Subam Basuthkar recently graduated with a PhD in Vision Science from the University of Waterloo, Centre for Contact Lens Research. Her research interests include: ocular discomfort with contact lenses, sensory and non-sensory pain processing, and pain measurement.
Download the poster (.pdf), which was originally shared at the Annual Meeting of The Association for Research in Vision and Opthalmology (ARVO), 2011.
Subam Basuthkar Sundar Rao1, Trefford Simpson2A, Desmond Fonn2B
1Optometry/Vision Science, CCLR University of Waterloo, Toronto, ON, Canada;
ASchool of Optometry,
BSchool of Optometry-CCLR,
2University of Waterloo, Waterloo, ON, Canada.
Purpose: To study the correlation of objective and subjective measurements of ocular discomfort.
Methods: 27 participants were enrolled for the study. Soft (HEMA) contact lenses of eight different lens designs varying by base curve and diameter were fitted on all participants. The study was conducted on two separate days with four lenses randomly assigned on each day. Subjective measurements of discomfort were obtained using numerical rating scales. The assigned contact lens was fitted on one eye and the equivalent corneal discomfort was matched on the fellow eye using stimuli delivered from a computer controlled pneumatic Belmonte esthesiometer. Corneal mechanical threshold was first measured using the ascending method of limits and after contact lens insertion, the match of discomfort with contact lens was set using the esthesiometer. Pearson product moment correlation was used to correlate the objective esthesiometer matches to the subjective ratings of discomfort reported by each participant.
Results: 13 out of 27 participants showed statistically significant correlation between objective and subjective discomfort (correlation ranged from 0.71 to 0.89). The remaining subjects showed a correlation between -0.04 to 0.70, which were not statistically significant. In the group of participants that showed a good correlation, subjective discomfort ranged from 14.23± 12.39 to 59.23± 26.99 for the most comfortable to the least comfortable lens with corresponding esthesiometer values between 40.38± 17.71 to 59.23± 26.99 ml/min. For the group with poor correlation, the subjective ratings were 21.43± 22.74 to 56.43± 25.38 for the most comfortable to the least comfortable lens. The corresponding esthesiometer values were 52.36± 25.78 to 56.43± 25.38 ml/min. The range of ethesiometer intensities used by the participants in poorly correlated group was insufficient to cover the subjective discomfort reported by them.
Conclusions: Subjective ratings of ocular discomfort can be scaled by corneal esthesiometry in a selective group of people. In the subset of subjects with poorer correlations, perhaps the pneumatic mechanical stimulus was too localized and specific to match the complex sensations experienced while wearing contact lenses. Proper training in esthesiometry procedure might ensure a better correlation. However, there is also a group of subjects who are poor at making judgments about ocular comfort. So special sensory panels should be used when ocular discomfort is the primary outcome.