Some children compensate for their visual field loss automatically with various adaptive mechanisms to increase their visual access to the remaining visual field. These adaptive mechanisms include:
- Unusual head posturing such as head tilt or face turn (note: head turn does not adequately correct for issues with reading/foveal vision);
- Exotropia or “turning out of the eye” which may create a more panoramic view and expand the visual field; however, this causes a lack of depth perception and more importantly a loss of binocular vision (whether intermittent or permanent) which is critical for reading.
- Children may adopt their own strategies that we do not understand. We need to be sure to understand that not only is each child unique, but compensatory strategies may be unique. Learning to understand the child and the way they see is important.
Also, there are many different interventional techniques designed for patients with brain-damaged visual field loss. These may work for some children, but need to be individualized. These include::
- optical therapies where the lost visual field is brought into view by the use of optical devices (such as prism glasses);
- eye movement-based therapies where the lost visual field is scanned with compensatory or adaptive eye movements.
Here’s an example of the Chadwick hemianopia lens. The lost left visual field is transferred to the top of the remaining visual field:
Prisms placed on (or in) glasses shift the seeing field by a certain amount (15-20 degrees) so that the non-seeing field is moved optically toward the seeing field. It’s important to understand that these glasses don’t actually expand the field, but rather compress some of the lost visual field into the existing visual field. This is similar to how the side view mirror allows a driver to see vehicles in the left lane that would otherwise be out of the normal visual field.
Not every child will require or be able to use a visual field expander, and those with potential to benefit should be fit by a doctor with experience in vision rehabilitation of hemianopia.
Compensatory approaches (known as vision therapy or visual capacities training) are often done with a developmental optometrist or an occupational therapist. These therapies teach children more effective ways of using their vision, principally to enlarge and reinforce their visual search strategies and by training them in various oculomotor strategies. These include:
- Saccadic eye movement therapy, such as Explorative Saccade Training (EST), Neuro Eye Coach, and the free online Eye Search and Read Right, includes visual search and training of saccadic eye movements to scan into the impaired visual field to develop more efficiency. Studies show that adults with homonymous hemianopsia generally perform saccades that are too short to compensate for their visual field loss. Improving the child’s ability to accurately perform both larger and more accurate saccadic eye movements to the side of the loss can improve the child’s functioning in mobility and activities of daily living;
- Reading training that includes training of saccadic eye movements may help improve reading, however, often more specific therapies and strategies are required, particularly in patients with right homonymous hemianopsia (such as boundary marking devices);
- Visual perceptual enrichment programs such as the Perceptual Enrichment Program (PEP) are usually administered by an occupational therapist. These programs identify visual perception difficulties. Through a series of tabletop puzzles and activities, students are taught to solve increasingly difficult perceptual problems. Areas of focus include: spatial organization, recognition of parts to whole relationships, figure ground perception, classification (attention to details) and inferences and abstractions (logic).
- Visual therapeutic websites such as eyecanlearn.com and coolmath.com provide online visual training.
Next – Color vision