Air-pulse corneal applanation signal curve parameters for characterization of astigmatic corneas

Effect of congenital blepharoptosis on corneal biomechanical properties and changes after ptosis surgery

OBJECTIVES

We studied the difference in the corneal biomechanical parameters of ptotic and fellow eyes in patients with congenital blepharoptosis. The correlations between corneal biomechanical parameters and demographic or ocular parameters, and the changes after surgery were also researched.

METHODS

The corneal biomechanical parameters were measured by Corvis ST tonometry. The central corneal thickness (CCT), axial length (AL) and keratometry measurements were performed with LenStar LS900, and intraocular pressure (IOP) by non-contact applanation tonometry. The parameters were evaluated for the effect of ptosis and the relationship of corneal biomechanical parameters. These examinations were repeated 6 months after blepharoptosis surgery.

RESULTS

Twenty-nine patients were enroled. The Corvis ST parameters (Deformation amplitude [DA], A1 times, and A1 velocity), CCT, IOP with NCT, IOP with corrected, differed significantly between ptotic and fellow eyes. CCT was significantly positively correlated with Length A1 and IOP with Corvis, and negatively correlated with IOP corrected by Corvis of the ptotic eyes. The same tendency was found in the fellow eyes. Six months after the ptosis surgery, the differences in corneal biomechanics parameters between ptotic eyes and fellow eyes were not significantly changed.

CONCLUSIONS

Congenital blepharoptosis causes significant corneal biomechanical changes measured by Corvis ST. The ptotic eyes had thicker and less deformable corneas. The differences in corneal biomechanics between ptotic eyes and fellow eyes were mostly related to CCT changes. Six months after surgery, these differences in corneal biomechanics did not change significantly.

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.

The Relationship between the Waveform Parameters from the Ocular Response Analyzer and the Progression of Glaucoma

PURPOSE

To investigate the usefulness of waveform parameters measured with the Ocular Response Analyzer (Reichert Ophthalmic Instruments, Depew, NY) in assessing the progression of glaucomatous visual field (VF).

DESIGN

Observational cross-sectional study.

PARTICIPANTS

One hundred and one eyes with primary open-angle glaucoma in 68 patients with 8 reliable VFs using the Humphrey Field Analyzer (Carl Zeiss Meditec, Inc., Dublin, CA).

METHODS

The mean of total deviation (mTD) value of the 52 test points in the 24-2 Humphrey Field Analyzer VF test pattern was calculated, and the progression rate of mTD was determined using 8 VFs. Ocular Response Analyzer measurement was performed 3 times in the same day, and the average values of the 3 measurements were used in the analysis. Then, the optimal linear mixed model was selected using 7 parameters: age, mean and standard deviation of intraocular pressure with the Goldmann applanation tonometry during the observation period, central corneal thickness, axial length, mTD in the initial VF, and corneal hysteresis (CH) other than waveform parameters, henceforth known as the basic model. In addition, using the 37 waveform parameters, the optimal model for the mTD progression rate was identified, according to the second-order bias-corrected Akaike information criterion (AICc) index, using 15 preselected waveform parameters with the least absolute shrinkage and selection operator regression (henceforth known as the waveform model).

MAIN OUTCOME MEASURES

Optimal linear mixed models for the mTD progression rate, as determined by AICc index.

RESULTS

The mean ± standard deviation mTD progression rate was -0.25±0.31 dB/year. The basic model was mTD progression rate = -0.94 + 0.075 × CH (AICc = 46.71). The waveform model was mTD progression rate = 1.25 - 0.066 × path2 - 0.000099 × p2area + 0.0021 × mslew2 (AICc = 44.95). The relative likelihood of the latter model being the optimal model was 6.23 times greater than that of the former model.

CONCLUSIONS

Ocular Response Analyzer waveform parameters were correlated significantly with glaucomatous VF progression and showed a stronger than correlation with VF progression than CH.