This study was planned to evaluate the effect of pregnancy on diurnal variation of intraocular pressure（IOP） after placing control on all the IOP affecting factors. The IOP was measured with the Goldmann ap-planation tonometer. Both in the control and 3rd trimester subjects

the peak of mean IOP appeared in themorning when the subJects waked

and the trough of mean IOP happened at 2 am to 4 am. The diurnal in-traocular pressure curves revealed that the lOP peaks were 15.4±0. 9 and 12. 9±0. 6 mmHg in the controland third trimester pregnant subjects

respectively. Whereas the trough were 13.1±0. 4 and 11. 8±0. 3mmHg

respectively. The mean diurnal variation were 2. 3±0. 6 mmHg （P<O.01 ）

and 1.1±0. 8mmHg in the control and third trimester subjects

respectively. There are two main findings of presentstudy: first

compared with non-pregnant control subjects

the IOP was significantly lower （P<0.001 ） inthe third trimester pregnant subjects. Second

in the third trimester of pregnancy

the lower IOP level wasassociated with the less degree of IOP fluctuations at various hours of the day.