4D.1 SUMMARY
(1) The VNRI has the advantage of expressing performance on the visual neglect battery as a single figure instead of as a profile of graded scores on individual tests.
(2) It is a better option than summating and averaging the graded scores because it expresses each grade in equivalent units of "neglect recovery", instead of arbitrary units of no real value.
(3) There is reasonable correlation between the VNRI and the individual test scores.
(4) The rate of recovery of visual neglect described by the VNRI is consistent with that of most stroke-related neuro logical deficits.
(5) The finding that visual neglect is more severe in right hemisphere stroke is consistent with previous studies and w i t h e v i d e n c e s u g g e s t i n g t h a t the r i g h t h e m i s p h e r e is dominant for sensory attention.
4D.2 Advantage of the VNRI
The visual neglect recovery index was developed in this study to p r o v i d e a single o v e r a l l m e a s u r e of v i s u a l n e glect.This expresses a patient's performance on the visual neglect test battery as a percentage of complete recovery from the maximum visual neglect measurable.
The advantage that the VNRI has over the previous method of expressing performance on the battery as a p r ofile of graded scores on the individual tests, is that the result is g i v e n as a s i n g l e figure. T h i s m a k e s it e a s i e r for clinicians to express the severity of visual neglect and compare patients' performance. It is a better option than s u m m ating and a v e r a g i n g the g r a d e d scores of i n d i v i d u a l tests because the VNRI expresses each grade in equivalent units of "neglect recovery" instead of arbitrary units of no real value. Visual neg l e c t m a y be t a s k - s p e c i f i c (De Gastello + W a r r i n g t o n 1987) and the VNRI m a y f a c i l i t a t e comparison between performance on different tests better than the original grading system. The VNRI is p r obably a reasonable reflection of the individual test scores, for both follow a similar pattern of change with time and the results of those Least Significant Difference analyses and A N O V A t h a t w e r e p o s s i b l e (Tables 3D.3, 3D.4), p r o v i d e further support for the correlation of the two. This sug gests that if a patient is unable to do 1 or 2 tests b e cause of aphasia or drowsiness, the VNRI derived from the tests done by the p a t i e n t is p r o b a b l y r e p r e s e n t a t i v e of their visu a l n eglect on the ent i r e battery. It c o u l d be argued that one test is as useful as the entire battery, but recent work has illustrated the differential sensitivi
ty of individual tests (Halligan et al 1989) and stressed that use of only one test might result in failure to detect a significant proportion of patients with visual neglect (Section 4B.2). The index, like the Behavioural Inattention Test (Wilson et al 1987, 1987a) from which the battery was derived, does not lateralize the omissions but, in p r a c tice, only 2% of test results are not clearly lateralized.
4D.3 Recovery of visual neglect
The rate of recovery of visual neglect is similar to that reported for other neurological deficits or disabilities in stroke. T h e p r e s e n t i n v e s tigation is the only d e t a i l e d study of the recovery of visual neglect in stroke survivors that has assessed visual neglect with a larger test battery t h a n is the clinical conven t i o n and w h i c h a s s e s s e s the s e v e r i t y of visu a l neglect r a t h e r t han its p r e s e n c e or absence (Hier et al 1983a). Wade et al (1988) examined the r e c o v e r y of visual neglect u s i n g a numb e r c a n c e l l a t i o n task. This test,as the authors point out, was itself diffi cult to interpret. In addition, by using only one test,the
presence of visual neglect may therefore have been under
estimated and they only found 15 out of 68 patients to have visual neglect. Despite these difficulties they too report r a p i d r e d u c t i o n of n e g l e c t in t h e f i r s t 10 d a y s w i t h resolution in most patients at 3 months.
The VNRI shows that visual neglect makes a reasonable
recovery in most patients and that even if it persists at 3 months in as many as 75% of patients with a right h e m i s p h e r e s t r o k e (Figure 3C.1), its s e v e r i t y at that stage tends to be mild (Table 3D.2, Figure 3D.1). It should be n o t e d t h a t all p a t ients with a VNRI at 3 m o n t h s of less
than 75% had a right hemisphere stroke and that only 2 of those with a left hemisphere stroke had a VNRI at 3 months of less than 80%.
T h e V N R I s h o w s a s i g n i f i c a n t d i f f e r e n c e in t h e severity of v i s u a l neglect b e t w e e n those w i t h r i g h t and left h e m i s p h e r i c stroke, w h i c h c o n f i r m s the f i n d i n g s of other studies (Chedru et al 1973; Chain et al 1979), the earlier findings of this study (Section 3A.3.6), and proba bly exp l a i n s w h y it per s i s t s for longer in r i g h t h e m i
sphere stroke (Figure 3C.1). This is consistent w ith the
view that the right hemisphere is dominant for the distri bution of sensory attention to environmental space (Section 1.2.7) .
4E PREDICTION OF THE SEVERITY OF VISUAL NEGLECT