Nomal kittens showed a gradual increase from 17.6% to 25.5% of BLS with aging from the fifth week to the ninth. Young kittens showed significantly less BLS than adult ones(p<0.1). There was no significant difference in BLS between exotropic and nomal kittens or alternating and non-alternating strabismic ones. However, there was a significant difference in BLS between esotropic and nomal ones(p<0.1). These results suggested that the BLS can be used as an index for the extent of total field from both eyes.