Hi V.: I don't have first hand experience, however I found some info on the internet... (By the way, mention it at your next pedi appointment... Between now and then, when you see him do it, write it down in a log, to record if it happens right after waking up or when he is tired, or after eating or when "straining" on a dirty diaper... or if it occurs at random times...)
From http://www.allaboutvision.com/parents/infants.htm:
Erratic Eye Movements
A vision condition called nystagmus can develop in infancy. Eyes that jump, dance, wiggle or oscillate back and forth is called nystagmus.
This condition may be caused by poor vision, defects in the nerve pathway from the eye to the brain or albinism (light-sensitive retinas in albinos contain too little pigment for the eyes to function properly). Nystagmus may also be inherited. Babies with nystagmus may have normal vision or poor vision. If your child's nystagmus persists past age three months, consult your pediatrician.
You're right if you notice that three to four months of age is an important time for vision development in your child. Take the opportunity during well-baby visits with your pediatrician to ensure that your child is visually on track.
From http://home.earthlink.net/~timler/infant.htmlIn:
The first few months after birth, the muscles that control eye pointing are still developing, so the eyes tend to wander, or even cross.
It should be noted that the visual cortex of the brain itself is also immature at this time. The brain’s dendrites are still growing, which limits contrast sensitivity and color recognition, even if the eye were providing ideal information to the brain. Continual visual stimuli and time will develop the neural connections, as the months progress.
After two months, the baby’s eye has improved. The rods and foveal cones have developed, but acuity is still quite limited: roughly speaking, the baby’s eye has the equivalent of adult 20/200 vision. However, color vision is starting to develop. The four types of photoreceptors (the rods, and three color cones) are in place, and the red/green channel of the neural connection is working, so that the baby can distinguish some colors from grayscale.
At three months, the eye has made its most progress, and the infant can now see colors, motion, and details. Color vision is now fully trichromatic, and the retina has developed such that the eye has the equivalent of 20/100 adult vision. (There is evidence that the limiting factor here is not the retina, but that the neural system cannot yet encode high-frequency spatial patterns.)
Furthermore, the eye muscles have developed so that the baby’s two eyes can move together, and follow a moving object. At this point too, the baby begins to respond to depth. The ability to accommodate starts to develop, and the child gains experience in judging distance.
After six months, great progress has been made. The eye has reached two-thirds of adult size. Acuity has improved so that the eye has about 20/50 adult vision. The eyes can coordinate for good binocular vision, and have good motion detection. Finally, depth perception has improved, and the ability to accommodate is near to adult-quality.