Leprosy Mailing List – March 26th, 2007
Ref.: Ocular
leprosy
From:
Ahmad L., Karachi, Pakistan
Dear Dr Salvatore,
Thank you for sending Kawuma
J's query (LML March 21st, 2007 ). Although I am not an
ophthalmologist, I had collected some notes from the lectures of
Dr Joffrion (an ophthalmologist that worked in leprosy) and
sending one pertaining to blinking.
Lecture notes from Dr
Joffrion’s course “Leprosy in the Eyes”. ALERT, Addis
Ababa, September 1980:-
“Blinking is a spontaneous
reflex which helps in moisturising and washing of cornea with
watery lacrimal fluid which drain it through lacrimal drainage
system located in medial canthus of the eye. The circular
orbicularis oculi muscle which has both origin and insertion into
fibrous band attaching medial canthus to nasal bone. With the
contraction of this muscle lacrimal gland secretion (located in
lacrimal fossa at the upper temporal part of the orbit ) is
forced to travel across cornea to be drained at medial canthus,
thus washing the cornea clean.
The TEAR FILM which protects
cornea from exposure is made of 3 layers. If we see it through a cross
section, the first is mucous layer over cornea, the second is
lacrimal fluid and third which is very important is the oily layer
which is formed by secretions from special sebaceous and sweat
glands (glands of Zeiss and Moll) located in eyelids whose ducts open
at the base of eye lashes. Now with
each blink a thin film of this oily secretion is spread over other 2
layers, (it is like watery secretion is sandwiched between oily and
mucus layers. This
mechanism allows cornea exposure to external environment for a longer
time.
The BLINK REFLEX is initiated
when this oily layer breaks down OR if there is a threat of
injury to the cornea OR when cornea is touched to check for corneal
anaesthesia.“ -
As far as CORNEAL
ANAESTHESIA TEST is concerned, we assume that examiner has normal
blink reflex. In a
particular environment of moisture, dust and air current a patient
with normal eyes will blink as many times as examiner does. If a patient is blinking less
frequently or not blinking at all, a corneal anaesthesia test
should be performed.
With regards,
Dr Latif Ahmad
