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F. J. Rucker, X. Zhu, M. Bitzer, F. Schaeffel, J. Wallman; Inter-Ocular Interactions in Lens Compensation: Yoking and Anti-Yoking. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3931.
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When a young animal wears a spectacle lens, the other eye often changes in the same direction as the lens-wearing eye (yoking). We explore an opposite effect: the untreated fellow eye of animals wearing a plus lens tends to grow longer than the untreated fellow eye of those wearing a minus lens (anti-yoking).
Eye length and choroidal thickness were measured by ultrasound before and after lens-wear. ZENK expression in glucagonergic amacrine (GA) cells was quantified by counting double-stained cells. Scleral proteoglycan (GAG) synthesis was measured after 5 d of form deprivation (FD) and 2 d of recovery.
(a) As shown in the figure, with brief lens-wear (30 min/12 hrs) the length of chick eyes was both yoked--the eyes were positively correlated--and anti-yoked--the average length of the untreated fellow eyes changed in the opposite direction as the lens-wearing eye (p=0.02). (b) Marmosets showed anti-yoking: the fellow eye of animals wearing a plus lens was longer (168 µm) and less hyperopic (1.1D) than that of animals wearing a minus lens. (c) Choroid thickening showed anti-yoking in chicks with brief lens-wear (p<0.05). (d) ZENK expression in GA cells in fellow eyes of chicks wearing plus vs minus lenses changed in the opposite direction as the lens-wearing eyes. (e) In chicks with monocular FD, scleral GAG synthesis was half as great in the untreated fellow eye of FD birds as in the fellow eye of birds recovering from FD (p<0.01). (f) An anti-yoking trend seen in scleral creep in tree shrew eyes wearing minus lenses vs. normal animals was reported (Siegwart & Norton, 1998).
In primates, anti-yoking might be due to yoked accommodation causing animals wearing a plus lens to use that eye for near vision, so that the fellow eye was under-accommodated and thus functionally hyperopic, provoking compensatory myopic growth. It seems less likely that chicks, with unyoked eye-movements, would have yoked accommodation, or that chicks with monocular FD would have a shorter fellow eye than those recovering from FD myopia. Perhaps anti-yoking reveals an isometropizing process that draws the two eyes together in refraction or anatomical parameters.
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