A quantitative study of the prenatal development of the aqueous outflow system in the human eye

There is a multiplicity of theories on the development and differentiation of the human iridocorneal angle. Many have arisen from the need to explain the pathogenesis of primary infantile (congenital) glaucoma or other related developmental disturbances. The present study, which is the first light and electron microscopical morphometric analysis of human fetal eyes, was designed to determine the nature of the changes in various tissue components during trabecular anlage formation and differentiation (between 12 and 22 weeks of gestation). The results demonstrate that the trabecular anlage doubles in cross-sectional area during this period. However, when circumferential growth is considered there is in fact a threefold increase in anlage volume. Cell density in sections decreases over the 10-week period, as does the number of cells per unit volume. However, employment of stereological analysis together with corrections for volume changes revealed a two to threefold increase in absolute number of cells per eye (2.8 x 10(5) to 7.5 x 10(5)). Relative and absolute volume data on the four major constituents of the trabecular anlage show that extracellular matrix increases in the most significant and predictable fashion (360% in absolute volume), with the increase in intertrabecular spaces being more variable (200%). The findings are discussed in relation to previous theories of trabecular meshwork development.