Systemic and ocular factors determining the circumpapillary retinal nerve fibre layer thickness in an unselected adult population

Introduction The retinal nerve fibre layer (RNFL) thickness assessed by optical coherence tomography (OCT) scanning is used for the diagnosis and monitoring of diseases in the retina and the optic nerve. The aim of the present study was to describe the independent contributions of age, sex, visual acuity, intraocular pressure and ocular biometric parameters to the variation in RNFL thickness in an unselected adult population. Methods In the cross-sectional FORSYN (Forekomst af synshandicap og synshjælpemidler i Danmark) study 10 350 population representative adult Danish citizens were between 1 May 2020 and 1 July 2022 invited for an eye examination that included measurement of visual acuity, ocular biometry, intraocular pressure and OCT scanning to assess the circumpapillary RNFL (cpRNFL) thickness in both eyes. The examination was supplemented with computerised perimetry when the cpRNFL thickness was flagged to be below normal. The invitation was accepted by and completed in 3384 citizens (32.7%), from which the results were expanded to represent the original sample on the basis of age, sex and socio-economic factors. The dependence of the cpRNFL thickness on sex, visual acuity, refraction, axial length of the eye, corneal curvature and intraocular pressure was studied. Results cpRNFL thickness (mean±SD) was significantly (p=0.001) larger in right eyes (102.8±13.8 μm) than in left eyes (102.0±12.8 μm), n=10 410. Increasing age, axial length of the eye, intraocular pressure and male sex, and decreasing visual acuity and corneal curvature contributed significantly to a decreasing thickness of the cpRNFL, p<0.001 for all comparisons. Conclusions The definition of normal values for cpRNFL thickness can be refined by including information about eye laterality, age, sex, axial length, visual acuity, corneal curvature and intraocular pressure in the evaluation. The limitation that only approximately one-third of the persons completed the examination was compensated by a correction of the data material.