Validation of grading scales for contact lens complications

The validity of use of two artist-rendered and two photographic sets of gra ding scales (grading 'systems') designed for gauging the severity of contac t lens-related ocular pathology was assessed in terms of precision and reli ability. Thirteen observers each graded 30 images - by interpolation or ext rapolation to the nearest 0.1 increment - of each of the three contact lens complications (corneal staining, conjunctival redness and papillary conjun ctivitis) that were common to all four grading systems. This entire procedu re was repeated approximately two weeks later, yielding a total data base c omprising of 9360 individual grading estimates. Analysis of variance reveal ed statistically significant differences in both precision and reliability between systems, observers and conditions (p < 0.03 for system reliability; p = 0.0001 for all other combinations). The artist-rendered systems genera lly afforded lower grading estimates acid better grading reliability than t he photographic systems. Corneal staining could be graded less reliably tha n conjunctival redness and papillary conjunctivitis. Grading reliability wa s generally unaffected by the severity of the condition being assessed. Not withstanding the above differences, all four grading systems are validated for clinical use and practitioners can initially expect to use these system s with average 95% confidence limits of +/-1.2 grading scale units (observe r range +/-0.7 to +/-2.5 grading scale units). In view of the significant b etween-system differences revealed in this study, it is advisable to consis tently use the same grading system. It may be possible to reduce between-ob server differences by applying personalised correction factors to normalise grading estimates. (C) 2000 The College of Optometrists. Published by Else vier Science Ltd. All rights reserved.