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Trefford L Simpson, Yunwei Feng, Ping Situ, Carolyn G Begley; Multidimensional Scaling of Belmonte Esthesiometer Stimuli.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6079. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relationship between mechanical, and chemical pneumatic stimulation of the cornea, using multidimensional scaling (MDS).
Using an ascending method of limits, central corneal thresholds in 9 normal subjects were measured with room- and eye-temperature mechanical and chemical stimuli using computer controlled Belmonte pneumatic esthesiometer. Warm & cool mechanical and chemical stimuli at 1.5x or 2x threshold (8 stimulus configurations in total) were then used for MDS. The similarities of all pair-wise combinations of these 8 stimuli (28 in total) were rated (in random order) on a continuous scale (0-100) “exactly the same” to “completely different”. For example, subjects had to rate the similarity of a cool mechanical stimulus, 1.5x threshold and a warmer chemical stimulus, 2x threshold. Average and individual dissimilarity matrices were analyzed using Smacof, Indscal and Proxscal in R and SPSS.
Scree plots showed that 2 dimensions were needed to account for the dissimilarity data. Fig. 1 shows a 2 dimensional solution with labels shaded using cluster analysis. The labels are c or m (chem/mech) 15 or 2 (1.5x / 2x thresh) and 24 or 50 (room/eye temp). The lower rightmost cluster includes all 4 chemical stimuli and to the left are the 2 eye-temperature mechanical stimuli. The upper rightmost stimuli are the coolest (room temperature mechanical) with the eye-temperature stimuli lower and more leftward. Indscal weights suggested that 1 subject’s ratings were dissimilar to the others.
This is the first integrated examination of whether the stimuli produce the desired sensory effects based on the underlying neurophysiology. Our results are not predicted by the physiology: There appear to be primarily ‘discomfort’ (mechanical-chemical) and thermal dimensions. This is surprisingly similar to the results obtained when words for the sensory attributes of the ocular surface were examined using MDS (ARVO 2012).
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