/- 1.28) mm. The thickness of the cataractous lens was directly proportional to age, with a mean of 3.78 (+/- 0. 2 1) mm in the third decade and a mean of 5.03 (+/- 0.46) mm in the 10th decade. Using one-way analysis of variance, the differences were statistically significant (P=.0002). The thickness of the lens was inversely proportional to the axial length of the eye (P < .003). The mean thickness was 5.03 (+/- 0.63) mm in eyes with axial length of less than 22 mm and 4.24 (+/- 0.58) mm in eyes with axial length of 27 mm or more. Eyes in patients younger than age 6 5 years (158 eyes) had a mean axial length of 24.08 (+/- 1.53) mm, eyes in patients aged from 65 to 75 years (252 eyes) had a mean axial length of 23.67 (+/- 1.19) mm, and eyes in patients older than age 75 years (190 eyes) had a mean axial length of 23.26 (+/- 1.03) mm. The differences were statistically significant using analysis of variance (P<.0001). Conclusions: The data confirm the fact that the lens thickens with age, at least in cataractous eyes. Axial length was shown to have an emmetropizing effect on lens thickness, being more optically powerful (thicker) in hyperopic eyes. These values are useful in determining average sound velocities for use with ultrasound A-scan instruments for measuring the axial length of the eye. Patients with axial myopia are more likely to develop cataracts at an earlier age than those with shorter axial lengths.