A morphological analysis of experimental myopia in young chickens

Devices that degrade vision were applied to the left eyes of 3-day old chicks. The dome device affected the entire visual field, and the arch device, only the lateral field. Control chicks wearing a circumorbital ring and untreated chicks were also examined. The dome device produced -15D and the arch device -4D of mean refractive error, while the ring and untreated chicks were emmetropic. Morphological measurements were made from macrophotographs of the intact and hemisected eyes fixed as for electron microscopy. The effects of the devices were analysed from the mean differences between the left (treated) and right (control) eyes. Nearly linear growth of the normal eye was found during the period in which measurements were taken (age 20-55 days). The ring device did not affect eye growth. The arch device significantly increased the dorsoventral equatorial diameter of the eye. The dome device had the greatest effect, and resulted in increases in both axial length and equatorial diameter during the treatment period. Dome eyes had a bulging cornea, increased anterior chamber depth, more open angle, and greater corneal diameter than controls. The axial length and equatorial diameter of the posterior segment also were increased. Two inflammatory responses of the eye were found, particularly in dome eyes; about 50% of treated eyes exhibited choroidal swelling, and vitreal clouding was found less frequently. The association between inflammation and excessive accommodation in producing the observed changes is discussed.