The authors present the first direct correlation of human foveal development visualized by spectral-domain optical coherence tomography (SD-OCT) with histologic specimens. This correlation is required for the clinical assessment of normal and pathologic development of infant retina by SD-OCT and aids in defining and validating SD-OCT bands for the adult eye.
They compared SD-OCT images from one eye of 22 premature infants, 30 term infants, 16 children, and one adult without macular disease to light microscopic histology from individuals of comparable ages.
SD-OCT and histology are fundamentally different techniques that generate images of microscopic tissue elements. Despite the differences, both of these methods agree closely on the sequence of events during human foveal development.
SD-OCT images correlated with major histologic findings at all time points. With both methods, preterm infants demonstrated a shallow foveal pit indenting inner retinal layers (IRL) and short, undeveloped foveal photoreceptors. At term, further IRL displacement forms the pit and peripheral photoreceptors lengthen; the elongation of inner and outer segments (IS and OS) separates the IS band from retinal pigment epithelium.
Foveal IS and OS are shorter than peripheral for weeks after birth (both methods). By 13 months, foveal cone cell bodies stack >6 deep, Henle fiber layer (HFL) thickens, and IS/OS length equals peripheral; on SD-OCT, foveal outer nuclear layer (which includes HFL) and IS/OS thickens. At 13 to 16 years, the fovea is fully developed with a full complement of SD-OCT bands; cone cell bodies >10 deep have thin, elongated, and tightly packed IS/OS.
The authors write that the most obvious finding was the extreme immaturity of the outer retina before and after birth, especially in the fovea. Peripheral IS/OS are longer until well after birth, and it is not until 13 to 15 months that foveal IS/OS length begins to overtake peripheral. This sequence explains the early absence of bands 8 and 9, and their appearance first in the midperiphery and last in the fovea. At approximately 5 years of age, foveal IS and OS are adult in both histology and SD-OCT. The presence of IRL at the fovea and their shift out of the foveal center is also a striking finding that was correlated between the two techniques.
They conclude that as SD-OCT becomes an established diagnostic tool in pediatric practice, it is critical to understand the marked changes taking place in foveal structures from midgestation to late childhood in order to recognize normal development and quantify disease states.