Abstract
Purpose :
To develop a method enabling quantitative comparison of filter and light source combinations used in ophthalmology. The cobalt blue filter plays a crucial role in ophthalmology for visualizing fluorescein in anterior eye examination using a slit lamp biomicroscope. Despite being widely employed, there is a lack of published data addressing essential factors like the optimal thickness and concentration of cobalt within the glass for visualizing fluorescein. Moreover, the impact of transitioning from halogen-tungsten light to white LED light on the performance of the cobalt blue filter remains unexplored. This study aimed to address these gaps by quantitatively comparing the performance of cobalt blue filters and light sources.
Methods :
A calculated Signal to Noise Ratio (SNR) was proposed to enable comparison of filters and light sources. This was found by multiplying the absorption spectra of fluorescein in tears with each of the blue light profiles measured by the Oceanview spectrophotometer. This was divided by the cross talk between the respective blue filter and Wratten 12 filter and multiplied by the human eye’s photopic response function. This SNR was used to compare the Haag-Streit 1957 900s' cobalt blue filter, Perkins tonometer cobalt blue filter (Western Ophthalmics Corporation), Wratten 47a filter (Kodak), Tiffen 47a filter (Tiffen), and BG3 filter (Edmund Optics) in conjunction with halogen and white LED light. Due to experimental limitations, the BG3 and Haag-Streit filters were not reported when using white LED light. A one-way ANOVA with Bonferroni correction was used to compare remaining combinations.
Results :
The Haag-Streit’s cobalt blue filter’s SNR (186±70) outperformed the Perkins cobalt blue filter (10.7±0.16), Kodak Wratten 47 (7.63±0.07), and Tiffen Wratten 47 blue filters (20.2±0.91) as well as all other reported combinations (adjusted P<0.0001%).
Conclusions :
The Haag-Streit’s cobalt blue filter uniquely reduced transmission of both green and near infrared light, outperforming the Perkins cobalt blue filter, both 47a filters and BG3 filter when using the halogen light source. These results may suggest better performance of darker cobalt blue glass. Further researching the optimum concentration and thickness of cobalt blue glass is indicated.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.