What do you need to know about pachymetry?
A pachymetry test is a simple, quick, painless test to measure corneal thickness. With this measurement, we can better understand the intraocular pressure reading and develop an appropriate treatment plan. The procedure takes just one minute to measure both eyes.
Pachymetry indicates the value of corneal thickness and is an investigation used in certain corneal refractive surgery procedures or in cases of glaucoma. It can be performed pre-operative, as an indication criterion for surgery, or post-operative, to measure certain post-operative values. Pachymetry can be performed using several devices, including the Nidek specular microscope and the Optopol OCT CT scanner, which also has a pachymetry function.
Pachymetry has traditionally been used to assess the functional state of the endothelial cell layer of the cornea. More recently, with the advent of refractive surgical techniques, corneal pachymetry is required to determine suitable candidates for ablation procedures. Furthermore, the identification of central corneal thickness (CCT) as an independent indicator of glaucoma risk has made corneal pachymetry to be a routine part of ophthalmic assessment. Pachymetry is an important part of the assessment and management of ocular hypertension and glaucoma.
What does pachymetry involve?
The examination is generally painless and non-invasive. For increased comfort during the test, anesthetic drops will be applied to the patient’s eye. A probe called pachymeter is placed gently on the front of the eye (cornea) to measure its thickness. Pachymetry can help in determining the diagnosis because corneal thickness has the potential to influence eye pressure readings. Depending on the device used to determine corneal thickness, the examination can take anywhere from a few seconds to a few minutes. The result will be generated by a computer which will continuously analyze the readings from different points on the cornea.
Pachymetry can be performed by two methods, ultrasound or optical techniques.
Ultrasound pachymetry: ultrasound pachymetry, as the name suggests, uses ultrasound principles to measure corneal thickness. This method uses portable devices. The biggest disadvantage of measuring corneal thickness by ultrasound is that the probe used to touch the cornea must be positioned perfectly. Any slight displacement and the reading may not be accurate. Some ultrasound pachymetry is designed more for glaucoma testing and includes built-in risk factor calculators.
Optical pachymetry: optical pachymeters vary by design. Some optical pachymeters are designed to be mounted on a biomicroscope that eye care providers use, called a slit lamp. Other devices can measure pachymetry using specular microscopy.
This device does not come into direct contact with the cornea. One type of optical pachymeter that has gained popularity is the OCT. OCT pachymetry also does not touch the cornea to make measurements.
OCT uses a principle called optical interferometry. Another method that uses imaging Scheimpflug is very good at obtaining more peripheral corneal thickness measurements, in addition to central corneal thickness, and at obtaining these measurements very quickly.
What can be diagnosed by pachymetry?
The pachymetry examination can be included in any type of examination for patients of all ages.
The specialist particularly recommends performing this test in the following situations:
- Patients at high risk of glaucoma;
- Patients suffering from corneal diseases;
- Patients preparing for crosslinking, corneal transplant or refractive
- To prepare and follow-up corneal surgery (corneal transplant)