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AJ German, JR Baker, TT Norton; Changes in Glycosaminoglycan Levels in Tree Shrew Sclera during Lens-Induced Myopia and Recovery . Invest. Ophthalmol. Vis. Sci. 2002;43(13):215.
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Purpose: To examine the time-course of changes in glycosaminoglycan (GAG) levels in tree shrew sclera during induced myopia development and recovery and to provide a direct measurement of sulfated and unsulfated GAGs. Methods: Capillary electrophoresis (CE) was used to measure levels of hyaluronan (HA), chondroitin sulfate (C0S, C6S, and C4S), and dermatan sulfate (DS) in the scleras of normal tree shrews (1, 16, 24, 28, 35, 39, 45 or ≷120 days of visual experience [VE]) (n=3 per group), tree shrews that received 1, 2, 4, or 11 days of monocular treatment with a –5 D lens starting at 24 days of VE (n=5 per group), and tree shrews that received 1, 2 or 4 days of recovery after 11 days of lens wear (n=5 per group). Results: In normal animals, GAG levels did not change significantly between 1 and 45 days of VE. In treated eyes, an initial transient variability in GAG levels was found after 1 day of lens wear. Increases in chondroitin sulfate (C0S, C6S, and C4S) of 100-300% occurred in some animals. In contrast, HA levels decreased in the treated eye relative to control. This transient variability in GAG levels preceded the development of significant myopia, which occurred at 2 days of lens wear. As the treated eye continued to compensate for the –5 D lens, all GAG levels, except DS, were significantly lower (–12% to –41%) in the treated eye relative to control at 4 days of lens wear. As treated eyes approached full compensation to the –5 D lens at 11 days, all GAG levels remained significantly lower in the treated eye relative to the control eye. Control eye GAG levels did not differ significantly from normal except at 11 days of treatment, when C0S was significantly higher. All differences in GAG levels between the treated and control eyes were no longer present at 1 day of recovery. GAG levels in the treated and control eyes were not significantly different during recovery except for HA, which was lower in the treated eye after 4 days of recovery. DS levels were not significantly altered in the treated eye in any group. Conclusions: The fluctuation observed in GAG levels at 1 day of lens wear and the absence of significant treated eye/control eye differences at 1 day of recovery suggest the existence of rapid changes that match or precede the detectable changes in refractive state and other scleral changes reported in previous studies. The absence of changes in DS suggest that the collagen-associated proteoglycan, decorin, may be relatively unaffected. The slower changes may be causally related to the continued axial elongation or be the result of elongation-related changes.
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