Touch is a crucial sense for perceiving the spatial characteristics of objects. The JVP dome was developed to evaluate tactile spatial acuity using a grating orientation task. The application of the traditional JVP dome to assess tactile function was limited by the ceiling effect, excessive transition gap between grating widths causing inaccurate tactile discrimination threshold measurement, and predictive bias due to the common execution protocol using grating widths in sequence. In this study, we included additional grating domes and proposed a modified examining protocol for estimating tactile discrimination thresholds to improve the accuracy of tactile function assessment. Twelve healthy participants were enrolled in this experiment. Extended JVP domes with 11 different groove widths were designed. Tactile discrimination thresholds were estimated using a modified two-down-one-up staircase method. The experiment comprised practice, training, and testing sessions, conducted by trained examiners who performed grating stimulation on participants index fingerpads. All participants passed the required accuracy in the practice and training sessions. Eight transition points were obtained in the testing session for each participant, and tactile discrimination thresholds were all within the width range of the extended JVP domes. The mean tactile discrimination threshold was 2.09 ± 0.84 mm. The results demonstrated that the proposed modified JVP dome set and protocol were successfully applied to assess tactile discrimination thresholds. The modified protocol with extended JVP domes provided an effective assessment of tactile function and improved the precision of threshold measurements, avoided the ceiling effect found in traditional JVP dome, and eliminated predictive bias.