Lens status and degree of lens opacity influence laser flare photometry (objective tyndallometry)

Purpose Objective tyndallometry using laser flare photometry can be utilized e.g., in management of uveitis. Previous studies showed a significant difference in flare values between pseudophakic and phakic eyes. We investigate a potential association between the degree of lens opacification and flare value in a large cohort phakic eyes. Methods Retrospective, non-interventional single center study. Laser flare values of 460 healthy fellow eyes from two large cohorts (primary rhegmatogenous retinal detachment (RRD), macular holes (MH)) were correlated with lens status, degree of lens opacity, and age. Results Out of 460 patients (mean age 64.6 +/- 11.2, 57% male) 30.4% were pseudophakic (70.2 +/- 10.9) and 69.6% phakic, of which 47.8% showed a clear lens (57.3 +/- 9.1), 43.2% an mild cataract (65.2 +/- 9.0) and 9.0% a moderate cataract (73.5 +/- 9.0). In pseudophakia, flare (8.14 +/- 4.6 pc/ms) was significantly higher compared to phakia (6.4 +/- 3.9 pc/ms; p < 0.001). In phakic eyes, flare values increased significantly with increasing lens opacity (clear lens 5.3 +/- 2.8 pc/ms; mild cataract 7.0 +/- 4.0 pc/ms; moderate cataract 9.5 +/- 6.1 pc/ms; p < 0.001). In clear lenses and mild cataract, age correlated significantly with flare (two-sided, p < 0.001, clear lenses R = 0.3; mild cataract R = 0.4). In clear lenses, flare values increased with age by 0.09 per year, in mild cataract by 0.17 (regression coefficients). No significant correlation was found between age and flare value in moderate cataract and pseudophakic eyes. Conclusion The level of objective tyndallometry seems to be dependent on lens status, degree of lens opacity and age. These factors should therefore be taken into account when interpreting laser flare values in the future.