The peripapillary retinal nerve fiber layer may start to thin from the third decade of life.
Researchers have provided reference data from a longitudinal study on age-related changes in peripapillary retinal nerve fiber layer (pRNFL) thickness and intraocular pressure (IOP) in healthy young adults. The findings, based on the Raine Study cohort in Western Australia, could help distinguish physiological changes from early signs of disease such as glaucoma.
Led by Samantha Sze-Yee Lee, of the University of Western Australia, the researchers assessed participants from the Generation 2 cohort of the Raine Study, who underwent comprehensive eye examinations at ages 20 years and 28 years. Measures included spectral-domain optical coherence tomography (SD-OCT) for pRNFL thickness (n = 693), rebound tonometry for IOP (n = 712), and Scheimpflug imaging for central corneal thickness (CCT; n = 680).
The researchers found that over the 8-year period, global pRNFL thickness decreased from an average of 100.6 μm to 97.9 μm. This change translated to an annual thinning rate of 0.27 μm, following adjustments for factors such as sex, ethnicity, axial length, baseline IOP, Bruch’s membrane opening diameter, and scan diameter. Sectoral thinning rates ranged from 0.06 to 0.38 μm/year, for which statistically significant changes were observed in most sectors except the inferonasal and superotemporal regions.
An interaction analysis revealed that patients with shorter axial lengths (less myopic eyes) exhibited slightly faster global pRNFL thinning—an additional 0.03 μm/year per mm decrease in axial length.
The researchers observed a significant reduction in IOP from a mean of 15.4 mmHg at age 20 years to 13.9 mmHg at age 28 years, which corresponded to an average annual decline of 0.18 mmHg. Multivariable analysis confirmed this trend and identified a significant interaction with CCT: for every 10 μm increase in CCT, the rate of IOP decline slowed by 0.008 mmHg/year.
Other variables such as sex, axial length, body mass index, blood pressure, and resting heart rate had limited or no significant effects on IOP change. “Further exploration on the factors that influence the longitudinal rate of pRNFL change is warranted,” the study authors wrote, as is the mechanism of the overall slight decline in IOP, they added.
CCT increased modestly during the study period, from an average of 537.5 μm to 540.2 μm, or an annual thickening of 0.18 μm. This change was not significantly influenced by sex, contact lens wear, or axial length.
The researchers acknowledged attrition of almost half of the study participants, partially as a result of COVID-19, and partially as expected given the phenomenon of higher attrition rates in longer follow-ups. Other limitations included a lack of differential rate of changes and imaging constraints.
They concluded: “Findings from the current study provide a reference with which the longitudinal change in pRNFL thickness and IOP in young adults could be compared. [S]uch reference data would be invaluable in assessing disease onset and progression in young [patients] with high genetic risk of glaucoma.”
A full list of author disclosures can be found in the published research.