POHS (histo) spots can and do multiply, as I do see new spots next to
old faded spots, in a number of people.  But, eventually, it does stop
progressing in virtually all patients.

One of my most interesting cases involved a woman who was a contact
lens wearer.  While checking the visual acuity she read fine with the
right eye, but as soon as she covered the right eye to read with the
left, she about jumped out of her chair.  She had a very dense central
scotoma that reduced her visual acuity to 20/200.  Upon examination,
she was found to have a large histo lesion in her macula.  She had an
eye exam somewhere about two years prior.

Another patient had been experiencing photopsia (sparkling lights) in
the periphery of one eye for about six weeks.  She diagnosed herself
with ocular migraine.  It turned out to be a florid case of POHS, with
slight macular involvement to the 20/50 level.  This would eventually
involve the maculas of both eyes, proceed to blindness, and total
disability despite aggressive medical management.

A similar case involved a macular POHS lesion in an adult female with
vision at about the 20/60 level.  She was treated aggressively with
steroids and later had submacular surgery to remove the fibrotic
neovascular scar.  The steroids led to a cataract and cataract surgery.
Her vision is 20/20 uncorrected today, and has been stable for several
years.

I could go on.  It can be very bad, but most cases don't seem to
develop the macular lesions, with the diagnosis being made during the
course of a routine eye examination.

DrG