Baby iris change - segment heterochromia?

[7Worfs]

My baby is 4 months old.
At birth his eyes were blurry dark blue; they gradually started to clear and the colour emerged as grey.

Today I noticed part of his left iris has turned brown (if it were a clock face, it would be the 11 to 12 o’clock segment). The whole iris appears ever so slightly darker than the other.

For comparison my firstborn also started with blurry blue eyes, they turned grey, then eventually hazel, then light brown, but it took a few years and change was gradual and identical in both eyes.

I will call the GP tomorrow, but can someone please advise if you’ve seen this before?

I’m worried about something sinister in the brain causing it.

Hopeful bump

I wouldn't personally worry as he is still so young. My daughters eyes didn't stop changing until she was about 2. Get him checked but I'm sure all will be okay. Could be a birthmark under his eye that's finally coming out as his eyes are settling.

Update for the sake of thread completion - the ophthalmologist confirmed the spot is just pigment, however suspects baby may have mild shortsightedness, so we were asked to bring him in for another check in a year.