Researchers have identified a positive correlation between thinning central corneas and optic nerve strain rate (ONSR), as well as orbital fat strain rate (OFSR), according to a study published in International Ophthalmology.
The investigation centered on finding the impact glaucoma and central corneal thickness (CCT) have on optic nerve head biomechanics. Neither glaucomatous damage nor CCT could be directly associated with changes to the optic nerve head biomechanics. As such, the usefulness of optic nerve head biomechanical studies requires further research.
“This was the first study evaluating the relationship between CCT and optic nerve elasticity.” the study says. Through a prospective study of patients in Turkey, researchers sought to evaluate how glaucoma and changes to the CCT, a known risk factor for glaucoma, changes could affect optic nerve head biomechanics. Investigators conducted a record review of patients with primary open-angle glaucoma and patients with CCT less than 510 µm and greater than 570 µm. Volunteers who applied to the clinic but had no ocular disorders were included as a control group.
All participants underwent grayscale ultrasonography and real-time elastography. Optic nerve strain rate and orbital fat tissue were assessed after 10 to 12 measurement cycles. Patients were divided into 1 of 4 groups based on CCT measurements and glaucoma presence: group 1 included those without glaucoma but with thin corneas (n=32), group 2 included those with glaucoma and thin corneas (n=34), group 3 included those without glaucoma with thick corneas (n=34), and group 4 included those with glaucoma and with thick corneas (n=10).
Among all groups, a statistically significant difference in optic nerve strain rate and orbital fat was not found, nor were differences in strain ratio of orbital fat to optic nerve head (SROFON), strain ratio of orbital fat to the medial part of the optic nerve (SROFMON), and strain ratio of orbital fat to the lateral part of the optic nerve (SROFLON). Real-time elastography results demonstrated a “positive but not strong” correlation between optic nerve strain rate, orbital fat strain rate, and mean CCT in participants with CCT 510 µm or less. No statistical difference between participants with and without glaucoma in terms of optic nerve strain rate and SROFON was found, regardless of mean CCT.
Study limitations include differences in the mean ages of each group, as well as the use of strain elastography techniques that are not eye-specific and may lead to variable results. Additionally, the investigators noted that CCT may not be sensitive enough to measure the mechanical properties of optic nerves.
“The usefulness of [optic nerve head] elastography techniques for understanding glaucoma and its risk factors should be investigated on [a] larger and more homogenous patient series,” the research suggests.
Aksoy NÖ, Çakir B, Aksoy YE, et al. Effects of glaucoma and central corneal thickness on optic nerve head biomechanics. Int Ophthalmol. Published online January 2, 2021. doi:10.1007/s10792-020-01686