Optic nerve head and retinal nerve fiber layer OCT values in a population-based sample of healthy older adults from urban areas of Parintins, Brazilian Amazon Region

Abstract

Purpose: The Brazilian Amazon Region Eye Survey (BARES) is an ongoing population-based study to determine the prevalence and causes of visual impairment/ blindness in older adults. Spectral-domain optical coherence tomography (SD-OCT) was performed in a subset of participants from urban areas to investigate optic nerve head (ONH) parameters and retinal nerve fiber layer (RNFL) thickness in healthy eyes.

Methods: Subjects were enumerated through a door-to-door survey and those with ages 45 years and older were invited for a comprehensive eye exam. ONH e RNFL measurements were obtained through dilated pupils using iVue-100 SD-OCT in a subset of participants with healthy eyes. ONH parameters included cup-to-disc area ratio, vertical and horizontal cup-to-disc ratios, disc and rim areas (mm²) and cup volume (mm³). RNFL thickness (µm) was measured overall and for inferior, nasal, superior and temporal quadrants. Data from one eye randomly chosen of each participant were analyzed. The influence of gender, age, IOP and refractive errors was also analyzed. Statistical significance was considered as p≤0.05.

Results: An overall sample of 1180 adults was examined and out of these, 64 (36 females) were eligible for this study. Age ranged from 45 to 65 years (mean=52±5 years). Considering ONH parameters, mean area, vertical and horizontal cup-to-disc ratios were respectively 0.34±0.16, 0.53±0.18 and 0.62±0.21. Mean disc area was 2.34±0.43mm², rim area 1.50±0.31mm², and cup volume 0.10±0.20mm³. The mean overall RNFL thickness was 104.14±9.72µm, with thickest RNFL in the inferior quadrant (132.56±15.62µm), followed by the superior (130.33±15.79µm), nasal (76.95±10.96µm) and temporal (76.48±10.99µm) ones. There were no significant differences in ONH and RNFL parameters for gender, IOP or refractive errors. Older age was significantly correlated with smaller rim area (β=-0.015, p=0.045), thinner overall RNFL (β=-0.497, p=0.032) and superior RNFL (β=-0.902, p=0.016).

Conclusions: This study provided SD-OCT normative values of ONH and RNFL parameters for this cohort of healthy older adults from urban areas of the Amazon region. It suggests that age should be considered while interpreting these measurements, which are important for detection of pathological conditions in this population.