Figure 1. Representative OCT image of the nine ETDRS subfield.C: central, SIM: superior inner quadrant in the macula, NIM: nasal inner quadrant, IIM: inferior inner quadrant, TIM: temporal inner quadrant, SOM: superior outer quadrant in the macula, NOM: nasal outer quadrant, IOM: inferior outer quadrant, TOM: temporal outer quadrant
Figure 2. pRNFL thickness (µ) in acute NAION, unaffected fellow eye and the control group. pRNFL(a): average, (in): inferonasal, (sn): superonasal, (n): nasal, (st): superotemporal, (t): temporal
Spectral domain optical coherence tomography (SD-OCT) imaging is a useful device used in neuro-ophthalmological diseases [5]. One might be able to indirectly document the loss of RGC by measuring the macular ganglion cell complex (mGCC) and the peri-papillary retinal nerve fiber layer (pRNFL) [6].
We aimed to investigate pRNFL and mGCC thickness in patients with acute NAION and compare with those of healthy control subjects.
Material and methods
The patients who were diagnosed as acute NAION between January 2013 and May 2015 were reviewed retrospectively. Patients with their first clinical presentation of unilateral acute NAION (within two weeks of onset of symptoms) were included.
We obtained SD-OCT (Spectralis; Heidelberg Engineering, Heidelberg, Germany) measurements for each eye. We then quantified the thickness of the following layers: (1) pRNFL (nasal, superonasal, superotemporal, temporal, inferotemporal, and inferonasal, as well as global RNFL thickness), (2) mGCC; GC layer+IPL + macular RNFL (mRNFL), and central macular thickness (CMT) (Figure 1).
Results and discussion
A total of 19 patients (9 male and 10 female) with acute NAION were eligible for the study. Furthermore, the control group consisted of 50 healthy subjects (26 male and 24 female) (Table).
The pRNFL thickness in eyes with acute NAION was significantly higher in all quadrants when compared to those of healthy control subjects and unaffected fellow eyes. The mGCC was significantly higher in central, outer nasal and outer inferior quadrants in acute NAION when compared to those of healthy control subjects, and no significant difference was observed in the other quadrants (Figure 2 and figure 3).
Figure 3. The mGCC thickness in the eyes with acute NAION, the unaffected fellow eyes and control group. SIM: superior inner quadrant in the macula, NIM: nasal inner quadrant, IIM: inferior inner quadrant, TIM: temporal inner quadrant, SOM: superior outer quadrant in the macula, NOM: nasal outer quadrant, IOM: inferior outer quadrant, TOM: temporal outer quadrant
Table Demographic and clinical characteristics among acute stage of NAION
Contreras et al. [11] observed that the pRNFL thickness in the eyes with NAION eyes was the highest in the acute phase. Yang et al. [12] reported that the changes in superior pRNFL were more evident in eyes with NAION. In our study, pRNFL thickness increased in all quadrants of the eyes with acute NAION that were consistent with previous literature.
Previous studies demonstrated that the apoptosis begins in RGCs at the first day of the ischemic injury [13]. Furthermore, in acute inflammation models of the optic tract, the death of RGC was shown 7 to 60 days after damage to the optic nerve [14-17]. However, Ho et al. [13] reported that there was a 31% increase in peripapillary GCC (pGCC) thickness in experimental murine NAION model one day after NAION. They suggested that the thickness might increase due to inflammatory response and the other factors. In our study, the mGCC thickness was increased eyes with acute NAION, which may be related to wrinkling of the surrounding tissues such as macula.
Maekubo et al. [18] reported that the mean inner retinal thickness in the eyes were significantly increased on the 1st, 3rd, 5th, and 7th days after optic neuropathy induction in a rat model of NAION. In contrast, Larrea et.al. [19] found lower mGCC values in the eyes with NAION compared to healthy controls. Goto et al. [20] did not report difference in the mGCC values in NAION patients at the initial admission.
Conclusion
We demonstrated that the mGCC and the pRNFL thickness are increased in the eyes with acute NAION in earlier period. Further studies are needed to describe more precisely the time point at which the GCC begins to show damage.
