Pachymetry: Measuring Corneal Thickness before LASIK

Measuring the Cornea with Pachymetry

What is the cornea?
Have you ever wondered about the clear, outer surface tissue that covers the front of your eye?
Yes, technically, it is known as cornea and can be considered as the "front door" of your eyes to the outside world.

Typically, the cornea is a dome-shaped covering and basic function is that it allows outside light into the eye and helps focus it on retina, helping you focus and see clearly. Any local injury, disease or genetic condition can make your cornea cloudy, distorted or scarred. If this happens, light cannot reach the rest of your eye as it normally does, eventually leading to vision problems such as blurred vision and / or blindness. If your cornea is injured or diseased, it can be very painful. Fortunately, however, due to the rapid advancements in the field of medical science, it is now possible to measure the thickness of your cornea and hence reduce the risk of any problems that may result later. One of such advancements is "pachymetry".

What is pachymetry?

Corneal pachymetry is the process of measuring the corneal thickness (usually in micrometers / microns). It is mainly of two types:

1-Ultrasound pachymetry: Corneal thickness is measured by means of an ultrasound probe
2-Optical pachymetry: Corneal thickness is measured by means of a small eye camera

Both ultrasonic and optical pachymetry are methods of measuring corneal thickness. Ultrasonic pachymetry is more reproducible, but optical pachymetry is especially helpful in measuring the depth or progression of corneal disease.

Pachymetry is the recommended way for knowing corneal thickness measurements because it offers several benefits such as:

  • It is reproducible
  • It is highly accurate
  • It helps one to take measurements anywhere on the cornea
  • Its measurements are not dependent upon patient fixation
  • It is simple & easy to use

When Pachymetry is used?
Pachymetry is generally used for the following:

  • To determine if the patient’s cornea is suitable for LASIK or should he / she opt for another variety of treatment
  • In routine eye exams when the doctor suspects any corneal abnormality
  • As an essential part of the glaucoma examination
  • To manage / treat various corneal diseases e.g. Fuch’s dystrophy, bullous keratopathy & keratoconus
  • After -surgery evaluation of patients undergoing corneal transplant
  • After -surgery follow-up and evaluation of corneal transplant rejection
  • Pachymetry can also assist in evaluating whether the current medical treatment is working well and is often an accurate means of assessing the progression of various eye disorders.

Relation of pachymetry with the LASIK surgery
Today, pachymetry is considered an integral part of the LASIK surgery as the thickness of cornea must be measured accurately to determine the suitability of the patient for the LASIK. For example, if the eye surgeon determines through pachymetry that the residual thickness of cornea is less than is 250 microns, it is advisable to avoid LASIK procedure because of the increased risk of various eye complications / side effects. In fact, as the LASIK removes tissue from the cornea, it is important to be certain that the cornea will retain a safe level of central tissue thickness. Therefore, most eye surgeons recommend leaving at least 275 or 300 microns so as to support the corneal flap.

Why a person with thin cornea is not a good LASIK candidate?
The answer to why a person with thin cornea is not a good LASIK candidate is simple. Since the cornea is made even thinner during LASIK surgery, an already thin cornea will reduce the natural function of cornea i.e. protection & focusing. In addition, evidence has suggested that in case of an abnormally thin cornea, risk of the following eye disorders is greatly increased:

  • Abnormal shaping of cornea (ectasia)
  • Blowing out effect is greatly increased

Alternative procedures for people with too thin cornea
If a patient has an abnormally thin cornea i.e. does not have the minimum safe level of cornea tissue thickness, the alternate laser vision correction procedures may be used: PRK: Photorefractive Keratectomy is the conventional type of laser eye surgery. In PRK procedure, the laser beam only affects the very surface of the cornea and, hence, the overall structure of cornea's structure is less modified than with LASIK surgery. This allows the surgeon to leave sufficient part cornea intact to protect against any eye injury or trauma in future.

Epi-LASIK: Epi-LASIK differs from conventional LASIK eye surgery as the very thin flap (called as epithelium) cut is so small that it does not go through the actual body of cornea. LASEK: The Laser Assisted Sub-Epithelial Keratomileusis (LASEK) combines PRK and LASIK technologies to treat the eye disorders. LASEK also cuts a flap in the eye and reshapes the exposed eye with a laser. There is less risk of hazing and more corneal tissue is preserved.

All in all, pachymetry does offer an exciting and accurate option for your eye doctor to accurately measure the thickness of your cornea and, hence, help you prevent from any complications or side effects during or after the LASIK surgery. It is, therefore, vital for you to remember its importance so that you could better know its benefits.

Did your surgeon measure your corneal thickness before LASIK? What where your results? Let us know below.

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