Leprosy Mailing List – March 17th, 2007
Ref.: Corneal sensory testing
From: Ebenezer D., Baltimore,
USA
Dear Salvatore,
The correspondence on corneal
sensory testing addresses several important problems. I
forwarded these questions and comments to Dr. Ebenezer Daniel, who
trained with Dr. Margaret Brand and then worked at Karigiri for many
years, and is now at Johns Hopkins University in the United States.
His reply follows.
Best regards,
David Scollard
-------------------------------------------------
Dear David,
There is impaired corneal sensation in
some leprosy patients but calibration of the amount of sensory loss is
not an easy task. The
question of whether there is anaesthesia or just hypoesthesia is
difficult to ascertain since we do not have good measuring tools to do
this.
In my clinic in India, over the 15 years
of examining leprosy patients under the biomicroscope, I have seen
patients with large foreign bodies embedded in their cornea sitting
without any discomfort and completely oblivious of the iron, sand or
wooden piece that had embedded in their eyes. They deny any problem with
their eyes and this can happen only if they have either anaesthesia or
hypoesthesia. In normal eyes these foreign bodies would have
caused intense and unbearable pain.
Using a Cochet and Bonnet aesthesiometer,
one could, to a certain extent, measure the corneal sensory threshold
and have cut off points that categorize them into normal, mild
hypoesthesia, severe hypoesthesia and total anaesthesia. I have tried doing this and
collected some data but they need to be analysed . . . There are
other instruments which have been used for estimating corneal
sensation (non-contact, gas, chemicals etc) but as far as I know none
of them have been used extensively nor standardized into useful
clinical tools.
Its been long taught that the cotton wisp
method could be used in field situations but an enthusiastic health
worker can easily disrupt the corneal epithelium by trying to produce
a reaction in the person being tested, to elicit normal corneal
sensation. The disrupted
cornea can easily become infected.
I would like to simply say here that the cotton wisp is
definitely not the tool one would like to use in measuring corneal
sensation. It is not only
hopelessly unreliable but is also extremely dangerous in the hands of
health workers who have not been trained adequately with its use. It can potentially produce a
catastrophic corneal ulcer in vulnerable eyes.
Ebenezer Daniel
Division of Ocular Immunology
The Wilmer Eye Institute
School of Medicine
The Johns Hopkins University
1620 McElderry Street
Reed Hall, 4th Floor
Baltimore, MD 21205
443.287.1897
