Myopia produced in young chicks by intermittent minimal form visual deprivation--can spectacles cause myopia?
Spectacle use has been postulated to aggravate or cause human myopia. Form visual deprivation, by complete full-time occlusion or refractive lenses, has been demonstrated to cause axial myopia in animals. We raised young chicks in conditions which closely approximate plano spectacle wear in humans. In addition, we sought to achieve more physiological conditions of form deprivation. Nine newborn chicks were raised with intermittent monocular visual deprivation and their eye growth and refraction monitored by retinoscopy, ultrasonic A-scan biometry and with a travelling microscope. After hatching, the nictitating membranes were sutured for 3-4 days. This was followed by a transparent plano plastic cover over the same eye for 3-4 days per week. After 3 weeks, the manipulated eyes were more myopic (mean refraction -0.72 D, axial length 13.11 mm) than fellow eyes (+0.83 D, 11.99 mm) (p < 0.05 and p < 0.01 respectively). These results suggest that the chick eye is exquisitely sensitive to disturbances in the visual environment; intermittent minimal manipulation by conditions simulating spectacle wear in man was myopiagenic. It is postulated that spectacles can cause form visual deprivation of foveal and nonfoveal neurons (and hence myopia) by reducing luminance and contrast, chromatic and spherical aberration (in nonfoveal neurons) and restriction and distortion from the frame.
Chew
S J
SJ
Department of Ophthalmology, National University Hospital, Singapore.
Balakrishnan
V
V
D000065:Accommodation, Ocular; D000818:Animals; D002645:Chickens; D005123:Eye / Q000033:anatomy & histology; D005556:Form Perception; D007909:Lenses / Q000009:adverse effects*; D009216:Myopia / Q000209:etiology*; D009541:Nictitating Membrane / Q000601:surgery; D010775:Photic Stimulation; D012029:Refraction, Ocular; D015348:Vision, Binocular