Growth of the human eye lens

Abstract

Purpose: To analyze human lens growth from the accumulation of wet weight as a function of age.

Methods: Wet weights were assembled for over 1,100 human lenses, ranging in age from 6 months prenatal to 99 years postnatal, and were examined using various growth models. Initially, prenatal and postnatal data were examined separately, to determine the growth modes and then all data were fitted to a single equation.

Results: Variations in weights due to tissue handling procedures and the unavailability of statistical data for averaged sets precluded the use of >500 values in the present analysis. Regression of age on log lens weight for the remaining 614 lenses indicated that, unlike other species, human lens growth appears to take place in two distinct phases. It was found that asymptotic growth during prenatal life and early childhood generates about 149 mg of tissue in a process, which can be modelled with a Gompertz function. Soon after birth, growth becomes linear, dropping to 1.38 mg/year, and this rate is maintained throughout the rest of life. The relationship of lens wet weight with age over the whole of the lifespan could best be described with the expression, W=1.38A(b) + 149exp;[exp;(1.6-3A(c))], where W is lens weight in mg, A(b) is postnatal age in years and A(c) is the time since conception in years. Comparison of 138 male and 64 female lenses indicated that there was no statistically significant difference between male and female lens weights in the linear (adult) growth mode.

Conclusions: Human lens growth differs from growth in other species in that it occurs in two distinct modes. The first follows a sigmoidal relationship and provides an initial burst of rapid growth during prenatal development with an apparent termination at or shortly after birth. The second growth mode is linear, adding 1.38 mg/year to lens wet weight, throughout life. Because of the variability in available lens wet weight data, further studies, preferably using lens dry weights or protein contents, will be required to establish precisely when the transition from one growth mode to the other occurs. In contrast to previous reports, it was concluded that, like other species, there are no gender differences in human lens weights.

Figure 1

Growth of the human lens. Human lens wet weight plotted as a function of age since conception. Data shown represent >1,100 lenses (open circle), obtained in the author's laboratory and from the literature. The 614 points retained for the present analyses are shown as filled circles.

Figure 2

Determination of growth mode. Regression of averaged lens wet weights on log Age for kangaroo (A) and human (B) lenses.

Figure 3

Modelling pre- and postnatal human lens growth. Best fits of the data for (A) 96 prenatal and early postnatal lenses using the Gompertz relationship (Wet weight = 149exp^[-exp^(1.6-3A_c)]; R²=0.96) and (B) 523 postnatal lenses, aged over 3 years, using a linear relationship (Wet weight=1.38A_b + 149; R²=0.96).

Figure 4

Modelling total human lens growth. Human lens wet weights, averaged for each age, with the best fit of all data according to the equation, Wet weight=1.38A_b + 149exp^[-exp^(1.6-3A_c)].

Figure 5

Gender and lens growth. Human lens wet weights for 138 adult male (green filled circles) and 64 adult female (blue filled circles) lenses. Best fits of the data were obtained with Wet weight=1.35A_b + 145 (R²=0.73) for males and 1.34A_b +146 (R²=0.72) for females. The line of best fit obtained with all postnatal lenses (Wet weight=1.38A_b + 149; Figure 3B) is included for comparison.