Influence of preoperative astigmatism on corneal biomechanics and accurate intraocular pressure measurement after micro-incision phacoemulsification.

AIM: To define the corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) prior to and following coaxial micro-incision phacoemulsification in patients with corneal astigmatism.

METHODS: Of 97 patients with cataracts were enrolled in the study. Group 1 included patients with corneal astigmatism (K1-K2) values of K1-K2<+1.0 D, and group 2 with values of K1-K2 ≥+1.0 D and ≤+2.25 D. Coaxial micro-incision phacoemulsification of a corneal incision of 2.0 mm with intraocular lens (IOL) implantation was performed. CH, CRF, IOPg, IOPcc, waveform score (WS) were measured preoperatively and one week, one month postoperatively using an Ocular Response Analyzer. Axial length (AXL) was calculated by Tomey Optical Biometer OA 2000.

RESULTS: Group 1 consisted of 51 patients with mean corneal astigmatism value of +0.49±0.25 D. Group 2 included 46 patients with astigmatism of +1.43±0.43 D. In group 1, CRF ( t =2.68, P <0.05), CH ( t =2.64, P <0.05) and WS ( t =3.51, P <0.05) were significantly lower one week postoperatively, when compared to the preoperative values. CRF significantly decreased ( t =3.61, P <0.05) when measured one month following the surgery. In group 2 CH ( t =5.92, P <0.05), and WS ( t =3.96, P <0.05) were significantly lowered one week after cataract surgery. Moreover, we observed a significant decrease in IOPg ( t =2.24, P <0.05), CRF ( t =5.05, P <0.05) and CH ( t =2.31, P <0.05) one month after phacoemulsification. There was no statistically significant ( t= -0.83, P =0.41) difference in AXL between study groups.

CONCLUSION: CRF, CH and IOPg are reduced in patients with preoperative corneal astigmatism equal or higher than +1.0 D and lower than +2.25 D. Hence, bias of IOPg measurement in these patients may cause underestimation of the real IOP both before and after cataract surgery. The measurement of IOPcc allows the precise assessment of IOP pre- and postoperatively, independently on corneal astigmatism, CH and CRF values.