Effects of interrupted lens wear on the compensation for minus lenses in tree shrews

Academic Article

Abstract

  • Purpose. To examine whether tree shrews (mammals closely related to primates) will compensate for a minus lens when the lens is removed for a small portion of each day. Methods Starting 24 days after natural eye opening, juvenile tree shrews began to wear a goggle frame that held a -5 D lens in front of one eye, with an open frame around the fellow control eye. The goggle was removed for 0, 0.5, 1, 2 or 7 hours, starting 0.5 hr after the start of each 14 hr light-on period in the colony room (N = 5, 4, 5, 4, 3 per group, respectively). After 21 days of treatment, retinoscopy and A-scan ultrasonography were performed under atropine cycloplegia and ketamine anesthesia. ResuJts As reported previously, (Siegwart and Norton, ARVO, 1996) the 0 hr group with continuous -5 D lens wear, compensated fully (or the lens (-5.8 D ±2.4 D, treated vs. control eye) and showed commensurate vitreous chamber and axial length increases (see figure.) The groups receiving 7 hr and 2 hr of "normal" visual exposure (e.g., lens removal) showed no compensation for the minus lens. The 1 hr, and 0.5 hr groups showed increasing compensation with decreasing time of lens removal. Conclusions. Like chicks {Schmid & Wildsoet, Vis. Res. 36: 1023, 1996), tree shrews can wear a minus power lens, which presumably increases retinal blur, for a considerable portion of the day without developing an induced myopia. These results suggest a threshold amount of "excess" blur must occur before axial elongation will increase beyond normal values. Once this threshold is exceeded, the axial elongation may be linearly related to the amount of "excess" blur.
  • Authors

    Author List

  • Shaikh AW; Siegwart JT; Norton TT
  • Volume

  • 38
  • Issue

  • 4