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What is a Corneal Pachymetry?
Corneal pachymetry involves measuring the thickness of the cornea. Eye doctors do this by using a pachymeter.
Pachymetry is important in corrective eye surgeries, like laser in situ keratomileusis (LASIK), which involves the cornea.
Measuring corneal thickness allows eye surgeons to determine eligibility for certain procedures. It also helps avoid any potential complications.
Pachymetry will also tell your surgeon if you have any inflammation or swelling in your cornea.
For example, people with Fuch's Dystrophy may have built-up fluid in their cornea, which can make it swell. Those who wear contact lenses are also prone to swollen corneas.1
Such defects are difficult to see using a microscope. Pachymetry can help diagnose corneal swelling.
Pachymetry in Glaucoma Investigation
More recently, pachymetry has become important in glaucoma investigation.2 Glaucoma is characterized by increased eye pressure, also known as intraocular pressure (IOP).
Studies show a close relationship between central corneal thickness and the risk of developing glaucoma.3 Increased pressure in the eyes can damage your optic nerve fibers. This can result in primary open-angle glaucoma or vision loss.4
Pachymetry in LASIK Surgery
In the case of LASIK surgery, your surgeon will perform pachymetry to ensure your cornea has enough tissue to allow for corneal flap creation.
People with thin corneas are prone to complications during corrective eye surgery. They may require alternative procedures.
The main advantages of pachymetry include:
- Ease of use
How is a Pachymetry Performed?
There are two types of techniques used to determine corneal thickness: ultrasound and optical.
As the name suggests, this procedure uses ultrasonic pachymeters to measure the central corneal thickness (CCT). It's considered cost-effective and convenient due to its portability.
Ultrasound pachymetry involves a probe that comes into contact with the eye as it measures CCT. A probe is a blunt surgical device used to examine an area of the body.
Once your eye doctor applies anesthesia to your eyes, you'll feel the effects within 15 minutes or less.
They will then use the probe to touch your cornea and take measurements without causing any discomfort.
Results from contact ultrasound pachymetry are instant. Your doctor will analyze them and discuss risks and expectations with you.
Eye experts have pointed out some notable downsides of this procedure.5
- Mildly invasive and requires topical anesthesia to eliminate pain or discomfort
- Success depends on your examiner's experience in using the technology
- There is a high risk of inaccuracy if the probe is poorly positioned or shifts when measuring corneal thickness
Optical pachymetry eliminates the downsides of ultrasound. The first difference is no contact between the measuring device and the eye. Eliminating this contact makes the procedure easier and safer to perform.
In many cases, optical pachymeters are attached to a slit lamp. This is a microscope with a bright light used to examine eye structures.
Other optical pachymeters use specular microscopy.6 This technique enables rapid diagnosis of the corneal structures.
Specular microscopy can reveal abnormalities in the cornea. This includes irregular cells, a common occurrence in people with iatrogenic corneal endotheliopathy.7
A notable optical pachymetry procedure is the optical coherence tomography or OCT. It uses light waves to examine distinctive structures in your eyes. This includes corneal thinning in keratoconus patients.
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Why Does Corneal Thickness Matter?
Corneal thickness is significant in optometry. Most notably, it influences diagnosis and outcomes in some eye conditions.
According to Ocular Hypertension Treatment Studies (OHTS), there's a connection between eye pressure readings and corneal thickness.8
For people with thin corneas (less than 540 microns), there is a higher chance of low eye pressure readings even when the pressure is significantly high.8
This is dangerous because high eye pressure is a glaucoma risk. If not detected early, it may lead to vision loss.
It's also possible to record high eye pressure readings in people with thick corneas, even if that's not the case. This is common, especially when using traditional measuring devices.
Such misdiagnosis can lead to ineffective treatment and other complications during and after surgery.
In LASIK surgery, a thick cornea is necessary for your surgeon to create a thick flap.
Your surgeon will also need room to remove tissue from the cornea. Ideally, they will still have enough room for effective healing or repeated procedures such as LASIK enhancement.
If you have thin corneas, your surgeon will present alternative options that explore the corneal epithelium instead of the corneal tissues. These may include:
Thin Cornea Complications
Having a thin cornea is normal, but the cause is not well understood. Limited research suggests the role of hormones. It notes that females are more likely to have thin corneas.9
Thin corneas become a problem when eyes develop vision issues that require a thick cornea to resolve. For example, refractive eye surgeries like LASIK.
Your doctor must consider your corneal thickness when creating a treatment plan.
If they don’t, you may be at risk of the following complications during and after treatment:
- Keratoconus (outward bulging of the cornea due to weak structures)
- Corneal ectasia (thinning of the cornea)
- Poor vision
- Vision loss
- Corneal perforation
- Flap folds
Who Should Get Their Corneal Thickness Measured?
Measuring corneal thickness is important for the successful treatment of glaucoma and other refractive errors like:
You should have a pachymetry test done to ensure your cornea is thick enough for LASIK surgery.
Also, ask about a pachymetry test if you notice significant vision changes. Some corneal abnormalities, such as keratoconus, can affect your vision.
You can also measure corneal thickness to assess the effectiveness of treatment for corneal swelling.
Pachymetry is a safe, accurate method for assessing the progression of many eye problems.
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