Do NVG's cause a deterioration in Eyesight?

[Tigs2]

Do any of you folks know if NVG's cause a deterioration in Eyesight? I used to have perfect vision until i started extensive flying using NVG's. I started on the early generation goggles (Gen 2) and have noticed a real drop in the effectiveness of my eyesight, including night vision. The opticians i go to dont have any answers, so i seek any knowledge from you folks into aviation medicine.
Thanks

[Loose rivets]

Can you be more specific in your description of the degrading of your eyesight. Is the focus measurably different, or is it a feeling of just not being able to interpret the visual images as well as you used to?

If you have a period of rest, does the condition get a little better?

What type of device gives the image in the NVGs that you use?