Effects of Long-Wavelength-Pass Filters on Refractive Development in Rhesus Monkeys

Abstract

Purpose: Because the refracting power of the eye varies with wavelength, altering the spectral distribution of environmental lighting can potentially influence refractive development. We investigated whether restricting the vision of infant monkeys to relatively long wavelength light would predictably alter refractive development.

Methods: Beginning at 25 ± 2 days of age, infant monkeys were fitted with helmets that secured long-wavelength-pass (red) filters in front of one (n=7) or both eyes (n=7). For the monocularly treated animals, neutral density filters were fitted in front of the fellow eyes to balance the luminance levels in the two eyes. The housing area was illuminated primarily with fluorescent tubes; tungsten lamps were added to provide broad-spectrum lighting. The animals wore the helmets continuously until 132 ± 15 days of age. Refractive development and the eye’s axial dimensions were assessed periodically throughout the observation period by retinoscopy and A-scan ultrasonography, respectively. Control data were obtained from 32 normal monkeys.

Results: At the end of the lens-rearing period, 5 of 7 monocularly treated monkeys exhibited anisometropias that were larger than the anisometropias found in 95% of the normal monkeys. In each case, the treated eye was more hyperopic than the fellow eye. Similarly, by 120 days of age, the median refractive error for the binocularly treated monkeys was significantly more hyperopic than that for normal monkeys (right eye ametropia: +4.41 D vs +2.53 D; p = 0.0002). The relative hyperopia observed in the red-filter-treated eyes was associated with slower vitreous chamber elongations rates.

Conclusions: Although the nature of the mechanism that mediated the observed filter-induced refractive-error changes is not known, contrary to predictions based on longitudinal chromatic aberration, the red lenses employed in this study produced hyperopic shifts in refraction rather than myopic shifts.

Keywords: 605 myopia • 677 refractive error development