Item	Item-total correlation (all subjects)	Item-total correlation (prHD subjects)	Item-total correlation (HD subjects)
Reading	0.389	0.340	0.360
Tracking while reading	0.489	0.202	0.639
Tracking objects with eyes	0.169	0.373	0.190
Balance on one foot	0.758	0.785	0.690
Balance when walking	0.858	0.817	0.857
Shifting gaze	0.289	0.333	0.349
Fine motor ability	0.718	0.257	0.774
Complex motor behavior	0.722	0.532	0.733
Writing	0.820	0.805	0.776
Clumsiness	0.795	0.744	0.774
Functional impact	0.858	0.902	0.828