Thinning rates of retinal nerve layer and ganglion cell-inner plexiform layer in various stages of normal tension glaucoma

Abstract

Aims: To compare the changes in the macular retinal nerve fibre layer (mRNFL), macular ganglion cell layer and inner plexiform layer (mGCIPL), and circumpapillary retinal nerve fibre layer (cpRNFL) in various stages of normal tension glaucoma (NTG) using spectral domain optical coherence tomography.

Methods: Eyes with NTG (n=218) were assigned into three groups based on initial mean deviation (MD) as follows: mild (MD>-6 dB), moderate (-6 dB≥MD≥-12 dB) and severe (-12 dB>MD>-20 dB). Annual rates of change in mRNFL, mGCIPL and cpRNFL thickness were calculated by linear regression analysis.

Results: Age, gender, spherical equivalent, and average intraocular pressure during follow-up were not significantly different among the three groups. There were significant differences in the mRNFL, mGCIPL and cpRNFL among the three groups at baseline (p<0.0001 in all sectors except for the mRNFL in the superonasal sector). The average thinning rates of the mRNFL, mGCIPL and cpRNFL were -0.38±0.32 µm/year, -0.62±0.46 µm/year and -0.86±0.83 µm/year, respectively. No significant difference in the rates of change in the mRNFL and mGCIPL were found among the groups in any sector. However, there was a significant difference in the rate of change in the cpRNFL among the groups (in all sectors: p<0.0001).

Conclusions: Changes in the mRNFL and mGCIPL can reflect the progression of NTG even in its advanced stage. However, careful interpretation of changes in the cpRNFL in the advanced stage of glaucoma is warranted due to a potential floor effect.

Keywords: circumpapillary retinal nerve fiber layer; macular ganglion cell layer and inner plexiform layer; macular retinal nerve fiber layer; normal tension glaucoma; optical coherence tomography.