Longer Axial Length Potentiates Relationship of Intraocular Pressure and Peripapillary Vessel Density in Glaucoma Patients

The Mirror Theory: Parallels between Open Angle and Angle Closure Glaucoma

Glaucoma is a widespread ophthalmological disease, with a high impact and frequent visual morbidity. While the physiopathology of the two types of primary glaucoma (open angle and angle closure) has been studied, there seems to be little relationship between the two. In this study, we gather clinical and preclinical data to support the idea that the two primary glaucomas are "mirrored" in terms of morphological parameters and disease physiopathology. In short, primary angle closure glaucoma (PACG) is associated with hyperopia and low axial length, and primary open angle glaucoma (POAG) is associated with myopia and high axial length. Moreover, in PACG and in primary angle closure or primary angle closure suspect cases, while there is extensive iridotrabecular contact, the intraocular pressure (IOP) is still maintained in the lower half of the normal range throughout the evolution of the disease, which suggests a baseline trabecular hyperfiltration in PACG. In the opposite case, myopic eyes with open angles and a higher risk of developing POAG often have a baseline IOP in the upper half of the normal range, suggesting a baseline trabecular hypofiltration. As we explore clinical, genetic and animal model data regarding these opposing aspects, we hypothesize the existence of a mirroring relationship between PACG and POAG. Defining the relationship between the two potentially blinding diseases, with a high prevalence worldwide, may aid in understanding the mechanisms better and refining diagnosis and treatment. Thus, our theory has been named the Mirror Theory of Primary Glaucomas.

Agreement of intraocular pressure measurement with Corvis ST, non-contact tonometer, and Goldmann applanation tonometer in children with ocular hypertension and related factors

AIM

To access the agreement of intraocular pressure (IOP) values obtained from biomechanically corrected tonometer [Corvis ST (CST)], non-contact tonometer (NCT), and Goldmann applanation tonometer (GAT) in children with NCT measured-IOP (NCT-IOP) values of 22 mm Hg or more, and related factors.

METHODS

A total of 51 eyes with NCT-IOP≥22 mm Hg in children aged 7 to 14y were examined and IOP was measured by CST, NCT, and GAT. Based on GAT measured IOP (GAT-IOP), ocular hypertension (OHT) group (≥22 mm Hg, 24 eyes) and the non-OHT group (<22 mm Hg, 27 eyes) were defined. We compared the agreement of the three measurements, i.e., CST measured IOP (CST-IOP), GAT-IOP, and NCT-IOP, and further analyzed the correlation between the differences in tonometry readings, central corneal thickness (CCT), axial length (AL), optic disc rim volume, and age.

RESULTS

Compared with the OHT group, thicker CCT, larger rim volume, and higher differences between NCT-IOP and GAT-IOP, were found in the non-OHT group. The differences between CST-IOP and GAT-IOP were lower than the differences between NCT-IOP and GAT-IOP in both groups. The mean differences in CST-IOP and GAT-IOP were 1.26 mm Hg (95% limit of agreement ranged from 0.1 to 2.41 mm Hg, OHT group) and 1.20 mm Hg (95% limit of agreement ranged from -0.5 to 3.00 mm Hg, non-OHT group), and the mean differences in NCT and GAT were 3.90 mm Hg (95% limit of agreement ranged from -0.19 to 9.70 mm Hg, OHT group) and 6.00 mm Hg (95% limit of agreement ranged from 1.50 to 10.50 mm Hg, non-OHT group). The differences between CST-IOP and GAT-IOP were not related to CCT, age, and AL in both groups; while the differences between NCT-IOP and GAT-IOP were related to CCT in the OHT group (r=0.93, P<0.001) and to CCT and AL in the non-OHT group (r=0.66, P<0.001, r=-0.81, P<0.001).

CONCLUSION

The accuracy of NCT in the diagnosis of pediatric OHT is low. The agreement of CST-IOP and GAT-IOP was significantly higher in children with and without OHT than in those with NCT-IOP and GAT-IOP. Therefore, CST can be used as a good alternative for IOP measurement in children. The impacts of CCT and AL on NCT measurement need to be fully considered when managing childhood IOP.

Comparison of Corvis ST Parameters between Primary Open-Angle Glaucoma and Primary Angle-Closure Glaucoma

BACKGROUND

We compared corneal visualization Scheimpflug technology (CST) parameters between eyes with primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

METHODS

A retrospective analysis was performed on data from 89 eyes with POAG and 83 eyes with PACG that had CST examinations. CST parameters were compared between eyes with POAG and those with PACG using a linear mixed model (LMM).

RESULTS

No differences were observed in age, central corneal thickness, intraocular pressure, or use of antiglaucoma eye drops between the two groups. Patients with PACG had a significantly shorter axial length (AL), a higher proportion of females, CST parameters, longer applanation 2 (A2) time, deeper A2 deformation amplitude, shorter peak distance, longer whole eye movement, and longer whole eye movement time than patients with POAG. The highest concavity (HC) length and PD showed a significant positive correlation with AL. However, A1 length, A1 deformation amplitude, A2 time, A2 velocity, A2 length, A2 deformation amplitude, HC time, whole eye movement, and whole eye movement time were negatively correlated with AL.

CONCLUSIONS

The biomechanical properties of the cornea differed between POAG and PACG. In some parts, AL differences between the POAG and PACG groups might contribute to the variation in CST parameters.

Ocular and systemic determinants of perifoveal and macular vessel parameters in healthy African Americans

PURPOSE

To determine the relationship of various systemic and ocular characteristics with perifoveal and macular vessel density in healthy African American eyes.

DESIGN

A population-based cross-sectional study of prospectively recruited African Americans ≥40 years of age. Participants underwent 3×3 mm and 6×6 mm macula scans using spectral-domain optical coherence tomography angiography (OCTA), clinical examinations and clinical questionnaires. Participants with glaucoma, severe non-proliferative diabetic retinopathy, proliferative diabetic retinopathy and macular oedema were excluded. Custom MATLAB based software quantified vessel area density (VAD) and vessel skeleton density (VSD) in the superficial retinal layer of the macula. Multivariable regression analysis, controlling for inter-eye correlation, was performed to determine systemic and ocular determinants of macular vessel metrics using stepwise selection. Candidate variables included: age, gender, body mass index, history of smoking, history of diabetes, diabetes duration, history of stroke or brain haemorrhage, systolic blood pressure, diastolic blood pressure (DBP), pulse pressure, mean arterial pressure, central subfield thickness (CSFT), visual field mean deviation, intraocular pressure, axial length (AL), mean ocular perfusion pressure and signal strength (SS).

RESULTS

A total of 2221 OCTA imaged eyes from 1472 participants were included in this study. Reduced perifoveal and macular VAD and VSD were independently associated with longer AL, reduced SS, reduced CSFT and older age. Male gender and lower DBP were also associated with reduced perifoveal and macular VSD.

CONCLUSIONS

When interpreting OCTA images in a clinical setting, it is important to consider the effects ocular and systemic characteristics may have on the macular microcirculation.

Change of Retinal Vessel Density After Lowering Intraocular Pressure in Ocular Hypertension

Purpose: To investigate the relationship between retinal microvasculature changes and intraocular pressure (IOP) for ocular hypertension (OHT) patients and further assess the factors associated with retinal microcirculation changes.

Methods: This was a single-center prospective study designed for OHT patients, which consisted of two visits. After collecting baseline data of those who met the eligibility criteria, these patients were treated with latanoprost 0.005% ophthalmic solution for 4 weeks. Peripapillary vessel density (VD) of radial peripapillary capillaries (RPC) layer, macular VD in both superficial and deep layers, and foveal avascular zone (FAZ) area were measured by optical coherence tomography angiography (OCTA) before and after the treatment. We compared the changes in IOP and VD among the two visits by paired-sample t-test. Bonferroni correction was applied. Factors associated with VD changes were analyzed by linear regression analysis.

Results: Thirty-four eyes of thirty-four patients were included. The mean IOP decreased by 6.5 ± 2.2 mmHg (p < 0.001). The peripapillary RPC VD increased significantly from 51.8 ± 2.5 to 53.0 ± 3.1% (Adjusted-p = 0.012). We found no significant difference in detailed sectors of the peripapillary region after correction. In the macular area, both the superficial and deep layers in foveal (superficial: 0.2 ± 1.9%, p = 0.523; deep: 0.0 ± 2.3%, p = 0.969) and parafoveal (superficial: 0.3 ± 3.0%, p = 0.565; deep: 0.5 ± 3.1%, p = 0.423) VD remained unchanged. The decrease of the mean FAZ area was insignificant (p = 0.295). The percentage of IOP reduction (β = 0.330, p = 0.031) and the baseline RNFL thickness (β = 0.450, p = 0.004) significantly correlated with the percentage of peripapillary RPC VD improvement in the multivariate linear regression analysis.

Conclusion: The peripapillary VD in OHT patients increased after the reduction of IOP. The mild change of IOP did not alter the microcirculation in the macula. In addition, the percentage of IOP change and the baseline RNFL thickness were independent factors for the peripapillary RPC VD improvement.