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American Academy of Optometry: Case Report
Rehabilitation of hemianopsia using expansion prism therapy
combined with scanning training
Kasey Suckow, O.D.
Resident: Ocular Disease / Low Vision Rehab
Hines & Jesse Brown VA Chicago
1157 W Diversey Pkwy
Apt 408
Chicago, IL 60614
[email protected]
Abstract
Scanning training to make the patient more aware of environmental conditions / hazards
is often used in conjunction with expansion prism therapy to rehabilitate patients with
hemianopsia . A scanning training video and two cases are presented.
Case Report
Case History #1:
Patient #1, a 67WM reported to clinic initially with a left homonymous hemianopia
secondary to a recent stroke. He had several functional complaints caused by field loss
such as bumping into people on the left, problems walking and avoiding object on the
left, difficulty in the kitchen, and problems shaving the left side of his face. He had no
head tilt noted on initial presentation. His medical history was significant for
hypertension, stroke, high cholesterol, renal failure and acid reflux.
Pertinent findings #1:
His corrected visual acuity was 20/25 OD and 20/20 OS. Humphery visual field testing
confirmed the left homonymous hemianopia previously. All other findings were within
normal limits.
Case History #2:
Patient #2, a 74WM reported to with longstanding left homonymous hemianopia
secondary to a gunshot wound occurring in 1954. His only previous vision training
included a recommendation that he turn his head to the left to view. He had been referred
from his primary eye care doctor for visual training. His medical history was significant
for HTN, traumatic brain injury secondary to gunshot wound, and a significant fall
causing cerebral hemorrhage and subsequent hospitalization for the past 18 months.
Pertinent findings #2:
His best corrected visual acuity was 20/40 OD and 20/32 OS. His visual field loss had
been confirmed previously by HVF testing. He also displayed a left head tilt with normal
posture, and was aware of his missing field. All other findings were within normal limits.
He did not state any visual goals or problems with mobility at this time, but was
interested in trying expansion prism therapy to improve his overall function.
Differential diagnosis:
Although visual field loss is relatively straightforward to diagnose with visual field
testing, it is also important to distinguish field loss from visual neglect, or spatial
inattention. A very deep case of neglect can present very similarly to a hemianopia. This
is a very important distinction because patients with neglect will require longer
rehabilitation programs secondary to greater functional disabilities6.
One of the differences between a true hemianopia and neglect lies within the patient’s
perception. A patient with only field loss will be aware of their lost field and will have
functional complaints. A patient with field loss and/or neglect will not attend to and may
not even notice the missing field. In both of the two cases mentioned above the patients
were aware of their missing field and had corresponding complaints in terms of
orientation and mobility.
Neglect typically occurs on the left field secondary to organization of neural processing.
Research into this area indicates that the left hemisphere of the brain attends only the
right visual field, whereas the right brain hemisphere attends to both sides of the visual
fields7. Therefore when the right hemisphere is damaged there is no cortical substrate
attending to the left visual field.
Neglect can be diagnosed with a number of different tests. Line bisection is a quick test
that differentiates between field loss and neglect8-9. A patient with left neglect will bisect
a line towards the right, whereas a patient who is aware of the loss will compensate and
bisect the line closer to the middle, if not slightly skewed towards the left10. Other test
strategies include simultaneous presentation on confrontation fields, drawing, copying,
and cross-out tasks8-10.
If the etiology of field loss is unclear a MRI should be performed to locate the lesion,
injury, or stroke.
Diagnosis:
In both cases mentioned above field defects were confirmed with Humphrey visual field
testing. Diagnosis is typically made with Goldmann visual field testing, or Humphrey
automated testing. Due to the nature of strokes and traumatic brain injury these tests can
be difficult and fatiguing for these patients alternative simplified testing can be
implemented11.
Another test that can be useful to determine prognosis for visual therapy is Amsler grid
testing. This is useful for determining the degree of macular sparing11. This is especially
pertinent for when initiating reading therapy.
Treatment and Management:
Treatment of these disorders is aimed at increasing awareness through prism or scanning
therapy. Scanning therapy uses trained, intentional head and eye movements for spotting
objects in the area of lost field. While this therapy proves beneficial to patients, it does
not increase the field of view and requires quite a bit of effort and training to become
natural. To increase the rate of success in the two cases presented, scanning therapy was
incorporated along with the prism therapy. Scanning training is aimed at teaching the
patient to never go where their vision has not gone. This means training in eye
positioning, head positioning, and the use of quick, accurate eye movements to scan into
the non-seeing field. The first step is to teach the patient to walk with his or her eyes
turned towards the scotoma, thus pushing it out of the way. The next step is to work with
turns. Bumping into objects after making a sudden turn into the scotoma is common, so
patients are trained to stop prior to making a turn and quickly scan the area before
proceeding. Eye movements for quick scanning are also taught, as the patient has to
constantly be scanning between the seeing and non-seeing field. When large angle scans
are needed, such as when crossing streets, a head turn can be added in to gain more range.
Some studies have theorized that scanning therapy may reconstitute some of the visual
field, by stimulating the zone between the damaged and intact fields. These findings
have been inconsistent and no definite conclusions can be drawn as to whether the field is
enlarged, or the patient has developed better visual searching skills12. In fact, field
testing with scanning laser ophthalmoscope (SLO) where fixation is monitored within
one degree, disputes the reconstitution theory13.
Yoked prisms are another option for shifting the field of view. This can be particularly
useful within the central 20 degrees of field. Prism adaptation to yoked prism has been
proposed as a mechanism to help with patients exhibiting visual neglect, but there have
not been any conclusive studies performed14.
Expansion prism therapy actually increases the patient’s field of view4. It does so by
creating peripheral diplopia, or confusion from the overlap of normal field and
prismatically shifted field. Monocular inferior and superiorly placed prisms (40 diopters)
shift the images from non-seeing to seeing field, allowing the patient to spot images in
the periphery. Once the images are spotted in the periphery they can be attended without
diplopia through the central portion of the lens.
Perimetric visual field testing indicates that expansion prism therapy increases the
superior and inferior field of view by around 20 degrees4.
Field expansion and Visual Field Testing with Left Homonymous Hemianopia4.
Fitting protocol4 with scanning training video:
Both patients were fit using the Eli Peli Protocol for Prism Expansion Therapy4. Forty
diopter Fresnel prisms were fit monocularly in the superior and inferior portion of lens on
the side of the defect. Prisms used are 8 x 22mm segments, which can be cut in office, or
ordered precut.
The upper prism was fit first with the inferior portion of the prism placed at 6mm above
the center of the pupil. The superior field generally contains fewer obstacles and thus
less important to orientation and mobility. This makes the superior prisms easier to adapt
to4. The diplopia was demonstrated to patients by presenting targets within and outside
of normal field.
Patients were instructed to fixate through the central portion of the lens. If an object was
spotted in the periphery through the prism the patient was too move their head up to
attend the object through the central portion of the lens, thus avoiding diplopia. Patients
were also instructed on walking, spotting, central viewing, and on general cleaning and
care of prisms.
Prism Expansion Therapy with Left Homonymous Hemianopia4.
After the initial fit and instruction the patients were sent home for a 2-3 week trial period.
If the patient noted improvement and was able to adapt, prism was fit into the lower
portion of the lens at 6mm below the center of the pupil. Again the patient is sent home
for a 2-3 week trial period. Upon returning, if the experience was positive the patient was
fit with permanent prisms.
Response to treatment: Follow Up Pt #1:
At the first follow-up with superior prism fitting, the patient noted improvement. The
fitting protocol was continued with the lower prism segment. At this point the patient
was lost to follow-up secondary to health problems with his kidneys. He set up
appointments within low vision clinic and with low vision therapy, but was unable to
make them.
He did not present to clinic again until several months later now seeking to reinitiate
prism therapy. He had lost the fresnel prisms around one month after initial fit, but he
did notice a vast improvement in his functioning and avoidance of objects on left side.
He noted his experience was extremely positive and was looking forward to getting
permanent prism in his spectacle prescription.
The fitting protocol was started again and patient is currently undergoing adaptation of
prism with positive subjective results.
Response to treatment: Follow Up Pt #2:
Upon returning to clinic after initial fit with superior prism, the patient did not notice a
significant improvement in his visual performance and wished to discontinue the fitting.
The patient was proficient with scanning techniques and required no additional training at
that time. He returned to clinic with trouble reading in dim lighting and seeing the
projected hymns at church. He did not wish to initiate prism therapy again, as he did not
see any improvement. His needs were addressed with devices and lighting.
Fitting him with permanent prisms would have been inappropriate because of poor
adaptation, and more importantly, he also had history of diminished balance and falls.
An inferiorly shifted field secondary to prism may disorient a patient, and may be a
potential risk factor for falls. It has been shown that the reduced depth perception
occurring inferiorly with bifocals is a risk factor for falls14. It is possible that prisms may
also be a risk factor and further studies should be performed to ascertain the relationship.
Conclusion:
Although many patients with hemanopic field loss have very good acuity, it is important
to address the functional loss and subsequent effects on orientation and mobility. Even a
small increase in an individual’s ability to function can have a significant impact in their
daily lives. Many of these effects can be achieved with scanning and expansion prism
therapy.
Patient #1 had a very positive response both types of therapy. Although he noted
disturbance with diplopia he was extremely motivated and appreciated the increased
field. In general he had not adapted to his field loss as well as the second patient, and had
several functional complaints concerning activities of daily living. Also, he had not
developed a compensating head tilt or posture and was having significant problems
scanning into his non-seeing field.
Patient #2 had a very different response to the prism and scanning therapy. He noted
disturbance with peripheral confusion. Further complicating the success rate is how
proficient he had become over the past 53 years with development of his own scanning
techniques and head posture. He noticed a difference with the prism, but preferred to use
his own scanning strategies.
The main differences between these two case presentations was length of field loss, level
of functional compensation, etiology of field loss, and age at time of field loss. All of
these factors may contribute to prognosis with prism therapy, but the level of previous
functional compensation appears to play a key role. The different responses to prism in
the two cases above illustrate how important scanning therapy is in addition to field
expansion. In his initial study, Dr. Peli also noted a similar outcome with a patient who
had developed good scanning and compensation strategies prior to prism therapy4.
Because case presentation and cognitive functioning varies so much between these
patients it is difficult to predict who will be successful. Although the two patients
described above had essentially the same amount of field loss, they had entirely different
responses to expansion prism therapy. Although there is little data analyzing the factors
contributing to success with therapy, some studies indicate age16 and binocular vision
disorders4 may play a role in determining outcome. Until these factors have been studied
more thoroughly it is important to look at the patient’s overall needs, motivation, goals,
as well as risk factors for falls when considering initiating therapy. Visual field loss is a
prevalent condition in the clinical population. It affects not only the success rate of
rehabilitation, but an individual’s quality of life. Therapy options should be discussed
and offered to any patient presenting with hemianopia.
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