The full-field electroretinogram (ERG) is a reliable diagnostic method used to determine whether a patient has dysfunction of the rod and/or cone systems of the retina. Inherited conditions (eg, Leber congenital amaurosis, congenital stationary night blindness, achromatopsia, and retinitis pigmentosa) show characteristic abnormalities on ERG testing.1 The test measures voltages produced in the retina via electrodes. According to the International Society for Clinical Electrophysiology of Vision (ISCEV), the standard method of obtaining a full-field ERG requires a Ganzfeld stimulator and active electrodes that contact the cornea, bulbar conjunctiva, or skin on the lower eyelid.2,3 This test often requires general anesthesia for children.4 In addition, this test requires time, appropriate ERG equipment, and trained staff. In 2016, the U.S. Food and Drug Administration approved the use of the RETeval handheld ERG device (LKC Technologies, Inc). The greatest values provided by this new technology are that the test is simple to operate, can be done easily without anesthesia and mydriatics, and uses skin electrodes that are similar to adhesive pads used in electrocardiogram recordings.5 The device can record full-field ERG responses compliant with ISCEV 5- and 6-step protocols. The purpose of this study was to provide normative data of full-field ERG responses in the pediatric population using the RETeval device in healthy children with normal retinas. To our knowledge, there are currently no published studies providing a range of normative full-field ERG values specifically in the pediatric population using the RETeval system.
Patients and Methods
This was a single-site prospective study approved by the Pediatric Institutional Review Board at Children's Mercy Hospital and Clinics. The study adhered to the tenets of the Declaration of Helsinki and was compliant with the HIPAA. Enrollment occurred from August 2017 to December 2018. Participants included children of Children's Mercy Hospital and Clinics employees or patients scheduled for routine eye examinations who were willing volunteers. Routine eye examinations consisted of monitoring low refractive errors or providing an updated glasses prescription. Patients were enrolled based on their predicted ability to cooperate, and tests were terminated at a patient's first sign of distress or lack of cooperation. Patients aged between 1 month and 18 years were enrolled with the informed written consent obtained from parents or legal guardians. Exclusion criteria were: (1) history of seizures given exposure to flashing lights, (2) adhesive allergy, and (3) distress or unwillingness to participate as assessed at the onset of testing. Patients with no retinal disease, no visual symptoms, and no family history of hereditary eye disease were included.
All patients received routine eye examinations, including dilated fundus examination, and a detailed history from the parent or legal guardian to confirm adherence to the inclusion and exclusion criteria. The full-field ERG responses were recorded via application of skin sensor strips placed 2 mm inferior to each lower eyelid margin according to manufacturer guidelines. Measurements were made with a standardized ruler across all patients. After cycloplegic drops were administered and appropriate pupillary dilation was achieved, an ISCEV 5-step protocol was implemented.2 The patients underwent dark adaptation for a minimum of 20 minutes followed by measurements of the rod system, including scotopic dim flash response (DA 0.01), scotopic standard flash response (DA 3), and scotopic oscillatory potential (DA 3). Then light-adapted cone responses were measured, including photopic cone response (LA 3) and photopic 28.3-Hz flicker response (LA 3). Scotopic responses were recorded first, followed by photopic measurements.
The background luminance was 0.0 cd/m2 for the dark-adapted tests and 30 cd/m2 for the photopic response. All data were stored in a secured drive and patients were assigned a random number. Full-field ERG responses were recorded on dilated pupils of each patient, and the mean between the two eyes of each patient was used for analysis. The mean values for measurements between the two eyes were compared to age using a scatter plot graph and Pearson correlation coefficient (r).
Thirty-eight eyes of 20 healthy patients (aged 4 to 17 years, 9 males and 11 females) were included in the study. The average ages of females, males, and all patients were 8.3 (median: 6 years; range: 4 to 17 years), 8.4 (median: 8 years; range: 5 to 13 years), and 8.4 years (median: 8 years; range: 4 to 17 years), respectively. Full-field ERG responses were successfully recorded in all eyes (Figures A–C, available in the online version of this article). All patients tolerated the examinations with no complications. The initial two patients were tested in one eye only. In one eye of one patient, the scotopic dim flash response did not record due to poor electrode adhesion. Two additional patients were missing values for scotopic standard flash response in one eye. When both eyes were tested, the mean values of each parameter were used in calculations. Table 1 shows mean, median, and range values.
Sample report from a study patient using the RETeval device (LKC Technologies, Inc). This depicts dark adapted electroretinogram responses in (A) test 1 and (B) test 2.
Sample report from a study participant using the RETeval device (LKC Technologies, Inc). This depicts oscillatory potential amplitudes in test 3.
Sample report from a study participant using the RETeval device (LKC Technologies, Inc). This depicts light adapted electroretinogram responses in (A) test 4 and (B) test 5.
Mean, Median, and Range Values of Scotopic (Rod) and Photopic (Cone) Responses
Pearson correlation of r = 0.59 was moderately positive between age and oscillatory potential, as well as age and scotopic dim flash amplitude (P = .006 for both). There was a strong positive correlation between age and cone a-wave implicit time (r = 0.67, P = .001) (Figure 1). No correlation between age and scotopic dim flash implicit time, scotopic standard flash responses (amplitude and implicit time), cone b-wave responses (amplitude and implicit time), cone a-wave amplitude, and flicker responses (amplitude or implicit time) was observed. Percentiles of scotopic and photopic responses are presented in Table 2.
Pearson correlation (r) of age versus average full-field electroretinogram (ERG) responses of participants. Moderate positive correlations were observed between age and oscillatory potential amplitude (r = 0.59, P = .006) and age with scotopic dim flash amplitude (r = 0.59, P = .006). There was also a positive correlation between age and cone a-wave amplitude (r = 0.67, P = .001).
Percentiles for Scotopic Mixed Rod-Cone Responses and Photopic Isolated Cone Responses
This study provides normative data for healthy children using the RETeval device. The handheld system was well tolerated by patients of all ages in our study and eliminated the need for sedation. Pearson correlation was moderately positive between age and oscillatory potential, along with age and scotopic dim flash amplitude (r = 0.59, P = .006 for both). There was a strong positive correlation between age and cone a-wave implicit time (r = 0.67, P = .001). No correlation between age and the other ERG measurements was found.
To date, there are no publications establishing normative full-field ERG values using the RETeval handheld device in children. The device does provide reference values for photopic responses obtained by a clinical trial by LKC Technologies, Inc.6 However, these should be used with caution because they cannot be extrapolated for pediatric patients. The research included patients between 2 and 85 years old. In general, there are few studies determining normal RETeval ERG values for any age range. A recent study published in 2017 by Asakawa et al7 provided normative values in 100 eyes of 50 healthy participants ages 20 to 24 years old. However, their study differed from ours given the older population within a small age range, and testing was performed on undilated pupils. Of note, they found the amplitude response had low intra-examiner reproducibility in comparison to implicit time. In 2018, Liu et al8 recorded normative values for a wider age range of 8 to 65 years (n = 57). They demonstrated a significant positive correlation between clinical full-field ERG (using Ganzfeld stimulator) and RETeval cone and rod amplitude responses.
Although we would need further studies to determine the normal reference values of RETeval ERG responses in pediatric patients, we believe this is a good baseline study that provides normative values in children. Our study could have benefitted from the addition of younger patients, because our youngest patient was 4 years old. The literature supports that conventional full-field ERG responses evolve with age.9 In comparison to adolescents, infant responses show longer implicit times and smaller amplitudes. B-wave amplitude of the rod response reaches adult levels at a later age of 84 months, whereas the mixed-rod cone response approaches adult levels earlier at 37 months. Additional literature has shown cone and rod responses tend to decline in adulthood, and decline at a more rapid rate after the age of 55 years.14 Normative values are important to establish in the pediatric population because it can aid in detecting early inherited retinal degenerations and prove beneficial in expediting treatment options. This is especially true given the advent of gene therapy for RPE-65 mediated inherited retinal diseases.10
Grace et al11 determined the RETeval cone flicker ERG was a worthwhile screening test that could differentiate between those with and without retinal dystrophy in patients with nystagmus. The test was tolerated by most patients with acceptable sensitivity and specificity. Although ERG responses were lower than conventional (sedated) ERG responses documented in the literature, they were able to establish amplitude and implicit values, which essentially excludes cone dysfunction or merits further investigation. In a follow-up study, the RETeval 30-Hz cone flicker responses were compared to conventional sedated full-field ERG responses (E3 Diagnosys) in pediatric patients with retinal dystrophy.12 They discovered RETeval amplitudes were smaller before and under general anesthesia when compared to conventional ERG under general anesthesia. This finding was attributed to the skin electrodes. Implicit times were shorter prior to and longer under general anesthesia in comparison to conventional ERG under general anesthesia. However, they found a positive correlation between the RETeval amplitude and implicit times with conventional ERG both with and without general anesthesia. The authors concluded the RETeval provides a viable method of screening for cone dysfunction, but abnormal or ambiguous responses ultimately require a conventional ERG. It is difficult to compare our ERG responses obtained from the RETeval and conventional sedated ERGs due to the discrepancy in the use of skin and corneal electrodes. To the best of our knowledge, there are no large-scale published studies, without the RETeval, detailing normative full-field ERG responses from skin electrodes in pediatric patients under general anesthesia.
In accordance with the ISCEV protocol, the testing for this study was performed with constant stimulus intensity after pharmacologic mydriasis. Although testing using variable illuminance without pupillary dilation is possible with the RETeval, cooperation with this modality can be problematic.12 Another potential limitation of the RETeval system is the necessity of precise electrode placement. Skin electrodes placed further from the eyelid margin can reduce amplitude responses.13
Limitations in our study are the small sample size and varying demographic factors within our population. Our results will need to be validated with larger studies that stratify patients according to ethnicity, age, sex, and pupil size. Although lower limits of normal full-field ERG parameters are represented by 5th percentile values in Table 2, the small studied population may present a lack of sufficient power for clinical use, and should be considered in conjunction with additional pediatric normative data. Multiple measurements for each eye would allow us to determine consistency of results and perhaps more reliable ERG responses. Additionally, our study did not incorporate parameters such as visual acuity and refractive error into our analysis. Although there have been no large studies in the literature regarding the relationship between refractive error and normative full-field ERG data, a study by Perlman et al15 has shown that patients with hypermetropia may have abnormal dark-adapted amplitudes with normal response patterns. McCulloch et al2 suggested that patients with high myopia may have full-field ERG amplitudes below the typical reference range. Larger scale studies with normative data and refractive error may be valuable in further characterizing this relationship. Finally, there were no patients younger than 4 years old due to the population sample available at the testing site.
The handheld RETeval system is a useful tool for obtaining full-field ERGs in children without anesthesia. Positive correlations were observed between age and oscillatory potential, scotopic dim flash amplitude and cone a-wave implicit time. Our study provides a baseline of normative full-field ERG values in children. Further studies involving healthy children will allow us to establish normal reference RETeval full-field ERG values for the pediatric population.
- Lambert SR, Taylor D, Kriss A. The infant with nystagmus, normal appearing fundi, but an abnormal ERG. Surv Ophthalmol. 1989;34(3):173–186. doi:10.1016/0039-6257(89)90101-X [CrossRef]
- McCulloch DL, Marmor MF, Brigell MG, et al. ISCEV Standard for full-field clinical electroretinography (2015 update). Doc Ophthalmol. 2015;130(1):1–12. doi:10.1007/s10633-014-9473-7 [CrossRef]. Erratum in: Doc Ophthalmol. 2015;131:81–83.
- Robson AG, Nilsson J, Li S, et al. ISCEV guide to visual electrodiagnostic procedures. Doc Ophthalmol. 2018;136(1):1–26. doi:10.1007/s10633-017-9621-y [CrossRef]
- Creel DJ. The electroretinogram and electro-oculogram: clinical applications by Donnell J. Creel. AccessedApril14, 2019. http://webvision.med.utah.edu/book/electrophysiology/the-electroretinogram-clinical-applications/
- RETeval Visual Electrodiagnostic System. RETeval brochure. Accessed April 15, 2019. https://test-lkc-technologies.pantheonsite.io/wp-content/uploads/2017/02/2017_LKC_RETeval_Brochure_USA_web.pdf
- LKC Technologies, Inc. RETeval All Comers Trial (REACT). NCT Identifier: NCT03065881. Accessed April 12, 2019. https://clinicaltrials.gov/ct2/show/NCT03065881
- Asakawa K, Amino K, Iwase M, et al. New mydriasis-free electroretinogram recorded with skin electrodes in healthy subjects. BioMed Res Int. 2017;2017:8539747. doi:10.1155/2017/8539747 [CrossRef]
- Liu H, Ji X, Dhaliwal S, et al. Evaluation of light- and dark-adapted ERGs using a mydriasis-free, portable system: clinical classifications and normative data. Doc Ophthalmol. 2018;137(3):169–181. doi:10.1007/s10633-018-9660-z [CrossRef]
- Westall CA, Panton CM, Levin AV. Time courses for maturation of electroretinogram responses from infancy to adulthood. Doc Ophthalmol. 1998;96(4):355–379. doi:10.1023/A:1001856911730 [CrossRef]
- Russell S, Bennett J, Wellman JA, et al. Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial. Lancet. 2017;390(10097):849–860. doi:10.1016/S0140-6736(17)31868-8 [CrossRef]. Erratum in: Lancet. 2017;390:10097:848.
- Grace SF, Lam BL, Feuer WJ, Osigian CJ, Cavuoto KM, Capo H. Nonsedated handheld electroretinogram as a screening test of retinal dysfunction in pediatric patients with nystagmus. J AAPOS. 2017;21(5):384–388. doi:10.1016/j.jaapos.2017.06.022 [CrossRef]
- Osigian CJ, Grace SF, Cavuoto KM, et al. Assessing nonsedated handheld cone flicker electroretingram as a screening test in pediatric patients: comparison to sedated conventional cone flicker electroretinogram. J AAPOS. 2019;23(1):34.e1–e5. doi:10.1016/j.jaapos.2018.09.009 [CrossRef]
- Hobby AE, Kozareva D, Yonova-Doing E, et al. Effect of varying skin surface electrode position on electroretinogram responses recorded using a handheld stimulating and recording system. Doc Ophthalmol. 2018;137(2):79–86. doi:10.1007/s10633-018-9652-z [CrossRef]
- Birch D, Anderson J. Standardized full-field electroretinography normal values and their variation with age. Arch Ophthalmol. 1992;110(11):1571–1576. doi:10.1001/archopht.1992.01080230071024. [CrossRef]
- Perlman I, Meyer E, Haim T, Zonis S. Retinal function in high refractive error assessed electroretinographically. Br J Ophthalmol. 1984;68(2):79–84. doi:10.1136/bjo.68.2.79 [CrossRef]
Mean, Median, and Range Values of Scotopic (Rod) and Photopic (Cone) Responses
| Dim flash amplitude (µV)||53.5||50.2||15.3 to 102|
| Dim flash implicit time (ms)||83.8||83.7||45.9 to 118|
| Standard flash (combined rod-cone) a-wave amplitude (µV)||50.6||47.8||30.6 to 87.3|
| Standard flash (combined rod-cone) a-wave implicit time (ms)||14.2||14.1||12.9 to 19.6|
| Standard flash (combined rod-cone) b-wave amplitude (µV)||73.7||67.1||40.1 to 125|
| Standard flash (combined rod-cone) b-wave implicit time (ms)||46.4||45.7||32.5 to 69.1|
| Oscillatory potential amplitude (µV)||59.8||53.5||22 to 114|
| Cone a-wave amplitude (µV)||8.5||7.5||0.35 to 23.6|
| Cone a-wave implicit time (ms)||12.6||12.4||10.4 to 25.1|
| Cone b-wave amplitude (µV)||38.8||35.8||18.2 to 192|
| Cone b-wave implicit time (ms)||28.1||28.2||26 to 30.3|
| Flicker amplitude (µV)||30.8||27.9||13.6 to 105|
| Flicker implicit time (ms)||24.7||24.5||23.3 to 28.3|
Percentiles for Scotopic Mixed Rod-Cone Responses and Photopic Isolated Cone Responses
|Parameter||Amplitude (µv)||Implicit Time (ms)|
| Dim flash||17.1||44.2||50.2||66.3||98.5||48.1||74.4||83.7||97.6||109|
| Standard flash (rod/cone) a-wave||35.5||41.0||47.8||57.1||81.1||13.0||13.4||14.1||14.5||17.8|
| Standard flash (rod/cone) b-wave||43.2||61.0||67.1||81.5||124||37.8||42.5||45.7||49.4||67.7|
| Standard flash (cone) a-wave||2.20||5.20||7.45||10.6||22.4||10.4||11.4||12.4||13.1||15.6|
| Standard flash (cone) b-wave||20.1||24.1||35.8||44.0||60.7||26.2||26.9||28.2||29.3||30.0|
| Cone flicker||14.1||20.0||27.9||36.0||48.5||23.6||24.1||24.5||25.2||26.6|