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 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 or call us on (02) 9290 1899 to get your peripheral vision tested.

What causes a scotoma?

There are several causes:

•    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.

14 Comments

  • by John Posted February 25, 2017 12:23 am

    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.

    • by admin Posted February 26, 2017 5:31 am

      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.

      • by John Posted February 27, 2017 8:04 pm

        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.

        • by Jim Kokkinakis Posted May 8, 2017 1:47 pm

          Yes a blocked blood vessel can be termed a “stroke”, although it is normally called a arterial or a venous occlusion, which can be seen on observation and does not normally required any sophisticated scanning. If it is a “stroke” or occlusion this normally occurs due to some systemic factor like hypertension or hyperlipidemia or even diabetes. There is another condition called anterior ischemic neuropathy and another called a Drance haemmorhage (that can be related to Glaucoma) that also needs to be ruled out. I would ask the surgeon where he thinks you fall into so we can better clarify what the appropriate treatment and lifestyle changes you are likely to need.

  • by Deb Posted August 23, 2016 9:27 pm

    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

    • by admin Posted October 2, 2016 9:54 pm

      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.

  • by gander Posted July 27, 2016 3:14 am

    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

    • by Jim Posted August 18, 2016 2:15 am

      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.

  • by nauman khan Posted July 8, 2016 6:08 pm

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

    • by admin Posted July 25, 2016 8:25 am

      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?

      • by amit tyagi Posted August 21, 2016 3:45 am

        Presently I am suffering from scotoma left eye last two years. What should I do. Please

        • by admin Posted October 2, 2016 9:55 pm

          Seek an eye examination from an eye care practitioner that can diagnose diseases of the eyes.

  • by SSEBAGGALA CCONSTAANT Posted May 20, 2014 3:28 pm

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

    • by admin Posted June 26, 2014 7:46 am

      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

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