Losing half of vision is no small matter

Juan Ding, OD, PhD

Today I will tell the story of a patient who lost half of his vision. 

Disclaimer: patient’s name is an alias, but the case is real.

I saw John once a year for a few years, monitoring his glaucoma suspicion. Glaucoma suspicion simply means that one’s suspected to have, but does not really have glaucoma yet. He had good vision in general, but usually had many complaints about his vision, mostly that he had to use glasses which he never needed to wear before. 

Once he splashed some chemicals in his right eye while doing house work, and saw my colleagues multiple times while I was on vacation. According to the medical record, the chemical burn had resolved. He came to see me shortly after that.  

‘Doc, I cannot see with my right eye’. My thought was, maybe he was having scars on the cornea. But his cornea looked clear with only a faint scar in the periphery that could not cause vision loss. What’s also interesting was that both his eyes had similar vision. But he insisted that since the chemical splash, he could not see well in the right eye. Could the chemical have reached the back of the eye and caused retinal or optic nerve damage? With a dilated exam, as well as photos of the optic nerve, everything still looked as good as before. There was no apparent retinal or nerve damage.

So I ordered a visual field test. This test examines the periphery vision rather than central vision. I have a couple of his results from previous glaucoma testing, and one looked like Figure 1 A. The dark spots mean vision is less sensitive in that region. So in this graph (Figure 1A), there are only a few minor defects in both eyes.

Figure 1. Gray scale graphs representing visual field results. Each eye was tested separately and darker the spot means worse vision in that particular region. Copyright: Boston Eye Blink

When I saw his visual field results on that day (Figure 1B), I knew the worst had happened. I immediately called him and said, ‘John, you have to go to the emergency room right now.’ 

 As you can see now he had lost a half of vision on the right side, both for right and left eyes. So while he was complaining of not seeing in the right eye, he was actually not seeing on the right side.

This is called a hemianopsia, which means ‘half no see’, or losing vision in one half of the visual field. Vision with hemianopsia is somewhat depicted in Figure 2. This is not an eye problem. This is a brain problem. Specifically, there is a problem in the left side of the occipital cortex, a part of the brain that gets signals from the eye. 

Figure 2. Simulation of vision with right-sided hemianopsia. Everything to the right side of the visual field appears gray out or dark.

You see, our eyes ‘see’ things, but it’s really the brain that perceives the action of ‘seeing’ and gives meaning to it. When the brain suffers damage, both eyes will lose vision on the same side. But often patients will perceive the right side of vision loss as vision loss in the right eye.

And one of the most common causes of such brain damage is a stroke. Especially in a patient like John who has high blood pressure and heart problems. John had a history of congestive heart failure and had a pacemaker. 

‘But I am not having a stroke. I feel fine.’ John said. I asked for several other symptoms, such as weakness or numbness on one side of the body, slurred speech, difficulty walking, and so on. He denied all of it. 

He had been to the ED before, it was not a pleasant experience. He sometimes waited for 8 hours and just left before being seen. 

I get that. But this time it is different. Hemianopsia can be the only symptom of a stroke. I managed to convince him to go that day. I also called his PCP to check up on him to manage his high blood pressure.

In the subsequent weeks, he developed other stroke symptoms including weakness in his leg. 

I saw John again after 2 months. Needless to say, John was very distressed about his vision problem. He’s bumping into things and felt unsafe to drive. He complained about the long wait in the ED. The head CT scan did not reveal much, but he could not do the MRI due to his pacemaker. His visual field looked like in Figure 1C above. Well, not much improvement, perhaps a little worse even. 

Research has shown that many stroke patients suffering hemianopsia recover partial or full vision within 6 weeks. He’s clearly not in the lucky team. If they don’t show any improvement by 6 months, it’s unlikely they will ever have improvement. About ⅓ of all stroke patients with hemianopsia will never recover or improve. I have seen some patients just like that, they permanently lose half of their visual field after a stroke.

I asked John to come back in 4 months, which will be 6 months post stroke, to check again.

This time his visual field looks like above (Figure 1D). It looked like he had a full recovery! I was relieved and felt very happy for him. I asked him, ‘how do you feel about your vision?’ I was surprised to hear him say, ‘Terrible. It’s getting worse.’ 

‘How come? Your visual field is much better. You are basically normal now.’

‘Oh THAT,’ he said, ‘yes that’s better, I can drive again. But my glasses are broken and I really cannot see anything for reading.’

You will be happy to learn that John now has new glasses and is seeing well. He’s seeing his PCP as well as his cardiologist to manage his high blood pressure. 

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