PROGRESSION OF VISUAL FIELDS IN POSTERIOR CORTICAL ATROPHY MIRRORS THAT OF COGNITIVE DEFICITS

Abstract

The significance of visual field defects (VFD) in posterior cortical atrophy (PCA) has been questioned in face of coexisting higher-order visual disturbances. The relationship between pattern of VFDs and that of cognitive deficits may give insight into the mechanism of VFDs in PCA. Twenty-one patients with PCA had visual field tests performed using Humphrey automated perimetry at baseline and follow-up (mean duration 2.5 years; number of assessments 2–4). Mean deviation (MD) per hemifield was calculated and the ratio between MD in the right and left hemifield (R/LMDratio) established for every assessment. Cognitive measures consisted of scores created to summarise performance on tests of unilateral (Object Perception (OP); Space Perception (SP); Spelling; Arithmetic) and bilateral cognitive functions (Shape Detection (SD); Figure-Ground Discrimination (FGD)). Cognitive scores were compared with R/LMDratio at baseline using Spearman's correlation. Progression in cognitive tests was analysed according to time and contemporary R/LMDratio using mixed model linear regression. All patients had abnormal HFA at presentation, consisting of incomplete homonymous hemianopia (HH) more marked in one hemifield in all but one patient. The more affected hemifield was the left in 14 patients (66%). At baseline R/LMD did not correlate with score on OP (ρ=0.23,p<0.3), SP (ρ=0.12, p<0.6), Arithmetic (ρ =-0.24, p<0.28), or Spelling (ρ =-0.25, p<0.28). On the longitudinal analysis, increment of one unit in RLMDratio was associated with decrement of -0.78 in Spelling (p<0.01) and -0.83 in Arithmetic (p<0.02), but had no effect on OP or SP (slope 0.001, p<0.9; and 0.01, p<0.9, respectively). Increasing 1 unit on the log of RLMDratio absolute value (RLMD approached 1) was associated with decline of 0.73 (p<0.03) in FGD and 0.55 (p<0.04) in SD. Predominant right HH was associated with greater decline on cognitive functions relying on the left hemisphere, suggesting that VFDs result from extension of degeneration into the contralateral occipital lobe. This was further supported by the association between bilateral VFDs and deterioration on bilateral occipital lobe functions. Predominant left HH did not correlate with greater right hemisphere deficits, which may be explained by the occurrence of the latter in all patients, as a consequence of PCA case definition.