Subdermal needle electrode

Electroretinography (ERG) was performed on both treated and untreated eyes at 5 weeks following microbead injection using an Espion Diagnosys system (Diagnosys LLC, Littleton, MA, USA). Tropicamide (0.5%, Akorn, Lake Forest, IL, USA) and 0.5% proparacaine hydrochloride (Falcon Pharmaceuticals, Fort Worth, TX, USA) were used for pupil dilation. Body temperature was maintained at 37 °C with a homeothermic controller and unit. Electrical signals were recorded with two 3 mm gold wire loop electrodes (Diagnosys) contacting the corneal surface of eyes precoated with a 2.5% hydroxypropyl-methylcellulose solution (Gonak, Akorn, Lake Forest, IL, USA). A subdermal needle electrode (Viasys Healthcare, Chicago, IL, USA) between the ears served as common reference while the other subdermal needle electrode inserted at the base of the tail acted as ground. Retinal responses were recorded simultaneously from both eyes. Light stimuli were delivered via a ColorDome unit. Three different light intensities, 1, 5 and 7 cd.s/m², were used in a 3-step examination. The stimuli were blue flashes (6.28 cd/m²) and green (560 nm) background (10 cd/m²). Each recording was an average of 10 sweeps with an inter-stimulus interval of 0.4 s. Signals were band-pass filtered at 1 kHz. The PhNR amplitude was measured from the baseline to the trough following the b-wave.