The regulation of eye growth and refractive state: An experimental study of emmetropization

Abstract

Abstract-During growth the vertebrate eye achieves a close match between the power of its optics and its axial length with the result that images are focused on the retina without accommodative effort (emmetropia). The possibility that vision is required for the regulation of eye growth was studied experimentally in chicks made myopic or hyperopic by different visual manipulations. After discontinuing these visual manipulations, the eyes returned quickly to emmetropia mainly by adjusting the growth of their vitreous chambers; growth stopped in eyes recovering from myopia and continued in eyes recovering from hyperopia. Because both hyperopic and myopic eyes were already larger than normal controls, the difference in growth indicates that refractive error, rather than eye size per se, guides the eye toward emmetropia. Evidence is also presented for nonvisual shape-related control of eye growth, but this is slow-acting and cannot explain the emmetropixation from induced refractive errors. Both the visually guided and shape-related mechanisms work even in eyes with the optic nerve cut, indicating that the two mechanisms are local to the eye. Although the optic-nerve-sectioned eye can sense the sign of a refractive error and initially adjust growth accordingly, it eventually overshoots emmetropia and reverses the sign of the initial refractive error. Whether this is due to loss of feedback from the central nervous system or retinal ganglion cells is unclear.

Development of the Visual System in a Burrow-Nesting Seabird: Leach's Storm Petrel

“…Within 7 days, they reach near emmetropia (the image is focused on the retina); however, rearing chickens in the dark retain hyperopia [Troilo and Wallman, 1991]. Troilo and Wallman [1991], as well as Schaeffel and Wagner [1996], have shown that retinal feedback is needed for controlled eye development to achieve emmetropia. While domestic chickens are precocial, American kestrels and barn owls are semi-altricial.…”

Screening for correctable visual acuity deficits in school-age children and adolescents

“…However, there is some evidence that optical correction can result in persistence of an error that might otherwise have naturally resolved or reduced. Emmetropisation appears to be partly reliant on normal visual experience and can be manipulated by optical correction (Dobson 1986;Hung 1995;Ingram 1991;Medina 1987;Troilo 1991). This raises the possibility that full refractive correction may not always be appropriate.…”

Emmetropization, visual acuity, and strabismus outcomes among hyperopic infants followed with partial hyperopic corrections given in accordance with dynamic retinoscopy

“…[1][2][3][4][5] However, if a decision on a prescription is made, it also introduces the tendency to place undue weight on with the wearing of spectacles in the face of deferring the development of emmetropization. [6][7][8][9][10][11][12][13][14][15][16][17] This concern raises a question that is yet to be answered: do hyperopic children really need the provision of full plus refractive error correction to meet these objectives?…”