The involvement of the retina in avian lid suture myopia was investigated by use of formoguanamine (FG), which induces blindness in chicks, characterized by damage to the retinal pigment epithelium and photoreceptor layers. In control chicks reared under a diurnal lighting schedule of 12L/12D, unilateral eyelid suture at 3 days of age induced a typical lid suture myopia response on the operated side (eye enlargement and bulging cornea) by 4 wks. of age. On the other hand, in FG-treated blind chicks also reared under 12L/12D, there was no difference in eye parameters, between sutured and non-sutured eyes. All globe parameters measured were very similar in FG-treated and control non-sutured chicks. Corneal diameter and anterior chamber depth in the eyes of FG-treated chicks were significantly smaller than in non-sutured control eyes.