Eye size of the premature infant around presumed term

Summary

Seventy-three premature infants were born at conceptional age 25–37.5 weeks (birth weight 728–2620 g) and examined ophthalmologically, including ultrasound oculometry, at conceptional age 36–54 weeks (mean 41.9 weeks). Axial length averaged 17.08 in girls (n = 33) and 17.38 mm in boys (n = 40).

With axial length on ordinate and conceptional age at examination on abscissa, the regression line was given by y = 12.40 + 0.116 × (r = 0.60). Using this measure for adjusting axial length to a 40 week value, the estimated mean term-value for girls became 16.90 mm and for boys 17.14 mm. This is close to previous results published for full-term infants, as reviewed for instance by Francois and Goes (1981).

Those having had signs of retinopathy of prematurity did not significantly differ from the rest of the sample except for a trend to more negative refractive values. Nine ROP girls had an adjusted 40 weeks axial length mean value of 16.75; in 10 boys with ROP it was 17.23 mm.

For the whole sample, thicker lenses and more shallow anterior chambers have contributed to the predominantly negative refractive values encountered. In most cases emmetropia or hypermetropia ensued, after weeks or months. Thus we are not dealing with the entity of myopia of prematurity in such cases.

As a consequence of the more foetal proportions of the eye, the marked correlation between axial length and refraction, so well-known from children and adults, could not be demonstrated in the present sample.

Summing up, the aim of the study is (1) to re-evaluate eye size in infants around term, and (2) to investigate the influence of short gestational age, low birth weight, and retinopathy of prematurity on eye size around presumed normal term. For the above purposes full-term infants are being included for comparison, but these results are not ready yet.

In ophthalmic literature there are indications of smaller eye size being a feature of children surviving the hazards of premature delivery (Fledelius, 1976, 1982).

Firstly, eyes with blinding cicatricial retinopathy of prematurity (ROP) are deep-set and small (Francois and Goes 1971; Bertenyi and Fodor, 1981). This is due to a combination of arrested growth and secondary involution. Many such eyes have axial lengths of 13–15 mm (Fledelius, 1988), which means a return to the size they had at the time of the premature birth.

Next, some infants show almost complete regression of their ROP, eventually to leave an eye with fair vision and ’myopia of prematurity’. Such eyes are shorter than expected from degree of myopia when compared to subjects of the same age with ordinary juvenile myopia (Fledelius 1976; 1977; Tane et al., 1979).

Finally, also seemingly normal eyes of low-birth weight children have shown features of arrested growth when compared to full-term controls, both at the age of ten years (Fledelius, 1976) and at follow-up 8 years later (Fledelius, 1982). This implies that premature birth as such may be regarded a trauma even for eyes that develop normally. Apparently, the exprematures never quite catch-up, a view at variance, however, with previous observations by Grignolo and Rivara (1968). Except for the publications quoted only little has been published about eye size and low birth weight.

Accepting a general eye size deficit in those prematurely born, the question is: How early does it happen? How early can we state it? One might assume it to be associated with—and possibly get apparent already after—the first few stormy months of life, so very decisive for survival of the immature infant. Examining eye size in such infants around their scheduled (normal) term might give a clue hereto.

The present paper is a report on such recordings. As part one of an ongoing investigation it is to be followed by oculometry findings in a control sample of full-term infants