This paper is supported in part by the James V. Bastek, M.D. Hereditary Retinal Disease Research Program, Bascom Palmer Eye Institute, University of Miami, FL, USA; NIH Center Core Grant P30EY014801; Research to Prevent Blindness Unrestricted Award and Career Development Awards; Florida Lions Eye Bank and the Beauty of Sight Foundation, Miami, FL, USA; and Henri and Flore Lesieur Foundation.

The protocol follows the operating room guidelines of the Bascom Palmer Eye Institute, University of Miami and is applicable to infants, young children, and uncooperative adults. Patients who cannot have general anesthesia due to safety issues should not have the procedure.
1. Operating room selection and modification
<ol>
	<li>Select an operating room with low 60 Hz background electric current noise and proper electrical grounding, to avoid ERG recording interference. Use a room with an isolated electrical circuit without connection to or is near heavy appliances (e.g., refrigerator).
	<ol>
		<li>Perform trial ERG recordings in the operating room at the location where the ERG recording will take place. Check the ERG recording baseline as well as the trial recording waveforms to determine the absence of 60 Hz background electric noise.</li>
	</ol>
	</li>
	<li>Inspect the operating room for light leaks from ceiling, door, and window openings. Perform human observation after full dark adaptation (30 to 45 minutes) given that the normal human eye can detect light as dim as approximately 4 photons, which is better than any man-made light meter except liquid nitrogen-cooled detectors for astronomy.</li>
	<li>Install opaque non-reflective black curtains on tracks to cover the operating room door and window openings fully without light leakage (Figure 1). Select curtain material that is washable and resistant to staining and bacterial growth. Follow local operating room regulations and procedures for proper interval cleaning. Block light leaks from the ceiling if present.</li>
</ol>
2. Foldable portable darkroom selection and modification
<ol>
	<li>Select a portable darkroom that is easy to install and store and large enough to enclose the patient&#8217;s head, the ERG examiner, and the ffERG stimulus. Use folding portable darkrooms designed for an optic physicist (e.g., www.scientex.co.jp/pdf/pdf-b-lp-eng.pdf, 48&#8221;x 48&#8221;x81&#8221; cross type) which are available commercially and optimizes the maintenance of retinal dark adaptation of the patient during scotopic ffERG recordings (Figure 2). 
	NOTE: The fabric of the portable darkroom mentioned was tested by the eye institute&#8217;s microbiology department for ease of disinfection and the optical transmission was tested by the eye institute&#8217;s biomedical department before purchase. This is recommended if a different portable darkroom is used.</li>
	<li>Add a small opening with double flaps at the rear of the portable darkroom to allow routing connections and cables (Figure 3). 
	NOTE: During scotopic ffERG testing, the ffERG light stimulus is inside the folding portable darkroom and the ERG recording system is outside of the portable darkroom. The ERG electrode wire connections and the cable connecting the ERG light stimulus to the ERG recording system go through the opening created with a double closure system to ensure total darkness. We use a small handheld ffERG light stimulus to ease ERG recording inside the folding portable darkroom and record one eye at a time. A larger ffERG light stimulus can record both eyes simultaneous but will need to be held by a metallic arm requiring a larger opening at the rear of the portable darkroom and will likely require a larger darkroom.</li>
</ol>
3. Patient preparation and retinal dark adaption
<ol>
	<li>Confirm medical reason for ffERG and obtain informed consent for examination under anesthesia, ffERG, and other procedures of interest for patient management such as retinal imaging (e.g., fundus imaging, optical coherence tomography, fluorescein angiography) and venopuncture for genetic testing. 
	NOTE: Most common reasons for ffERG in infants and young children include decreased vision, nystagmus, nyctalopia, visual photosensitivity, abnormal fundus, and medication with risk of retinal toxicity (e.g., vigabatrin). Important to recognize factors that are likely to affect ERG recordings including high myopia and albinism. In general, ffERG responses from infants younger than age 6 months are small and still developing, making interpretation of recorded responses difficult.</li>
	<li>Place ocular anesthetic drop (proparacaine 0.5%) followed by pupillary dilation combo drop (cyclopentolate 1% + phenylnephreine 0.5%) to each eye. Repeat the combo drop to each eye 2 to 3 times with 5 minutes between drops. 
	NOTE: The proparacaine decreases burning sensation and increases corneal absorption of the dilating drops but may have to be skipped in patients with very poor cooperation.</li>
	<li>Patch both eyes for retinal dark adaptation of at least 30 minutes. With eyelids gently and completely closed, place 2 regular-size self-adhesive eye occlusion patches over each eye without significant pressure on the eye.
	<ol>
		<li>Place the first patch conventionally and oriented horizontally with the wider end of the patch temporally. Place the second patch horizontally over the first patch with the wider end nasally and adjust the position typically with a tilt counterclockwise to prevent light leak nasally.</li>
	</ol>
	</li>
	<li>After placing the eye patches over each eye, place opaque black tape horizontally across to cover both eyes without significant pressure on the eyes. Make a small vertical cut at the inferior edge of the black tape before placement at the location across the bridge of the nose to avoid pressure on the nose.</li>
	<li>Place the black opaque relaxation sleeping mask with head headband over the patched eyes (Figure 4). 
	NOTE: ISCEV international standard for dark adaptation is 20 minutes. Dark adaptation of at least 30 minutes is preferred to facilitate optimal scotopic ffERG recording given the retinal dark adaptation curve reaches a more asymptotic point compared to 20 minutes. Based on our experience, vast majority of infant and young children are tolerant of bilateral patching, and parental support and encouragement are critical. Explaining the purpose of dark adaptation and the benefit of reducing general anesthesia time helps the parents to understand. Parental tender loving care including cuddling, music from cell phone, and pacifier are very helpful during the dark adaptation period. Of over 120 infants and young children who underwent the method, only 2 patients could not tolerate bilateral patching for dark adaptation. Both patients were dark-adapted after general anesthesia induction instead and the ERG responses were subsequently successfully recorded using the same method.</li>
</ol>
4. Dark-Adapted full-field electroretinogram recording in the operating room
<ol>
	<li>Prepare the operating room by placing translucent red filter films over monitors and opaque black tape over LEDs and light sources (Figure 5A-5B). Set up folding portable darkroom. Close curtains over door and window openings.</li>
	<li>Induce general anesthesia or sedation by anesthesiology team on bilaterally-patched patient followed by continued anesthesiology monitoring. Perform timeout to verify procedures to be performed.</li>
	<li>Place ERG recording electrodes, ffERG light stimulus, a very dim red light mounted on a forehead band, topical 0.5% ophthalmic proparacaine, 2.5% ophthalmic hydroxypropyl methylcellulose (if Burian-Allen electrode is used), and sterile gauze (for wiping excess methylcellulose) close to ERG examiner position before placing the portable darkroom to enclose the head of the patient and ERG examiner (Figure 6A). The ERG examiner will be using the mounted red forehead band to perform scotopic ffERG recordings. 
	NOTE: The red light mounted on a forehead band is modified by placing layers of red light filter films over the LEDs. The red light should be as dim as possible to allow the ERG examiner to perform the procedure so dark adaptation is maintained. Helpful for the examiner to wait a few minutes to have some of his or her own partial dark adaptation before placing the electrodes. Experienced ERG examiners tend to use very dim red light or can do the procedure by feel without any red light if Burian-Allen electrode is used.</li>
	<li>Place the ground ERG electrode clip with conductive paste on one ear lobe. Snake the ground ERG electrode connection and ffERG light stimulus cable through the modified flap opening of the portable darkroom and the ERG technician connects them to the ERG system outside of the darkroom.</li>
	<li>Close the front opening of the portable darkroom with large binder clips. Turn off room lights and check and cover any remaining uncovered light sources with black tape.</li>
	<li>Remove the black mask over both eyes. Remove the black tape and patches over the right eye only and place the corneal ERG recording electrode on the right eye to record the scotopic ffERG responses using the hand-held full-field light stimulus in accordance to the ISCEV standards (Figure 6B).
	<ol>
		<li>Snake the ERG recording electrode connection through the modified flap opening of the portable darkroom for the ERG technician to connect it to the ERG system outside of the darkroom. Take care to use the dimmest red light possible, and a brief period of additional dark adaptation, approximately 5 min, is recommended for recovery after lens insertion in accordance to the ISCEV standards.</li>
		<li>After checking for electrical baseline stability and ERG electrode impedance, proceed with recording of the rod responses (dark-adapted 0.01 cd&#183;s&#183;m-2 flash ERG), followed by the combined rod-cone responses (dark-adapted 3.0 cd&#183;s&#183;m-2 flash ERG and 10 cd&#183;s&#183;m-2 flash ERG) and the dark-adapted 3.0 flash oscillatory potential responses. Be mindful of the recommended time intervals between the light stimulus to maintain dark adaptation. 
		NOTE: When a handheld ERG light stimulus is used to test one eye at a time, keep the other eye monocular patched to maintain dark adaptation during scotopic recordings of the first eye. Dawson Trick Litzkow (DTL) fiber electrode or bipolar Burian-Allen ERG corneal electrodes are typically used. The DTL electrode is better tolerated by a conscious patient and has lower amplitude-to-noise ratio compared to the Burian-Allen ERG corneal electrode. Given patient tolerance is not an issue during sedation or general anesthesia, Burian-Allen electrode is preferred for sedated ERG recordings given its superior amplitude-to-noise ratio.</li>
	</ol>
	</li>
	<li>Remove the black tape and patches of the left eye and proceed with scotopic ffERG recording of the left eye following same procedures as for the first eye as in step 4.6 with the hand-held full-field light stimulus. 
	NOTE: Recorded scotopic ffERG amplitudes tend to be mildly lower in the second recorded eye given the retinal dark adaptation of the second eye is typically affected by the ERG stimulus flashes diffusing to the eye through bone and tissue during ERG recording of the first eye.</li>
</ol>
5. Light-Adapted full-field electroretinogram recording in the operating room
<ol>
	<li>After completion of the scotopic ffERG recordings, turn on all overhead room lights. Disconnect the ERG electrode connections and the ffERG light stimulus cable from the ERG recording system and snake them back to the inside the portable dark room through the modified flap opening. Remove the portable dark room.</li>
	<li>Light adapt both eyes for 10 minutes by using the overhead room lights in accordance to the ISCEV standards (background luminance 30 cd&#183;m-2). Keep the bipolar Burian-Allen ERG electrodes in place for both eyes given the built-in eyelid speculums of the electrodes will hold the eyes open. If DTL lenses are used, use eyelid speculums to keep both eyes open with instillation of periodic lubricating eye drops to avoid corneal drying.</li>
	<li>Connect the ERG electrode connections and the ffERG light stimulus cable to the ERG system and proceed to record, in accordance to the ISCEV standards, the cone flash responses (light-adapted 3.0 cd&#183;s&#183;m-2 flash ERG) followed by the cone flicker responses (light-adapted 3.0 flicker ERG). 
	NOTE: This completes the ffERG recording. Other diagnostic retinal imaging including OCT, fundus photos as well as venopuncture for genetic testing can easily follow while the patient remains sedated.</li>
</ol>

<ol>
	<li>McCulloch, D. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ISCEV+Standard+for+full-field+clinical+electroretinography+(2015+update).">ISCEV Standard for full-field clinical electroretinography (2015 update).</a> Documenta Ophthalmologica. 130 (1), 1-12 (2015).</li><li>Robson, A. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ISCEV+guide+to+visual+electrodiagnostic+procedures.">ISCEV guide to visual electrodiagnostic procedures.</a> Documenta Ophthalmologica. 136 (1), 1-26 (2018).</li><li>Holder, G. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=International+Federation+of+Clinical+Neurophysiology:+recommendations+for+visual+system+testing.">International Federation of Clinical Neurophysiology: recommendations for visual system testing.</a> Clinical Neurophysiology. 121 (9), 1393-1409 (2010).</li><li>Fulton, A. B., Hartmann, E. E., Hansen, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophysiologic+testing+techniques+for+children.">Electrophysiologic testing techniques for children.</a> Documenta Ophthalmologica. 71 (4), 341-354 (1989).</li><li>van Genderen, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+key+role+of+electrophysiology+in+the+diagnosis+of+visually+impaired+children.">The key role of electrophysiology in the diagnosis of visually impaired children.</a> Acta Ophthalmologica Scandinavica. 84 (6), 799-806 (2006).</li><li>Lalwani, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+'dark'+side+of+sedation:+12+years+of+office-based+pediatric+deep+sedation+for+electroretinography+in+the+dark.">The 'dark' side of sedation: 12 years of office-based pediatric deep sedation for electroretinography in the dark.</a> Pediatric Anesthesia. 21 (1), 65-71 (2011).</li><li>Guidelines, ICfPCE, et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pediatric+clinical+visual+electrophysiology:+a+survey+of+actual+practice.">Pediatric clinical visual electrophysiology: a survey of actual practice.</a> Documenta Ophthalmologica. 113 (3), 193-204 (2006).</li><li>Wongpichedchai, S., Hansen, R. M., Koka, B., Gudas, V. M., Fulton, A. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+halothane+on+children's+electroretinograms.">Effects of halothane on children's electroretinograms.</a> Ophthalmology. 99 (8), 1309-1312 (1992).</li><li>Andreasson, S., Tornqvist, K., Ehinger, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Full-field+electroretinograms+during+general+anesthesia+in+normal+children+compared+to+examination+with+topical+anesthesia.">Full-field electroretinograms during general anesthesia in normal children compared to examination with topical anesthesia.</a> Acta Ophthalmologica (Copenhagen). 71 (4), 491-495 (1993).</li><li>Brigell, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidelines+for+calibration+of+stimulus+and+recording+parameters+used+in+clinical+electrophysiology+of+vision.">Guidelines for calibration of stimulus and recording parameters used in clinical electrophysiology of vision.</a> Documenta Ophthalmologica. 107 (2), 185-193 (2003).</li></ol>

The authors have nothing to disclose.

The methodology and protocol describe how to effectively perform valid and reliable ffERG in infants and children under sedation or general anesthesia in the operating room. The major concept and aim of the technique are to provide and maintain optimal retinal dark adaptation during scotopic ffERG recordings. This is essential to provide accurate objective assessment of rod photoreceptor function given retinal dark adaptation is rapidly diminished by exposure even to dim light leading to erroneous recorded responses. The critical steps of the method are (i) to choose an operating room with low 60 Hz background electric current noise, proper electrical grounding and to modify and prepare the room meticulously to block light sources (ii) to pharmacologically dilated the pupils fully and to place multi-layer eye patches that completely blocks light to induce retinal dark adaptation (iii) to use a modified portable foldable darkroom that encloses the patient&#8217;s head and the ERG examiner, and (iv) to use the least amount of dim red light needed inside the darkroom during scotopic ffERG recording.
The method is significantly superior to existing alternative methods. While performing ffERG without sedation in infants less than 1 year old may be possible by using a feeding bottle and some children can cooperate with ffERG recording, cooperation is poor in most infants and young children. Performing ffERG with oral sedation in a conventional ERG recording darkroom lacks the ability to monitor the patient&#8217;s cardiopulmonary function safely and the spectrum of responses to the oral sedation is wide and unpredictable. Performing ffERG in a darkened operating room without a portable darkroom is typically not dark enough to adequately achieve and maintain dark adaptation given the growing number of new anesthetic and operating room equipment.
The method works well with a small handheld ffERG light stimulus given the limited space inside the portable darkroom, and ffERG recording is done one eye at a time. A larger full-size full-field ERG stimulus dome will allow simultaneous ERG recording of both eyes and shorten examination time. A full-size ERG stimulus dome would require a metallic arm to hold it securely over the supine patient and a larger portable darkroom with a much larger flap opening would be required to accommodate the metallic arm. Such modification is possible with care to create a large flap opening that is not prone to light leak.
Limitations of the method are few and include the effect of sedative and general anesthetic agents in reducing ERG responses, which is not substantial enough to influence accurate clinical diagnosis and follow-up testing to assess progression. The method requires the cooperation of the pediatric anesthesiology team to monitor patient in a dimly lit operating room for 15 minutes during scotopic ffERG recording. If anesthetic emergency arises, the procedure can be aborted immediately and the portable darkroom can be moved rapidly to allow full patient access.

The electroretinogram (ERG) is the only clinical objective test available to assess retinal function and the full-field ERG (ffERG) is the only objective test to assess rod-photoreceptor generated activities1,2. The ffERG measures the electrical responses from the entire retina elicited by a full-field flash stimulus and is a gold standard test in the diagnosis and management of inherited retinal diseases2,3. Thus, the ffERG is an important test in infants and young children to detect early onset inherited retinal diseases such as Leber congenital amaurosis where approved gene therapy and clinical trials are available4,5.
Adherence to ffERG standards established by the International Society for Clinical Electrophysiology of Vision (ISCEV) are critical to acquire valid and reliable dark-adapted (scotopic) and light-adapted (photopic) ffERG responses1,3. Failure to properly maintain adequate retinal dark adaptation during scotopic ffERG recordings results in falsely-impaired recorded responses and patient mismanagement. Performing ffERG in infants and children is challenging given limited cooperation and often requires general anesthesia in the operating room6. A recent survey among ISCEV members showed 12-14% of ERG&#8217;s are performed under sedation or general anesthesia7. Maintaining retinal dark adaptation in the operating room is difficult given the numerous light sources from anesthesiology monitoring systems and other equipment. While anesthetic agents may have an effect in reducing ERG responses, ERG responses under sedation or general anesthesia are reliable in providing accurate diagnosis6,8,9.
A simple and widely applicable method is described for ffERG testing in the operating room that adheres to the international standards and optimizes retinal dark adaptation. The goal of this practical method is to provide valid reliable scotopic and photopic ffERG recordings to assess objective retinal function in infants and young children, which is particularly relevant in this young age group given subjective assessment of visual function such as visual acuity and visual fields are typically not possible. The operating room is modified to promote retinal dark adaptation, and the procedures reduce operating room time by dark-adapting the patient before sedation or general anesthesiology is instituted. A modified portable foldable darkroom encloses the patient&#8217;s head and the ERG examiner during ffERG scotopic recordings to minimize any remaining light source including light emission from the ERG system. The portable darkroom allows rapid access to the patient by the anesthesiologist when necessary. After the completion of ffERG, diagnostic retinal imaging including optical coherence tomography (OCT) and fundus imaging as well as venopuncture for genetic testing can easily be performed while the patient remains under anesthesia.
The method is suitable for practitioners and practices that manage pediatric patients with retinopathies. An average sized ocular operating room provides adequate space, and a room with low background electrical noise is desirable to allow quality ffERG recording. While the ERG examiner is inside the foldable darkroom during scotopic ffERG recording, a trained technician is needed to operate the ERG system outside of the foldable darkroom. Conferring with the anesthesiology team is essential in modifying the operating room and to promote the safety of the patient in a darkened environment.
The advantages of the method over alternative techniques include optimizing and maintaining retinal dark adaptation, promoting valid reliable ffERG recordings, improving patient safety, and facilitating additional diagnostic testing such as retinal imaging and venopuncture for genetic testing. Optimal dark adaptation is also critical given ffERG stimulators should be calibrated for complete darkness conditions as recommended by ISCEV10. Alternative methods include the use of oral agents such as chloral hydrate with variable sedative responses in infants and children, which affects the quality of ffERG recordings and causes difficulties in monitoring vital signs. While some children can cooperate with ffERG recording in the clinic, the testing session may be prolonged depending on cooperation, and the validity of ffERG recordings may be affected by eye movement and blink artifacts as well as difficulty in maintainng retinal dark adaptation4. The current method provides additional dark adaptation and safety measures compared to the previously described deep sedation ffERG method6.

<table><tbody><tr><td>Black tape</td><td>3M Industrial Adhesives and Tapes Division, St Paul, MN 55144-1000 USA</td><td>3M ID 70016070396</td><td></td></tr><tr><td>Conduction skin paste</td><td>Redux Electrolyte Paste, Hewlett Packard company, USA</td><td>67-05</td><td></td></tr><tr><td>Darkroom - Portable foldable</td><td>Scientex Inc., Japan</td><td>B-LP1/B-LP1-X</td><td>Requires modification as described in Protocol</td></tr><tr><td>Dark adaptation mask (relaxation sleeping mask)</td><td>Mindfold Inc, Durango, CO, USA</td><td>6576493</td><td>Flexible black plastic face plate backed with a high-density soft foam padding that allows total darkness.</td></tr><tr><td>Ear clip for electric grounding</td><td>Natus - Nicolet Neurodiagnostic, UK</td><td>F-E34DG-72</td><td>Grass 10mm Gold Cup EEG Ear Clip with touchproof connector 72&quot; wire - Set of 2</td></tr><tr><td>Electrodes ERG recording (Burian-Allen, DTL)</td><td>Burian-Allen, Hansen Ophthalmic Develoment Lab, Iowa, USA; DTL, Diagnosys, Lowell, MA 01854, USA.</td><td>303-20LA, 303-20A, 303-20P, 303-20I, 303-20SI</td><td>Available in different sizes</td></tr><tr><td>ERG systems including handheld full-field stimulus</td><td>Any system meeting the standards established by the International Society for Clinical Electrophysiology of Vision (ISCEV).</td><td></td><td>Authors use Diagnosys and Roland systems; other ISCEV standard systems available.</td></tr><tr><td>Eye drops and Gel, proparacaine, phenylephrine, cyclopentolate, methylcellulose</td><td>Ophthalmic drops, Proparacaine 0.5%, phenylephrine 2.5%, cyclopentolate 1%, Akorn, Inc. Forest, IL 60045 USA; ophthalmic gel, methylcellulose 2.5%, Alcon Laboratory, Inc. Fort Worth, TX 76134 USA</td><td></td><td></td></tr><tr><td>Eye patch</td><td>BSN Medical Inc, Rutherford College, NC, USA</td><td>46430-00</td><td>Coverlet eye occlusor for treatment of lazy eye</td></tr><tr><td>Head band with light</td><td>REMIX PRO. Princeton Tec,&lt;br/&gt; Trenton, NJ 08650 USA</td><td>RMX300PRO-RD-BK</td><td>Requires placing layers of red filters over LED as described in protocol</td></tr></tbody></table>

electroretinogram recording for infants and children under anesthesia to achieve optimal dark adaptation and international standards

Electroretinogram (ERG) is the only clinical objective test available to assess retinal function. Full-field ERG (ffERG) measures the panretinal rod and cone photoreceptor function as well as inner retinal function and is an important measure in the diagnosis and management of inherited retinal diseases as well as inflammatory, toxic, and nutritional retinopathies. Adhering to international standards and maintaining retinal dark adaptation are critical to acquire valid and reliable dark-adapted (scotopic) and light-adapted (photopic) ffERG responses. Performing ffERG in infants and children is challenging and often requires general anesthesia in the operating room. However, maintaining retinal dark adaptation in the operating room is becoming increasingly difficult given the numerous light sources from anesthesiology monitoring systems and other equipment. A practical and widely applicable method for ffERG testing is described in the operating room that optimizes retinal dark adaptation. The method reduces operating room time by dark-adapting the patient before general anesthesiology is instituted. The operating room is modified for dark adaptation and any remaining light source in the darkened operating room is minimized with the use of a modified portable foldable darkroom that encloses the patient&#8217;s head and the ERG examiner during ffERG scotopic recordings. The simple method adheres to ffERG international standards and provides valid reliable scotopic and photopic ffERG recordings that are critical to assess objective retinal function in this young age group where subjective assessment of visual function such as visual acuity and visual fields are not possible. Furthermore, the ffERG is the gold standard clinical test in detecting early onset inherited retinal diseases including Leber congenital amaurosis where approved gene therapy has become available. In sedated conditions, very low amplitude ffERG signals can be detected due to minimal orbicularis muscle activity interference, which is particularly relevant in patients after gene therapy to detect improved amplitude responses.

Using the method described, valid, reliable, interpretable normal and abnormal ffERG responses are feasibly obtained in the operating room for infants and young children under sedation or general anesthesia. In particular, falsely low scotopic ffERG responses are avoided, and common retinal causes of decreased vision and nystagmus in this age group are readily identified. For instance, the preservation of scotopic ffERG responses is important to differentiate Leber congenital amaurosis from achromatopsia where the cone ffERG responses are diminished in both conditions but the scotopic ffERG responses are preserved in achromatopsia but not in Leber congenital amaurosis (Figure 7). Obtaining good quality scotopic ffERG responses is also important to diagnose conditions where distinct scotopic ffERG waveform morphology is present. For example, the presence of a negative b-wave in the scotopic combined rod-cone ffERG response is a key feature of congenital stationary night blindness (Figure 7). While anesthetic agents may reduce ERG responses, ERG responses under anesthesia are reliable in providing accurate diagnosis.6 The lower limit of the normal range of the ERG responses is age dependent and increases with age. For instance, the lower limit of normal for age 12 months to 24 months for the scotopic rod responses with the Burian-Allen electrode is 75 &#181;V. As recommended by ISCEV, individual ERG labs are encouraged to collect own normal values.
The method is used reliably to determine disease progression over time. For instance, the systemic features of Alstr&#246;m syndrome are subtle in very young patients and the initial ffERG responses may be similar to achromatopsia with relative preservation of scotopic ffERG responses and diminished cone responses (Figure 8). Over time, the scotopic ffERG responses worsen showing a cone-rod dysfunction pattern that is consistent with conditions including cone-rod dystrophy and secondary syndromic cone-rod degenerations such as Alstr&#246;m&#8217;s syndrome (Figure 8).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61734/61734fig01.jpg" /> 
Figure 1: Dark proofing of openings of operating room.&#160;Opaque non-reflective black curtains cover operating room door and window openings. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2A" src="/files/ftp_upload/61734/61734fig02A.jpg" /> 
Figure 2A: <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig02Alarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2B" class="xfigimg" src="/files/ftp_upload/61734/61734fig02B.jpg" /> 
Figure 2B: Folding portable darkroom.&#160;Commercially available foldable portable darkroom (A) isolates the patient&#8217;s head and the ERG examiner (B) to optimize the maintenance of retinal dark adaptation during scotopic ffERG recordings (photo taken with lights on before starting case for illustration purposes). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig02Blarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3A" src="/files/ftp_upload/61734/61734fig03A.jpg" /> 
Figure 3A: <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig03Alarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3B" src="/files/ftp_upload/61734/61734fig03B.jpg" /> 
Figure 3B: <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig03Blarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3C" class="xfigimg" src="/files/ftp_upload/61734/61734fig03C.jpg" /> 
Figure 3C: Modification of the rear of the darkroom.&#160;Small opening created at the rear of the darkroom (A) covered by double flaps (B) allow routing connections and cables to the ERG recording system outside of the darkroom (C). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig03Clarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61734/61734fig04.jpg" /> 
Figure 4: Dark adaptation with bilateral patching.&#160;A dark relaxation mask is placed over the patient after each eye is patched by placing a layer of black tape over 2 eye pads over closed eyelids. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5A" src="/files/ftp_upload/61734/61734fig05A.jpg" /> 
Figure 5A: <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig05Alarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5B" class="xfigimg" src="/files/ftp_upload/61734/61734fig05B.jpg" /> 
Figure 5B: Dark proofing of operating room. 
Translucent red filter films (A) are taped over monitors and opaque black tape (B) covers LEDs and light sources. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig05Blarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6A" src="/files/ftp_upload/61734/61734fig06A.jpg" /> 
Figure 6A: <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig06Alarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6B" class="xfigimg" src="/files/ftp_upload/61734/61734fig06B.jpg" /> 
Figure 6B: Recoding scotopic ffERG responses inside darkroom. 
Patient with darkroom in place (A). Scotopic ffERG responses are recorded in a very darkened environment inside darkroom (B) with a very dim red light mounted on a forehead band used to place corneal ERG recording electrodes in place (photo taken with lights on before starting case for illustration purposes). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig06Blarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/61734/61734fig07.jpg" /> 
Figure 7: Normal and abnormal ffERG examples.&#160;Standard ffERG responses obtained with method in infants and young children showing normal responses and valid reliable scotopic and photopic responses that easily differentiate Leber congenital amaurosis (LCA), achromatopsia, and congenital stationary night blindness (CSNB). LCA example is a 6-year-old with RDH12 genotype; achromatopsia example is a 3-year-old with PDE6C genotype; CSNB example is a 3-year-old with TRPM1 genotype. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/61734/61734fig08.jpg" /> 
Figure 8: ffERG example showing disease progression.&#160;Standard ffERG responses obtained with method obtained in a 2-year-old patient with follow-up 2 years later. Progression of the scotopic ffERG responses is evident, and patient was found to have Alstr&#246;m syndrome. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61734/61734fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Electroretinogram Recording for Infants and Children under Anesthesia to Achieve Optimal Dark Adaptation and International Standards at JoVE.com

Electroretinogram Recording for Infants and Children under Anesthesia to Achieve Optimal Dark Adaptation and International Standards

Adhering to international standards and maintaining retinal dark adaptation are critical to acquire valid full-field electroretinogram responses in the diagnosis and management of inherited retinal diseases. A practical protocol using a portable darkroom is provided to obtain full-field&#160;electroretinogram for infants and children under sedation or general anesthesia in the operating room setting.

Electroretinogram (ERG) is the only clinical objective test available to assess retinal function. Full-field ERG (ffERG) measures the panretinal rod and ...

electroretinogram-recording-for-infants-children-under-anesthesia-to

Nanyang Technological University

Research

JoVE Journal

Medicine

6.0K Views.  University of Miami Miller School of Medicine. Full-field elektroretinogram is een belangrijke objectieve retinale functie test. Onze methode optimaliseert retinale donkere aanpassing om geldige en betrouwbare full-field ERG reacties te verwerven bij zuigelingen en jonge kinderen onder narcose. Het uitvoeren van full-field ERG bij jonge kinderen onder algemene anesthesie in de operatiekamer verbetert de patiëntveiligheid en vergemakkelijkt de prestaties van het werk dat ze hebben opgemerkt.Full-filled ERG is belangrijk voor het op...

Video: Electroretinogram Recording for Infants and Children under Anesthesia to Achieve Optimal Dark Adaptation and International Standards

A Novel Rescue Technique for Difficult Intubation and Difficult Ventilation

We describe a novel non surgical technique to maintain oxygenation and ventilation in a case of difficult intubation and difficult ventilation, which works especially well with poor mask fit.
Can not intubate, can not ventilate" (CICV) is a potentially life threatening situation. In this video we present a simulation of the technique we used in a case of CICV where oxygenation and ventilation were maintained by inserting an endotracheal tube (ETT) nasally down to the level of the naso-pharynx while sealing the mouth and nares for successful positive pressure ventilation.
A 13 year old patient was taken to the operating room for incision and drainage of a neck abcess and direct laryngobronchoscopy. After preoxygenation, anesthesia was induced intravenously. Mask ventilation was found to be extremely difficult because of the swelling of the soft tissue. The face mask could not fit properly on the face due to significant facial swelling as well. A direct laryngoscopy was attempted with no visualization of the larynx. Oxygen saturation was difficult to maintain, with saturations falling to 80%. In order to oxygenate and ventilate the patient, an endotracheal tube was then inserted nasally after nasal spray with nasal decongestant and lubricant. The tube was pushed gently and blindly into the hypopharynx. The mouth and nose of the patient were sealed by hand and positive pressure ventilation was possible with 100% O2 with good oxygen saturation during that period of time. Once the patient was stable and well sedated, a rigid bronchoscope was introduced by the otolaryngologist showing extensive subglottic and epiglottic edema, and a mass effect from the abscess, contributing to the airway compromise. The airway was secured with an ETT tube by the otolaryngologist.This video will show a simulation of the technique on a patient undergoing general anesthesia for dental restorations.

We describe a technique to maintain oxygenation and ventilation using an endotracheal tube inserted nasally to the level of the naso-pharynx while sealing the mouth and nares for successful positive pressure ventilation.

We describe a novel non surgical technique to maintain oxygenation and ventilation in a case of difficult intubation and difficult ventilation, which ...

Multifocal Electroretinograms

A limitation of traditional full-field electroretinograms (ERG) for the diagnosis of retinopathy is lack of sensitivity. Generally, ERG results are normal unless more than approximately 20% of the retina is affected. In practical terms, a patient might be legally blind as a result of macular degeneration or other scotomas and still appear normal, according to traditional full field ERG. An important development in ERGs is the multifocal ERG (mfERG). Erich Sutter adapted the mathematical sequences called binary m-sequences enabling the isolation from a single electrical signal an electroretinogram representing less than each square millimeter of retina in response to a visual stimulus1.
Results that are generated by mfERG appear similar to those generated by flash ERG. In contrast to flash ERG, which best generates data appropriate for whole-eye disorders. The basic mfERG result is based on the calculated mathematical average of an approximation of the positive deflection component of traditional ERG response, known as the b-wave1. Multifocal ERG programs measure electrical activity from more than a hundred retinal areas per eye, in a few minutes. The enhanced spatial resolution enables scotomas and retinal dysfunction to be mapped and quantified.
In the protocol below, we describe the recording of mfERGs using a bipolar speculum contact lens.
Components of mfERG systems vary between manufacturers. For the presentation of visible stimulus, some suitable CRT monitors are available but most systems have adopted the use of flat-panel liquid crystal displays (LCD). The visual stimuli depicted here, were produced by a LCD microdisplay subtending 35 - 40 degrees horizontally and 30 - 35 degrees vertically of visual field, and calibrated to produce multifocal flash intensities of 2.7 cd s m-2. Amplification was 50K. Lower and upper bandpass limits were 10 and 300 Hz. The software packages used were VERIS versions 5 and 6.

The development of the multifocal electroretinogram (mfERG) is an important advance in the diagnosis and characterization of retinopathy. Multifocal electroretinograms are a mathematical average of an approximation of a b-wave. Software programs can derive ERGs from more than a hundred retinal areas in a few minutes per eye. Scotomas and retinal dysfunction can be mapped and quantified.

A limitation of traditional full-field electroretinograms (ERG) for the diagnosis of retinopathy is lack of sensitivity.  Generally, ERG results are ...

Implantation and Recording of Wireless Electroretinogram and Visual Evoked Potential in Conscious Rats

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both laboratory and clinical settings. Currently, preclinical ERG and VEP measurements are performed with anesthesia to ensure stable electrode placements. However, the very presence of anesthesia has been shown to contaminate normal physiological responses. To overcome these anesthesia confounds, we develop a novel platform to assay ERG and VEP in conscious rats. Electrodes are surgically implanted sub-conjunctivally on the eye to assay the ERG and epidurally over the visual cortex to measure the VEP. A range of amplitude and sensitivity/timing parameters are assayed for both the ERG and VEP at increasing luminous energies. The ERG and VEP signals are shown to be stable and repeatable for at least 4 weeks post surgical implantation. This ability to record ERG and VEP signals without anesthesia confounds in the preclinical setting should provide superior translation to clinical data.

We show surgical implantation and Recording procedures to measure visual electrophysiological signals from the eye (electroretinogram) and brain (visual evoked potential) in conscious rats, which is more analogous to the human condition where recordings are conducted without anesthesia confounds.

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both ...

Behavior

Direct-Coupled Electroretinogram (DC-ERG) for Recording the Light-Evoked Electrical Responses of the Mouse Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) is a specialized monolayer of cells strategically located between the retina and the choriocapillaris that maintain the overall health and structural integrity of the photoreceptors. The RPE is polarized, exhibiting apically and basally located receptors or channels, and performs vectoral transport of water, ions, metabolites, and secretes several cytokines.
In vivo noninvasive measurements of RPE function can be made using direct-coupled ERGs (DC-ERGs). The methodology behind the DC-ERG was pioneered by Marmorstein, Peachey, and colleagues using a custom-built stimulation recording system and later demonstrated using a commercially available system. The DC-ERG technique uses glass capillaries filled with Hank&#8217;s buffered salt solution (HBSS) to measure the slower electrical responses of the RPE elicited from light-evoked concentration changes in the subretinal space due to photoreceptor activity. The prolonged light stimulus and length of the DC-ERG recording make it vulnerable to drift and noise resulting in a low yield of useable recordings. Here, we present a fast, reliable method for improving the stability of the recordings while reducing noise by using vacuum pressure to reduce/eliminate bubbles that result from outgassing of the HBSS and electrode holder. Additionally, power line artifacts are attenuated using a voltage regulator/power conditioner. We include the necessary light stimulation protocols for a commercially available ERG system as well as scripts for analysis of the DC-ERG components: c-wave, fast oscillation, light peak, and off response. Due to the improved ease of recordings and rapid analysis workflow, this simplified protocol is particularly useful in measuring age-related changes in RPE function, disease progression, and in the assessment of pharmacological intervention.

Direct-Coupled Electroretinogram DC-ERG for Recording the Light-Evoked Electrical Responses of the Mouse Retinal Pigment Epithelium

Here, we present a method for recording light-evoked electrical responses of the retinal pigment epithelium (RPE) in mice using a technique known as DC-ERGs first described by Marmorstein, Peachey, and colleagues in the early 2000s.

The retinal pigment epithelium (RPE) is a specialized monolayer of cells strategically located between the retina and the choriocapillaris that maintain ...

Chemistry

Glutamate and Hypoxia as a Stress Model for the Isolated Perfused Vertebrate Retina

Neuroprotection has been a strong field of investigation in ophthalmological research in the past decades and affects diseases such as glaucoma, retinal vascular occlusion, retinal detachment, and diabetic retinopathy. It was the object of this study to introduce a standardized stress model for future preclinical therapeutic testing.
Bovine retinas were prepared and perfused with an oxygen saturated standard solution, and the ERG was recorded. After recording stable b-waves, hypoxia (pure N2) or glutamate stress (250 &#181;m glutamate) was exerted for 45 min. To investigate the effects on photoreceptor function alone, 1 mM aspartate was added to obtain a-waves. ERG-recovery was monitored for 75 min.
For hypoxia, a decrease in a-wave amplitude of 87.0% was noted (p &#60;0.01) after an exposition time of 45 min (decrease of 36.5% after the end of the washout p = 0.03). Additionally, an initial decrease in b-wave amplitudes of 87.23% was recorded, that reached statistical significance (p &#60;0.01, decrease of 25.5% at the end of the washout, p = 0.03).
For 250 &#181;m glutamate, an initial 7.8% reduction of a-wave amplitudes (p &#62;0.05) followed by a reduction of 1.9% (p &#62;0.05). A reduction of 83.7% of b-wave amplitudes (p &#60;0.01) was noted; after a washout of 75 min the reduction was 2.3% (p = 0.62). In this study, a standardized stress model is presented that may be useful to identify possible neuroprotective effects in the future.

With this study, we introduce a standardized stress model for the isolated superfused bovine retina for future preclinical therapeutic testing. The effect of either hypoxia (pure N2) or glutamate stress (250 &#181;M glutamate) on retinal function represented by a- and b-wave amplitudes was evaluated.

Neuroprotection has been a strong field of investigation in ophthalmological research in the past decades and affects diseases such as glaucoma, retinal ...

Using the Electroretinogram to Assess Function in the Rodent Retina and the Protective Effects of Remote Limb Ischemic Preconditioning

The ERG is the sum of all retinal activity. The ERG is usually recorded from the cornea, which acts as an antenna that collects and sums signals from the retina. The ERG is a sensitive measure of changes in retinal function that are pan-retinal, but is less effective for detecting damage confined to a small area of retina. In the present work we describe how to record the &#8216;flash&#8217; ERG, which is the potential generated when the retina is exposed to a brief light flash. We describe methods of anaesthesia, mydriasis and corneal management during recording; how to keep the retina dark adapted; electrode materials and placement; the range and calibration of stimulus energy; recording parameters and the extraction of data. We also describe a method of inducing ischemia in one limb, and how to use the ERG to assess the effects of this remote-from-the-retina ischemia on retinal function after light damage. A two-flash protocol is described which allows isolation of the cone-driven component of the dark-adapted ERG, and thereby the separation of the rod and cone components. Because it can be recorded with techniques that are minimally invasive, the ERG has been widely used in studies of the physiology, pharmacology and toxicology of the retina. We describe one example of this usefulness, in which the ERG is used to assess the function of the light-damaged retina, with and without a neuroprotective intervention; preconditioning by remote ischemia.

The electroretinogram (ERG) is an electrical potential generated by the retina in response to light. This paper describes how to use the ERG to assess retinal function, in dark-adapted rats, and how it can be can be used to assess a neuroprotective intervention, in the present case remote ischemic preconditioning.

The ERG is the sum of all retinal activity. The ERG is usually recorded from the cornea, which acts as an antenna that collects and sums signals from the ...

Neuroscience

Simultaneous Recording of Electroretinography and Visual Evoked Potentials in Anesthetized Rats

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. The ERG waveform can be broken down into components that reflect responses from different retinal neuronal and glial cell classes. The early components of the VEP waveform represent the integrity of the optic nerve and higher cortical centers. These recordings can be conducted in isolation or together, depending on the application. The methodology described in this paper allows simultaneous assessment of retinal and cortical visual evoked electrophysiology from both eyes and both hemispheres. This is a useful way to more comprehensively assess retinal function and the upstream effects that changes in retinal function can have on visual evoked cortical function.

This protocol describes simultaneous measurement of electroretinogram and visual evoked potentials in anesthetized rats.

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the ...

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in retinal diseases, and testing therapeutic interventions. The ex vivo electroretinogram (ERG) allows the quantification of contributions from individual cell types in the isolated retina by addition of specific pharmacological agents and evaluation of tissue-intrinsic changes independently of systemic influences. Retinal light responses can be measured using a specialized ex vivo ERG specimen holder and recording setup, modified from existing patch clamp or microelectrode array equipment. Particularly, the study of ON-bipolar cells, but also of photoreceptors, has been hampered by the slow but progressive decline of light responses in the ex vivo ERG over time. Increased perfusion speed and adjustment of the perfusate temperature improve ex vivo retinal function and maximize response amplitude and stability. The ex vivo ERG uniquely allows the study of individual retinal neuronal cell types. In addition, improvements to maximize response amplitudes and stability allow the investigation of light responses in retina samples from large animals, as well as human donor eyes, making the ex vivo ERG a valuable addition to the repertoire of techniques used to investigate retinal function.

Optimizing the Setup and Conditions for Ex Vivo Electroretinogram to Study Retina Function in Small and Large Eyes

Modification of existing multielectrode array or patch clamp equipment makes the ex vivo electroretinogram more widely accessible. Improved methods to record and maintain ex vivo light responses facilitate the study of photoreceptor and ON-bipolar cell function in the healthy retina, animal models of eye diseases, and human donor retinas.

Measurements of retinal neuronal light responses are critical to investigating the physiology of the healthy retina, determining pathological changes in ...

Direct-Coupled Electroretinogram Recording of the Retinal Pigment Epithelium in a Mouse

Source: Miyagishima, K. J., et al. <a href="https://app-jove-com.remotexs.ntu.edu.sg/v/61491">Direct-Coupled Electroretinogram (DC-ERG) for Recording the Light-Evoked Electrical Responses of the Mouse Retinal Pigment Epithelium.</a> J. Vis. Exp. (2020).
This video demonstrates the recording of a direct-coupled electroretinogram (DC-ERG) on a dark-adapted, anesthetized mouse retinal pigment epithelium (RPE). After applying dilating drops, the animal is placed in a recording setup, and the capillary electrode filled with a salt buffer is placed on the cornea. After establishing the baseline, DC-ERG is recorded.

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. Mouse ...

JoVE Encyclopedia of Experiments

Neurophysiology

Imaging and Optical Techniques

Recording of Electroretinogram and Visual Evoked Potential in a Rat

For recording dark-adapted signals, animals are dark-adapted for 12 hours, and all procedures are performed in a dark room with the aid of dim red light. For illustration purposes, recordings will be conducted under normal room lighting conditions here.
Before recording, apply topical anesthesia and dilating drops to the cornea of the rat. Next, guide the conscious animal into a custom-made clear restrainer. Place the rat in front of the Ganzfeld bowl with its eyes aligned with the opening of the bowl.
Turn on the indwelling transmitter by passing a magnet within 5 centimeters of it. Verify that the transmitter is on by checking the LED status light on the receiver base. Then, collect signals over a range of luminous energies.

Electroretinogram Recording for Infants and Children under Anesthesia to Achieve Optimal Dark Adaptation and International Standards

Samenvatting

Meer video's verkennen