# What is Pachymetry?

Source page: https://www.kudretgozistanbul.com/en/blog/eye-diseases/what-is-pachymetry

**Author:** Kudret Eye İstanbul | **Medical Approval:** Op. Dr. Mehmet Ali Özdil | **Date:** 2026-09-06

> **Summary:** Pachymetry measures the thickness of the cornea to an accuracy of microns. It is a quick, painless test used to decide who is a safe candidate for laser eye surgery, to interpret intraocular pressure correctly in glaucoma, and to follow corneal conditions such as keratoconus.

## Quick Facts
- **What is measured:** Corneal thickness, in microns
- **Average central corneal thickness:** Around 540 to 550 microns (varies from person to person)
- **Duration:** A few minutes
- **Comfort:** The contact (ultrasound) method uses an anaesthetic drop, so the patient generally feels nothing; the optical method does not touch the eye
- **Methods:** Ultrasonic (contact) or optical (non-contact)

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## Why the Cornea Matters
The cornea is the outermost layer of the eye. It protects the eye and is the first place light is refracted, providing around two thirds of the eye's total refractive power. Its thickness and biomechanical integrity affect both vision quality and the success of some medical procedures.

## Why is Pachymetry Carried Out?

### Planning refractive (laser) surgery
- LASIK, PRK and SMILE reshape the cornea by removing tissue from its middle layer (the stroma).
- Safety depends on how much corneal tissue remains afterwards. If the cornea is too thin, the remaining bed may not resist the pressure inside the eye, leading to **post-operative ectasia**: the cornea bulges forwards and vision is permanently disturbed.
- Pachymetry is an absolute necessity before surgery and helps decide who is a suitable candidate.

### Diagnosing and following glaucoma
- Intraocular pressure readings are affected by corneal thickness.
- A thick cornea makes pressure read **higher than it is**, which can lead to a mistaken glaucoma diagnosis.
- A thin cornea makes pressure read **lower than it is**, which is more dangerous: a glaucoma patient can be missed and treatment delayed.
- Pachymetry lets the doctor correct the measured pressure. A thin cornea is also an independent risk factor for glaucoma progression.

### Managing corneal conditions
- **Keratoconus:** thickness maps identify the thinnest point and track progression.
- **Fuchs endothelial dystrophy:** measures the increase in thickness to follow oedema and treatment effectiveness.
- **After a corneal transplant (keratoplasty):** regular measurements assess graft health and possible rejection or oedema.

## Types of Pachymeter
- **Ultrasonic pachymeter:** after an anaesthetic drop, a small probe lightly touches the cornea and measures with sound waves. Very precise.
- **Optical pachymeter:** measures without touching the eye, using a Scheimpflug camera or optical coherence tomography (OCT). Quicker, more comfortable, and produces a thickness map of different points on the cornea.

The method is chosen according to the patient's situation and the doctor's preference; both give reliable results.

## Interpreting the Results
- Average central corneal thickness is generally around 540 to 550 microns, but varies with ethnic origin and individual differences.
- The result is not enough on its own: an ophthalmologist assesses it together with the rest of the eye examination, the intraocular pressure and the patient's complaints.

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## Frequently Asked Questions

**Q: Is pachymetry painful?**
A: No. With the contact (ultrasound) method an anaesthetic drop is used beforehand, so the patient generally feels nothing; the optical method does not touch the eye at all.

**Q: How thick should the cornea be?**
A: 540 to 550 microns on average, although this varies from person to person.

**Q: Why does pachymetry matter so much for laser surgery?**
A: Patients with a thin cornea may not be suitable for surgery; the measurement is always taken to reduce the risk of complications.

**Q: How long does the measurement take?**
A: Generally a few minutes.

**Q: Is pachymetry only for people who want to be free of glasses?**
A: No. It is also used to diagnose and follow conditions such as glaucoma and keratoconus.

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## References
- Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach, Doughty MJ, Zaman ML, Survey of Ophthalmology
- The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma, Gordon MO et al., Archives of Ophthalmology
- Glaucoma: diagnosis and management, NICE