Correlation Between Optical Coherence Tomography and Photopic Negative Response of Flash Electroretinography in Ganglion Cell Complex Assessment in Glaucoma Patients

Figures & data

Table 1 Age, Clinical Characteristics, SAP Parameters and OCT Parameters in Both Groups

Variable		Control Group	Study Group	Z-Score	P*
Age (years)	Median	47.00	49.00	1.32	0.184
	IQR [25%-75%]	23.75	23.50
BCVA (logMAR)	Median	1.00	0.80	2.99	0.003
	IQR [25%-75%]	0.00	0.50
SE (diopters)	Median	0.00	0.375	1.32	0.187
	IQR [25%-75%]	0.30	2.44
IOP (mmHg)	Median	16.00	22.00	4.01	< 0.0001
	IQR [25%-75%]	3.00	7.75
C/D ratio	Median	0.50	0.70	7.07	< 0.0001
	IQR [25%-75%]	0.175	0.20
MD (dB)	Median	−1.52	−7.215	6.78	< 0.0001
	IQR [25%-75%]	1.81	20.43
PSD (dB)	Median	1.68	4.01	7.47	< 0.0001
	IQR [25%-75%]	0.58	4.00
VFI (%)	Median	99.00	84.50	7.69	< 0.0001
	IQR [25%-75%]	1.75	64.75
C/D ratio (OCT -Vertical)	Median	0.50	0.76	7.08	< 0.0001
	IQR [25%-75%]	0.18	0.21
C/D ratio (OCT - Horizontal)	Median	0.52	0.80	6.66	< 0.0001
	IQR [25%-75%]	0.21	0.195
R/D ratio (minimum)	Median	0.21	0.09	7.33	< 0.0001
	IQR [25%-75%]	0.04	0.06
Cup area (mm^2)	Median	0.54	1.34	5.99	< 0.001
	IQR [25%-75%]	0.49	0.99
Average RNFL thickness (µm)	Median	105.00	70.00	7.70	< 0.001
	IQR [25%-75%]	11.50	30.75
Average GCC thickness (µm)	Median	98.00	72.00	7.69	< 0.0001
	IQR [25%-75%]	6.75	26.50

Note: *Mann–Whitney U-test.

Abbreviations: P, probability value; IQR, interquartile Range; BCVA, best corrected visual acuity; LogMAR, logarithm of the minimum angle of resolution; SE, spherical equivalent; IOP, intraocular pressure; C/D, cup/disc; MD, mean deviation; dB, decibel; PSD, pattern standard deviation; VFI, visual field index; R/D, rim/disc; RNFL, retinal nerve fiber layer; GCC, ganglion cell complex.

Table 2 Photopic ERG Parameters in Both Groups

Variable		Control Group	Study Group	Z-Score	P*
a-wave latency (ms)	Median	17.15	16.60	2.04	0.041
	IQR [25%-75%]	1.18	2.00
a-wave amplitude (μV)	Median	8.70	7.35	3.97	< 0.0001
	IQR [25%-75%]	1.33	1.50
b-wave latency (ms)	Median	29.10	29.40	0.96	0.337
	IQR [25%-75%]	2.28	2.48
b-wave amplitude (μV)	Median	24.55	24.20	1.53	0.126
	IQR [25%-75%]	11.95	8.30
PhNR latency (ms)	Median	67.55	68.10	0.79	0.430
	IQR [25%-75%]	4.15	3.60
BT PhNR amplitude (μV)	Median	15.25	8.80	7.67	< 0.0001
	IQR [25%-75%]	1.90	6.28
PT PhNR amplitude (μV)	Median	32.05	28.60	4.72	< 0.0001
	IQR [25%-75%]	11.65	6.55
BT/b-wave ratio	Median	0.59	0.34	6.73	< 0.0001
	IQR [25%-75%]	0.18	0.25
PT/b-wave ratio	Median	1.27	1.10	6.07	< 0.0001
	IQR [25%-75%]	0.14	0.26

Note: *Mann–Whitney U-test.

Abbreviations: P, Probability value; IQR, interquartile range; PhNR, photopic negative response; BT, baseline to PhNR trough; PT, b-wave peak to PhNR trough.

Table 3 PhNR Measurements Among the Control Group and the Three Glaucoma Subgroups

Variable	1. Controls	2. Mild Glaucoma	3. Moderate Glaucoma	4. Severe Glaucoma	F*	P*	P^# (1 vs 2)	P^# (1 vs 3)	P^# (1 vs 4)	P^# (2 vs 3)	P^# (2 vs 4)	P^# (3 vs 4)
	Mean ± SD
PhNR latency (ms)	67.27 ± 2.64	67.56 ± 2.58	69.25 ± 2.55	66.31 ± 3.03	2.56	0.061	0.990	0.170	0.754	0.296	0.565	0.015
BT PhNR amplitude (μV)	15.50 ± 1.26	11.79 ± 1.32	8.28 ± 2.25	4.46 ± 1.95	195.66	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
PT PhNR amplitude (μV)	34.86 ± 6.10	31.29 ± 3.63	26.00 ± 5.11	24.15 ± 5.70	18.55	<0.001	0.178	<0.001	<0.001	0.016	<0.001	0.714
BT/b-wave ratio	0.58 ± 0.10	0.45 ± 0.05	0.35 ± 0.09	0.17 ± 0.06	81.06	<0.001	<0.001	<0.001	<0.001	0.007	<0.001	<0.001
PT/b-wave ratio	1.28 ± 0.09	1.19 ± 0.07	1.08 ± 0.12	0.92 ± 0.07	66.45	<0.001	0.027	<0.001	<0.001	0.002	<0.001	<0.001

Notes: *ANOVA. ^#Post Hoc (Tukey’s honestly significant difference) analysis.

Abbreviations: SD, standard deviation; F, Friedman correlation coefficient; P, probability value; PhNR, photopic negative response; BT, baseline to PhNR trough; PT, b-wave peak to PhNR trough.

Figure 1 Photopic electroretinograms with measurements (latency and BT amplitude) of PhNR in (A) a control, (B) a mild glaucoma case, (C) a moderate glaucoma case and (D) a severe glaucoma case.

Table 4 Correlation of PhNR Measurements with Age, SAP Parameters and OCT Parameters in the Study Group

Variable	PhNR Latency		BT PhNR Amplitude		PT PhNR Amplitude		BT/b-Wave Ratio		PT/b-Wave Ratio
	r	P	r	P	r	P	r	P	r	P
Age	0.15	0.366	0.05	0.774	−0.12	0.479	−0.11	0.509	0.13	0.413
MD	0.08	0.623	0.88	< 0.0001	0.53	0.0004	0.84	< 0.0001	0.72	< 0.0001
PSD	−0.07	0.653	−0.73	< 0.0001	−0.44	0.004	−0.65	0.00001	−0.55	0.0003
VFI	0.13	0.415	0.85	< 0.0001	0.53	0.0005	0.80	< 0.0001	0.72	< 0.0001
C/D ratio (Vertical)	−0.15	0.356	−0.75	< 0.0001	−0.51	0.0008	−0.74	< 0.0001	−0.71	< 0.0001
C/D ratio (Horizontal)	−0.14	0.389	−0.65	< 0.0001	−0.47	0.002	−0.63	< 0.0001	−0.59	< 0.0001
R/D ratio (minimum)	0.14	0.389	0.73	< 0.0001	0.49	0.001	0.72	< 0.0001	0.69	< 0.0001
Average RNFL thickness	−0.07	0.653	0.77	< 0.0001	0.40	0.010	0.82	< 0.0001	0.79	< 0.0001
Average GCC thickness	−0.13	0.429	0.76	< 0.0001	0.47	0.002	0.75	< 0.0001	0.71	< 0.0001

Abbreviations: PhNR, photopic negative response; BT, baseline to PhNR trough; PT, b-wave peak to PhNR trough; r, correlation coefficient; P, probability value; MD, mean deviation; PSD, pattern standard deviation; VFI, visual field index; C/D, cup/disc; R/D, rim/disc; RNFL, retinal nerve fiber layer; GCC, ganglion cell complex.

Figure 2 Scatter plots showing the correlation of PhNR measurements with (A and B) Mean deviation, (C and D) RNFL thickness and (E and F) GCC thickness in the study group.