Improving scanning efficiency of individuals with homonymous hemianopia
Written by Raman Deol, O.D., a member of the AOA's Vision Rehabilitation Committee
Individuals with homonymous hemianopia (HH) sometimes report being told to simply move their heads more to improve their efficiency with reading or mobility tasks. With such instruction alone, individuals who are aware of their deficit tend to adapt disorganized scan paths, often scanning excessively into their blind field and putting themselves at risk for missing obstacles in their intact field, and those who are unaware of their deficit are not inclined to scan at all.
Scanning training can help individuals with HH to expand their search field as well as reduce search time. Various scanning training strategies may be employed, including ocular motor exercises for improved accuracy of pursuits and saccades, including large saccades into the affected side, developing an organized horizontal or vertical method to scan for a target, and identifying targets on the affected side while walking or multitasking. My team often uses low-tech strategies like identifying letters on a hallway wall on the affected side while walking and identifying playing cards spread on a table, as well as the high-tech DynaVision, which employs techniques to improve multitasking skills and reaction time.
As an adjunct to—but not a substitute for—scanning training, we may use peripheral prisms to improve object and hazard detection during mobility tasks. To my knowledge, there are two available peripheral prism designs: Gottlieb and Peli. It is my understanding that both designs have been used widely and successfully. Because I do not have any experience fitting the Gottlieb sector prism, I cannot provide clinical pearls for fitting this design, but this will be the topic of a future clinical pearl. I do, however, have experience in fitting the Peli Peripheral Prism design and offer the following insights when considering this as an option for your patients:
- The following are two of many websites that have information on how the Peli Prisms work:
hemianopsia.biz/how-the-peli-lens-works and chadwickoptical.com/peli-lens-2
- This design generally involves two prism sectors, base out on the spectacle lens ipsilateral to the affected side of vision, one crossing above and the other crossing below the patient's line of sight. With this design, one does not have to scan into the prism to be alerted to objects on their affected side. I often tell patients that this is a "heads-up" prism, to let them know that "Heads-up! Something is on (the affected side)," thus providing them a stimulus to move their head and eyes toward the affected side to identify objects and hazards. When they move their eyes to identify the object and/or hazard, they are looking through the carrier lens, not the sector prism, as looking through the prism would create a double image.
- The prisms are available as temporary stick-on Fresnels, which may be applied to existing spectacles, or may be ordered as permanent Fresnels within new spectacle lenses. I have found the stick-on option to be convenient, cost-friendly, easy to adjust positioning, and durable.
- There are several YouTube videos that demonstrate techniques for in-office training to use the Peli Prism Design. Training to use the prism design efficiently may take two or more visits with the clinician or therapist. It is recommended that the patient try the temporary press-on sector prisms for at least six weeks before deciding on whether to order new lenses with permanent prisms.
I am hopeful that this information will assist in your quest to improve the quality of life of your patients with homonymous hemianopia.
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Disclaimer: The information contained in this article represents the opinion of the author and not the AOA. These are not clinical practice guidelines, nor has the evidence been peer reviewed.
There are additional aspects to this topic that may not be presented, or considered, based on the specifics of the case.
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