By: Stanley Teplick, M.D.
If you no longer want to wear glasses or contact lenses to treat your nearsightedness, farsightedness, or astigmatism, LASIK surgery is a great alternative. Rather than simply compensating for the corneal aberrations that cause these lower-order refractive errors, LASIK actually corrects the corneal aberrations, thereby providing patients with clear vision.
In order to correct the corneal irregularities that cause nearsightedness, farsightedness, and astigmatism, a surgical procedure is required. At Teplick Custom Vision, an NVISION Company, I perform LASIK surgery to help patients achieve clear, unaided vision. To be considered a good candidate for LASIK, patients must meet a number of requirements, including meeting the corneal thickness guidelines. In this blog post, I'll discuss LASIK and corneal thickness so patients understand why this requirement is so important.
The LASIK Procedure
Nearsightedness, farsightedness, and astigmatism are caused when the shape of the cornea is too flat, too round, or irregular. When the eyes are processing images, this can result in light being directed in front of or behind the retina, rather than directly on it.
During LASIK surgery, a flap incision is created in the outer, epithelial, layer of the cornea. With the flap open, the surgeon can then reshape the stromal layers of the cornea to achieve the precise shape upon which light can directly reflect off the retina and produce clear vision.
Why Is Corneal Thickness Important?
Because LASIK surgery requires the creation of a LASIK flap, patients must have a sufficiently thick cornea. If the patient does not have enough corneal thickness to support the flap, they would be more likely to experience LASIK complications such as corneal ectasia, a bulging of the cornea that can actually worsen vision. Since patient safety is the priority, LASIK should not be performed on thin or weak corneas.
Corneal Thickness Guidelines
After LASIK surgery, the patient should have a minimum of 250 microns of corneal thickness remaining. The surgery involves:
- About 160 microns of tissue for the corneal flap
- The removal of 12 to 14 microns per diopter of vision corrected
- To calculate how much corneal tissue you will have left after your LASIK surgery, I'd measure your corneal thickness with the corneal pachymetry test. During this test, patients stare straight ahead while the device is placed next to the eye and ultrasonic technology measures the cornea.
In addition, I'll measure the degree of your refractive error and the amount of prescription power needed to correct it. Then, I'll determine how much tissue will need to be removed to achieve improved vision. For example, if you have a -3.00-prescription power, 36 to 42 microns of corneal tissue would be removed during your LASIK surgery. Add this to the 160 microns for the corneal flap, plus the 250 microns that must be remaining after surgery, and you would need at least 452 microns of corneal tissue before LASIK to be considered a good candidate for surgery with a -3.00-prescription power. For most patients, the cornea is 540 to 550 microns thick.
Patients with natural thin corneas, and those with high prescription powers may not have sufficient corneal thickness for LASIK surgery. However, these patients may be good candidates for PRK surgery. Contact us today at 877-455-9942 to learn more about your vision correction options and to book a free LASIK consultation.