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Left eye movement causing momentary white crescent

When I look at a white wall, sky etc, I often see a momentary white crescent which almost immediately disappears.  I noticed this 9 days ago, but might have been around long before then without me really registering it.

Went to the hospital to get my pupils dilated and check the retina for any tears or anything.  The lady found no problems apart from lots of floaters and suggested it was a type of floater.  But this is not a floater, or at least it doesn't float, and only has a momentary existence.  Anyone have any suggestions?
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I've had my eyes checked for retinal tears etc 4 days ago.  No tears or anything were found.
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Cosmic: There are all types of 'eye doctors" to have the proper examination you need to have seen an Eye MD ophthalmologist that dilated your pupils and did an extensive peripheral retina exam.  Flashes from  RD usually occur in dark or dim light, are extremely bright and momentary.  If you did not see eye MD (for instance you saw non MD optometrist) see an Eye MD.  If you saw eye MD and your eye is normal the most common thing that would cause this might be sudden awareness of entopic phenomena such as afterimages.  Read the section in wikipedia on entopic phenomena.   All Eye MDs tell people with flashes/floaters if something changes for the worse or new symptoms develop come back for a re-exam and i would say the same thing.
Hi, thanks for that.  I live in the UK and it was an eye clinic at a NHS hospital.  Not sure what the qualifications of the person who performed the exam, although it was an extensive one.

However, these are not seen in dim light and are not particularly bright and I can bring them on at will if looking against a bright background.  I have experienced the occasional flash in the past, these are not really similar.

I was thinking of something like a pressure phosphene?   I also suffer from silent migraines with the scintillating scotoma  where my vision is temporarily affected.  But I guess there's no possible connection here?
Ocular migraines that have scintillation scotoma usually last for 5-30+ minutes and can be seen with eyes shut.  Pressure phosphenes are an entopic phenoma. HOWEVER as the name implies they come from the retina being stimulated by pressure (for example a finger pushing against an eyelid).  Also momentary blue arcs from rapid movement of the eye in darkness. None of which sound like what you are describing.  The qualifications of the person examining you make all the difference in the world.  Would you want a pilot flying your plane? Or the steward? Or mechanic?  They all work "in airplanes" but training is wholly different.   If you are not paying for your meal you get what you're served and like it.
Someone's informed me that unless an emergency where A&E consultants are used, the only people allowed to dilate your eyes in the NHS are ophthalmologists.

OK, if not a tear or detached retina, and not pressure phosphenes, what are the other possibilities?

you don't need to go that further down the road if your pupils were not dilated. that is STEP 1.
My eyes were dilated and examined.  

Could it be a type of "floater" as the  ophthalmologist suggested?  Even though they don't float and only have a momentary existence?
Not at all likely
Above you mentioned the possibility of afterimages.  A week ago, just before I noticed this visual anomaly, I was examining some CDs and DVDs for scratches, and they were reflecting very bright light into my eyes.   But I assume any afterimages couldn't last a week?  If so I don't see how it could be an afterimage?
Cosmic - please don't take this the wrong way.   When I had the anomaly I mentioned above I scoured the internet, googled, stood in front of the wall and kept recreating the issue to see if anything changed, posted here and elsewhere.  To be honest I was making myself crazy and ended up with sleepless nights with worry.  I think you have a couple of choices to make.

1).  Do nothing but monitor and get annual exams - You had a dilated exam by what you were told was an opthalmologist.  Use that exam as your baseline, monitor yourself and go back if anything changes.

2).  Get a second opinion from another MD to set your mind at ease.  In my case my retina doctor is my go to guy with my history.

Best of luck to you,  Jim

To set my mind at ease that it's not a detached retina?  Apart from the fact the opthalmologist discovered nothing, the symptom is not indicative of a detached retina.  The flashes associated with getting a detached retina are supposed to be very bright, and can be especially seen in dim light -- quite the opposite of my symptom.  I go back there in 3 months for another dilated pupil test, it's standard procedure.  

I would just like to know what the most likely causes are of the symptom I have.

If you saw eye MD and your eye is normal the most common thing that would cause this might be sudden awareness of entopic phenomena such as afterimages.  Read the section in wikipedia on entopic phenomena.  
Avatar universal
The Dr. will probably be coming in at some point to offer suggestions.  I don't want to scare you but I had similar symptoms with my eye.  Mine was a crescent shaped white line and a smudge area just off the center of sight.  Only would appear on eye movement and just for an instant while staring at certain lightly colored walls and etc..  Due to a previous retina detachment in my other eye, I was already an established patient with a retina opthalmologist and saw him right away.  Found partial PVD and was monitored for months.  Long story short I ended up getting retina detachment symptoms after living with this for 5 months.  Ended up with 5 retina tears which required vitrectomy to correct.  So I would suggest getting an appointment with a retina MD to at least get a baseline on both eyes.   Feel free to look at my post regarding smudge in vision.  Its a long one.   I would see the retina md sooner than later.  Its an emergency if you start to lose vision (like a curtain),  many floaters (like ink/soot), flashes of light like a lightning storm.  Search hear for retina detachment symptoms and you will get the idea.   The goal is that if this is an issue to catch and treat ASAP before permanent damage occurs.
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Avatar universal
I should have also said this only occurs with eye movement, and only in my left eye.
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