Abstract
To evaluate the influence of ocular axial length on circumpapillary retinal nerve fiber layer and ganglion cell-inner plexiform layer thickness in healthy eyes after correcting for ocular magnification effect. In this cross-sectional study, we evaluated 120 eyes from 60 volunteer participants (myopes, emmetropes, and hyperopes). The thickness of the circumpapillary retinal nerve fiber layer and ganglion cell-inner plexiform layer were measured using the spectral optical coherence tomography (OCT)-Cirrus HD-OCT and correlated with ocular axial length. Adjustment for ocular magnification was performed by applying Littmann's formula. Before the adjustment for ocular magnification, age-adjusted mixed models analysis demonstrated a significant negative correlation between axial length and average circumpapillary retinal nerve fiber layer thickness (r=-0.43, p<0.001), inferior circumpapillary retinal nerve fiber layer thickness (r=-0.46, p<0.001), superior circumpapillary retinal nerve fiber layer thickness (r=-0.31, p<0.05), nasal circumpapillary retinal nerve fiber layer thickness (r=-0.35, p<0.001), and average ganglion cell-inner plexiform layer thickness (r=-0.35, p<0.05). However, after correcting for magnification effect, the results were considerably different, revealing only a positive correlation between axial length and temporal retinal nerve fiber layer thickness (r=0.42, p<0.001). Additionally, we demonstrated a positive correlation between axial length and average ganglion cell-inner plexiform layer thickness (r=0.48, p<0.001). All other correlations were not found to be statistically significant. Before adjustment for ocular magnification, axial length was negatively correlated with circumpapillary retinal nerve fiber layer and ganglion cell-inner plexiform layer thickness measured by Cirrus-OCT. We attributed this effect to ocular magnification associated with greater axial lengths, which was corrected with the Littman's formula. Further studies are required to investigate the impact of ocular magnification correction on the diagnostic accuracy of Cirrus-OCT.
Highlights
Progressive thinning of the circumpapillary retinal nerve fiber layer due to ganglion cell death is a characteristic feature of glaucoma, which has been harnessed for aiding diagnosis and monitoring of glaucoma[1,2]
ganglion cell-inner plexiform layer (GCIPL), the Cirrus-optical coherence tomography (OCT) software is packaged with circumpapillary retinal nerve fiber layer (cpRNFL) measurements from a normal population data base[11], and does not distinguish individuals with moderate or high degrees of myopia, which may lead to an inaccurate diagnosis
Proper interpretation of the data obtained by Cirrus HD-OCT examination requires an evaluation of the influence of ocular axial length on cpRNFL and GCIPL thickness, which despite an extensive investigation, presents conflicting data in the literature[7,12,13,14]
Summary
Progressive thinning of the circumpapillary retinal nerve fiber layer (cpRNFL) due to ganglion cell death is a characteristic feature of glaucoma, which has been harnessed for aiding diagnosis and monitoring of glaucoma[1,2]. Despite OCT being a modern imaging device that measures thickness of cpRNFL and GCIPL, the Cirrus-OCT software is packaged with cpRNFL measurements from a normal population data base[11], and does not distinguish individuals with moderate or high degrees of myopia, which may lead to an inaccurate diagnosis. In this regard, proper interpretation of the data obtained by Cirrus HD-OCT examination requires an evaluation of the influence of ocular axial length on cpRNFL and GCIPL thickness, which despite an extensive investigation, presents conflicting data in the literature[7,12,13,14]. The aim of the present study was to evaluate the influence of different ocular axial lengths on thickness of cpRNFL and GCIPL and their correlations in healthy eyes, in healthy eyes, considering correction for ocular magnification effect
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