We all live in the jet age. We want everything to happen immediately including freedom from glasses by getting laser vision correction surgery. I often hear patients tell me- Lasik is just a laser and not a surgery; so what is the big deal about it- I should be able to get it done whenever I want! As a Lasik Surgeon my advice is – Yes, you can plan it whenever you want as long as you know that your eyes parameters are suitable for it and you have scheduled few days for the procedure and the recovery after lasik surgery. There are several important aspects especially pertaining to the suitability for laser vision correction procedure. A detailed pre-LASIK evaluation is mandatory before laser vision correction.

As a part of pre-LASIK check-up, the pupil in the center of the eye is dilated and it takes a day to get back to its normal size and shape. A dilated pupil can interfere with the laser vision correction procedure. Hence, the earliest a pre-LASIK evaluation can be done is at least a day prior to the lasik surgery.

Through these blogs, I wish to re-emphasize the importance of pre-Lasik evaluation. I will be writing a series of blogs to highlight the importance of each of the tests that are conducted as a part of pre-Lasik evaluation.

Besides a detailed history, proper vision and eye power check, pre-LASIK check-up involves a series of tests-

  • Corneal Thickness by Pachymetry
  • Corneal topography( Corneal Maps)
  • Pupil Diameter ( in dim and light conditions)
  • Eye ball measurements like- Horizontal diameter of cornea, length of eye ball, depth of front part of the eye
  • Ocular Aberrations
  • Dry Eye Tests
  • Muscle balance testing
  • Ensuring healthy cornea( healthy endothelium and the other layers)
  • Dilated Retina check-up

The present blog will make sure that you have a complete understanding about corneal thickness- why it is done, how it is checked and why it is important?

Why do we need to measure the corneal thickness before lasik?           

Laser vision correction procedures make the cornea thinner. The amount of thinning is dependent on the patient’s eye power.  Thin corneas can become even thinner and very weak after the lasik treatment procedure and develop problems like post-LASIK ectasia (bulging of the cornea due to weakness and this induces high power). Hence, Pachymetry is a vital test before lasik. We need to ensure 2 things when we are considering suitability with respect to corneal thickness.

  • Corneal thickness prior to the laser vision correction:

If it is too less prior to the procedure, then usually we advise against the laser vision correction procedure.

If the thickness is borderline, then we can consider safer laser vision correction procedures like PRK, SMILE Lasik (given that other parameters are normal).

  • Correction of high powers leaving cornea thin:

Initial corneal thickness is good but is likely to reduce a lot after the laser vision correction procedure due to correction of higher powers. In these situations either we advise against the procedure or advice correcting lesser power or advise alternatives like ICL (Implantable Contact Lens).

How is the corneal thickness measured?

Corneal thickness is usually measured by 2-3 different instruments to ensure that there is no error. One of the commonly used methods is with the help of ultrasound technology especially modified for eye measurements. A small pencil shaped probe is touched on the cornea and that gives the reading (Figure 1).

Two other methods employ light based technology. One of them is called OCT (Optical coherence tomography) as seen in Figure 2 and the other is with the help of Scheimpflug corneal topography system. These 2 are non-touch methods and quickly give the readings.

What information we try to gather?

Through this test we try to find the corneal thickness in the center, at the thinnest point, the variability of thickness at different points on the cornea (Figure 3) and the difference between the two eyes.

I know all this must appear very confusing! Let me try to simplify it. We are trying to rule out any pre-existing corneal disease. So we want to make sure that the readings in the two eyes are not very different, the thinnest location is not far from the center and the difference in corneal thickness at different points is not of concern. Some of the corneal diseases like Keratoconus can be picked up on these tests and they may have only early signs. One of the important clues is reduced corneal thickness and presence of thinnest point away from the center of cornea.

How we put all this information together?

First and foremost, we want to determine if laser vision correction is safe for your eyes or not and secondly which of the laser vision correction procedures like PRK, LASIK, Femto Lasik or Relex SMILE Lasik will best suit your eyes.  Corneal thickness measurement is assessed keeping in perspective patient’s age, eye power, previous history, and corneal topography maps.

Besides trying to give you a glass free future we have the utmost responsibility to ensure long term safety of your eyes to the best of our capability. Corneal thickness is a very important test to determine suitability for lasik. It is also assessed keeping in perspective other tests and collectively a decision is made for the suitability and most suitable type of laser vision correction procedure for your eyes.

 

We all live in the jet age. We want everything to happen immediately including freedom from glasses by getting laser vision correction surgery. I often hear patients tell me- Lasik is just a laser and not a surgery; so what is the big deal about it- I should be able to get it done whenever I want! As a Lasik Surgeon my advice is – Yes, you can plan it whenever you want as long as you know that your eyes parameters are suitable for it and you have scheduled few days for the procedure and the recovery after lasik surgery. There are several important aspects especially pertaining to the suitability for laser vision correction procedure. A detailed pre-LASIK evaluation is mandatory before laser vision correction.