Moving the retina: Choroidal modulation of refractive state

Abstract

The chick eye is able to change its refractive state by as much as 7 D by pushing the retina forward or pulling it back; this is effected by changes in the thickness of the choroid, the vascular tissue behind the retina and pigment epithelium. Chick eyes first made myopic by wearing diffusers and then permitted unrestricted vision developed choroids several times thicker than normal within days, thereby speeding recovery from deprivation myopia. Choroidal expansion does not occur when visual cues are reduced by dim illumination during the period of unrestricted vision. Furthermore, in chick eyes presented with myopic or hyperopic defocus by means of spectacle lenses, the choroid expands or thins, respectively, in compensation for the specific defocus imposed. Consequently, when the lenses are removed, the eye finds its refractive error suddenly of opposite sign, and the choroidal thickness again compensates by changing in the opposite direction. If a local region of the eye is made myopic by a partial diffuser and then given unrestricted vision, the choroid expands only in the myopic region. Although the mechanism of choroidal expansion is unknown, it might involve either a increased routing of aqueous humor into the uveoscleral outflow or osmotically generated water movement into the choroid. The latter is compatible with the increased choroidal proteoglycan synthesis either when eyes wear positive lenses or after diffuser removal.

Ionic control of ocular growth and refractive change

“…The rapid increase in choroidal thickness seen during recovery from form deprivation myopia was initially hypothesized to be a consequence of the choroid actively pushing the retina back toward the image plane of the highly myopic eye (29). Three speculations as to the source of choroidal expansion were offered: increased synthesis of extracellular matrix (i.e., proteoglycans) and͞or modulation of the nonvascular smooth muscle spanning the choroid, increased uveoscleral outflow, or choriocapillaris leakage.…”

The effect of topical anti-muscarinic agents on subfoveal choroidal thickness in healthy adults

“…[4][5][6][7][8] In addition, it is known that ChT is affected by various factors such as blood pressure, age, gender, time of the day, refractive status, axial length, and forced hyperopic or myopic defocus. 2,[9][10][11] Further, a recent experimental study showed that anti-muscarinic agents could affect ChT. 12 Therefore, in the present study, we aimed to investigate the effects of tropicamide and cyclopentolate, which are two anti-muscarinic agents commonly used in the ophthalmologic practice, on subfoveal ChT measured by EDI OCT in healthy adults.…”

“…It has several functions including procurement of oxygen and nutrients for the outer retina, adjustment of retinal position, regulation of retinal temperature, protection of the photoreceptors, and secretion of some growth factors. 1,2 The introduction of enhanced depth imaging (EDI) optical coherence tomography (OCT) technology by Spaide et al 3 has provided accurate measurement of choroidal thickness (ChT) for investigating the in vivo anatomy of normal choroid and the choroidrelated ocular pathologies.…”

The Influence of Light Exposure and Seasonal Changes on Short-Term and Longer-Term Changes in Axial Length of the Human Eye

“…Animal studies show that the diurnal axial length rhythms are altered (magnitude increased) in form-deprived chicks (which stimulates excessive eye growth), resulting in myopia development (Weiss & Schaeffel, 1993;Wallman et al, 1995;Nickla et al, 1998b;Papastergiou et al, 1998). On the other hand, when chicks are exposed to myopic defocus (which slows/retards the eye growth), the diurnal axial length variations are found to be phase delayed, leading to a slowing of eye growth (Nickla et al, 1998b;Papastergiou et al, 1998;Nickla, 2006).…”

“…Studies with chicks show that the diurnal variations in choroidal thickness and axial length are altered in fast growing eyes of form-deprived chicks (Weiss & Schaeffel, 1993;Wallman et al, 1995;Nickla et al, 1998b;Papastergiou et al, 1998). During form-deprivation, the rhythms of axial length and choroidal thickness shift to an exact anti-phase relationship (i.e.…”