Abstract
Purpose: :
To study the functional properties in the glaucomatous DBA/2J mouse and in the C57/B6 mouse as a control and to correlate them with intra-ocular pressure (IOP).
Methods: :
20 DBA mice and 23 C57 mice were measured five times at ages between two and ten months with about 8 weeks intervals. 5 Control mice between 12 and 22 months of age were also measured to study normal ageing. One day prior to ERG recordings, the IOPs were measured. The animals were dark adapted over night. Flash ERGs were measured in dark- adapted animals. Subsequently, the animals were light adapted and flash ERG measurements were repeated. Furthermore, flicker ERGs at different temporal frequencies and different stimulus strengths were measured in light-adapted animals.
Results: :
The IOPs in the DBA mice were lower than those in the C57 mice during the whole period although there was a significant increase after about 4 months of age whereas they remained constant in the control mice. The amplitudes of flicker ERGs in the DBA mouse were significantly decreased compared with those of the C57 from the beginning and continued to decrease through the 8 months’ period at the end of which they were hardly measurable. Flicker ERGs in the C57 mice decreased only slightly as a function of age. The a- and b-waves of the flash ERG amplitudes were of about the same amplitude in the two mouse strains at two months but decreased more strongly in the DBA mouse. At an age of 6 months the flash responses were significantly smaller than in the C57 mouse. The IOPs and the ERG amplitudes measured in the same animals at different ages and measured in different individuals at an age of about 6 months were correlated. The inter-individual differences were smaller in the DBA mice.
Conclusions: :
The flicker ERG seems to be more affected by retinal degeneration than the flash ERG indicating the early involvement of post-receptoral pathways. The retinae of DBA mice show functional signs of retinal degeneration already at an age of two months. An increased IOP affects the retinal responses, but the fact that the ERGs were already decreased at an age where the IOPs were even lower than in the control mouse indicates that other factors play an important role in retinal degeneration.
Keywords: electroretinography: non-clinical • intraocular pressure