7 Visual Field Loss
What are visual fields?
Visual fields are the whole area seen through the eyes and described as if you were standing behind the person. A typical visual field (Spector, 1990) has the following parameters:
- 90 degrees temporally from a central fixation point
- 50 degrees superiorly and nasally (upper fields)
- 60 degrees inferiorly and nasally (lower fields)
Causes of visual field loss
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. Loss of part of the field of vision can also occur due to a genetic condition, glaucoma, or toxic exposures.
Types of visual field loss
Field loss can affect different parts of the field of vision depending on what part of the system is affected. Visual field loss can be central (e.g., in macular degeneration) or peripheral (e.g., “tunnel vision”), impact a quadrant (quadrantanopia), or affect half (hemianopia) of the visual fields. Visual field loss can also be limited to the nasal half (towards the nose) or the temporal half (towards the temples) of the field of vision.
Homonymous hemianopia is when the same half of the visual field is affected in both eyes. This occurs due to damage to the visual pathways, between the optic chiasm and the visual cortex, on the opposite side of the vision loss. Many children with homonymous hemianopia will also have weakness or paralysis on the same side of the body as the vision loss.
1. Complete loss of vision right eye
2. Bitemporal hemianopia
3. Left homonymous hemianopsia
4. Upper left quadrantanopia
5&6. Quadrantanopia with macular sparing
Visual field loss and reading
Central vision is essential for reading as there is a high density of cones in the center (fovea) of the retina. This high acuity vision allows the reader to clearly see about four to five letters at a time in optimally sharp focus. The parafovea, the around the fovea, gives the reader a “big picture” of the scene, allowing a preview of upcoming words. When reading text from left to right, the “perceptual span” (or area viewable with parafoveal vision) – extends about three to four letters or spaces to the left and up to 15 letters or spaces to the right. This span allows the reader to plan where to fixate the eyes next along the line of text.
With longer words, the reader with homonymous hemianopia can only see part of the word, which can lead to guessing the beginning or ending of a word. In addition, with the loss of the right visual field, the reader misses out on having a large perceptual span to the right and must spend extra time scanning text to find the next fixation spot. Reading with right-sided homonymous hemianopia is described as “reading into nothingness.” Left-sided homonymous hemianopia can lead to difficulty keeping place between lines (Lawrence et al., 2018).
To learn more about visual field loss and its impact on reading, please see Vision After Hemispherectomy, TPO Disconnection, and Occipital Lobectomy: An Introductory Guide (Lawrence et al., 2018).
References
Lawrence, L., Jones, M., & Vernick, A. (2018). Vision after hemispherectomy, TPO disconnection, and occipital lobectomy: An introductory guide. The Brain Recovery Project: Childhood Epilepsy Surgery Foundation. https://epilepsysurgeryalliance.org/wp-content/uploads/2017/06/FINAL-Vision-After-Hemispherectomy-TPO-Disconnection-and-Occipital-Lobectomy.pdf
Spector, R. H. (1990). Visual fields. In H. K. Walker, W. D. Hall, & J. W. Hurst (Eds), Clinical methods: The history, physical, and laboratory examinations (3rd ed., Figure 116.1). https://www.ncbi.nlm.nih.gov/books/NBK220/figure/A3545/?report=objectonly
