[A clinical comparative study of tyndallometry using 2 laser flare meters]

Area of Science:

• Ophthalmology
• Biomedical Optics
• Medical Instrumentation

Background:

• The Kowa laser flare meter FM-500 is a simplified version of the FC-1000.
• Both instruments utilize lasers to measure aqueous flare, a marker of intraocular inflammation.

Purpose of the Study:

• To compare flare measurements between the Kowa FM-500 and the established Kowa FC-1000 laser flare-cell meter.
• To assess the in vivo reproducibility of both instruments for quantifying aqueous flare.

Main Methods:

• Compared flare measurements from the FM-500 and FC-1000 in 10 normal subjects and 21 uveitis patients.
• Examinations were performed by a single examiner under comparable, randomized conditions.
• Reproducibility was assessed by repeat measurements on normal eyes the following day; statistical analysis included linear regression and intraclass correlation.

Main Results:

• Flare values did not significantly differ between the FM-500 and FC-1000 in normal eyes (3.3 vs 3.5 photon counts/ms) or uveitis eyes (16.2 vs 16.4 photon counts/ms).
• High correlations were observed between instruments in normal eyes (r=0.73) and very high correlations in eyes with mild to moderate flare (R=0.99).
• Intraclass correlation coefficients were high for both instruments (0.70-0.76 in normal eyes, 0.99 in uveitis eyes), though the FM-500 indicated higher values in one case of acute fibrinous iridocyclitis with very high flare.

Conclusions:

• The Kowa FM-500 and FC-1000 provide comparable aqueous flare measurements in eyes without or with mild to moderate blood-aqueous barrier breakdown.
• Discrepancies in measurements may arise when assessing eyes with significantly elevated flare levels.