This is a retrospective multi-centered analytic study that included the patients with nystagmus referred to the electrophysiology units from the ophthalmology outpatient clinics at the University Hospitals of Minia, Ain Shams, Banha, and Cairo, Egypt during the period from January 2019 to June 2019.
The study included 60 (120 eyes) patients with horizontal nystagmus, which is the most prevalent form of nystagmus that needs investigations especially by electrophysiology to help in the diagnosis of the underlying causes. Patients with associated neurological disorders, strabismus, or media opacity were excluded from the study. The study was approved by the Faculty of Medicine, Research Ethics Committee (FMREC) of Minia University (approval number 291:9/2019). The Ethical committee waived the patient consent due to the retrospective nature of the study.
All enrolled patients had full ophthalmological examination and investigations including electrophysiology that was performed on another day of the same week. The sequence of testing was as follows: first without dilatation in the form of pattern visual evoked potential, flash visual evoked potential (FVEP), and pattern electroretinography (PERG), followed by pupillary dilatation for full-field electroretinography (ffERG), optical coherence tomography (OCT), OCT-angiography (OCT-A), and fundus autofluorescence (FAF).
The FVEP [9] , ffERG [10] , and PERG [11] were performed following the standard protocols of the International Society for Clinical Electrophysiology of Vision (ISCEV). All electrophysiological tests were performed without sedation or anesthesia and were recorded with the RETI-port/scan 21 (Roland Consult, Brandenburg, Germany). Young children can have all the investigations performed, in the hands of well-trained experts, without sedation; however, they need a longer test duration.
Monocular visual evoked potential (VEPs), starting with the right eye according to the machine protocol settings, were recorded without pupillary dilatation using three electrodes: red active electrode (Oz) attached 1.5 cm above the occipital protuberance, blue reference electrode (Fz) attached at the mid forehead, and black ground electrode (Cz) attached at the midline anterio-auricular line midway between Oz and Fz electrodes. Stimuli for VEP testing were flash VEPs elicited by a white flash (3 cd.s/m 2 ) luminance. ffERGs were recorded in both eyes simultaneously. The pupils were dilated with topical eye drops in the form of 1% tropicamide (Alcon, Fortworth, Texas, USA) and 5% phenylephrine hydrochloride (Cooper Pharmaceuticals, Athens, Greece). After dark adaptation for 20 min, topical anesthetic eye drops (Benoxinate hydrochloride 0.4%, Eipico, Nasr City, Cairo, Egypt) was used. The HK Loop electrodes were then installed under the dim red light into the lower fornix, while the reference skin electrodes were attached on the skin near the orbital rim temporally of each eye, and the ground skin electrodes were attached on the central part of the forehead. Using white flash Ganzfeld (GF) stimulation, recording was with the standard ISCEV ERG measurements (six steps): Dark-adapted (DA) 0.01 ERG (rod response), DA 3 and 10 ERG (combined rod and cone responses), and DA oscillatory potentials (amacrine cells responses). Subjects were then light-adapted for ten minutes by exposure to a white 30 cd/m 2 rod-saturating background, and photopic ERGs were recorded to standard ISCEV intensity: Light-adapted 3 ERG (cone response) and to white 30 Hz flicker ERG (cone photoreceptors response). The examination parameters were GF LED flash (3, 00 cds/m 2 ) 29.412 Hz, Avg: 8, Amplifier:±1 mV 1-300 Hz.
Whenever available, the patients underwent color fundus photography, FAF, OCT, and OCT-A by Solix Optovue, (Haag-Streit USA, Mason, Ohio, USA) and Retina scan RS-3000 advance (Nidek, Gamagori, Japan).
The analyzed data included age, sex, fundus findings, electrophysiological diagnosis, and test findings and characteristics. The final electrophysiological diagnosis was obtained after combining the features of history, fundus picture, and results of the investigations performed.
The study included 60 (120 eyes) patients with horizontal nystagmus, which is the most prevalent form of nystagmus that needs investigations especially by electrophysiology to help in the diagnosis of the underlying causes. Patients with associated neurological disorders, strabismus, or media opacity were excluded from the study. The study was approved by the Faculty of Medicine, Research Ethics Committee (FMREC) of Minia University (approval number 291:9/2019). The Ethical committee waived the patient consent due to the retrospective nature of the study.
All enrolled patients had full ophthalmological examination and investigations including electrophysiology that was performed on another day of the same week. The sequence of testing was as follows: first without dilatation in the form of pattern visual evoked potential, flash visual evoked potential (FVEP), and pattern electroretinography (PERG), followed by pupillary dilatation for full-field electroretinography (ffERG), optical coherence tomography (OCT), OCT-angiography (OCT-A), and fundus autofluorescence (FAF).
The FVEP [9] , ffERG [10] , and PERG [11] were performed following the standard protocols of the International Society for Clinical Electrophysiology of Vision (ISCEV). All electrophysiological tests were performed without sedation or anesthesia and were recorded with the RETI-port/scan 21 (Roland Consult, Brandenburg, Germany). Young children can have all the investigations performed, in the hands of well-trained experts, without sedation; however, they need a longer test duration.
Monocular visual evoked potential (VEPs), starting with the right eye according to the machine protocol settings, were recorded without pupillary dilatation using three electrodes: red active electrode (Oz) attached 1.5 cm above the occipital protuberance, blue reference electrode (Fz) attached at the mid forehead, and black ground electrode (Cz) attached at the midline anterio-auricular line midway between Oz and Fz electrodes. Stimuli for VEP testing were flash VEPs elicited by a white flash (3 cd.s/m 2 ) luminance. ffERGs were recorded in both eyes simultaneously. The pupils were dilated with topical eye drops in the form of 1% tropicamide (Alcon, Fortworth, Texas, USA) and 5% phenylephrine hydrochloride (Cooper Pharmaceuticals, Athens, Greece). After dark adaptation for 20 min, topical anesthetic eye drops (Benoxinate hydrochloride 0.4%, Eipico, Nasr City, Cairo, Egypt) was used. The HK Loop electrodes were then installed under the dim red light into the lower fornix, while the reference skin electrodes were attached on the skin near the orbital rim temporally of each eye, and the ground skin electrodes were attached on the central part of the forehead. Using white flash Ganzfeld (GF) stimulation, recording was with the standard ISCEV ERG measurements (six steps): Dark-adapted (DA) 0.01 ERG (rod response), DA 3 and 10 ERG (combined rod and cone responses), and DA oscillatory potentials (amacrine cells responses). Subjects were then light-adapted for ten minutes by exposure to a white 30 cd/m 2 rod-saturating background, and photopic ERGs were recorded to standard ISCEV intensity: Light-adapted 3 ERG (cone response) and to white 30 Hz flicker ERG (cone photoreceptors response). The examination parameters were GF LED flash (3, 00 cds/m 2 ) 29.412 Hz, Avg: 8, Amplifier:±1 mV 1-300 Hz.
Whenever available, the patients underwent color fundus photography, FAF, OCT, and OCT-A by Solix Optovue, (Haag-Streit USA, Mason, Ohio, USA) and Retina scan RS-3000 advance (Nidek, Gamagori, Japan).
The analyzed data included age, sex, fundus findings, electrophysiological diagnosis, and test findings and characteristics. The final electrophysiological diagnosis was obtained after combining the features of history, fundus picture, and results of the investigations performed.
