A study performed at the Keck School of Medicine at the University of Southern California recently suggested that axial length (AL) disturbs the IOP-microvascular autoregulation relationship in patients with glaucoma but not in healthy individuals.

The study focused on African Americans, a particularly important population in the study of how vascular factors contribute to glaucoma onset and progression. The researchers examined the association between IOP and peripapillary vessel density with a focus on how this relationship is modulated by AL in subjects with and without glaucoma. The team performed optic disc OCT-A 6x6mm scans on a total of 1,093 participants (1,028 non-glaucoma subjects and 65 subjects with glaucoma), with measurements on a total of 1,539 eyes (1,453 eyes without glaucoma and 86 eyes with glaucoma). The specific cutoff to differentiate long and short AL was 23.46mm, based on the median AL of all eyes in the study.

After controlling for age, signal strength and RNFL, higher IOP was significantly associated with decreased peripapillary vessel density (pVD) in subjects with glaucoma, specifically among those with longer ALs. Interestingly, this relationship between IOP and pVD was not seen among subjects with glaucoma with shorter ALs or among healthy subjects in either AL group, even among those nonglaucomatous eyes with IOP≥20mm Hg.

“Our cross-sectional findings support (but do not prove) the idea that myopic eyes with glaucoma may be susceptible to retinal autoregulation breakdown in the setting of higher IOP,” the researchers concluded. “Longitudinal data is needed to verify this idea as well as further investigate the mechanisms of the interactive effect of AL and IOP on peripapillary vessel density reduction and glaucomatous development.”