Application of Corvis ST to evaluate the effect of femtosecond laser-assisted cataract surgery on corneal biomechanics

Association between Ocular Parameters and Intraocular Pressure Elevation during Femtosecond Laser-Assisted Cataract Surgery in Open-Angle Glaucoma and Nonglaucoma Individuals

In this study, we evaluate the association between biometrics and intraocular pressure (IOP) during femtosecond laser-assisted cataract surgery (FLACS) in normal patients and those with open-angle glaucoma (OAG). A retrospective cross-sectional study was conducted. A total of 103 patients who had received elective FLACS were enrolled, and those with OAG who received FLACS were further divided into a subgroup. The perioperative IOP of FLACS was measured before, during, and after the suction procedure. Demographic data and preoperative biometrics were collected from the medical records. The generalized linear model was applied to yield the adjusted odds ratio (aOR) and corresponding 95% confidence interval (CI) of each biometric for the IOP elevation in the whole group and the OAG subgroup. The mean preoperative IOP was 20.96 ± 4.79 mmHg, which rose to 55.37 ± 11.58 mmHg during suction, and decreased to 23.75 ± 6.42 mmHg after suction; the IOP both during and after suction was significantly higher than the presuction IOP (both p < 0.001). The mean IOP elevation was 34.41 ± 9.70 mmHg in the whole study population, and the difference in IOP elevation between OAG and nonglaucoma subgroups was not significant (p = 0.159). In the whole group, the presuction IOP, postdilated pupil size (PPS), and central corneal thickness (CCT) were positively corrected to higher IOP elevation (all p < 0.05), while axial length (AL) was negatively related to IOP elevation (aOR: 0.020, 95% CI: 0.008–0.699, p = 0.042). For the OAG subgroup, the longer AL was more significantly correlated to lower IOP elevation compared to those without glaucoma (aOR: 0.231, 95% CI: 0.106–0.502, p = 0.006). In conclusion, presuction IOP, PPS, and CCT are related to higher IOP during FLAC, while the AL is negatively correlated to the IOP elevation in FLACS, especially for patients with OAG. Reviewing these parameters before FLACS may enable physicians to find patients who are at risk of IOP elevation.

Corneal Biomechanics for Ocular Hypertension, Primary Open-Angle Glaucoma, and Amyloidotic Glaucoma: A Comparative Study by Corvis ST

BACKGROUND

To evaluate biomechanical parameters of the cornea provided by Corvis ST in patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma and to compare with healthy controls.

METHODS

This was a cross-sectional study of patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma that underwent Corvis ST imaging. Primary outcome was the comparison of corneal biomechanical parameters between study groups after adjusting for age, gender, Goldmann intraocular pressure (GAT-IOP), and prostaglandin analogues medication. Secondary outcome was the comparison of different IOP measurements in each group.

RESULTS

One hundred and eighty-three eyes from 115 patients were included: 61 with primary open-angle glaucoma, 32 with amyloidotic glaucoma, 37 with ocular hypertension and 53 were healthy controls. Amyloidotic glaucoma group had smaller radius (p=0.025), lower deflection amplitude at highest concavity (p=0.019), and higher integrated radius (p=0.014) than controls. Ocular hypertension group had higher stiffness parameter at first applanation (p=0.043) than those with primary open-angle glaucoma, and higher stress-strain index (p=0.049) than those with amyloidotic glaucoma. Biomechanically corrected intraocular pressure was significantly lower than Goldmann intraocular pressure in group with primary open-angle glaucoma (p=0.005) and control group (p=0.013), and Goldmann intraocular pressure adjusted for pachymetry in group with primary open-angle glaucoma (p=0.01).

CONCLUSION

Eyes with amyloidotic glaucoma have more deformable corneas, while eyes with ocular hypertension have less deformable corneas. These findings may be linked to the susceptibility to glaucomatous damage and progression. There were significant differences between Goldmann applanation tonometry and biomechanically corrected intraocular ocular pressure provided by Corvis ST.

Relationship of axial length and corneal biomechanical properties with susceptibility to unilateral normal-tension glaucoma

PURPOSE

Corneal biomechanics, reflecting structural vulnerabilities of the eyeball, may participate in the pathogenesis of unilateral normal-tension glaucoma. This study investigated the pathophysiology of unilateral normal-tension glaucoma using Corvis ST (OCULUS Optikgeräte GmbH) and other ocular characteristics.

METHODS

Eighty-three patients with normal-tension glaucoma with unilateral visual field loss and structurally unaffected fellow eyes and 111 healthy controls were included in this prospective study. Dynamic corneal response parameters, intraocular pressure measured by rebound tonometry, central corneal thickness, and axial length were assessed on the same day. Measurements were compared between affected eyes, unaffected fellow eyes, and control eyes. Risk factors for normal-tension glaucoma and unilateral involvement were the main outcome measures.

RESULTS

A shorter first applanation time (adjusted odds ratio, 0.061; 95% confidence interval, 0.018-0.215) and a larger peak distance (adjusted odds ratio, 4.935; 95% confidence interval, 1.547-15.739) were significant risk factors for normal-tension glaucoma and were associated with greater glaucoma severity (both P < 0.001). Axial length (adjusted odds ratio, 29.015; 95% confidence interval, 4.452-189.083) was the predominant risk factor for unilateral involvement in patients with normal-tension glaucoma.

CONCLUSION

The eyes with normal-tension glaucoma were more compliant than healthy eyes. Axial elongation-associated optic nerve strain may play an important role in unilateral normal-tension glaucoma with similar corneal and scleral biomechanics in both eyes.

Effects of Femtosecond Laser-Assisted Cataract Surgery on Macular and Choroidal Thickness in Diabetic Patients

Introduction

This study aimed to compare the short-term changes in retinal and choroid thickness in diabetic patients after femtosecond laser-assisted cataract surgery (FLACS) and phacoemulsification (PE) surgery.

Methods

A total of 47 eyes in the PE group and 44 eyes in the FLACS group were included. All patients underwent measurement of central macular thickness (CMT) and subfoveal choroidal thickness (SFCT) before and after surgery using optical coherence tomography (OCT).

Results

The effective phaco time (EPT) in the FLACS group was significantly reduced. The BCVA differed significantly between the two groups at 1 week and 1 month after surgery. The CMT in both groups increased at 1 week after the operation. It did not return to the preoperative level until month 12 in the PE group. In the FLACS group, the CMT began to decrease at month 3 and recovered to the preoperative level at month 12. The SFCT of the two groups increased at week 1; it began to decrease at month 6 in the PE group but did not recover to the preoperative level until month 12. The SFCT in the FLACS group recovered to preoperative levels at month 6. In the PE group, baseline CMT values predicted CMT change at week 1 and months 1, 3 and 12 after surgery. In the FLACS group, baseline CMT predicted CMT changes at week 1, month 1 and month 3. In the FLACS group, EPT predicted SFCT change at month 3.

Conclusion

FLACS is safe and effective in patients with no fundus change or mild diabetic retinopathy. It has advantages in effectively reducing EPT, achieving good vision earlier and promoting faster recovery of the retinal and choroidal thickness. Preoperative CMT is a significant predictor of CMT changes in the early period after FLACS.

A comparison of the corneal biomechanics in pseudoexfoliation glaucoma, primary open-angle glaucoma and healthy controls using Corvis ST

Purpose

To compare the corneal biomechanical parameters between pseudoexfoliation glaucoma (PXG), primary open-angle glaucoma (POAG) and healthy controls using Corvis ST.

Methods

A prospective, cross-sectional study was conducted which included 132 treatment-naïve eyes which underwent Corvis ST. The study cohort comprised of 44 eyes with PXG, 42 eyes with POAG and 46 healthy controls. Corneal biomechanical parameters, which included corneal velocities, length of corneal applanated surface, deformation amplitude (DA), peak distance and radius of curvature, were compared between the groups using analysis of variance models.

Results

The 3 groups were demographically similar. The mean IOP was 15.7 ±3 mmHg in the control group, 21.3 ±5 mmHg in the POAG group and 25.8 ±7 mmHg in the PXG group (p<0.0001). Corneal pachymetry was similar across the 3 groups. Mean DA was significantly lower (p<0.0001) in the PXG group (0.86 ±0.18 mm) compared to the POAG group (0.97 ±0.14mm) and the control group (1.10 ±0.15mm). Corneal velocities were also found to be statistically significantly different between the groups. However, after adjusting for IOP, there was no difference in any of the biomechanical parameters between the 3 groups.

Conclusion

Corneal biomechanical parameters measured on Corvis ST are not different between eyes with PXG, POAG and healthy controls after adjusting for IOP.

A comparison of the corneal biomechanics in pseudoexfoliation syndrome, pseudoexfoliation glaucoma, and healthy controls using Corvis® Scheimpflug Technology

Purpose

To compare the corneal biomechanical parameters among pseudoexfoliation syndrome (PXF), pseudoexfoliation glaucoma (PXG), and healthy controls using Corvis Scheimpflug Technology (ST).

Methods

A prospective, cross-sectional study of 141 treatment-naïve eyes that underwent Corvis ST was conducted. These included 42 eyes with PXF, 17 eyes of PXF with ocular hypertension (PXF + OHT) defined as intraocular pressure (IOP)> 21 mmHg without disc/field changes, 37 eyes with PXG, and 45 healthy controls. Corneal biomechanical parameters, which included corneal velocities, length of corneal applanated surface, deformation amplitude (DA), peak distance, and radius of curvature, were compared among the groups using analysis of variance models.

Results

The four groups were demographically similar. The mean IOP was lower in the controls (15.6 ± 3 mmHg) and PXF group (16.0 ± 3 mmHg) compared to the other two groups (>24 mmHg). Corneal pachymetry was similar across the four groups. Mean DA was significantly lower (P < 0.0001) in the PXG group (0.91 ± 0.18 mm) and the PXF + OHT group (0.94 ± 0.13 mm) when compared to the PXF (1.10 ± 0.11 mm) and control groups (1.12 ± 0.14 mm). Corneal velocities were also found to be statistically significantly lower in PXG and PXF + OHT compared to the PXF and control groups. However, after adjusting for age and IOP, there was no difference in any of the biomechanical parameters among the four groups.

Conclusion

Corneal biomechanical parameters measured on Corvis ST are not different between healthy controls and eyes with PXF and PXG. Since PXG is a high-pressure glaucoma, corneal biomechanics may not play an important role in its diagnosis and pathogenesis.

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.

Changes in Corneal Biomechanics and Intraocular Pressure Following Cataract Surgery

PURPOSE

To investigate the effects of cataract surgery on corneal biomechanics and intraocular pressure (IOP) measured with the updated Corvis ST tonometer (CST).

DESIGN

Prospective, interventional case series study.

METHODS

This study included 39 eyes of 39 cataract patients. CST measurements were performed at presurgery (Pre) as well as 1 week (1W), 1 month (1M), and 3 months (3M) postsurgery. The following CST parameters were recorded: deformation amplitude max (DA max), DA ratio max 1 mm and 2 mm, integrated radius, stiffness parameter at applanation 1 (SP A1), Ambrosio relational thickness to the horizontal profile (ARTh), Corvis biomechanical index (CBI), central corneal thickness (CCT), noncorrected intraocular pressure (IOPnct), and biomechanically corrected IOP (bIOP). IOP was also measured with Goldmann applanation tonometry and the noncontact tonometer CT-90A. All measurements were compared at each period using the linear mixed model, with and without adjustment for bIOP and CCT.

RESULTS

All IOP measurements decreased over time (P < .01). CCT was increased at 1W and 3M (P < .01), whereas ARTh was decreased at 1W and 1M (P < .01), but returned to its Pre level at 3M. DA max and Integrated radius were increased at 3M (P < .01), whereas SP A1 was decreased at 3M (P < .01). CBI was increased at 1W (P < .01), but returned to its Pre level at 1M.

CONCLUSIONS

IOP and Corneal biomechanical properties are changed after cataract surgery. In particular, SP A1 decreases while DA max and integrated radius increase, even at 3M, suggesting a less stiff cornea.