Here is an example of a thick nail but you should know that all nails that are thick are not fungus. In the case of this picture do you see that one of the toenails comes on contact with the ground. The toe is curved or hammered because of the nature it is pointing down. If you walk on a toe like that and it can't straighten out the skin gets a callus. Since your nail is only an extension of your skin the nail also gets thick. This is not a fungus in the beginning but the nail is more likely to get a fungal infection due to the constant injury.
This can be treated with a crest pad to straighten the toe or with surgery to straighten the toe. The surgery involves either cutting the tendon or taking out some of the bone in the toe.
To your health.
Dr. Donald Pelto