Homonymous hemianopia

Homonymous hemianopia is a loss of half the central field as well as the entire parafoveal and peripheral field opposite the side of surgery. Homonymous hemianopia is a type of cerebral or cortical visual impairment (CVI). Cerebral/cortical vision impairment is a problem with how the brain processes what the eyes see and there are many different types of CVI.

Remember the target that is your field of vision?

Here’s how a person with right homonymous hemianopsia sees it:

Does the child see black in the lost visual field?

No. The child lacks vision in the lost visual field in the same way that you lack vision behind you. You do not see black behind you, but instead see nothing.

One way to describe this is by imagining a cape or curtain behind you which hides what you cannot see. Now pull the curtain in front of you so that it now hides everything in the lost visual field, up to half of your face. What is hidden behind the curtain is the lost visual field.

When the eyes take a picture of the object and send the message to the brain, but the message is not properly processed because of problems with the optic nerves, damage to the optic tracts or radiations, or injury to the occipital lobe, CVI is the result. In other words, there is no problem with the structure or function of the eyes, but once the visual message reaches the brain, it is lost or distorted.

Some children may have homonymous hemianopia before surgery because of the brain malformation, stroke, or disease which caused the seizures in the first place. After these surgeries, however, homonymous hemianopia is an irreversible and permanent result.

Navigating the world with homonymous hemianopia

Children with homonymous hemianopia often require a lot of effort to recognize that there are moving objects, people, or obstacles in their missing visual field. This makes it difficult to move from one place to another with ease, especially outdoors or in an unfamiliar environment.

For example, they may bump into pedestrians or obstacles that they simply cannot see because the object or person is in the lost field of vision. They have difficulty moving safely within their home, school, or community (known as orientation and mobility skills) and often have trouble with activities which require good vision, like team sport activities, playground games, or choosing food in a cafeteria line.

This is how persons with normal vision might view a teammate on a football field:

See how a child with left homonymous hemianopsia would miss a football player running towards him, but might still be able to catch the ball:

See how a child with right homonymous hemianopsia would see the football player, but might get hit in the face with the ball:

Some of these challenges can cause significant distress for the child which often makes them unable to fully participate in classroom and recreational activities. They may be startled when something suddenly appears in their field of vision – like a soccer ball in mid-flight – or may fear falling because they are unable to see obstacles. Although children with hemianopia may search the lost visual field by turning their head, this search may be slow. These slow search patterns do not allow them to fully understand the environment around them fast enough to avoid an obstacle, so children with homonymous hemianopia often avoid new environments altogether.

This may also affect the child’s socio-emotional well-being. For example, the child may not be chosen for team sports during recess. Because the eyes look normal, other children and teachers may not understand how the visual field loss affects the child. They may think “they are not trying hard enough”. Homonymous hemianopia may be hidden to all.

Homonymous hemianopia can seriously affect daily activities such as walking in crowded areas such as sidewalks, shopping malls and supermarkets, classroom hallways and playgrounds, seeing playmates or teammates, identifying and finding objects, crossing the street, reading and learning, and other activities of daily living such as cooking, pouring beverages, and especially driving. Driving can be particularly dangerous – research shows that adults with homonymous hemianopsia often do not scan far enough into their lost visual field to see pedestrians or cars coming into the intersection. (This blogger shares how she came to terms with her homonymous hemianopia and decided not to drive.

These problems can lead to leaving out of important parts of a scene and, consequently, to poor comprehension and social misunderstanding.

Watch this video which simulates right homonymous hemianopia. You can see how difficult it is to view oncoming cars and pedestrians.

Reading requires us to move our eyes smoothly across a line of text, see each word, and understand the meaning of each word in a fraction of a second. In languages like English, Spanish, and French, the eyes must scan smoothly from left to right and top to bottom across the page, briefly fixating on a word before moving on to the next word.

Because homonymous hemianopia causes a loss of half the central field of vision, the child only sees part of the word when looking at it. This makes word identification very difficult. The child must scan to see the entire word before reading it, adding an additional step to the process of reading the word. Longer words are never seen as a whole word resulting in various reading accuracy errors. This can include misidentifying a word, omitting letters, syllables, skipping over short words unintentionally, or guessing errors.

Why Guessing Happens When Reading With Homonymous Hemianopia

Children with vision loss often make guessing errors while reading, not because they’re lazy or not trying, but because they literally can’t see the whole word.

If they can only see part of a word (like the ending), their brain may try to fill in the blank based on what they’ve seen before. For example:

A child with left homonymous hemianopia (caused by surgery on the right side of the brain) may try to read the word peach but only see each. They might guess each or beach based on what makes sense in the sentence.

This kind of guessing is understandable, but it leads to frequent reading mistakes, especially with unfamiliar words.

Why Left-Sided Vision Loss Is Especially Tough for Reading

In left homonymous hemianopia (from right-sided epilepsy surgeries), reading can be particularly challenging. Here’s why:

• The child may miss the first part of a word, which often contains the clues to identify it quickly.
• They may lose their place on the page, especially when moving from the end of one line to the beginning of the next.
• They may skip entire lines without realizing it.
• Beginning readers, who are still learning how to decode words, may find this especially frustrating and discouraging.

These challenges can affect a child’s confidence, but with targeted support, they can still become strong, successful readers.

The greatest challenge – reading with right hemianopia

Right homonymous hemianopia – vision loss on the right side of both eyes – happens after left-sided brain surgeries. This type of vision loss poses the greatest challenge for learning to read in languages like English, Spanish, and French, which are written and read from left to right.

Why? Because your child is now reading into their blind side – the very direction reading flows in.

What Skilled Readers Normally See

In fluent readers, the eyes don’t just see one word at a time. As they focus on a word, they also take in a small area of text around it — called the perceptual span.

• About 4 letters to the left

• And about 15 letters to the right

The letters to the right help readers predict which word is coming next, and guide their eye movement so they can read smoothly and quickly. This right-side “preview” is a big part of reading fluency.

The more letters you can see on the right, the faster your reading speed (known as fluency) because you know which word to focus your eyes on next. Reading after left-sided surgeries is particularly challenging because not only is most of the word missing, but the right parafoveal vision – which includes those 15 letters to right – is gone. Like this:

What Happens After Left-Sided Surgeries

After a surgery on the left side of the brain, a child loses their right parafoveal vision — including that important 15-letter preview zone.

Here’s what that means for reading:

• Most of the next word is missing

• The child has to guess or hunt for where to move their eyes next

• They may need to re-focus or re-read words repeatedly

• Reading becomes slow, effortful, and can be mentally exhausting

This creates a “bottleneck” effect: it takes much longer for the child to process what they’re seeing, which can make reading aloud (oral fluency) especially difficult.

Emotional Impact

Adults with right homonymous hemianopia often describe the experience as trying to read into nothingness. This can be frustrating, fatiguing, and discouraging.

For a child who’s just learning how to read, this can lead to:

• Avoidance of reading

• Low confidence

• A growing dislike of books and school

But there’s hope: with the right tools and support, many children learn to work around these challenges and develop a love for reading again.