What is the normal corneal thickness?

The thickness of each person's cornea may be different. The thickness of a person's cornea is related to many factors. First of all, it is related to age. For example, a child's foot membrane is thicker than an adult's. Even for the same person, the thickness of the cornea will change slightly during the day. For example, after a person has enough sleep, the thickness of the cornea will increase. In addition, it will be affected by wearing contact lenses, etc. So what is the normal range of human corneal thickness?

What is the normal corneal thickness?

The transparent front part of the outer layer of the eye wall. It is round in shape, occupies one-sixth of the outer layer area, is about 1 mm thick, and is mainly composed of avascular connective tissue. The front is slightly protruding and curved like a sphere, which has a refracting effect. The cornea contains abundant sensory nerve endings, and any slight stimulation, damage or inflammation can cause pain and tearing. If you touch the cornea lightly with cotton, it will cause a protective reaction of closing the palpebral fissure, called the corneal reflex. The junction of the cornea and sclera is called the limbus. The blood vessels at the cornea's edge and the aqueous humor inside the eyeball supply nutrition to the cornea. The curvature of each diameter of the normal cornea is consistent, so the refractive index is the same. If the curvature is not uniform, it will cause abnormal refraction, called astigmatism.

Excimer laser surgery uses excimer laser to perform refractive cutting on the stromal layer under the corneal flap, thereby reducing the corneal curvature in the pupil area to achieve the purpose of correcting myopia. It can correct myopia of 200 degrees to 2000 degrees. This surgery is currently a commonly used procedure for correcting high myopia. This surgery has high requirements for corneal thickness and is only suitable for adults whose myopia has been stable for more than two years. The normal corneal thickness is about 550 microns. If the cornea is too thin, excimer laser surgery to treat myopia cannot be performed. After laser surgery, the remaining cornea of ​​each patient must be retained to a safe thickness of 410 microns. If the remaining corneal thickness is less than 410 microns, it will be difficult to withstand the imbalance between the intraocular pressure and the atmospheric pressure, and keratoconus may occur, leading to the sequelae of severe vision loss! Before performing this operation, the doctor will accurately measure the thickness of the cornea to see if it is suitable for laser surgery.

Normal range of corneal thickness:

To measure the thickness of the entire cornea, we generally choose 9 measurement points for the cornea thickness, including the central cornea, paracentral cornea (1.5-2.0 mm from the center of the cornea), peripheral cornea (0.5-1.0 mm within the edge of the cornea), nasal side, temporal side, superior side, and inferior side. The normal whole corneal thickness range is as follows: (for reference only)

1. Central corneal thickness: the thinnest part of the cornea, with an average value of 0.5±0.04 mm (500±40 μm);

2. Paracentral corneal thickness: average value 0.58 ± 0.04 mm (580 ± 40 μm);

3. Peripheral corneal thickness: average value 0.69±0.04 mm (690±40 μm).