Measurement of aqueous cells and flare in normal Eyes

Abstract

The Kowa laser cell flare meter has been recently introduced to quantify the assessment of aqueous cells and flare in vivo by measurement of light scattering from a low power He- Ne beam. Computer analysis of this scattered light can distinguish cells (expressed as cell count) from protein (expressed as photon count/ms), and in-vitro work with albumin solutions has shown that the photon count/ms is linearly related to protein concentration. This study of 106 normal eyes (53 subjects) assesses the accuracy and sensitivity of the instrument and the factors affecting the interpretation of its results. Using in-vitro solutions of human albumin we found a highly significant linear correlation (r=1, p=0·0001) between photon count and protein concentration. The results show that the instrument has a photon count/ms reproducibility of 8·26% and that there is a within-subject variability in photon count/ms (aqueous flare) of 12·2% in normal eyes. No significant difference in photon count/ms (aqueous flare) was found to exist between right and left eyes (p>0.4), between sexes (p>0·5), or between irides of different colour (p>0·8). There was also no statistically significant variation in photon counts/ms with time of day over the period of measurement (1000-1900 h) (p=0·4). There was, however, an increase in photon count/ms with age (r=0·57, p<0·001) and a decrease with pupillary dilatation at both 30 and 60 minutes after instillation oftropicamide 1% (p<0·05). An occasional cell was found in only 10·4% of normal eyes, and there was no significant increase in the cell counts on mydriasis (p>0·05). These findings indicate that the Kowa laser flare meter is an accurate and sensitive instrument with potential application in the investigation of the blood-aqueous barrier.