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Time to Take an Ax to the Wood’s Lamp?

February 13, 2019

Written by Nicole McCoin

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The overall sensitivity of the Wood’s lamp, compared to the gold standard slit lamp, to establish the diagnosis of common corneal and conjunctival abnormalities was found to be an abysmal 52%.

Why does this matter?
The Wood’s lamp has advantages: cheaper, quicker, and easier to store and use. However, let’s face it folks…if you have the resources in your emergency department to have a functioning slit lamp, then you need to be using it. Albeit a small study, the numbers made me super nervous about the ol’ Wood’s lamp.

It’s like not performing a rectal exam for a patient with dark, tarry stool; for the love…if you have a slit lamp, use it!
OK, I will get off of my soap box now. For a little background, the standard Wood’s lamp uses long-wave ultraviolet light with a magnification of 2-3 times. The slit lamp uses a magnification of 8-40 times. Thus, it makes sense that the slit lamp would catch more pathology than the Wood’s lamp, but just how much better is it? They performed this study in an ophthalmologist’s office. When a patient arrived with complaints centered on potential anterior chamber pathology, fluorescein was instilled into the affected eye; the ophthalmologist would examine the eye using the Wood’s lamp and record the results. Then the ophthalmologist would examine the eye using the slit lamp, and results were recorded. Here is what they found:

  • Wood’s lamp detected only 56% of the corneal abrasions.

  • Wood’s lamp detected only 50% of the corneal ulcers.

  • Wood’s lamp detected only 44% of corneal foreign bodies.

  • Non-herpetic and herpetic keratitis cases were also missed.

This study was small, with 73 adult patients participating and just one ophthalmologist performing the exams. The gold standard (slit lamp) was also one of the tests being studied, which increases risk of incorporation bias. Additionally, everyone may not have the luxury of having a slit lamp at their fingertips. However, the numbers of missed diagnoses that could have potential complications were high. No more excuses ladies and gentlemen. Dust off the chin rest and lenses and let’s get back to slit lamp business. The more you do it, the more natural it becomes. The extra time it takes is worth it for the patient. Good luck, and happy slit lamping!

Prospective study of the sensitivity of the Wood’s lamp for common eye abnormalities. Emerg Med J. 2019 Jan 10. pii: emermed-2018-208235. doi: 10.1136/emermed-2018-208235. [Epub ahead of print]

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Reviewed by Clay Smith and Thomas Davis

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