15 Visual field loss and psychology assessments

Definition/cause: Loss of vision in part of the field of vision may be due to traumatic brain injury, tumor, surgery, or infarct in the posterior cerebral artery. Field loss can affect different parts of the field of vision depending on what part of the system is affected. When the same half of the visual field is affected in both eyes, it is called homonymous hemianopia (HH).  Many children with HH will also have weakness or paralysis on the same side of the body as the vision loss. 

Field loss in right HH:^[1]

What someone with left homonymous hemianopia would see^[2]:

Course: In some cases, a new field loss can resolve on its own within a few months after the injury. In general, however, it is a permanent loss. It is not reversible with therapy. The person with field loss may learn to use special scanning techniques (e.g., when reading). Children who have HH from a young age may not be aware that their vision is different than other children.

Functional impact on reading:   When we read, our eyes make rapid eye movements (saccades) between fixations. We are using our central vision to see the small amount of letters which are in focus during the fixation (see image below).  The central area is only about 5% of our visual field. When reading a longer word, the child with HH would not see half of the word and would need to scan to see it, creating an extra step. The area outside central vision is called the parafoveal region. When we are reading, we use this surrounding region to preview what is coming up and see what was previously read. When reading left to right, our perceptual span (how many letters we can see) extends about 4 letters to the left and up to 15 letters to the right.  This is like a “preview” of upcoming words and helps your eyes plan where to land the next time they move. Thus, with languages which are written from left to right, right HH has a stronger impact on reading than left HH as the person is not able to preview the upcoming words.  HH particularly impacts reading beyond the single word stage, and can cause a decrease in reading speed. Left HH can also impact reading by causing difficulty finding the next line of text and causing reading errors as the first letters of the word may be missed. HH can make reading slow, frustrating, and tiring.

^[3]

Other functional impacts:

• The individual with HH may miss information on the affected side. They may bump into things,  have difficulty with stairs, or miss self-care on one side of body. In physical education class or on the playground, the child may not see children running or a ball approaching. They would not see a car approaching from their blind side.
• Driving can be dangerous.
• Children may adapt to field loss by moving their eyes or head to maximize their vision. 

Recommendations during assessment:

• During the assessment, place yourself on the child’s “good side.”
• Place your materials slightly off centre to take advantage of the child’s intact visual field.
• Watch how the child scans pages to ensure they are looking at all options.  Remind the child to scan the whole page, using your finger to point to each part if needed. Make sure you are giving consistent reminders and not ONLY when the child makes a mistake.
• Observe: Do they lose their place when reading? Miss the ends or beginnings of words?

Recommendations for school/home:

• It is important that the child is made aware of their condition for safety, particularly street safety. The individual must be taught to actively scan their blind side.  It would also be appropriate to walk down the hallway with the wall to the affected side. Orientation and Mobility Instruction within the school and community is suggested.
• Teaching compensatory strategies for reading is important. For children with right HH, this would include teaching children to scan to the end of each word, and to the end of each line. For children with left HH, this would include strategies such as using a ruler to keep place, and a line down the left side of the page to help orient to the start of the text. Some children would benefit from smaller text (so that more text is within their central vision), or text written diagonally. Students should have support from the Vision teacher at school to implement these strategies and supports.
• In the classroom, children should be seated with their intact visual fields facing the teacher and the classroom (blind side to the wall).
• Children should be approached from the side with intact vision.
• It can be helpful in the classroom to leave furniture in place throughout the year.
• Children must be allowed extra time to read.