Age-associated changes in the equine flash visual evoked potential.

OBJECTIVE: To investigate age-associated changes of flash visual evoked potentials (FVEPs) in sedated horses.

ANIMAL STUDIED: Twenty-eight clinically healthy Standardbred Warmblooded trotters, aged 36 hours to 28 years.

PROCEDURES: Light-adapted FVEPs and FERGs were recorded (An-vision RETIport, Roland-consult, Germany) in response to flash stimuli. Sedation was obtained using alpha-2-agonists intravenously. Akinesia of the eyelids was induced and pupils were dilated.

RESULTS: Reproducible FVEPs and FERGs were readily recorded from all foals and horses. The FVEP waveform included up to four positive components (P1-P5) and two negative components (N1 and N2) and FVEP waveform morphology was similar across all age groups. Some differences in peak times and amplitudes associated with increasing age were observed. FVEP amplitudes recorded from newborn foals were well above the amplitudes observed in normal adult horses and FVEP peak times were somewhat shorter. In adult horses, a significant increase in P4 peak time and a gradual decrease in amplitudes, mainly for N2P4, were seen across the life-span.

CONCLUSIONS: The overall equine FVEP waveform was similar across the normal life-span of the horse in our cross-sectional study. We found that the visual system of the foal seems to be well developed already at birth. Furthermore, our results showed a decrease in amplitudes and increase in some peak times with increasing age. We recommend that age-matched controls should be used when evaluating foals and young horses in clinical practice, whereas horses over the age of three years can be compared to other adult horses.