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Robert J Munro, James D Akula, Toco Yuen Ping Chui, Ronald M Hansen, Tara L Favazza, Anne Moskowitz, Sanjay P Prabhu, Anne Fulton; Modeling the Developmental Growth of the Eye in Subjects Born at Term and Subjects with Retinopathy of Prematurity (ROP). Invest. Ophthalmol. Vis. Sci. 2014;55(13):4448.
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© ARVO (1962-2015); The Authors (2016-present)
Influenced by development and visual experience, oblate infant eyes become relatively prolate. It is unknown specifically where and when the eye grows to transform from its neonatal form to its adult form. We modeled the development of the eye to evaluate growth as a function of age, and challenged our model against the abnormal ROP eye.
We reviewed extant MRIs from term-born and preterm-born ROP patients, aged 0-20 y, for images suitable for generation of high-resolution, transverse, pupil-optic-nerve sections. Subjects were categorized as ‘Term’ if they were ≥37 wk postmenstrual age (PMA) at birth (n=77) or ‘ROP’ if they were preterm and had ROP (n=29). Using custom software (Chui et al., Ophthalmology 2012; Akula et al., ARVO 2013, 3058), we segmented the inner surface of the globe. For every subject, we measured the length of rays from the centroid to the surface of the eye at 5° intervals. We described the length of each ray (Lray) as Lray(x) = b × xn / (xn + kn), where x is PMA at test, b is asymptotic length of the ray, k is the age at which the ray reaches length b/2, and n is related to the slope. We determined the rate of ray elongation, Eray(x) from Lray dy/dx. The scleral growth that accounts for Eray is 2π×Eray. We note that scleral growth at point θ, G(x,θ), and at point θ±180°, contribute nothing to elongation in Eray; conversely, half of the scleral growth at θ±90° contributes and growth at intermediate angles contributes intermediate amounts. We solved for growth G(x,θ) at every age and position.
G was highest at young ages and rapidly declined thereafter. Relative to Term eyes, growth in ROP eyes was low at young ages but high at older ages. In Term eyes, G was highest at the equator early and smoothly shifted to the axial poles with age; in ROP eyes, G was highest near the axial poles early and abruptly shifted to the periphery.
Eyes become prolate because, at young ages when scleral growth is fast, it is predominantly peripheral, and later, when scleral growth is slow, it is predominantly at the axial poles. The loci of maximum growth is offset by ~90° at term in ROP eyes. Our model predicts that the small ROP eye becomes normal (or even supranormal) in size in adulthood because it is characterized by a delay in growth followed by prolonged expansion.
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