Pachymetry
What is it?
Pachymetry is a diagnostic procedure often carried out during the screening process. It measures the thickness of the cornea – which also determines other parameters of the eye, such as eye pressure. Specifically, a pachymeter measures the thinnest point of the cornea.
Corneal pachymetry can be mapped using optical devices such as tomography scanners – MS-39, Pentacam, Orbscan, and Galilei. However, the gold standard for pachymetry measurement is an optical coherence (OCT) scanner.
Pachymetry is a vital step, particularly if there is reason to believe the patient suffers from glaucoma or keratoconus.
Types of Pachymetry
There are three main types of pachymetry:
Hand-held ultrasound probes: This type of pachymetry takes readings to measure the thickness of the eye by placing a hand-held probe over the eye. A topical anaesthetic will first be administered to each eye to numb it for approximately 15 minutes. The optometrist will then apply the probe to the surface of the eye to take the readings.
Very high-frequency (VHF) ultrasound 3D scanning: Again, the patient’s eyes will be numbed using anaesthetic drops before their eyes are positioned over a watertight rubber eyepiece. A saline solution (artificial tears) will then fill the eyepiece and the patient is asked to open their eyes. The scanner takes a number of map-like pictures where different colours represent the different thicknesses across the cornea. Some optical devices will also measure the epithelium.
Find out more about Very high-frequency digital ultrasound
Optical pachymetry devices: These devices feature a padded chin support where the patient places their head and an examining instrument. The examining instrument is aligned with the patient’s eyes and, like VHF scans, it takes several multi-coloured map-like pictures that show the thickness of the cornea. Again, some devices also measure the epithelium.
Pictures taken during a pachymetry procedure will be added to the patient’s medical record.
What are the Benefits?
Having a precise impression of the thickness of the cornea and epithelium is an important consideration when determining the safety and suitability of Laser Eye Surgery. Using a pachymeter and a topography device provides accurate data on the thickness of the cornea and ensures it is within the safety limits for treatment. Your surgeon uses the pachymetry measurements to determine your suitability for different kinds of Laser Eye Surgery procedures.
The most accurate pachymetry device – the Artemis Insight 100 VHF digital ultrasound scanner – is only available in a handful of clinics around the world – including London Vision Clinic.
What will I feel?
Some types of pachymetry will require direct contact with the eye: the use of a probe in hand-held procedures, and the eye bath during VHF digital ultrasound scanning. However, anaesthetic drops are used to numb feeling in the exposed area of the eye. Furthermore, VHF digital ultrasound scanning does not require any instrument to touch the eye directly.
In optical pachymetry scans, the patient feels nothing (as in a topography/ tomography scan).
