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Chapter Five
Dr. Genalin A. Ang
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` Measurement of the Central Corneal Thickness
` Relevance in many clinical situations such as:
` A. Pre-Operative assessment of refractive surgery
patients ( LASIK )` B. Diagnoses of corneal conditions , fitting of the
contact lenses
` C. The accurate assessment of intra ocularpressure
`
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` . However, if the cornea is thinner than normal,
then the eye will feel softer to the tonometer and
the measured reading will actually be falsely low
(i.e. the true pressure inside the eye is actuallyhigher than what is being measured)
` If the CCT is thicker than normal, then the eye
pressure number read by the tonometer, will be
falsely high (i.e. the machine thinks that the eyeis firmer (higher pressure) than it really is)
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` The surface of the eye (cornea) comes in different
thicknesses just like all parts of our body vary from
human to human.
` Devices that measure eye pressure (tonometers)are calibrated for the normal range of central
corneal thickness (CCT).
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` A child who has had cataract surgery comes to see their
eye doctor 6 months after surgery for a check-up.
` The eye doctor measures the eye pressure to be 30.
The rest of the eye exam is completely normal. The eye
has not gotten any bigger,
` the cornea is not cloudy, there is no swelling of the
cornea (corneal edema), and the optic nerve shows no
cup. In other words, there are absolutely no signs of
glaucoma.` But what about the high pressure of 30? The doctor
measures the patients CCT to be well above normal.
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` Therefore, the doctor may safely conclude that
this child does not have glaucoma and that the
elevated pressure reading is an artifact brought on
by the thicker cornea often seen in children whohave had cataract surgery.
` Management : The doctor probably should not be
absolutely certain and dismiss this outright.
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` It may be more prudent to see this child again in
the not too distant future to recheck the value and
make sure that none of the other signs of
glaucoma (e.g. optic nerve cupping
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` A Child with severe congenital glaucoma has a
routine follow-up examination.
` The child is on 3 different antiglaucoma eye drops,
and has a pressure of only 15. Is the glaucomawell controlled? The CCT turns out to be low (thin
cornea), and the optic nerve cup is bigger than the
last visit. It may very well be that the glaucoma is
not adequately controlled and that the pressurereading is a falsely low value due to the thin
cornea. Further treatment may be required.
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` The use of corneal pachymetry in the
management of patients at risk for or with
glaucoma is becoming increasingly recognized as
important and necessary. Interpretation of theinformation is complex and requires a careful
consideration of all factors involved in assessing
the childs disease.
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` I s know risk factor for glaoucoma
` (Least than 555 micron)= thinner corneal (
Primary open angle gloucoma ) POAG
` Thickness of Corneal affect the tonometricreading.
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` Device used to measure the apparent thickness
of the cornea.
` Several Teachniques
` A. Optical` B. Ultrasonic principle
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` Figure 6-4. Pachymeter.A
pachymeter (Pocket Pachymeter,Quantel Medical, Bozeman, MT)
is an ultrasound device that mthe
easures cornea thickness by
determining the time it takes for asound wave to reflect off inner
surface of the cornea.
Measurements are taken by
placing an anesthetic drop on theeye and gently touching the probe
to the surface of the cornea.
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figure6-5. Pachymetry. Corneal thickness is measured by
administering an anesthetic drop to the eye and then
gently placing the pachymeter probe against the outersurface of the cornea.
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