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Medical Forum / General / Vision / October 2006Bad Vision
When I blink on a night time or against a light background like a cloud the centre of my vision is a roundish black or white dot which disappears after about 2 seconds. I have had a few vision tests by opticians and the eye hospital and they have said my retina and macular are perfectly fine but cannot explain why it is happening. This normally happens on an evening and really badly on a night time when I lie down. I use a computer for most of the day every day and was wondering whether it could be something to do with my lens or whether is was the blood not reaching my eye or something. Please help. On 9/25/06 10:39 AM, in article 1159205986.143529.123520@b28g2000cwb.googlegroups.com, > When I blink on a night time or against a light background like a cloud > the centre of my vision is a roundish black or white dot which [quoted text clipped - 9 lines] > > Please help. It is not clear, from your description, just what the lighting conditions are when you make your observation. I have seen phenomena you are describing under conditions of low light such as at dusk. I look at a lightly colored background. I attribute the effect to the difference between photopic (cone mediated) and scotopic (rod mediated) vision. The macular region is full of cones that do not work well at low light levels. That means that that there are no rods there to see with in dim light. As light levels increase, there is ample light for the cones to work properly. Oliver Sacks describes a group of people with photopsia, a condition in which there are NO cones. Those people had not central vision at all. Bill -- Fermez le Bush Hi, Thank you for responding. Its mainly in low light conditions and on a light background the spot is dark and on a dark background the spot is white or grey. It is always in the same placeand varies in size depending on how far away the background is (bigger when object is closer), I can see within 2 seconds perfectly and its when I go from dark to light conditions very quickly. I can open my eyes slowly and the spot is not there but when I open it just a little quicker than normal it appears, its not a floater as it does not move and is in the exact same place all the time. > On 9/25/06 10:39 AM, in article > 1159205986.143529.123520@b28g2000cwb.googlegroups.com, [quoted text clipped - 29 lines] > Bill > -- Fermez le Bush > I can open my eyes slowly and the spot is not there but when I open it > just a little quicker than normal it appears, its not a floater as it > does not move and is in the exact same place all the time. If it occurred in one eye only, it might be something to worry about. You seem to indicate it's simultaneous in both eyes. If so, that's reassuring, possibly a "physiological" result of having fewer rods in the center of your vision. -MT On 9/25/06 12:18 PM, in article HIadna0FXewGtoXYnZ2dnUVZ_vOdnZ2d@giganews.com, "Mike Tyner" <mtyner@mindspring.com> wrote: > If it occurred in one eye only, it might be something to worry about. You > seem to indicate it's simultaneous in both eyes. If so, that's reassuring, > possibly a "physiological" result of having fewer rods in the center of your > vision. What is the density of rods in the macula? Do people with achromatopsia described by Sacks have rods in the macula? From the little I know of Sacks's study, I inferred that with achromatopsia, in the absence of other genetic defects, rods occur only the portion of the retina where normal people have rods, thereby achromatopsia sufferers have few central vision sensing cells. Please note that I erred in an earlier post when I used the term "photopsia" when I should have used "achromatopsia". Bill -- Fermez le Bush > What is the density of rods in the macula? 160,000 rods/mm2 at 18 degrees off-axis; but it approaches zero at the fovea. > Do people with achromatopsia > described by Sacks have rods in the macula? I'd expect they have a pretty normal rod density profile, maximum 18 degrees off-axis, fovea zero. > From the little I know of > Sacks's study, I inferred that with achromatopsia, in the absence of other > genetic defects, rods occur only the portion of the retina where normal > people have rods, thereby achromatopsia sufferers have few central vision > sensing cells. So they get around OK (with sunglasses) but measured acuity might be 20/50 at best. And congenital visual limitations like this often cause nystagmus as well. I recall being told that rod monochromatism is usually accompanied by other congenital disorders, but that was long before Sacks' publication.. -MT This has only happened to me in the past 3 - 4 months maybe or I havent noticed it until then, it was after about 3 weeks of extensive computer use that this happened. I thank you all for your responses, I really appreciate it. Thank you. On 9/26/06 5:24 AM, in article 1159273456.428476.17620@i3g2000cwc.googlegroups.com, > This has only happened to me in the past 3 - 4 months maybe or I havent > noticed it until then, it was after about 3 weeks of extensive computer > use that this happened. I also did not notice the effect until after I retired. I probably noticed it more because deteriorating vision led to my paying more attention to visual anomalies. Bill -- Fermez le Bush So will this keep getting worse until I have no central vision or will it stay the same or improve over time. It does seem to be better some days than others, Im 24yrs old and find the whole thing distressing and nowhere to turn to where I live and thankfully these groups can help. I don't think anyone can say, since you really haven't had a diagnosis yet. My guess is you are experiencing an afterimage or some such entopic phenomenon. Just ignore it, unless it gets worse or persists much beyond a second or two. w.stacy, o.d. >So will this keep getting worse until I have no central vision or will >it stay the same or improve over time. [quoted text clipped - 4 lines] > > Thank you William Stacy, what you mentioned is exactly what I have and not 1 Optician or Eye Doctor has told me about that or mentioned anything like that and next week I am at a Neurologist because they said it was my brain. I dont think you all understand how big a help you's are when answering these questions we all raise, once again thank you to everyone who has replied. On 9/27/06 12:12 PM, in article 1159384350.427366.248700@i3g2000cwc.googlegroups.com, > Thank you William Stacy, what you mentioned is exactly what I have and > not 1 Optician or Eye Doctor has told me about that or mentioned [quoted text clipped - 4 lines] > these questions we all raise, once again thank you to everyone who has > replied. I still think that what you are seeing is normal. Have you ever had the effect in bright illumination? If not, I think that you are just observing the way cones work. Try it in the middle of a sunny day against a lightly colored wall of uniform texture. Bill, definitely not a health professional -- Fermez le Bush It sometimes happens in bright light, what I have noticed is that if I have an afterimage even if its not in the centre of my vision I dont see the spot (loss of vision in the centre). Its went from being a dark spot/loss of vision to a white spot/loss of vision, I actually went out one night and was quite drunk so I slept soundly and the next day I didnt have as much of a problem with them so maybe its to do with not having enough sleep. Its funny because now I have had 15 emails from people who have the same problem and cannot really find the answer to the problem but I think its our inability to describe the problem properly because I cannot explain it too well. On 9/25/06 10:58 PM, in article JbmdnWG-oecBXIXYnZ2dnUVZ_qudnZ2d@giganews.com, "Mike Tyner" <mtyner@mindspring.com> wrote: > 160,000 rods/mm2 at 18 degrees off-axis; but it approaches zero at the > fovea. That is pretty far off axis. I do not think that I would be able to read that far away even with cones. It might be different if my vision were trained under such circumstances, Bill -- Fermez le Bush |
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