Data analysis of the ocular response analyzer for improved distinction and detection of glaucoma

Corneal retardation time as an ocular hypertension disease indicator

Objective.A detailed analysis of the corneal retardation timeτas a highly related parameter to the intraocular pressure (IOP), and its plausible role as an indicator of ocular hypertension disease.Approach.A simple theoretical expression forτis derived within the corneal viscoelastic model of Kelvin-Voigt with 3 elements. This retardation time can be easily calculated from the well-known signal and pressure amplitudes of non-contact tonometers like the Ocular Response Analyzer (ORA). Then, a population-based study was performed where 100 subjects aged from 18 to 30 were analyzed (within this group, about 10% had an elevated IOP with more than 21 mmHg).Main results.A clear relationship between the corneal retardation time and the corneal-compensated intraocular pressure (IOPcc) was found, underlying the risk for ocular hypertensive (OHT) subjects with lowerτvalues to develop hypertension illnesses (due to the inability of poorly viscoelastic corneas to absorb IOP fluctuations, resulting in probable optic nerve damage).Significance.Our results might provide an useful tool to systematically discern which OHT patients (and even those with normal IOP values) are more likely to suffer glaucoma progression and, consequently, ensure an early diagnosis.

Short-Time Changes of Intraocular Pressure and Biomechanics of the Anterior Segment of the Eye during Water Drinking Test in Patients with XEN GelStent

Purpose: Little is known about short-term changes in intraocular pressure (IOP) following minimally invasive glaucoma surgeries, such as post-XEN GelStent implantation. Although the importance of corneal biomechanics in glaucoma diagnostics has been reported, little work has been conducted on postoperative description of changes when the structure of the anterior segment is altered. The aim of presented study was to evaluate the changes in the biomechanical parameters of the anterior segment of the post-XEN GelStent implantation eyes. Patients and Methods: This investigator-initiated, open-label, prospective, single-center study recruited patients. Patients with primary open-angle glaucoma (POAG) after XEN GelStent implantation versus matched POAG controls (considered as control group/CG) treated pharmacologically were screened. Water loading was conducted using 10 mL of water per kilogram of body weight for ≤5 min. Goldmann applanation tonometry (GAT), corneal hysteresis (CH), and corneal resistance factor (CRF) were performed before water loading and after every 15 min up to 1 h. Results: The water drinking test (WDT) was positive in 3.7% (1 out of 27) of patients in the post-XEN group compared with 22.7% (5 out of 22) of patients in the control group (CG; p < 0.05). Mean fluctuations in GAT during the WDT were higher in the CG group (3.6 ± 2.5 mmHg vs. 2.9 ± 1.3 mmHg, p < 0.001). CRF and CH changed significantly only in the post-XEN group. The mean peak of CH and CRF occurred at 15 and 30 min of the test in the post-XEN group (p = 0.001). Conclusion: WDT is important to assess the ability of compensation mechanisms to reduce fluctuations in IOP after water upload. The relationship between biomechanics of the anterior segment and glaucoma may have substantial impact on surgical outcome evaluation.

Effects of glaucoma and central corneal thickness on optic nerve head biomechanics

PURPOSE

To evaluate effects of glaucoma and central corneal thickness (CCT) on optic nerve head biomechanics.

METHODS

Four groups were formed according to CCT measurements and the presence of glaucoma. Glaucomatous patients with thin (< 510 µ) and thick (> 570 µ) corneas composed groups 1 and 3, respectively. Nonglaucomatous patients with thin and thick corneas composed groups 2 and 4, respectively. Real-time elastography (RTE) was performed on all groups, and optic nerve strain rate (ONSR), orbital fat strain rate (OFSR), and strain ratio of orbital fat to the optic nerve and medial and lateral parts of the optic nerve (SROFON, SROFMON, SROFLON, respectively) were obtained and compared between groups. The correlations between CCT and these parameters were also investigated.

RESULTS

Statistically significant difference was not found between groups in terms of strain rate of optic nerve and orbital fat, SRFON, SROFMON and SROFLON. There was a positive correlation between ONSR and OFSR and mean CCT in patients with CCT thinner than 510 µ (p: 0.03 r: 0.26, p: 0.01 r: 0.32 respectively).

CONCLUSION

SROFON, SROFLON and SROFMON values did not differ between glaucomatous and nonglaucomatous patients with thin or thick CCTs. The correlations between CCT and OFSR and ONSR were found to be statistically significant in patients with thin CCT.