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Neville A. McBrien, Patrick Lawlor, Alex Gentle; Scleral Remodeling during the Development of and Recovery from Axial Myopia in the Tree Shrew. Invest. Ophthalmol. Vis. Sci. 2000;41(12):3713-3719.
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purpose. Recent investigations have suggested that scleral thinning in mammalian
eyes with axial myopia is a consequence of the loss of scleral tissue,
rather than the redistribution of existing tissue as the eye enlarges.
The present study investigated whether further changes in the
distribution and metabolism of scleral tissue occur during the process
of recovery from axial myopia. Scleral glycosaminoglycan (GAG)
synthesis and content as well as scleral dry weight changes were
monitored as indicators of remodeling in myopic and recovering tree
methods. Myopia was induced in tree shrews by monocularly depriving them of
pattern vision. Some animals then had the occluder removed and were
allowed to recover from the induced myopia for periods of 1, 3, 5, 7,
and 9 days. Newly synthesized GAGs were radiolabeled in vivo with[ 35S]sulfate. Sulfate incorporation and total GAG content
in the sclera was measured through selective precipitation of GAGs from
proteinase K digests with alcian blue dye. Dry weights of the sclerae
were also determined. Changes in ocular refraction and eye size were
monitored using retinoscopy, keratometry, and ultrasonography.
results. Eyes developing myopia showed a significant reduction in scleral GAG
synthesis, particularly in the region of the posterior pole (−36% ±
7%) compared with contralateral control eyes. Scleral dry weight was
also significantly reduced in these eyes (−3.7% ± 1.2%). In
recovering eyes, significant changes in GAG synthesis were apparent
after 24 hours of recovery. After 3 days of recovery, significantly
elevated levels of GAG synthesis were found (+79% ± 15%), returning
to contralateral control eye values after 9 days of recovery.
Interocular differences in scleral dry weight were shown to follow a
similar pattern to that observed for GAG synthesis.
conclusions. Active remodeling, resulting in either the loss or replacement of
scleral tissue and not passive redistribution of scleral tissue, is
associated with changes in eye size during both myopia development and
recovery. Regulatory changes in scleral metabolism can be rapidly
evoked by a change in visual conditions and the direction of regulation
is related to the direction of change in eye
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