Electroretinogram evaluation of equine eyes with extensive ‘bullet-hole’ fundic lesions

Objective To evaluate the impact of extensive bullet-hole nontapetal fundic lesions in horses on retinal function as measured by full-field electroretinography (ERG). Materials and Methods Full-field ERG was performed on two horses with numerous bullet-hole lesions in the nontapetal fundus of both eyes. The ERG was first recorded from the eye with the more extensive lesions in response to a low-intensity light stimulus (0.03 cd s/m2) that was given at times (T) T = 5, 10, 15, 20 min of dark adaptation. Consecutively, combined rod–cone response was evaluated bilaterally in response to high-intensity light stimulus (3 cd s/m2), followed by cone function evaluation by flicker stimulus (3 cd s/m2 at 30 Hz). Off-line analysis of the ERG recordings was then performed. Results Despite extensive bullet-hole lesions in the nontapetal fundus bilaterally in both horses, retinal function as measured by ERG did not show any observable deficits. The b-wave amplitude of the full-field ERG increased continuously from 5 to 20 min of dark adaptation peaking at 446 μv and 377 μv for horse number 1 and 2, respectively. The b-wave amplitudes of the combined rod–cone response were OS- 459 μv and OD- 392 μv for horse number 1 and OS- 491 μv and OD- 608 μv for horse number 2. The amplitude of the flicker ERG for horse number 1 was OS- 86 μv and OD- 110 μv and for horse number 2, OS- 80 μv and OD- 74 μv. Conclusions Extensive bullet-hole chorioretinal lesions do not appear to compromise outer retinal function in these horses.