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. 

My eye is a mess

It was the end of the clinic day. I finished my last patient’s chart and was ready to go, before noticing that a procedure result just popped out. I clicked into it, it’s a visual field testing result of a 60 year old gentleman I saw a few days ago. He complained that after ceiling plaster dropped into his right eye, his right eye could not see in the periphery. 

This is a regular patient of mine. When the plaster incident happened 2 weeks ago I was on vacation so he saw another doctor in the practice. He initially went to the emergency room, received plenty of eye washing and antibiotic eye drops. He then saw my colleague two more times and according to the notes, his eye was recovering well. When I saw him his right eye was white and quiet, cornea completely healed, no defect, scar or edema. Internal structures of the eye were also normal. His visual acuity was 20/20. He did have trouble seeing fingers on the right side in his right eye. But his optic nerve appeared healthy. He’s a glaucoma suspect at baseline and I have been monitoring this over 2 years. The RNFL OCT that measures nerve thickness was stable to before. So the question is, why would he have a new visual field defect? 

Dr. House says, patients always lie. He insisted that this problem came about after the plaster accident. ‘My eye is a mess’, he said. ‘First it hurt like hell for three whole days, then I cannot see out of my right eye’.

For a chemical injury to hurt the optic nerve, there had to be other signs, like inflammation in the anterior chamber, vitreous and retina. But there was none. 

Also it made no sense that he’s losing vision from glaucoma progression, which is typically slow. 

It happened suddenly so it’s not a tumor pressing onto his optic nerve either.

Could he be exaggerating because he was frustrated about the whole thing? After all, he waited in the ED for 4 hours, and he was on hold for scheduling to see eye doctors for a long time and did not get call backs. 

Of course a formal visual field testing is in order. And that result just arrived in my inbox.

One peek at it, I knew I would not be going home any time soon (Figure 1). 

Figure 1. Visual field testing result of the right eye (top image) and the left eye (bottom image). The dark color indicates that the patient was not able to see in that part of the visual field.

The right eye was not seeing the right side of things, just as he complained. Problem is, his left eye was also missing quite a few things on the right side. The left eye was much less severe and it was not picked up in the confrontational visual field test we did in the exam room. 

This is what we call a hemianopsia (Figure 1), and it’s an emergency because a stroke was on the differential list. 

I called him immediately. I advised him to go to ED immediately, even though he did not have any other stroke symptoms. He does have a history of heart attack and has a pacemaker.

I then called his primary care doctor and she was going to follow up with him. 

Hemianopsia happens when one side of the brain that is in charge of vision becomes defective. This can happen with a stroke, a tumor or inflammation. In fact, according to the Cleveland Clinic, 70% of hemianopsia is due to stroke, 15% from brain tumors and 5% from bleeding in the brain [1].  Patients’ eyes can be completely normal, because the problem happens in the brain. It can happen as the only abnormal finding, without other telltale signs of a stroke. The dangerous part is that it is easily missed and over-looked, because the visual acuity can be 20/20, and you don’t find anything wrong with the eyes. Further, patients often describe this in a non-specific manner. Over the years I have heard ‘floaters in the left eye’, ‘my right eye is blurry’, or ‘my eye is a mess’. It is vitally important to always do a confrontational visual field and if suspicious, a formal visual field to clarify and confirm. Otherwise a critical, potentially life-threatening condition may be missed.

Hemianopsia from a stroke may improve over time though may not return to baseline completely, depending on the severity of the damage. Most start recovery within months of the stroke, but it may take up to 18 months for maximum recovery to occur [1]. I will see my patient in 3 months to check his visual field again. To help with vision deficit, certain prism may be used to expand the visual field, but that would the subject of another article.

References: 

[1] https://my.clevelandclinic.org/health/diseases/15766-homonymous-hemianopsia-