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Q and A: Can Shrapnel Blind My Soldier Without Leaving Behind Any Visible Evidence of His Injury?

07 Jun

Q: I have a Lt. Colonel blinded by shrapnel when he is ambushed while on patrol in Iraq. I have it that the projectile enters his temple and other shrapnel pocks his neck. Is this possible without visual damage to the eyes although he has scars on the temple? In other words, his eyes “look” fine, but he’s blind. Could a hit like that destroy the optic nerve without brain damage? I know that most blinding incidents occur from direct hits to the eye or from the pressure of explosives, so I want to be correct when explaining his injury.

A: First, a little anatomy. Here is a link to a diagram that will help you understand the explanation: http://www.medicalook.com/human_anatomy/organs/Optic_nerve.html

The optic nerves connect the optic cortex, which is the portion of the cerebral cortex involved with vision, with the retinas in a crossover pattern at what is called the optic chiasm. The left sided optic cortex supplies fibers through the brain to the left portion of the retina of each eye. This portion of the retina sees to the right. The right side optic cortex supplies fibers to the right portion of the retina of both eyes and sees to the left. Study the diagram in the link and this should be easy to see.


An injury on one side of the head that involves the optic nerve, say to the left eye, could cause blindness in the left eye only. The same would be true of the right. If the injury were deep enough that it reached the base of the brain and damaged the optic chaism and was severe enough to damage all the optic fibers then blindness would be bilateral because none of the optic fibers would be able to reach the retina. This would be a very severe head injury since these fibers lie deep into the skull at the base of the brain. He could survive it but it would require luck and fairly immediate cranial surgery.

The injury could also come to the back of the head and the optic cortex could be damaged. The optic cortex is the hind-most portion of each brain hemisphere. Injuries to these areas can result in what we call cortical blindness since the blindness comes from an injury and malfunction of the cortex of the brain. If the injury were to the right sided optical cortex he would be blind in his left visual field. We call this a left homonymous hemianopsia which is a big word meaning blindness in the left side of the visual field of both eyes. Here his visual field would be cut in half. The right half of the field would be normal and the left half dark as if a curtain had been pulled before his face. Of course if the left-sided cortex were damaged, he would be blind in his right visual field and would have a right homonymous hemianopsia. If the damage was to both of the optic cortices he would be completely blind.

So he could be blind in one eye with an injury to the optic nerve, both eyes if the injury involved the optic chiasm, a homonymous hemianopsia if one side of the cortex were damaged, and total cortical blindness if both optic cortices were damaged.

The chiasm could be damaged by a penetrating wound or from the concussion of the blast without penetration while damage to a single optic nerve would more likely occur with a penetrating wound. Complete or partial cortical blindness could follow either blunt or penetrating trauma to the optical cortices. But almost anything is possible.

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5 Comments

Posted by on June 7, 2011 in Medical Issues, Q&A, Trauma

 

5 responses to “Q and A: Can Shrapnel Blind My Soldier Without Leaving Behind Any Visible Evidence of His Injury?

  1. Jonathan Quist

    June 7, 2011 at 3:12 pm

    Going beyond the medical answer regarding the “without visible damage to the eyes” part of the question, I would add a caveat that “it depends”.

    It partly depends upon how you intend to use the information.

    If your soldier is in a situation where he is interacting with a sighted antagonist in close quarters over a prolonged period, then some differences will be apparent, even after he has mastered the mechanics of living and working blind in a sighted world.
    If, on the other hand, he has a brief meeting with someone, he may very well pass as sighted.

    In one of my previous jobs I worked with two blind coworkers. Joe (not his real name) had lost his eyesight over a period of years following an automobile accident. I do not know the details of his injuries, but when I worked with him he had been completely blind for more than five years. Ted, on the other hand, was a 19-year-old summer intern, who lost his sight to disease when he was a young boy.

    In Joe’s case, any scars he may have had from the accident were ten years gone; Ted never had any scars.

    Under close scrutiny, neither man would be described as “without visible damage to the eyes” – not because there was anything that looked like a grievous injury, but because their eyes did not track like those of a person with normal vision.

    When in conversation that required turning his head to address different people, Joe’s eyes would lead when turning his head, like a sighted person’s, but they were not coordinated together. One eye always appeared aimed a bit higher than the other, and they tended to diverge slightly (compared so a sighted person whose eyes were converged to see a near object). Ted had been blind so long, his eyes seldom moved independent of his head movements, and his eyes also did not appear aimed to the same spot. I think Joe once told me that autonomic coordinated eye motion continues for a while immediately after onset of blindness, but I have no authoritative information on that phenomenon. (If anyone knows this to be incorrect, please correct me.)

    Both men used normal facial expressions involving their eyes, Joe more than Ted.

    The first time I met Joe, he swiveled in his chair, said hello, and extended his hand. My first hint that he couldn’t see me was that our hands did not meet. I made a slight adjustment for our hands to meet, he did not. My second clue was when he introduced himself as one of the company’s blind system administrators. That was when I noticed that his computer terminal was talking. This was in 1985, before personal computers had sound cards. There were other people there who had not figured out Joe was blind for several months. Usually because he enjoyed letting them reach that conclusion in amusing ways.

    Eventually, one of Joe’s eyes developed a cataract-like discoloration, related to his injury. He eventually had the eye removed, and got a glass prosthesis. It became much more difficult to notice anything unusual about the appearance of his eyes after that.

    So if you intend for your blind protagonist to blend in, yes, it is possible for a blind person to fool a sighted person for a while. If he’s got someone supporting the illusion, probably for a long while. If the person he’s trying to fool has prior experience with blind acquaintances, he’d be detected much sooner.

    I hope that’s helpful. If it’s not at all what you were looking for, I hope it helps someone else…

    jeq

     
  2. Maryn Sinclair

    June 8, 2011 at 7:01 am

    In describing cortical blindness from a shrapnel injury to the back of the head, for example, in simple terms–terms the victim would use to describe his blindness–would he say the damage resulted from an injury to the optic cortex, the optic chiasm, or the optical cortices? If cortical blindness is caused by this type of trauma–blood seeping into the optic cortices, how long would it take for blindness to set in?

     
    • D.P. Lyle, MD

      June 8, 2011 at 8:32 am

      Yes those terms would work. The blindness could be immediate or delayed for hours, days, or weeks due to slow bleeding and swelling in the area. It could then be permanent or temporary.

       
      • Travis Johnson

        September 19, 2013 at 2:43 pm

        Could I ask a related question to eye damage? I have always had 20/20 vision but after a period of unconciouseness from being backed over by a heavy vehicle, to which I received lacerations to the left side of my face and right side of the top of my head, I noticed upon waking up in the hospital that my eyesight was fuzzy and it hasn’t changed since. Has not worsened either. Both opthomologists that I’ve seen have inspected and photographed the inside of the eye and said that there is no evidence of trauma. I have an eye exam from a year before the accident with 20/20 (just after moving to Australia from Canada) and one three months post accident with worsened vision. Is it possible that my optic nerves were damaged and the opthomologists did not detect it?

        Travis travis.b.johnson@gmail.com

         
      • D.P. Lyle, MD

        September 19, 2013 at 3:20 pm

        For medico-legal and ethical reasons I never give medical advice to those who are not my patients. I suggest you take this up with your physician.

         

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