The recovery of electroretinographic responses in dogs after fundus photography and indirect ophthalmoscopy

Abstract

Abstract: : Purpose:To investigate the recovery of the electroretinogram (ERG) in dogs after fundus photography and indirect ophthalmoscopy. Methods:ERGs were recorded from six young adult crossbred dogs. The dogs were anesthetized, and after 20 minutes of dark adaptation, a control intensity series flash ERG was recorded (intensities ranging from –2.6 to 0.857 log cdS/m²). A Jet–lens recording electrode and a BPM–100 Electro–diagnostic system v5.50 (RetinoGraphics, Inc) were used. After recording the control ERG, ten fundus photographs were taken, one every 30 seconds using a Kowa RC–2 fundus camera. Following a further 20 minutes of dark adaptation a second intensity series ERG was recorded. The same procedure was repeated on the same group of dogs, but with 60 minutes of dark adaptation following fundus photography. To measure the recovery after indirect ophthalmoscopy a similar protocol was used with indirect ophthalmoscopy (Keeler Dualite Indirect Ophthalmoscope) being continuously performed for 5 minutes. Results:Fundus photography: Following 20 minutes of dark adaptation after photography, the ERG had significantly decreased b–wave amplitudes at all intensities and reduced a–wave amplitudes at the brighter intensities (P<0.05) compared to pre–photography. After 60 minutes of dark adaptation following photography, the ERG amplitudes had returned to the control values. Indirect ophthalmoscopy: Following 20 minutes of dark adaptation after indirect ophthalmoscopy, a– and b–wave amplitudes from all flash stimuli were significantly lower than controls. A– and b–wave latencies were also significantly reduced at several flash intensities. After 60 minutes of dark adaptation, the ERG amplitudes were not significantly different from the controls (P<0.05), except for b–wave intensities from the dim flashes of light (dimmer than – 0.62 log cdS/m²). Conclusions:Exposure of the retina to bright lights, such as for fundus photography or indirect ophthalmoscopy, increases the time required for dark–adaptation. Veterinary ophthalmologists commonly use 20 minutes of dark adaptation prior to recording clinical ERGs. If dogs have been subjected to fundus photography or indirect ophthalmoscopy, dark adaptation of at least 60 minutes is required for the recordings to be comparable with those from dogs that have had 20 minutes of dark adaptation following exposure to normal room lighting.

Keywords: electroretinography: non–clinical