Tactile spatial acuity in elderly persons: assessment with grating domes and relationship with manual dexterity

In this study, we sought to better define the limit of spatial resolution at the fingertips of elderly participants (n = 30, age 60-95 years) using an extended set of JVP grating domes, incorporating four new grating dimensions (2.5-, 3.5-, 4.0- and 4.5-mm width). A secondary aim was to examine whether deficits in tactile acuity could be related to hand dysfunction in older adults. Spatial resolution thresholds were determined by the finest grating whose orientation (dominant index finger) could be reported reliably. Manual dexterity was assessed with the Grooved Pegboard Test (GPT). The extended set of domes improved threshold measurements in a majority of participants (21/30). Still, accurate threshold estimates could not be obtained in one third of the participants, mostly in the older age group (8/9, 74-95 years). Grating resolution thresholds at the index finger were strongly correlated (r = 0.66, p<0.01) with dexterity scores derived from the GPT. From these results, we conclude that the 2.5- and 3.5-mm grating domes are suitable additions when assessing spatial acuity at the fingertips of older subjects between 60 and 70 years of age (mean threshold, 2.7+/-0.6 mm). For the older ones, the 4.0- and 4.5-mm domes can improve threshold measurements but interpretation of values can be complicated by the presence of undiagnosed pathologies (e.g., diffuse polyneuropathy) as people advance in age. The strong relationship between grating resolution thresholds and dexterity scores indicates that an impaired spatial acuity at the fingertips may translate into great difficulties in tasks requiring fine manipulations. These findings have important implications for the assessment of hand function in older adults.