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.

Corneal biomechanical changes and intraocular pressure in patients with thyroid orbitopathy

AIM：To determine the relevance of the objective parameters addressing the altered biomechanical properties of cornea for glaucoma monitoring in patients with mild or moderate thyroid associated orbitopathy（TAO）,and in healthy individuals.· METHODS：Twenty-five patients with TAO（group 1）and 25 healthy adults（group 2） were included to the study.Both groups were of a similar age and the ratio women：man.For each patient,the following parameters of both eyes were measured with ocular response analyzer（ORA）：corneal hysteresis（CH）,corneal resistance factor（CRF）,Goldmann correlated intraocular pressure（IOPg） and corneal compensated intraocular pressure（IOPcc）.In both groups participating in our study,all measurements were performed within minutes to reduce the diurnal effects.· RESULTS：The mean age in group 1 was 56±11y and76%were women,24%were men.The mean age in group 2 was 64±11y and 68%were women,32%were men.CH correlated negatively with IOPg in group 1（r^2=0.10,P 〈0.05）.IOPg strongly correlated with IOPcc in both groups（group 1：r^2=0.79,P〈0.0001;group 2：r^2=0.85,P〈0.0001）.There was positive correlation between CRF and IOPg in group 1（r^2=0.12,P〈0.05） and in group 2（r^2=0.31,P〈0.0001）.Statistical analysis revealed no significant correlation between CRF and IOPcc in group 1（r^2=0.009,P 〉0.05） and also no significant correlation in group 2（r^2=0.04,P〉0.05）.CRF mean value in group 2（11.51±1.72 mm Hg） was higher than in group 1（10.85±1.45 mm Hg）（P〈0.05）.IOPg strongly correlated with IOPcc in both groups（group 1：r^2=0.79,P〈0.0001;group 2：r^2=0.85,P 〈0.0001）.There was also strong correlation between CRF and CH in both populations：group 1：（r^2=0.58,P〈0.0001）,group 2：（r^2=0.41,P 〈0.0001）.· CONCLUSION：Biomechanical parameters of cornea,as quantified by CH and CRF,and measured together with IOPcc,precisely reveal glaucoma staging in TAO and thus are reliable for diagnosing and follow-up in clinical practice. 〈/tr〉