Good Hope, Heartlands, and Solihull Eye Clinics

Corneal thickness & Intraocular Pressure (IOP)

David Kinshuck

Wwhy is corneal thickness relevant?

When the eye pressure is measured, the measurement taken by pressing the cornea...it is impossible to measure the pressure inside the eye without making a hole in it. So if the cornea is very thick or very thin, the measurement may be inaccurate.

We now know that corneal thickness influences IOP. This is a graph of the relationship, modified from Ko here. In reality, here is only a very approximate relationship between thickness and the pressure adjustment that would be ideal.

 

corneal thickness...a vauge relationship with iop

Thus if the cornea is very thin (say 400µ), the pressure may read 10mmHg. But the real or equivalent pressure (for the average eye of 560µ) would be 16mmHg. So the pressure in an eye with a thin cornea reads to low...the real pressure is higher. However, this is very approximate, as there is such a wide variation between eyes.

Similarly if you have Fuchs corneal dystrophy with a thick cornea, perhaps 640µ, the pressure may be 18mmHg...equivalent to 15 for a 560 (normal) cornea.

Goldmann tonometry is least influenced by thickness, air tonometry the most, blood flow tonometry in between. See here. Corneal curvature also influences pressure measurement.