In Part 1 we introduced a book published last year on Homonymous Visual Field Defects. Although it may seem like splitting hairs, I do think it’s important to differentiate between the terms “defect” and “deficit”.
“Defect” is certainly appropriate when discussing the results of a visual field test, and documenting jigsaw pieces of a puzzle missing as plotted on a two-dimensional scale. But that tells us little if anything about how an individual with that snapshot in time is functioning in multidimensional space. Furthermore, it emphasizes imperfection, inadequacy, limitation, and shortcoming. “Deficit” on the other hand refers to abnormal or altered function. It is this property of the visual field that that interests us once we’ve localized the visual field loss in order to aid differential diagnosis.
Toward that end, Dr. Susanne Trauzettel-Klosinski introduces the final chapter of HVFD, titled Adaptation and Rehabilitation in Patients with Homonymous Visual Field Defects with the following statement: “In recent years, many new treatment options were achieved in neuro-ophthalmology. However, visual deficits often persist and cannot be treated by pharmacological or surgical interventions. Those will require rehabilitative interventions with the goal to compensate for the deficits to regain independence and to maintain the patient’s quality of life.”
There are three principal approaches to rehabilitation in homonymous hemianopia overviewed by Dr. Trauzettel-Klosinski:
- Substitutive Intervention with Optical Devices – binocular sector prisms have been helpful with visual neglect, but not effective in homonymous hemianopia. Most vision rehab patients find sector prisms and mirrors confusing to use, and after a year less than half of the patients still wear them. Real prisms rather than sector prisms subjectively confer more benefits, but more objective studies are needed.
- Restitutive Training – the aim is to reactivate incompletely damaged neurons in the blind hemifield and to enlarge the visual fields by visual stimulation. Bernhard Sabel has been the main proponent of this approach, and it has been packaged into Vision Restoration Training (VRT) . The Journal of Neuro-Ophthalmology printed a lively debate between Sabel and Trauzettel-Klosinski, and she is clearly not impressed with the transfer effects of VRT.
- The Compensatory Approach – compensating training aims to enlarge the functional visual field by utilizing the field of gaze with scanning eye movements into the blind hemifield. This is known as explorative saccade training, and is supported by a randomized controlled trial published by Trauzettel-Klosinski and colleagues in Neurology in 2009.
Dr. Trauzettel-Klosinski and her team in Tubingen (the town that laid claim to the first automated perimeter) packaged the compensatory scanning procedures into a computer program known as VISIOcoach. Sato and colleagues utilized this approach in their ARVO presentation in 2014 titled Modified Visiocoach training in Hemianopia.
Well … I thought I could finish the discussion in two parts when I started writing, but looks like we’ll need to wrap this up in a Part 3.