Attenuated Amplitude of Pattern Electroretinogram in Glaucoma Patients with Choroidal Parapapillary Microvasculature Dropout

Abstract

This study aims to investigate whether parapapillary choroidal microvasculature dropout (MvD) is related to visual function measured by pattern electroretinogram (PERG) in glaucomatous eyes with β-zone parapapillary atrophy (PPA). A total of 79 patients with open angle glaucoma and preperimetric glaucoma with β-zone PPA was included in this cross-sectional study. Through the deep layer of the Swept-source optical coherence tomography angiography image, the angular width and the area of MvD were measured. Visual function was evaluated with a standard automated perimetry and PERG. N95 and P50 PERG amplitudes in eyes with MvD were noticeably decreased compared to those without MvD (p = 0.004 and p = 0.007, respectively), although the mean deviation was not significantly different (p = 0.107). The lower N95 amplitude was associated with the presence of MvD (β = -0.668, p = 0.017) and wider angular width of MvD (B = -7.612, p = 0.014). Old age (p = 0.001), average ganglion cell's inner plexiform layer thickness (p = 0.003), and the presence of MvD (p = 0.020) were significantly related to low N95 amplitude. Association between the presence and extent of the MvD and PERG amplitudes suggests that the presence of MvD has relevance to the generalized dysfunction of retinal ganglion cells.

Keywords: N95 amplitude; glaucoma; microvascular dropout; optical coherence tomography angiography; pattern electroretinogram; β-zone parapapillary atrophy.

Figure 1

Measurement of the area and angular width of choroidal parapapillary microvasculature dropout (MvD). Fundus photo (A) and deep layer of OCT angiography (B) are shown. Yellow circle denotes margin of the optic disc. The area of MvD was defined by the demarcation of the orange line. As to the angular width of MvD, two lines were drawn from the center of the optic disc to the border points where MvD and the margins of the optic disc meet. The measured width between these two lines was defined as the angular width of MvD. All measurements were carried out by using a built-in calculating tool in the OCTA viewer software (IMAGEnet6; Topcon, Tokyo, Japan).

Figure 2

A representative case of comparing patients with MvD and without MvD. A female glaucoma patient (59 years old) without MvD (C) presented an inferotemporal RNFL defect (A,B) and showed 80 μm average RNFL thickness and 74 μm average GCIPL thickness (D–F). On her VF test, a central VF defect with MD of −2.35 dB was shown (G). The measured P50 and N95 amplitudes were 3.65 mV and 6.99 mV, respectively (H). Another female patient (60 years old) who had an inferotemporal RNFL defect (I,J) and MvD (K) showed a similar degree of glaucoma severity; MD was −1.95 dB (O), and average RNFL and GCIPL thicknesses were 85 μm and 70 μm, respectively (L–N). Nevertheless, the amplitudes of P50 and N95 in the patient with MvD were significantly lower (2.66 mV for P50 amplitude and 5.6 mV for N95 amplitude; (P)).

Figure 3

A representative case of comparing patients in terms of angular width of MvD. A 53-year-old male with multiple RNFL defects (A,B) had the MvD with an estimated angular width of 9.9° (C). Another patient (63 years old) (I,J) presented with larger MvD (angular width 54.9°; (K)). Regarding the level of disease severity, the patient with smaller MvD had average 67 μm RNFL and 72 μm GCIPL thicknesses (D–F), and VF MD was −8.43 dB (G). Similarly, the patient with larger MvD had average 64 μm RNFL and 65 μm GCIPL thicknesses and MD −8.92 dB (L–O). Despite the equivalent glaucoma stage, the patient with lager MvD saw significantly reduced P50 and N95 amplitudes than the patient with smaller MvD (2.46 mV and 2.96 mV, respectively, (P) vs. 2.58 mV and 6.58 mV, respectively, (H)).