Abstract
Abstract: :
Purpose: Previous studies in marmoset showed that months after the end of form deprivation that produced stable axial myopia scleral proteoglycan/glycosaminoglycan (PG/GAG) synthesis was decreased (IOVS 41:8, 2000) and retinoic acid (RA) levels in the choroid were increased (ARVO 2001). In this study we explore PG/GAG synthesis in sclera and RA levels in choroid and retina of marmoset eyes during the period of experimentally altered eye growth. Methods: Monocular form deprivation was used to change eye growth in 13 marmosets. Eye size was monitored until changes between the exp and con eyes were detected. The animals were divided into two groups based on the interocular difference in vitreous chamber (VC) depth: (grp1) exp eyes longer than fellow con eyes (n=8), and (grp2) exp eyes shorter than con eyes (n=5). The animals were then euthanized and the eyes enucleated. The retina and choroid (with RPE attached) were dissected and incubated with radiolabeled all–trans–retinol. After 2 hrs the tissues were homogenized and run through HPLC to measure retinoic acid. Scleras were incubated in medium with S–35 for 6 hrs. Scleras were digested, the GAGs were precipitated, and radioactivity was measured. Results: Scleral PG/GAG: The rate of VC growth in all exp eyes was negatively correlated with PG/GAG synthesis in the posterior sclera (p<0.05). In grp1 (exp eyes longer than cons) scleral PG/GAG levels were significantly lower in exp eyes relative to con eyes (p<0.01). In grp2 (exp eyes shorter than cons) while some exp eyes showed an increase in PG/GAG synthesis relative to cons, the mean difference was not significant. Retinoic Acid: The RA level in all exp eyes was not significantly correlated with the rate of VC growth. However, the interocular difference (exp–con) in choroidal RA level was positively correlated with the interocular difference in VC depth (p<0.05). In grp1 choroidal and retinal RA in exp eyes was significantly higher than cons (p<0.01) while in grp2 there was no significant difference. RA levels and PG/GAG synthesis were not correlated with one another. Conclusions: In young marmoset eyes undergoing changes in eye growth scleral PG/GAG synthesis is negatively correlated with induced eye growth, similar to what was reported in older animals but with stable axial myopia. RA levels are higher in experimentally elongated eyes, again similar to that found in older myopes. The fact that these changes persist in older animals in which growth has stabilized, and the lack of a change in RA level in eyes with growth reduced suggests that two different signals may mediate increasing and decreasing growth.
Keywords: myopia • sclera • choroid