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Y. Lin, A. Gentle, N. A. McBrien; The Effect of Positive Lens Defocus on Scleral Collagen Gene Expression in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5933.
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The process of ocular growth must be facilitated by scleral remodeling. The main components of the mammalian sclera are the fibril-forming collagens. Previous studies on myopic eyes demonstrated a reduction in collagen I production and a subsequent increase in the ratios of collagen III/I and V/I. This implicates a role for fibril forming collagens as a determinant in eye size. The present study investigated the expression of these collagen subtypes in the sclera of tree shrews with slowed eye growth.
Animals were treated monocularly with a +4D lens for 5 days, with a plano lens over the contralateral control. Retinoscopy and A-scan ultrasonography measurements were taken at the start and end of the treatment period. Gene expression of scleral collagens I, III and V was determined using quantitative and semi-quantitative real-time PCR. In addition, scleral collagen gene expression was analyzed in hyperopic tree shrews that had been previously treated with a binocular sequential positive lens paradigm similar to that used by Smith and Hung (1999).
Slowed ocular growth was induced in the treated eye of animals wearing monocular +4D lenses. The resultant relative hyperopia (+2.1±0.3D; p<0.01; mean±SEM) correlated with a reduced vitreous chamber depth (-0.04±0.02mm; p<0.05) and axial length (-0.02±0.01mm; p<0.05). Collagen I was the predominant scleral subtype followed by collagens III and V. Expression of collagens I, III and V was not significantly different to their corresponding controls (1±26%, -9±28% and 26±40%; p>/=0.55). Similarly, there was no significant change in the scleral collagen subtypes between the binocular treatment group and their controls (66±60%, 39±52% and 29±42%; p>/=0.79).
While monocular negative lens defocus induced increases in ocular size are linked to a change in the expression of scleral fibril-forming collagens, no changes in collagen subtype expression were observed in positive lens defocus induced changes in ocular size. However, the refractive and structural change in the present study was less than half that observed in tree shrews undergoing 5 days of myopia induction. The data indicate that changes in the expression of fibril-forming collagens are not an initial feature of slowed eye growth.
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