THE DEVELOPMENT OF INVOLVED TISSUES

As an introduction to a study of congenital glaucoma, it is essential to consider the structural changes that occur during embryonic and early life in the anterior ocular tissues. There are two periods of relatively rapid ocular growth after birth, separated by a time when little change is found. The first period is during the first few years of life, and during this time it is the area in front of the muscle insertions that grows. This period and the tissues affected during it correspond with the time and site of the main development of hydrophthalmia.

The second period is from about puberty until the early twenties. During this time the tissues of the posterior segment are mainly affected, but the distance between the fovea and the optic disc remains the same as at birth. It is during this later period that the other common form of distension, viz. myopia, occurs, and the tissues growing then are those principally affected. If, later in life when growth is finished, hypertension occurs, the only part that can distend is the weakest part, viz. the lamina cribrosa. Medullation is complete during the first three weeks, and probably the lamina cribrosa is fully grown by then.

The sclera. In all species the anterior part of the sclera appears first and progresses farthest during embryonic life (Mann). The first sign of condensation of the outer sclera is found at the 48.0 mm. stage in that part which will later overlap the angle of the anterior chamber. At this stage condensation of the deep corneal layers is relatively advanced and a deep band runs towards the equator. Scleral condensation is more advanced by the 65.0 mm. stage, but the sclera is still thinner than the cornea.

The greater likelihood of scleral distension during the first two decades is suggested in the following paragraph. “At birth the sclera is immature and is lacking particularly in elastic fibres and until the beginning of the third decade it is particularly poor in this tissue. From then on, until the age of sixty years, this increases greatly” (Krekler, 1923).