BACKGROUND: The evaluation of stereoacuity can provide an unambiguous assessment of haplopia. It is valuable in assessing the diagnosticaccuracy and the therapeutic effect in strabismus, amblyopia and ametropia. OBJECTIVE: This investigation was designed to evaluate the stereopticdevelopment and the occurrence rate of strabismus in 3-6 years old children, and so that to provide objective data for prevention and treatment of strabismus and steropsis. DESIGN: It was a randomized sampling investigation. SETTING: Department of Ophthalmology,Haikou People's Hospital. PARTICIPANTS:Totally 8326 children in 25 urban and suburban kindergartens, with an age of 3-6 years old, were selected randomly in Haikou city from June 2000 to April 2002. METHODS: 8 326 3-6 years old children in Haikou city underwent vision examinations on hyperopia, eye position and the myopia. Those having eyesight lower than 1.0D or abnormal eye position received atropine drops to dilate the pupil of the eye for optometry. ① 4-6 years old children were examined using standard visual chart and logMAR chart (logarithm of the minimum angle of resolution chart), 3 years old children were examined using hroken wheel acuity cards or symbols chart. The results of the exminations were conversed and recorded in form of decimal fraction uniformly. ②The corneal reflection and the cover test procedure were used for the position of gaze. ③ Stereoacuity were examined using the stereoptic visual testing cards (made by the Institute of Biophysics, Chinese Academy of Sciences). Stereoacuity were defined as normal when the test value was ≤ 60 s and were defined as abnormal when it was ≥ 100 s. Each examination was performed by same selected physicians. MAIN OUTCOME MEASURFS: The main outcome measurements included ① results of eye position examination and stereoptic examination in children in all age brackets, ② results of optometry in children with strabismus, ③ The relation between eyesight and stereopsis in participants,④Stereoacuity of children in all age brackets, ⑤and possible causations involve in stereopsis. RESULTS: Practically, 8326 participants receiving examinations of eysight and eye position entered the statistical analysis procedure, while an other 662 children were omitted for their poor expression for the examinations. ① Results of stereoptic examination and eye position examination for participants in all age brackets: 165 (2％) with strabismus, in which 89.7％were first diagnosed; 2016 (27.5) with myopia, whose stereoptic value were ≥ 100 s. ②Results of optometry in children with strabismus: 93.5％ esotropia occurred in children with hyperopia. The rate of hyperopia/myopia was not significantly different between exotropia and vertical strabismus.③ Relation between eyesight and stereoacuity of participants: 75.5％ children have a normal stereoacuity.With a decreasing in eyesight,the stereoacuity decreased (P ＜ 0.05 or P ＜ 0.01). ④ Stereoacuity of the children in all age brackets: With an increasing age, the rate of children with normal stereoacuity increased. ⑤ Possible causations involved in stereopsis: strabismal amblyopia might have the greatest influence on stereopsis. CONCLUSION: ①About 90％ children with strabismus were firstly diagnosed in the investigation. Causations responsible for abnormal stereopsis include ametropia, strabismus, and amblyopia, and so on. ② Concomitant esotropia has close relation with binocular accommodation, while exotropia and vertical strabismus are not linked to refractions. Stereoacuity decreases with a decreasing in eyesight. ③ The results of the investigation support the view that mature stereopsis is achieved early than 4 years old although certain variance of stereoptic development can be observed among individuals.