Pachymetry is a quick, non-invasive diagnostic test used in eye care. It provides valuable information about the eye’s structure. This article will explain what pachymetry measures and why this measurement holds significance for eye health.
Corneal Thickness Measurement
Pachymetry measures the thickness of the cornea. The cornea is the clear, dome-shaped outer layer at the front of the eye. It acts as a protective window and helps focus light onto the retina. The average central corneal thickness (CCT) ranges from 540 to 550 micrometers. While this measurement alone does not indicate a problem, it provides context for other eye health indicators.
Why Measuring Corneal Thickness Matters
Measuring corneal thickness is important for assessing eye conditions and planning procedures. It influences the accuracy of intraocular pressure (IOP) readings, which measure the fluid pressure inside the eye. Devices like the Goldmann Applanation Tonometer are calibrated for average corneal thickness. If a person has a thinner cornea, their true eye pressure might be higher than recorded, potentially masking glaucoma risk. Conversely, a thicker cornea can lead to an overestimation of pressure. Understanding corneal thickness helps eye care professionals adjust IOP readings for greater accuracy and better management of eye conditions.
Additionally, corneal thickness is a factor in evaluating suitability for refractive surgeries, such as LASIK and PRK. These procedures reshape the cornea by removing tissue to correct vision. Sufficient corneal thickness is necessary to ensure enough tissue remains after the procedure for safety and good outcomes. A minimum corneal thickness of at least 500 micrometers is often required before refractive surgery to prevent complications such as corneal thinning and bulging.
Pachymetry also helps monitor other eye conditions. It can help detect changes in thickness from corneal swelling (edema) or corneal dystrophies. In cases of keratoconus, a condition where the cornea progressively thins and bulges into a cone shape, pachymetry helps detect this abnormal thinning.
How Pachymetry is Performed
Pachymetry is performed using two main methods: ultrasound pachymetry and optical pachymetry. Both methods are quick and provide immediate results.
Ultrasound pachymetry involves a small, handheld probe that gently touches the cornea. Anesthetic eye drops are applied to numb the eye before the procedure. The probe emits ultrasound waves, and the device calculates thickness based on the time it takes for the waves to return.
Optical pachymetry, often using Optical Coherence Tomography (OCT), is a non-contact method. During this procedure, the patient rests their chin on a support while the machine uses light waves to create cross-sectional images of the cornea. This allows for precise measurement without physical contact.