Visual evoked potential repeatability using the Diopsys NOVA LX fixed protocol in normal older adults

Figures & data

Table 1 Subject demographics comparing those who had a single examination and those who returned for a second examination

	Total	V1	V2	P-value
Subjects, n	46	37	9
Age
Mean age in years (SD)	51 (9)	52 (9)	59 (10)	0.05a
Range, years	40–84	40–84	47–77
Sex
Male, n (%)	14 (31)	12 (32)	3 (33)	0.96b
Female, n (%)	31 (69)	25 (68)	6 (67)
Race
White, n (%)	9 (20)	7 (19)	2 (22)	0.21b
Black, n (%)	9 (20)	8 (22)	1 (11)
Hispanic, n (%)	27 (58)	22 (60)	5 (56)
Asian, n (%)	1 (2)	0 (0)	1 (11)

Notes:

a Unpaired two-tail t-test;

b Pearson chi-squared.

Abbreviations: V1, one examination; V2, two examinations.

Figure 1 Histogram of age for the entire cohort of subjects at the time of their first examination.

Figure 2 Representative VEP report generated by the Diopsys NOVA device.

Note: Permission received from Diopsys Inc. Diopsys NOVA vision testing system (software version 2.18; Diopsys Inc., Pine Brook, NJ, USA) Available from: http://diopsys.com/visual-electrophysiology-products/visual-evoked-potential-vep/).³⁴
Abbreviations: VEP, visual evoked potential; uv, microvolt; ms, millisecond; OD, right eye; OS, left eye; VA, visual acuity; Lc, low contrast; Hc, high contrast.

Table 2 Mean P100 parameters at first examination

	Low contrast stimulus$			High contrast stimulus‡			P-value*
	N	Mean (SD)	95% CI	N	Mean (SD)	95% CI
Amplitude (µv)
OD	134	9.56 (3.87)		138	12.80 (5.16)		<0.001
OS	131	9.75 (3.98)		136	12.74 (4.49)		<0.001
P-value*		0.68			0.95
Total	265	9.66 (3.92)	1.97–17.34	274	12.77 (4.84)	3.28–22.25
Latency (ms)
OD	134	111.53 (10.39)		138	106.29 (8.40)		<0.001
OS	131	111.95 (10.89)		136	104.41 (7.15)		<0.001
P-value*		0.38			<0.001
Total	265	111.74 (10.64)	90.89–132.59	274	105.35 (7.86)	89.94–120.77

Notes:

* Paired two-tailed t-test;

$ 15% Michelson contrast;

‡ 85% Michelson contrast.

Table 3 Intrasession repeatability outcomes

	Trial	N	Mean (µv)	Sw	CV (%)	ICC(2,1)	(95% CI)a
Amplitude
LCA
OD	1	45	9.30	2.25	24	0.58 (0.42–0.73)
	2	45	9.36
	3	44	10.05
OS	1	44	9.31	3.28	33	0.34 (0.14–0.54)
	2	44	10.12
	3	43	9.81
HCA
OD	1	46	12.53	2.96	23	0.69 (0.56–0.80)
	2	46	12.16
	3	46	13.71
OS	1	46	12.20	2.71	21	0.58 (0.42–0.73)
	2	45	13.25
	3	45	12.78
	Trial	N	Mean (ms)	Sw	CV (%)	ICC(2,1)	(95% CI)a
Latency
LCL
OD	1	45	110.92	7.86	7	0.39 (0.20–0.57)
	2	45	111.75
	3	44	111.92
OS	1	44	110.10	7.11	6	0.38 (0.19–0.58)
	2	44	113.51
	3	43	112.26
HCL
OD	1	45	105.53	7.82	7	0.76 (0.65–0.85)
	2	45	106.02
	3	44	107.32
OS	1	44	103.94	3.58	3	0.75 (0.63–0.84)
	2	44	105.43
	3	43	103.86

Note:

a ICC two-way mixed effects model for absolute agreement of single measures of log-transformed values.

Abbreviations: LCA, low contrast amplitude; HCA, high contrast amplitude; LCL, low contrast latency; HCL, high contrast latency; Sw, within-subject SD; CV, coefficient of variation; ICC, intraclass correlation coefficient.

Figure 3 Mean P100 parameters for each of the three trials at the first examination session.

Notes: (A) Amplitude using the low contrast stimulus; (B) amplitude using the high contrast stimulus; (C) latency using the low contrast stimulus; and (D) latency using the high contrast stimulus. Error bars represent the SD. An asterisk above a bar indicates the trial that was significantly different from the other trials for that eye. An asterisk joining two bars indicate paired trials that were significantly different between right and left eyes.
Abbreviations: RLCA, low contrast amplitude, right eye; LLCA, low contrast amplitude, left eye; RHCA, high contrast amplitude, right eye; LHCA, high contrast amplitude, left eye; RLCL, low contrast latency, right eye; LLCL, low contrast latency, left eye; RHCL, high contrast latency, right eye; LHCL, high contrast latency, left eye.

Figure 4 (A) Serial P100 amplitude recordings and (B) serial P100 latency recordings for each of the 46 subjects at the first examination.

Notes: Each subject underwent three trials per eye under low and high contrast stimulus conditions (Trial 1: Circle; Trial 2: Square; Trial 3: Triangle). (A1) P100 amplitude for right eyes with low (15%) stimulus contrast, (A2) P100 amplitude for left eyes under low stimulus contrast, (A3) P100 amplitude for right eyes under high (85%) stimulus contrast, (A4) P100 amplitude for left eyes under high stimulus contrast. (B1) P100 latency for right eyes with low (15%) stimulus contrast, (B2) P100 latency for left eyes under low stimulus contrast, (B3) P100 latency for right eyes under high (85%) stimulus contrast, (B4) P100 latency for left eyes under high stimulus contrast. For each test condition, the ICC and it’s 95% CI are presented.
Abbreviation: ICC, intraclass correlation coefficient.

Figure 5 Bland–Altman plots of P100 parameter limits of agreement between fellow eyes at visit 1.

Notes: Each data point represents the difference between the corresponding trials (first, second, or third) for a given subject. (A) P100 amplitude with low (15%) stimulus contrast, (B) P100 amplitude under high (85%) stimulus contrast, (C) P100 latency under low stimulus contrast, and (D) P100 latency under high stimulus contrast. Regression analysis revealed a relationship between parameter difference and parameter magnitude only for high contrast amplitude (dashed line). Colored dots in (B) are the data points that were excluded during regression analysis.

Table 4 P100 amplitude and latency by age, sex, and ethnicity

	N	Mean (SD)	N	Mean (SD)	P-valuea
Age		<51 years		51+ years
LCA
OD	23	9.97 (3.83)	23	9.15 (3.00)	0.42
OS	23	10.34 (3.74)	23	9.33 (2.58)	0.30
HCA
OD	23	13.50 (4.76)	23	12.10 (4.59)	0.32
OS	23	13.35 (3.79)	23	12.30 (3.90)	0.64
LCL
OD	23	108.89 (6.05)	23	113.88 (8.99)	0.03
OS	23	109.08 (6.33)	23	116.39 (14.03)	0.03
HCL
OD	23	103.09 (7.07)	23	109.49 (8.99)	0.005
OS	23	101.71 (4.60)	23	107.08 (7.18)	0.04
Sex		Male		Female
LCA
OD	15	8.66 (2.02)	31	9.99 (3.89)	0.22
OS	15	8.62 (2.17)	31	10.42 (3.50)	0.07
HCA
OD	15	10.84 (3.86)	31	13.75 (4.80)	0.05
OS	15	10.88 (2.99)	31	13.77 (3.89)	0.02
LCL
OD	15	112.37 (8.12)	31	110.91 (8.01)	0.57
OS	15	114.41 (17.50)	31	111.93 (7.03)	0.50
HCL
OD	15	106.58 (7.67)	31	106.15 (7.93)	0.86
OS	15	105.49 (7.16)	31	103.86 (6.29)	0.43
Race		Hispanic		Non-Hispanic
LCA
OD	27	9.75 (4.04)	19	9.28 (2.35)	0.66
OS	27	10.22 (3.72)	19	9.29 (2.31)	0.34
HCA
OD	27	13.36 (5.27)	19	12.00 (3.67)	0.34
OS	27	12.90 (4.13)	19	12.73 (3.50)	0.89
LCL
OD	27	110.23 (7.25)	19	113.03 (8.87)	0.25
OS	27	112.29 (13.68)	19	113.37 (7.27)	0.76
HCL
OD	27	104.73 (7.07)	19	108.50 (8.34)	0.11
OS	27	103.19 (6.39)	19	106.10 (6.57)	0.14

Note:

a Unpaired two-tailed t-test.

Abbreviations: LCA, low contrast amplitude in microvolts; HCA, high contrast amplitude in microvolts; LCL, low contrast latency in milliseconds; HCL, high contrast latency in milliseconds.

Table 5 Coefficient of variation for P100 parameters by age, sex, and ethnicity

	Age (years)		Sex		Race
	<51	51+	M	F	H	~H
LCA
OD	26%	21%	24%	23%	23%	26%
OS	34%	25%	36%	34%	38%	25%
HCA
OD	19%	24%	20%	21%	20%	20%
OS	20%	26%	27%	19%	21%	25%
LCL
OD	7%	8%	5%	8%	9%	6%
OS	7%	6%	7%	7%	6%	7%
HCL
OD	2%	6%	3%	5%	3%	6%
OS	4%	3%	3%	4%	3%	4%

Abbreviations: LCA, low contrast amplitude in microvolts; HCA, high contrast amplitude in microvolts; LCL, low contrast latency in milliseconds; HCL, high contrast latency in milliseconds; M, male; F, female; H, Hispanic; ~H, non-Hispanic.

Table 6 P100 parameters of the returning subjects

	N	Mean (SD)	Range	CV (%)	P-valuea
LCA
OD
V1	25	8.24 (1.84)	5.3–12.9	22	0.44
V2	27	8.67 (2.20)	5.4–14.1	21
OS
V1	26	9.27 (4.19)	3.5–25.9	19	0.46
V2	27	8.77 (1.98)	5.5–11.7	18
HCA
OD
V1	27	11.40 (3.41)	5.3–20.9	21	0.45
V2	27	12.08 (4.37)	5.9–19.9	25
OS
V1	26	12.67 (5.16)	6.2–28.5	28	0.57
V2	27	12.06 (3.59)	5.9–19.0	20
LCL
OD
V1	25	110.74 (7.09)	96.7–125.0	3	0.05
V2	27	113.02 (6.94)	92.8–125.0	5
OS
V1	26	111.66 (10.18)	98.6–148.4	10	0.89
V2	27	111.47 (7.56)	91.8–125.0	6
HCL
OD
V1	27	104.39 (5.02)	94.7–116.2	3	0.18
V2	27	105.44 (5.31)	99.6–117.2	3
OS
V1	26	101.72 (4.39)	90.8–110.3	3	<0.001
V2	27	105.43 (5.47)	92.8–115.2	4

Note:

a Paired two-tailed t-test.

Abbreviations: V1, first examination; V2, second examination; LCA, low contrast amplitude in microvolts; HCA, high contrast amplitude in microvolts; LCL, low contrast latency in milliseconds; HCL, high contrast latency in milliseconds; CV, coefficient of variation.

Figure 6 Bland–Altman plots of intersession P100 parameter limits of agreement.

Notes: Each data point represents the difference between corresponding trials (first, second, or third) for a given subject. The green circles represent right eyes, and blue squares represent left eyes. (A) P100 amplitude with low (15%) stimulus contrast, (B) P100 amplitude under high (85%) stimulus contrast, (C) P100 latency under low stimulus contrast, and (D) P100 latency under high stimulus contrast.

Table 7 Intersession repeatability values

	ICC(2,1) (95% CI)a	SEM	MDC	SD (dB)
LCA
OD	−0.08 (−0.47 to 0.33)	2.33 µv	6.46 µv	1.10
OS	0.35 (−0.04 to 0.65)	1.62 µv	4.50 µv	0.82
HCA
OD	0.35 (−0.04 to 0.64)	3.59 µv	9.95 µv	1.04
OS	0.41 (0.02 to 0.68)	2.81 µv	7.79 µv	1.32
LCL
OD	0.45 (0.10 to 0.71)	5.24 ms	14.54 ms	0.16
OS	0.49 (0.13 to 0.74)	5.51 ms	15.26 ms	0.25
HCL
OD	0.70 (0.45 to 0.85)	2.95 ms	8.16 ms	0.14
OS	0.42 (−0.01 to 0.71)	4.24 ms	11.76 ms	0.12

Note:

a ICC two-way mixed effects model for absolute agreement of single measures of log transformed values.

Abbreviations: LCA, low contrast amplitude; HCA, high contrast amplitude; LCL, low contrast latency; HCL, high contrast latency; SEM, standard error of measurement; MDC, minimum detectable change; SD, within subject SD; ICC, intraclass correlation coefficient.

Figure 7 (A) P100 amplitude recordings and (B) P100 latency recordings for each of the 27 recordings performed on nine returning subjects at the first (circle) and second (square) examination sessions.

Notes: (A1) P100 amplitude for right eyes with low (15%) stimulus contrast, (A2) P100 amplitude for left eyes under low stimulus contrast, (A3) P100 amplitude for right eyes under high (85%) stimulus contrast, and (A4) P100 amplitude for left eyes under high stimulus contrast. (B1) P100 latency for right eyes with low (15%) stimulus contrast, (B2) P100 latency for left eyes under low stimulus contrast, (B3) P100 latency for right eyes under high (85%) stimulus contrast, and (B4) P100 latency for left eyes under high stimulus contrast. For each test condition, the ICC and its 95% CI are presented.
Abbreviation: ICC, intraclass correlation coefficient.

DiopsysDiopsys NOVA vision testing system software version 2.18 Available from: http://diopsys.com/visual-electrophysiology-products/visual-evoked-potential-vep/Accessed August 30, 2018

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