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G.E. Lytle, S. Yom, C.–S. Kee, D.L. Nickla; Ameliorating The Development Of Myopia In Response To Form Deprivation, Negative Lenses Or Constant Darkness By Brief Daily Visual Stimuli Or Apomorphine Is Associated With Transient Daily Increases In Choroidal Thickness . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1141.
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In chickens, transient increases in choroidal thickness are found in conditions in which the eye is slowing its growth in response to different types of visual stimuli that prevent excessive elongation (Nickla et al., OVS, 2005). To test the hypothesis that the choroidal and growth responses are linked, we used a variety of "transient" stimuli known to ameliorate the development of myopia and assessed the concurrence of the responses. If true, they should always be correlated.
All experiments lasted 4 days. High–frequency A–scan ultrasonograpy was done at different times. (1) Form deprivation w/vision or strobe. Vision: Diffusers were removed daily for 2 hrs in (a) one block of 2–hr (n=16) or (b) two 1–hr periods (n=10). Strobe: Birds were given half hr episodes of 12 Hz strobe 12 hrs apart (n=11). (2) Negative lenses w/vision or strobe. Vision: Lenses (–10D) were removed daily for 2 hrs (n=14). Strobe: same as above (n=11). (3) Constant dark/vision. Birds in darkness were given daily half–hr episodes of light 12 hrs apart (n=6). In all, a control group had the myopia–inducing treatment (e.g. deprivation) but did not receive the visual stimulation. (4) Negative lenses/Apormorphine. Apomorphine (n=8) or saline (n=8) was injected intravitreally into eyes wearing –10D lenses for 4 d.
All daily stimuli prevented the development of myopia in response to the conditions. (1) Deprivation: vision: (a) –1.2 D and (b) –1.4 D vs –9.8 D; strobe: –1.8 D vs –9.8 D. (2) Negative lenses: vision: –1.2 D vs –8 D; strobe: –4.3 D vs –8 D. (3) Constant dark: –0.7 D vs –1.8 D. (4) Negative lenses/apomorphine: (drug vs saline): –3.5 D vs –6.9 D (p<0.05 for all comparisons). In all experiments the effect was axial. Furthermore, there were significant (p<0.05 for all) increases in choroidal thickness over the period of "preventative" stimulation (exp vs control change in thickness: (1) Deprivation: vision: (a) 58 µm and (b) 14 µm vs –3 µm; strobe: 15 vs –17 µm (2) negative lenses: vision: 74 vs 3 µm; strobe: 17 vs –17 µm (3) Dark: 56 vs 11 µm. (4) Apomorphine resulted in increases in choroidal thickness 2 hrs later (41 vs –5 µm; p<0.005). These choroidal effects were largely transient; i.e. they did not result in "long term" increases in thickness.
All conditions under which ocular growth is inhibited are associated with transient (but not long term) increases in choroidal thickness, suggesting that these brief choroidal responses may play a role in ocular growth regulation.
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