Retinal function with lens-induced myopia compared with form-deprivation myopia in chicks.

Background: The retina is known to be involved in the development of form-deprivation myopia (FDM); however, it is not clear whether the retinal changes that lead to lens-induced myopia (LIM) are the same as those involved in FDM. To gain insight into the retinal mechanism(s) that cause myopia, we investigated differences in the results of electroretinography (ERG) in eyes with FDM and LIM.

Methods: LIM or FDM was induced in chick eyes by placing various powers of spectacles or an occluder over the left eyes of 6-day-old chicks. After 6 days, the spectacles or occluder was removed, refraction and axial length were measured and ERG was performed. Results for eyes treated with spectacles and those treated with occluders were compared.

Results: Refraction and axial length changed concomitant with the power of the lens used, but components of the ERG of eyes with LIM were not related to the power of lens added. Refraction and axial lengths of eyes covered with a -16 D lens did not differ from these values in eyes covered with an occluder. The a- and b-waves were also similar for the two groups. However, oscillatory potentials decreased significantly in the chicks with FDM.

Conclusions: Retinal function differs in LIM and FDM, as indicated by differences in the oscillatory potentials. This difference may stem from the fact that in FDM the retinal image is continuously defocused, whereas images are ultimately focused on the retina in LIM.