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Question: What’s normal corneal thickness and why do we check it?
Answer: Normal corneal thickness is about 540nm (half of a millimeter). Thickness is checked with a handheld ultrasound device called a pachymeter.
We check corneal thickness mainly for two reasons:
1. People with thin corneas (500 or less) are at a higher risk for having glaucoma. The mechanism for this is not entirely clear.
2. Cornea thickness allows us to callibrate our applanation tonometer readings. The goldman tonometer (the device with the blue light on the microscope) checks eye pressure by pushing on the cornea. This is analogous to kicking a car tire to estimate the air pressure. However, if you drive a truck with a thick rubber tread on the tire, the tire “feels” harder when you kick it. Likewise, if you have a thick cornea, the pressure reading seems higher than it really is.
There are many other uses for corneal thickness, such as determining/following corneal edema and evaluating patients for refractive LASIK surgery.
Comments and Feedback
13 Comments
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Is normal 540 nm or did you mean 540 mm?
Comment by Karri — May 6, 2009 @ 5:05 pm
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Um, nevermind. I figured it out. I’m sorry I said anything.
Comment by Karri — May 6, 2009 @ 5:16 pm
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thaaaaaaaaaaaaaaanks
Comment by fadi — August 13, 2009 @ 3:44 am
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Actually even not nm, but μm !!!
Comment by Kilometer — August 20, 2009 @ 6:16 am
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corneal thickness about three fifths of a millimeter in the center and reaches to one millimeter at the periphery
Comment by Dr.A.G. Daudpota — February 25, 2010 @ 11:16 am
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I had a Dr. tell me my left cornea measured in the high 600’s. What does that mean? He immediately told me I had Fuch’s dystrophy. Another Dr. said I don’t. What other things can a thicker cornea mean?
Comment by Cheri — April 19, 2010 @ 10:36 am
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Please let me know how much min thickness of cornea should be left after lasik surgery
Comment by Aarti — November 29, 2010 @ 1:26 am
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hi, i recently visited the hospital for a pre-checkup for lasik. They asked me to remove my soft toric contacts and wear glasses for a week before the checkup. But my doctor forgot and gave me an appointment within that week. So on the day of my appointment i wore glasses only for 5 days. My corneal thickness measured 496 and 498. So she said we will check again after 5 days and measure the thickness. I really want to get lasik done. But am worried whether i will reach 500 microns for both eyes even after 5 days waiting. Please respond.
Comment by swathi — December 21, 2010 @ 1:11 am
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I have been doing Ophtholmology as certified tech, surgical tech, and a CEBT for about 20yrs. when i was working for a Dr. in San Antonio when a person came in to see if they met the criteria for lasik’s and they were wearing contacts, we would ask them for how long have they been wearing cl’s and if they could stay out of them for 2week or 3 so that the cornea would allow its self to come back to its normal shape. By doing this gives you a more accurate corneal photography.make sure that they get a base line to see the change after 2 to 3 weeks. People who wear hard cl’s is best to stay out of them a month.
Comment by James — February 11, 2011 @ 1:13 pm
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Hello,
Does the corneal thickness change from one reading to another?
Comment by Liz Snavely — August 12, 2011 @ 9:08 am
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6/9/2011
good after sir ,i had an eye test on 01/11/2010 for laser treatment, but doctor told me that i have a 426 and 432 micron left and right eye .they told it is not possible for treatment so ,continue with ur eye glass,now the days are passed now my microns wheather any changes will happen or not.plz respond me as soon .
Comment by prathap — September 6, 2011 @ 3:17 am
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if u hv thin cornea u may be suffering from keratoconus.. U should go for c3r operation. Im suffering from keratoconus n goig for this operation in center for sight. Safderjung. B 5/24. Delhi.
Comment by sunita — January 1, 2012 @ 9:49 am
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