The Effect Of A Unique Lens Designed For Myopia Progression Control (MPC) On The Level Of Induced Myopia In Chicks

Abstract

Purpose: : It is well established that newly hatched chickens fitted with minus lenses demonstrate a myopic shift approximately equal to the lens power. Evidence has shown that the level of defocus in the retinal periphery may play a role in refractive development. The aim of this experiment was to determine if lens induced myopia in chickens can be inhibited when the minus power is combined with a unique hyperopic peripheral lens design aimed at decreasing myopic progression, while still maintaining clear vision.

Methods: : Fifteen chicks were fitted unilaterally with the MPC lenses, attached by Velcro (TM). Eight chicks were fitted with a MPC test lens, with central power of -10.00D. The remaining seven chicks were fitted with conventional -10.00D control lens of the same physical parameters as the test lens. Refractive error was measured by retinoscopy before lens application and at days 3 and 7. Birds were given food and water ad libitum and raised on a 14h light/10h dark cycle. Lenses were only removed for brief periods for retinoscopy and lens cleaning. Mean differences between treated and untreated eyes (MDiff) are reported, to avoid the problem of the small eye artifact.

Results: : The difference between the refractive error of the treated and the non-treated eyes was insignificant (p=1.00) on day zero for both groups. Test group MDiff was -0.06D ± 0.50, range +1.00 to -0.50D; control group MDiff was +0.29 D ± 0.76, range +1.00 to -1.00D. By day 7, chicks treated with the MPC test lenses had become slightly hyperopic in the treated eye relative to the untreated eye (p=0.32); MDiff +2.17 D ± 2.71, range +6.00 to -1.00 D. At this time-point those treated with the control lenses had become significantly more myopic (p=0.0007) in the treated eye relative to the untreated eye; MDiff -8.10 D ± 3.07, range -5.00 to -12.00 D.The MDiff for the test and control groups were significantly different at day 7 (p=0.0002).

Conclusions: : The results of this study indicate that lens-induced myopia in chickens can be affected by this novel lens design and provide further evidence of the role of peripheral retinal hyperopic focus in the mechanism which controls eye growth. Further studies are required to determine if these results can be obtained in human subjects with this unique MPC lens.

Keywords: emmetropization • myopia • development