Effect of light backscattering from anterior segment structures on automated flare meter measurements

Abstract

Background: To evaluate effect of maximal anterior cortical lens density, iris scatter and anterior chamber depth on laser flare photometry. Methods: Patients diagnosed with clinical uveitis were enrolled in the study. Clinical flare gradings were recorded upon the Standardization of Uveitis Nomenclature. Aqueous flare was measured with an automated device (Kowa FM-700). Back-scattering from anterior cortical lens and anterior iris surface was calculated from Scheimpflug images. A curvilinear regression model was used to calculate estimated values for each clinical grade. These values were used to split cases in Group I (laser flare photometry lower than estimated) and Group II (laser flare photometry higher than estimated). Mean anterior chamber depth, pupil aperture, maximal anterior cortical lens density and iris scatter values were compared between two groups. A stepwise multiple regression analysis was performed to determine the effect of clinical flare gradings and ocular parameters on aqueous flare measurements. Results: The study included 228 eyes of 114 cases. Scheimpflug images were obtained from 105 eyes. Estimated aqueous flare measurements (in photons/milliseconds) were 4.87, 8.50, 14.81, 25.83, 45.04 and 136.93 for 0, 0.5+, 1+, 1.5+, 2+ and 3+ clinical flare respectively. Group II had higher maximal anterior cortical lens density than Group I (96.6 ± 37.1 vs 77.9 ± 17.1 pixel unit, p = 0.001). The measured aqueous flare was significantly related to clinical flare, maximal anterior cortical lens density and pupil aperture (adjusted R2: 0.480, p < 0.001). Conclusion: The back-scattered light from anterior cortical lens could affect laser flare photometry measurements. This effect might be quantified by Scheimpflug imaging.

Factors influencing aqueous flare after cataract surgery and its evaluation with laser flare photometry

“…26 However, the properties of the cataract may falsely change the flare due to increased background light journals.sagepub.com/home/oed TherapeuTic advances in Ophthalmology scatter. 131 Cataract surgery technique influences postoperative flare and can be minimized with small incisions, efficient phacoemulsification and in-the-bag IOL placement. The majority of IOLs used today do not affect flare differently from one another.…”

Assessing quantitatively the state of the blood-aqueous barrier by laser flare photometry: a review

“…Повідомляється про зв'язок значень ЛФ зі щільністю передньої кортикальної зони кришталика [18]. Водночас думка про вплив розсіювання світла помутнінням у кришталику на значення ЛФ залишається дискусійним [19,20].…”

Laser flare photometry in uveitis

“…It is well known that backscatter form cataractous lenses has a considerable effect over LFP measurements,[ 20 ] although it has been shown that milder light backscatter from a noncataractous anterior cortical lens could also have an additional effect over LFP readings. [ 21 ] Iris scatter is also a contributing factor, which could be decreased by mydriasis[ 1 ] or proper positioning of the calculation window during LFP acquisition, for the amount of scattering is inversely proportional with the distance to the scattering surface. [ 22 ]…”