Commentary: Pocketable blue smartphone flash filter turns dyed eyes fluorescent green

Portability of gadgets is always useful, and ultra-portable pocketable tools can be most useful in the field of ophthalmology. The authors of the accompanying article[1] made a highly pocketable filter for a smartphone to document fluorescein-stained cobalt blue illuminated images. It is very useful to have a method to photograph/videograph and document these ocular findings on a smartphone.[2]

What is cobalt blue?

Cobalt blue (cobalt aluminate - CoAl₂O₄) is a blue pigment made by sintering cobalt oxide with aluminum oxide (alumina) at 1200°C. Cobalt glass is a deep blue–colored glass prepared by including a cobalt compound—typically cobalt oxide, smalt or cobalt carbonate—in a glass melt. This is used as an optical filter that transmits only blue light in the wavelength range of 450 to 490 nm. This can be used to excite fluorescein sodium dye and observe its green fluorescence.[3]

Cobalt blue illumination in ophthalmology

The slit-lamp microscope, direct ophthalmoscope, indirect ophthalmoscope, fundus fluorescein angiography (FFA) retinal camera, Perkin’s tonometer and some surgical microscopes filter for cobalt blue illumination. The portable one in a direct ophthalmoscope is too dim to clearly do a bedside fluorescein dye test. The device made by the authors of the accompanying article[1] seems to have adequate brightness to visualize and photograph fluorescein dye tests and seems to be very useful at bedside or wherever a slit-lamp is not available.

Cobalt blue illumination by itself without fluorescein dye is useful in visualizing the iron lines of corneal epithelium[4] such as Fleischer’s ring of keratoconus, Stocker’s line of pterygium, Ferry line of bleb, and Hudson–Stahli line of elderly. Some researchers tried using it to grade cataracts and predict visual acuity loss but did not find a correlation.[5]

Fluorescein sodium dye with cobalt blue illumination is used to visualize corneal epithelial defects including abrasions, superficial punctate keratitis (SPKs), and corneal ulcers. It is used for Jones dye test, tear break-up time, tear meniscus height, Seidel test, contact lens fitting, Goldmann applanation tonometry, Perkins tonometry, and FFA.

Other innovations in cobalt blue illumination

As pointed out by the article, Puthalath et al.[3] from the All India Institute of Medical Sciences (AIIMS), Rishikesh, has also made a portable cobalt blue filter for smartphones. They obtained excellent photos and videos of cobalt blue illumination as published. 3D printing technology finds its way into several avenues in ophthalmology.[6] Lemanski et al.[7] from New York used a fused deposition modelling (FDM) 3D printer and poly ethylene terephthalate glycol (PETG) filament to 3D print a cobalt blue filter of thickness of 2.5 mm at 100% infill in a crosshatch layer pattern at a layer height of 0.14 mm using 0.2 meters of filament. They noted that this had similar properties as a slit-lamp cobalt blue filter.

What’s in a filter? #Softwarefilter #blueblocker

The authors have demonstrated excellent images[1] taken with the cobalt blue illumination. It takes some skill and effort to take good smartphone slit-lamp photos,[2] especially with cobalt blue illumination, as the dim blue lighting confuses the focus and exposure settings of the smartphone camera. Some slit-lamp microscopes have an additional paired yellow-colored filter in the viewing scope that blocks the blue background illumination, thus making the fluorescence better visible. These would help in much better imaging of the lesions as well. That type of blue-blocking filter could be incorporated between the camera lens and the Anterior Segment Photography with Intraocular Lens (ASPI)[8] in this innovation. Another innovative option would be to incorporate the blue-blocking filter in the camera software itself. This could be done in a crude manner by changing the white balance or, more accurately, in an advanced camera software.

Blue or green (red-free), that is the question

Though cobalt blue has been traditionally taught to be the ideal illumination for these purposes, some researchers such as Shakih and Adams[9] have shown that the green filter (red-free filter) may be the superior option to visualize fluorescein–stained structures in almost all clinical situations except for tear breakup time. This is because the red-free is brighter than the cobalt blue light. Interestingly, this green(red-free) light excites the fluorescein but allows visualization of surrounding ocular structures better than coblat blue.

The frugal, pocketable, do-it-yourself innovation described by the authors[1] seems to be another essential tool in the pocket of an ophthalmologist.