Unilateral Spatial Inattention
by Dr. April Eryou
Unilateral special inattention(USI) is an attention problem that most commonly occurs following a hemispheric cerebral vascular accident (CVA) affecting the parieto-occipital junction. At first, clinically, it may present fairly similarly to a left or right field hemianopia. For example, in the optometry setting, the patient when asked to read the acuity chart will leave off letters on one side. However, unlike a new onset hemianopia, the patient will be unaware that they are missing things in the affected field as the problem is not a problem of the optic pathway from retina to visual cortex, but a problem in either the right or left hemisphere. The challenge with unilateral spatial inattention is that the patient is unaware that they are ignoring stimuli on the side opposite the lesion. Interestingly, because of the redundancy for certain functions in the brain, it is usually the left side that is affected in USI. When a patient presents with left field USI, the lesion can usually be traced to the right frontal-paretal lobe. The fact that right side USI is rarely seen clinically is described by Penelope S. Suter in her chapter ‘rehabilitation and management of visual dysfunction following traumatic brain injury’ (1995, p. 207). She explains that “…the right hemisphere allocates attention to both visual fields where as the left hemisphere allocates attention to only the contralateral field.”6. Meaning, if a left side injury occurred, the right side of the brain would be able to help with attention to both the right and left sides, but if a right sided injury occurred, the left side would only provide information about the right side. Additionally, it is important to note that USI neglect symptoms can also be due to trauma, neoplasms and neurogenerative disease affecting both the parieto-occiplital junction and certain subcortical areas.
USI is fairly common, for example, can be seen in up to 30% of people who have had a CVA7. The treatment for USI is different than that for a hemianopsia, thus, it is important for the clinician to differentiate between the two. One should always keep in mind that it can be possible for a patient to have both a hemianopsia and USI. A careful history involving the patient and caregivers can help differentiate between the two. As mentioned above, a person presenting with a new onset hemianopsia will be symptomatic and will be aware that their vision on one wide has been affected. A patient with USI will be unaware of their inability to attend to the affected field. Additionally, USI can involve more than just the inability to attend to visual stimuli. USI can involve personal neglect, where the patient behaves as though half of their body doesn’t exist (grooms only half of their head), USI can involve near extra personal neglect, where they don’t attend to stuff in their reach (may eat only half the food on their plate) and USI may involve far extra personal neglect where they don’t attend to the space behind arm’s reach (reads only half of the eye chart). Observation of the patient (do they behave as though they have both hands? How is their grooming?) and questioning the care giver (do they eat everything on their plate without reminder?) can help in diagnosing USI. Clinically there are also tests that have been developed to help diagnose neglect, some examples include: comb and razor test, albert’s test, baking tray test, balloons test, Bell’s test, Clock drawing test, double letter cancellation test, draw a man test, line bisection test, single letter cancellation test and star cancellation test. Hemianopsia’s can cause a shift in the perceived midline for a patient towards the missing field, whereas USI can cause a shift in the perceived midline away from the neglected field. Thus, when having the patient do a line bisection test, if the patient has both a USI and hemianopsia, they may be able to accurately bisect the lines, where as those with only USI or only hemianopsias, would inaccurately bisect the line either towards one side on the other. This is a critical test when trying to determine if a patient has both USI and a hemianopsia.
If cognition permits, visual field testing is helpful. If visual field testing is normal, then one might also consider testing for extinction. Extinction is when the patient ignores one side only when both sides are stimulated at the same time and this may exist in patients with USI. To test for this, confrontation visual field testing is performed where stimuli are simultaneously presented in both the right and left fields, if extinction exists, the patient will only attend to stimuli in one field.
A patient with USI will benefit from a multidiscipline approach to rehabilitation. Optometrists may use yolked prisms or filters to help the patient attend to the field they are ignoring. In practice, I have used right sided translucent filters on the right edge of a patient’s lenses (temporal occlusion on the right side and nasal occlusion on the left side) to help with attention to the left side. Neuro-rehabilitation therapy with an optometrist would also be very beneficial. If the patient is not tracking objects towards the affected field then dolls eye movements can be used to help the patient start to move the eyes in the affected direction. Optokinetic nystagmus therapy can also be done to help the patient move their eyes to the affected side. After involuntary eye movement have been generation, pursuits where the patient is tracking something they are touching could be done to help initiate voluntary eye movements. A patient with USI may find saccades very difficult, that is because a saccade is an engagement and a disengagement of attention. As the attention part of the brain is affected with USI, saccade rehabilitation therapy will be necessary. Using verbal and proprioceptive feedback can help the patient initiate these skills. Prism adaptation can also be used to treat patients with USI. Ballistic pointing is used to determine if this is a good treatment option for the patient. For a patient with left USI, when a target is placed on their midline, they may interpret it as being off to the right and this will be seen when they ballistically try to touch the target. Yolked base left prism glasses (10pd) are then worn by the patient, for 10 minutes they repeat the task of ballistically hitting the target on their mid line. At first they will continue to point further towards the right. Then, they will start to adapt to the prism and point on target. Once the glasses are removed, the patient will then point left of the target. Physiotherapists would be involved if the patient was having mobility problem and/or if they were preferentially using one side of the body more than the other. Therapy could include neck/hand vibration, activities where both sides of the body are used alternatively (ball games alternating left and right hands for example) and mannequin projection where the patient’s body part is tapped and they have to tap the corresponding part on another person. Occupational therapists would help the patient regain the daily skills they had lost. They would begin by helping the patient become aware of predictive stimuli. Therapy options include: tracking print on a story as it is read aloud, colouring certain letters on a page and I spy books. After predictive stimuli have been mastered, non-predictive stimuli would be targeted. The patient may be encouraged to use another sensory system to help perform the visual scanning task. The Margolis Eye throwing technique may be implemented to use the motor system to initiate visual scanning instead of relying on visual cues. List gathering tasks may be used with the patient to help with finding things in their home (cupboard, fridge, closet etc). Bringing awareness to neglect is also very helpful in the rehabilitation process. Having the patient do tasks that require symmetry can help with this. For example, have them set a table. If errors are made, the patient is then guided to see if they can figure out what occurred.
6. Suter, P.S. ‘Rehabilitation and management of visual dysfunction following traumatic brain injury’, in Ashely, M..J. and Krych, D.K. (ed.) Traumatic Brain Injury Rehabilitation. New York: CRC Press, p. 207.
7. Riestra AR, Barrett AM. Rehabilitation of spatial neglect. Handb Clin Neurol. 2013; 110: 347-355.