Interdigitation Zone Change According to Glaucoma-Stage Advancement

Purpose To compare the macular interdigitation zone (IZ) of normal eyes with eyes showing different normal-tension glaucoma (NTG) stages. Methods Forty-two normal eyes (age, 56 ± 5.4 years), 45 pre-perimetric eyes (age, 59 ± 6.9 years), 51 mild-to-moderate glaucoma eyes (age, 58 ± 7.2 years; mean deviation [MD], –5.5 ± 3.0 dB), and 50 severe glaucoma eyes (age, 59 ± 6.9 years; MD, –15.1 ± 5.4 dB) were enrolled. All of the subjects underwent high-resolution spectral-domain optical coherence tomography (SD-OCT) to obtain 19 horizontal and 19 vertical macular B-scans 9 mm in length. The en face image of the scan area was divided into 589 rectangular boxes (side length of 375 µm). The IZ locations were marked on the corresponding image boxes. The IZ area was then quantified according to the number of boxes showing IZs among the 589 total boxes. Results The IZ area in the severe glaucoma eyes was significantly smaller than in the mild-to-moderate glaucoma eyes (28.99 ± 7.88 mm 2 vs. 40.79 ± 7.46 mm 2 ; P < 0.001), was smaller in the mild-to-moderate glaucoma eyes than in the pre-perimetric glaucoma eyes (40.79 ± 7.46 mm 2 vs. 49.92 ± 8.10 mm 2 ; P < 0.001), and was smaller still in the pre-perimetric glaucoma eyes than in the normal eyes (49.92 ± 8.10 mm 2 vs. 56.85 ± 7.94 mm 2 ; P < 0.001). In the 146 NTG eyes, a statistically significant correlation was found between IZ area and MD ( r = 0.64; P < 0.001). Conclusions SD-OCT revealed a reduction in IZ area in NTG eyes, and the extent of the reduction was positively associated with glaucoma severity. These findings suggest, though tentatively, that changes in the outer retinal layer can occur in the course of glaucoma progression.