AIM:To investigate changes in the normal intraocular pressure(IOP)fluctuation range after the small incision lenticule extraction(SMILE)in patients with low, moderate and high myopia and to explore new methods for postoperative IOP(IOP_post)correction.

METHODS: In this prospective case series study, 79 patients(158 eyes)who underwent SMILE at the Affiliated Hospital of Qingdao University from March 2018 to September 2019 were involved, and they were divided into low myopia(A), moderate myopia(B), and high myopia(C)groups. The 24-hour IOP was measured by the non-contact tonometer(NCT)and Goldmann applanation tonometer(GAT). Spherical equivalent(SE), central corneal thickness(CCT), the horizontal corneal diameter(WTW), corneal curvature, corneal volume(CV), ratio of the central 3-mm diameter CV(CCV_3mm)to the total CV, and the ratio of the cutting CV(ΔCV)to the CV were measured 3d preoperatively and 6mo postoperatively. The correlation between the postoperative NCT measurements(NCT_post)and various factors was statistically analysed, and the IOP_post expression model was established by phased multiple linear regression analysis.

RESULTS:The differences in IOP measured by NCT and GAT were not statistically significant(P>0.05), but the differences in IOP of the three groups were statistically significant(P<0.05). The IOP_post range by NCT were 8-17 mmHg in group A, 7-16.3 mmHg in group B, and 7.7-14.3 mmHg in group C. The IOP_post range by GAT were 8-17 mmHg. The IOP_post fluctuation was <6 mmHg. The IOP_post difference between the right eye and left eye was 0-4 mmHg. A staged multivariate regression model was established: NCT_{post corrected(A)}= 0.349 × NCT_post + 4.137 × CCV_pre3mm - 1.533; NCT_{post corrected(B)}= 0.477 × NCT_post + 3.643 × CCV_post3mm -1.125; NCT_{post corrected(C)}= 0.638 × NCT_post + 3.426 × CCV_post3mm -0.716.

CONCLUSION:The IOP measured by NCT and GAT after SMILE was lower than that measured before surgery. For different patients, the greater the rate of change in CV before and after surgery, the lower the IOP_post. CCV_post3mm is an important index for evaluating IOP after SMILE and thus guide postoperative medication administration.