I have just examined a 55-year-old male with myopia who was complaining of flashes, new small floaters and one large floater which is in the middle of their vision. Following a retinal examination through dilated pupils, I diagnosed a posterior vitreous detachment in the left eye and discharged the patient with advice on typical retinal detachment symptoms. A colleague later asked me if I’d looked for ‘tobacco dust’. What is tobacco dust? How do I look for it?
Tobacco dust occurs when retinal pigment epithelium (brown) and/or blood (red) cells are liberated from retinal tear or hole into the vitreous. These particles congregate in the vitreous. The blood means there is a vitreous haemorrhage and a 70% chance of a retinal break. Retinal pigment epithelium cells mean a 90% chance of retinal tear.
There are best seen using a slit lamp (no auxiliary lens required), to focus beyond the plane of the dilated pupil. This is best achieved by pushing the slit lamp biomicroscope forward. The vitreous then needs to be agitated by asking the patient to look up and down. As the vitreous settles, the best opportunity for detecting the pigmented particles arises.
The agitation causes much of the anterior vitreous to pass through the slit lamp field of view. The pigmented cells occur throughout the vitreous but only the anterior third can be visualised with the slit lamp without using an auxiliary lens.
Another name for tobacco dust is Shafer’s sign. Unfortunately, a retinal tear can sometimes be present if there is no Shafer’s sign. The best way to handle this is to dilate (if you are licenced to do so), have a good look inside and then look for tobacco dust, noting all your findings in the clinical records. If after all this you can’t find a tear or hole, advice the patient on the symptoms of retinal detachment and what to do if they notice one or more of these symptoms. Do this verbally and in writing. You can’t do any more than that.