PURPOSE. The evaluation of corneal staining is key when assessing the clinical performance of soft contact lens care products. Several studies have highlighted differences in corneal staining between multi-purpose (MP) care systems. The conventional method of grading corneal staining, however, is inherently subjective and therefore prone to measurement error and variability. The purpose of this study was to evaluate an objective method of measuring corneal staining and to compare the clinical performance of three commonly used MP systems. METHOD. Twenty-four subjects used each of three different MP systems for 2-weeks in a randomised single-masked (investigator) crossover study. Two of the MP systems contained polyhexanide as the disinfectant (PX1, PX2) while the third system contained polyquaternium-1 (PQ). High water Group 2 soft lenses were used throughout the study and were discarded at each crossover. After 2 weeks of care system use, corneal staining was recorded on video and analysed using an image-processing program (ImageTool) to provide the total area of staining for a given eye. Conjunctival hyperaemia and papillae were also evaluated at the follow-up visits. Test-retest evaluation was used to compare investigator grading of corneal staining with image analysis.
RESULTS. Image analysis coefficient of repeatability was similar to investigator grading (COR 1.05 vs 0.90 respectively) and there was a high correlation between the two (r=0.92, P<0.0001). Significantly less corneal staining area was noted with the polyquat system than with the polyhexanide systems (PX2 0.91 vs PQ 0.12 mm2, P=0.01). Inferior palpebral papillae were significantly greater with PX2 vs PQ (mean grade 1.0 vs 0.7, P=0.01), however, there were no significant differences in comfort.
CONCLUSIONS. The technique was shown to be an effective objective method of monitoring corneal staining. The physiological response differentiated formulations despite short-term exposure. Practitioners cannot rely on patient symptoms to indicate adverse responses to MP care products.