If you have considered LASIK in the past but were ineligible because of having thin corneas, it is important to understand why and know what alternatives to LASIK are available.
What is the cornea?
The cornea is the clear, dome shape outermost layer of the eye. The cornea shields the eyes from harmful substances and contributes about 75% of the eyes total focusing power.
How is the Cornea Measured?
A pachymeter is used to measure the thickness of the cornea to ensure there is sufficient tissue for refractive correction. There are two types of pachymeters:
- Ultrasound pachymeter
- Optical Pachymeter
Both work by placing the device on the cornea to measure its’ thickness.
What is a thin cornea?
The average corneal thickness is 560 microns. Any cornea that is less than 500 microns thick is said to be a thin cornea.
What causes corneas to be thick or thin?
There are many reasons why the corneas could be thick or thin which include but are not limited to:
- Previous refractive surgery
- Ongoing diseases (example: any corneal infections)
How is the information used?
Depending on the thickness of the cornea, eye doctors can determine if a patient is a good candidate for LASIK and check for eye conditions.
Why should thin cornea patients not undergo LASIK?
Patients who undergo LASIK with thin corneas run the risk of developing Ectasia. Ectasia is a form of Keratoconus, an eye disease that affects the structure of the cornea. This occurs when the round shape of the eye becomes cone shaped resulting in vision problems. Ectasia can be treated with Rigid Gas Permeable contact lenses or a corneal transplant if needed.
The criteria that excludes candidates from LASIK includes:
- Abnormal Topography: Topography maps the surface curvature of the cornea. An abnormal topography is often a red flag of other eye conditions, which could cause the patient to be excluded as a candidate.
- Pachymetry: There is no magic number for how thick the cornea should be but it is essential that enough cornea be present after the surgery. There should also be enough cornea to allow for retreatment if necessary.
- Refractive Error: A patient with a high refractive error will need more cornea removed during LASIK than a patient with a lower refractive error. Therefore, it is necessary that they have a thicker cornea.
If you are deemed a non-candidate for LASIK, PRK may be a good alternative. This is because PRK is performed without a corneal flap, which means less cornea is needed.
Only a LASIK surgeon can deem a person to be a good candidate. If you are considering refractive surgery in the Raleigh/Durham area of North Carolina, consider Raleigh Eye Center. For more information or to schedule a consultation, visit us online or call (919) 876-2427.