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24

Scotoma – Simply a Natural Blind Spot?

Mammals, and that of course includes humans, have eyes that effectively contain a blind spot.

The blind spot occurs because where the optic nerve connects to the eye there are few if any retinal cells to transmit light messages to the brain.

So everyone has a blind spot in each eye and there is a simple demonstration that can be carried out to prove it:

•    On a piece of paper write the letters R and L boldly about 5cm apart – but don’t put R on the right and L on the left, but rather the other way round:

R                                                           L

•    Next hold the paper about 15cm away from your eyes, and close say the left eye. Then focus the RIGHT eye on the letter R.

•    Then slowly move the paper away or maybe towards you until the letter just suddenly seems to disappear.

•    You can repeat the demonstration with the right eye, this time of course focussing the LEFT eye on the letter L

The blind spot you get in this instance is a naturally occurring blind spot.

The natural blind spot also can be found using the red square and blue circle above.  Cover your left eye and look at the red square.  Slowly come closer until the blue circle disappears! Move further in and it reappears again.

On the other hand if a blind spot occurs in the field of vision under ordinary conditions because of some disorder or lack of eye function, it is given the medical term “scotoma” from the Greek word used to describe darkness.

So then – answering the question set in the title of this article – a scotoma is NOT simply a natural blind spot, the term really being used in the clinical medical sense.

What does a scotoma appear like?

A scotoma may indeed be a spot-like dark area located usually in the centre of the field of vision, but it may also be a wider dark area on the periphery of vision.

Generally a central scotoma presents a serious loss of vision, whilst a peripheral scotoma may in fact go unnoticed by a sufferer because the eye doesn’t focus the peripheral area of vision information quite so accurately.

If around half of the central area of vision is affected then this is designated as another type of scotoma – a hemianopic scotoma.

Detection of a scotoma is readily carried out using a “field of vision” test that uses a computerised instrument called a Field Analyser.  When you have your vision tested we are all familiar with with reading smaller and smaller letters off a standardised letter chart.  Many scotomas cannot be found using this technique, as it is only testing the central vision.  Many scotomas occur in the periphery of your vision.

At The Eye Practice we routinely perform a computerised visual field screening.  What is frustrating is that most eye care practices only perform a computerised visual field eye test on “indication”.  This means that they need to suspect something.  The problem with this protocol is that a scotoma can be symptomless.  A comprehensive eye test should be more than just reading a letter chart.  Find out what a real eye test (http://www NULL.theeyepractice NULL.com NULL.au/eye-care/comprehensive-eye-test) should involve.

It adds another few minutes to the eye exam, but there is peace of mind knowing that more of the vision has been tested.  Book an appointment online by CLICKING HERE (http://www NULL.theeyepractice NULL.com NULL.au/bookeyeexam)or call us on (02) 9290 1899 to get your peripheral vision tested.

What causes a scotoma?

There are several causes:

•    Glaucoma (http://www NULL.theeyepractice NULL.com NULL.au/education-advice/Glaucoma)

•    Suffering a stroke or sustaining a brain injury might lead to development of a type of scotoma

•    Side effects from multiple sclerosis and high blood pressure

•    Toxic substances are also thought to play their part, particularly methyl alcohol and quinine

•    Poor nutrition and serious vitamin deficiencies

•    Blockages in veins in the retina and in particular the optic nerve

Treating a scotoma

In the past there has been little that could be done by way of treatment for a scotoma; however research into the plasticity connections of the brain and how they can be renewed is showing great promise.

New research includes drug trials and both radiation therapy and radiosurgery.

About the Author

Dr Jim Kokkinakis (Optometrist) graduated in 1983 from the Optometry School University of NSW. He is currently a Senior Lecturer there and regular speaker to both Optometrists and Ophthalmologists in Australia and Internationally. He has a specialist clinical practice in the Sydney CBD with interests in Eye Strain, Computer Vision problems, Treatment of Eye Diseases and complex Contact lens Fittings.

Comments (24)

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  1. SSEBAGGALA CCONSTAANT says:

    why is it that normally we dont see that scotoma?Yet we do have the optical disc.

    • admin says:

      The brain does a great job at ignoring the blind spot. the vision around the blind spot is no where near as sensitive as our central vision so it is easy for the brain to suppress the blind spot

  2. nauman khan says:

    I am suffering scotoma from several years.. what should i do ??? Please email me :'(

    • admin says:

      Hi
      This depends on whether it is progressive and what the actual cause is.
      The first thing you need to do is see an optometrist who is an expert in this area. Where are you from?

  3. gander says:

    hi . i just noticed several months ago that i have scotoma in my left eye but it is very small that i could hardly notice it , maybe u can call it natural base on ur article which if i look L and start to moved it further the R disappears but if i moved much further it reappears. but i just noticed yesterday that on my ryt eye does also have scotoma, my wuestion is , does scotoma spreads across your entire eye?? what is tge treatment to this? please help me. this will affect my goals in life if it goes serious

    • Jim (http://www NULL.optometrist NULL.com NULL.au) says:

      Gander depending on what country you are in, you must see an eye specialist or an optometrist and have your peripheral vision measured with a computerised visual field analyser. This will help in diagnosing on whether you have anything to worry about and diagnose the condition. Different conditions have different treatment.

  4. Deb says:

    A week ago when I was a the show and I was unconciously tilting my head I saw a black spot that appears near the center of my vision. It’s opaque and can’t see right through it and gets large when I continue to tilt my head from side to side. It only appears on my left eye. Earlier I saw the same black spot this time without tilting my head sometimes when I look and focus on a blank wall it seems like a spot is slowly building up in my vision. Could it be scotoma? I haven’t been to a doctor since Feb due to financial issue and im so worried about whats causing it 🙁 please help! I’m from the Philippines

    • admin says:

      This is likely to be a floater, Obviously a comprehensive examination will reveal precisely what this is. Usually they are nothing to worry about (called vitreous condensation), but occasionally they can be a sign of a retinal detachment.

  5. John says:

    I had a computerized visual field test which found an extra scotoma in one eye. I was unaware of it and I still don’t even know which eye it is in (I forgot what they told me). The MD said it was from a stroke but I never experienced any other stroke symptoms and if it was a stroke I never even noticed it. I just had a brain and brainstem MRI and I’m waiting for the report . However I did, last year, experience reflected laser from a laser powerful enough to burn a business card. It was reflected off a clear hard plastic box (trying to mark the plastic). Is it reasonable to think I could have a stroke that caused a scotoma and not notice the stroke or the scotoma? Or is it more reasonable to blame specular laser reflection? When the optomitrist first told me about the extra blind spot I suggested it could be a laser injury and he said “that shouldn’t happen” which is obvious. I think maybe he presumed that people only had class 1 lasers.

    • admin says:

      John this is a complicated question. I assume you are comparing one visual field test to another to try and make these conclusions. A scotoma in just one eye is unlikely to be a stroke in the brain as it normally affects both eyes. You can get a scotoma from a blocked blood vessel in the affected eye. I assume this has been ruled out.

      Could a laser cause this? Maybe, but I doubt it, especially from a reflection. I would be interested in finding out how you go with the MRI’s.

      • John says:

        I was diagnosed with glaucoma last year and I had a computerized visual field test then which showed the scotoma. I had another visual field test a couple of months after which showed it again. I’d previously had a non-computerized visual field test years ago which, as I recall, was focused on peripheral vision and, I don’t think, would have found it, so I don’t have any clue as to how long I’ve had it. So, no, I’m not comparing one visual field test to another to try and make these conclusions. I was simply told that I had an extra blind spot in one eye and that they think it was from a stroke.

        Would a blocked blood vessel in the affected eye be called a “stroke”? Would the eye doctor who diagnosed the glaucoma and gave the visual field tests be able to see a blocked blood vessel in his examination or would that require the MRI?

        Thanks for your response. I’ll write again when I find out more.

        • John says:

          Largely unremarkable MRI. Specifically, no evidence of acute ischemia, hemorrhage or mass effect. The optic chiasm appears normal. The midline structures are symmetric.

          A small nidus of hemosiderin in the left temporal lobe appears chronic…could be from a small hemorrhage in the remote past, perhaps, from a venous angioma.

          So, excellent news, I think. First time I’ve ever been happy that someone found my brain unremarkable!

          I’m getting a echo stress test in a few days.

        • admin says:

          Yes a blocked blood vessel in the back of the eye can be called an ischemic stroke, just as it can in the brain. The fact you have been diagnosed with glaucoma also increases the chances that you can have a vascular (blood vessel) issue. You can see the blocked blood vessel but often this requires an invasive test called an angiogram. I assume you have had systemic and blood tests done?

          • Johh says:

            Yes. I’ve had blood tests. Which values are you interested in? Systemic tests? I don’t know what you mean.

            The stress test showed no heart problem. I’m still waiting for the radiologist’s report on the echo-cardiogram.

            I have an ophthalmologist appointment soon. Any suggestions as to what I should talk to him about or tests I should ask for? I was under the impression that he should be able to see a blocked blood vessel issue by looking at my retina. (funduscope)?

            Is it unusual that I could have this occur without ever noticing anything?

            Why does everyone reject my idea of a laser injury? Is it just because it would be so unusual?

            If it is from a blocked vein or artery how would they decide which?

          • admin says:

            Angiograms often need to be performed to decide veins or arteries, or it can be visualised with a fundoscope, it depends on how subtle it is.

          • John says:

            I’ve had blood tests… what would you be looking for?

            Why does everone reject the laser injury hypothesis?

            Would I be likely to have a stroke to the eye without even noticing anything? Is there anyway to tell when it might have happened?

            I’ll be seeing the opthomolgist soon; what questions should I ask him/

            Thanks.

          • admin says:

            Systemic tests are checking the heart, which you have done. Blood tests are to look for anything that can be associated with extra blood viscosity, which can lead to stroke. The laser theory hypothesis will depend on the size and shape of the scotoma. A laser burn will is very specific in size and shape, as is a stroke at the back of the eye. It is too hard to explain this in a blog like this, let the ophthalmologist explain this to you. The only thing you need to worry about is progression in size of the scotoma, which the ophthalmologist will monitor for you.

          • John says:

            Yesterday my opthamologist said that he had already eliminated “stroke to the eye” before he suggested the MRI. He was only concerned that I had had a brain stroke. My primary care doctor misinterpreted the opthamologist’s report and told me definitively that I had had a stroke. He didn’t think there was any need for the MRI. When the clear MRI report came back the opthamologist said, definitively, that I DID NOT have a stroke and that the scotoma was solely a result of the glaucoma.

            So my stroke scare is over, thank goodness. On the plus side I’ve improved my diet and fitness regime.

            Bye bye

          • admin says:

            Glad to hear John. The most common reason for a scotoma is in fact glaucoma. Great to hear that you have improved your diet and fitness. It is important in the context of glaucoma, as it regular eye checks now to monitor your visual field result and make sure the scotoma does not increase in size.

  6. Kate says:

    I was just wondering if cataracts can cause scotomas?

    • admin says:

      Thats a very good question. Scotomas can be complete blind spots or relatively less sensitive (visual field depression) compared to an age matched normal. Once the cataract is fixed surgically these visual field depressions come back to normal.

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