Objective measurement of contact lens-induced conjunctival redness

Ocular redness is the principal clinical sign of any inflammatory response affecting the anterior segment of the eye. The aims of the current investigation were: (1) to develop an objective method to quantify the severity and geographic distribution of redness, (2) to validate that technique by determining its precision and compare its finding to clinical rating, and (3) to apply this technique to evaluating the diurnal variation in ocular redness associated with daily and extended soft contact lens wear. The objective capture and analysis technique involved the following steps: (1) direct image formation on the CCD array of a high resolution, high sensitivity 3/4 inch Cohu camera via a Nikon Macrolens and (2) capture and image analysis with a PC-based dedicated transputer. The key steps were: filtering to accurately locate the limbus and electronic sectioning with differential intensity color analysis at fixed intervals away from the limbus. The technique gave a direct measurement of the number and size of the vessels present. The result obtained lead to the following conclusions: (1) the digitization and analysis of video recordings of the bulbar conjunctiva provide a precise measurement of the level of conjunctival redness, (2) subjective rating of low level of conjunctival redness, using an overall nine increment clinical scale, did not relate closely to the objective measurement of conjunctival redness, (3) for non-contact lens wearers, redness in the evening was similar to redness measured upon waking, and greater than redness 2 h postwaking. In contrast, in daily soft contact lens wearers, redness was maximal in the evening and greater than before insertion or during wear in the morning. In extended soft contact lens wearers, redness was maximal upon waking when it was greater than in the evening, and (4) digitization and analysis video recordings of the redness response of the bulbar conjunctiva are sufficiently sensitive clinical research tools to monitor diurnal variation of the inflammatory response of the anterior segment of the eye.