Physiological change in ganglion cell inner plexiform layer and nerve fibre layer thickness over six years.

Background: To evaluate the 6-year physiological rates-of-change in ganglion cell inner plexiform layer (GCIPL) and retinal nerve fibre layer (RNFL) thickness measured with optical coherence tomography.

Methods: We included 2202 out of 2661 subjects from the population-based Singapore Chinese Eye Study who returned for follow-up 6 years after baseline examination (follow-up rate 87.7%). OCT scans with signal strength (SS) <6, imaging errors, and ocular pathologies were excluded. A linear mixed model was used to measure the rates-of-change in GCIPL and RNFL thickness. Time and difference between baseline and follow-up scan SS were modelled as fixed effect. Baseline age, baseline measurement, gender, hypertensive medication, diabetes status, cardiovascular disease, smoking status, body mass index, spherical equivalent (SE), intraocular pressure and optic disc area were each analysed in an interaction term with time.

Results: The adjusted mean rate-of-change in average GCIPL was -0.312 μm/year in males and -0.235 μm/year in females. Older age and thicker GCIPL thickness at baseline were associated with higher rates-of-change while females and more hyperopic SE were associated with lower rates-of-change. The adjusted mean rate-of-change in average RNFL was -0.374 μm, with higher rates-of-change in the vertical quadrants and no differences between genders. Older age and thicker RNFL thickness at baseline were associated with higher rates-of-change in average RNFL and RNFL thickness in the vertical quadrants, and vice versa for each unit increase in scan SS and SE.

Conclusion: Our population cohort provides data on physiological thinning of GCIPL and RNFL with age. Differentiating physiological changes in GCIPL and RNFL is important for more accurate clinical assessment.