Abstract
Purpose :
For normal eye development at the early childhood the crystalline lens is coordinately thinning with the eye growing to achieve emmetropia at the adulthood, while abnormal lens development is associated with myopia development. The developmental changes of the lens thickness (LT) and the axial length of the eye (AL) have been documented in the literature, but the relative change of the LT with the AL elongation has not been well explored. The purpose of this study was to test the quantitative relationship of the changes between the LT and the AL for both emmetropic and myopic children.
Methods :
The developmental changes in the LT and the AL for the children aged from 6 to 9 years old were analyzed from the publications of three longitudinal studies, the OLSM (Jones et al. IOVS2005), the NLS (Garner et al. OVS 2006), and the SCORM (Wong et al. IOVS 2010) studies. A ration of the change of LT per year (dLT) over the change of AL per year (dAL) was calculated to test the relationship of the growing speeds between the lens and the eye ball. The ratio of dLT/dAL was examined for both emmetropic and myopic groups (or became myopia in SCORM), and compared between the refractive groups.
Results :
For the emmetropic children, the mean ratio of dLT/dAL from 6 (or 7 in SCORM) to 9 years old were -0.24, -0.21 and -0.15 for the OLSM, NLS and SCORM studies respectively. As compared to the emmetropic group, a lower dLT/dAL retio was found for the myopic group with the values of -0.14, -0.14 and -0.10 for the OLSM, NLS and SCORM studies respectively. The lower myopic dLT/dAL ratio, compared to the emmetropic one (myopia vs. emmetropia), was observed as early as 6-7, 6-7, and 7-8 year old for the OLSM (-0.12 vs. -0.21), NLS (-0.14 vs. -0.22) and SCORM (-0.11 vs. -0.23) studies respectively, while the myopia onset was after 8 year old for all of the studies.
Conclusions :
The normal shortening of the lens thickness is about 20% of the axial length elongation in speed for children at the early middle childhood. A slower speed of LT shortening relative to the AL elongation (about 10%) early before myopia onset implies an abnormal structural development of the eye associated with myopia development. A test of the dLT/dAL ratio at the early middle childhood could be useful to identify the children becoming myopia and to apply intervention early before myopia onset.
This is a 2020 ARVO Annual Meeting abstract.