The choroid as a sclera growth regulator

Abstract

Emmetropization is a vision dependent mechanism that attempts to minimize refractive error through coordinated growth of the cornea, lens and sclera such that the axial length matches the focal length of the eye. It is generally accepted that this visually guided eye growth is controlled via a cascade of locally generated chemical events that are initiated in the retina and ultimately cause changes in scleral extracellular matrix (ECM) remodeling which lead to changes in eye size and refraction. Of much interest, therefore, are the molecular mechanisms that underpin emmetropization and visually guided ocular growth. The choroid, a highly vascularized layer located between the retina and the sclera is uniquely situated to relay retina-derived signals to the sclera to effect changes in ECM synthesis and ocular size. Studies initiated by Josh Wallman, Ph.D., clearly demonstrate that the choroid plays an active role in emmetropization, both by modulation of its thickness to adjust the retina to the focal plane of the eye (choroidal accommodation), and well as through the release of growth factors that have the potential to regulate scleral extracellular matrix remodeling. His discoveries prompted numerous investigations on the molecular composition of the choroid and changes in gene expression associated with visually guided ocular growth. This article will review molecular and functional studies of the choroid to provide support for the hypothesis that the choroid is a source of sclera growth regulators that effect changes in ocular growth in response to visual stimuli.

Choroidal Thickness and Ametropia in Children: A Longitudinal Study

“…Due to its location between the retina and the sclera, the choroid is uniquely situated to relay retina-deprived signals to the sclera. It may also act as a barrier to the diffusion of growth factors (37,38), a thinner choroid thus allowing the passage of a greater number, resulting in stimulation of axial elongation and myopia. On the other hand, choroidal molecular synthesis may also play a role in the regulation of scleral growth (39,40).…”

Advances of optical coherence tomography in myopia and pathologic myopia

“…Given its unique position between the retina and sclera, the choroid may be a source of scleral growth regulators in response to such local visual stimuli, making it potentially important in emmetropization and axial elongation. 28 The advent of high-resolution SD OCT enabled the evaluation of choroidal biometry in vivo, elucidating important information regarding the choroid in human myopia progression and susceptibility to pathologic myopia. In general, there was good intersystem reproducibility of choroidal thickness measurements between EDI OCT and SS OCT and also between three different SD OCT devices: Cirrus HD OCT, Spectralis SD OCT, and RTVue.…”

Change in choroidal thickness and the relationship with accommodation following myopic excimer laser surgery

“…1 The choroid, which located between the retina and sclera, is uniquely situated to transfer retina-derived signals to the sclera to effect changes in ocular size. 2 It is also the source of many vision-threatening diseases such as macular degeneration and polypoidal choroidal vasculopathy. 3,4 In profoundly affected myopic eyes, the choroid is thinner than in normal eyes, and it undergoes further thinning with age and increasing myopia.…”