Traditional laser vision correction treats two patients with the same Refractive Errors essentially in the same manner because this treatment is based mainly on their refractive errors which are classified as lower order aberrations.
Higher order aberrations are optical imperfections or distortions that are measured using a wavefront of light as it passes through all the refractive surfaces of the eye. The main refractive surfaces of the eye which bend or focus the light are the cornea and lens. These higher order aberrations are measured using wavefront aberrometry. Every eye has optical imperfections that can affect the quality of your vision especially at night causing glare, halos, starburst and/or double vision. Higher order aberrations cannot be corrected with glasses.
In addition to correcting the lower order aberrations such as nearsightedness, farsightedness and astigmatism which are addressed in traditional laser vision correction, wavefront aberrometry was incorporated in the Excimer laser treatment in order to measure and give a 3D map of the pre-existing higher order aberrations which are unique for each patient like a fingerprint. These higher order aberrations can be treated by the computer- controlled Excimer laser to reshape the cornea and achieve a more optically perfect eye. The results of this wavefront – guided treatment are enhanced by correct registration of the eye in 3 dimensions and correct tracking of the eye during treatment referred to as Active Trak. This treatment, called custom laser vision correction, gives superior visual results as compared to traditional laser vision correction since it has the potential to treat refractive imperfections or higher order aberrations and diminishing unwanted visual effects especially those associated with decreased contrast sensitivity and night vision such as glare, halos, starburst and/or ghost images. Custom laser vision correction has the potential not only to improve the quantity of your vision (i.e. your vision measured as 20/20 on the eye chart), but also the quality of your vision to the extent that you can see even better than you could with glasses or contact lenses.
VISX Wavescan Wavefront System and iDesign System
The VISX Wavescan system was the first wavefront aberrometer to be FDA approved for custom laser vision correction in 2003. 94% of patients who had the custom laser vision correction procedure during the FDA clinical trials, achieved 20/20 or better vision. The trial participants were 4 times more likely to say they were very satisfied with their night vision following custom laser vision correction than they were with their glasses or contact lenses. The Wavescan was later upgraded to the iDesign Advanced WaveScan Studio System by VISX. The iDesign system, which was FDA approved in 2015, is superior to the Wavescan because treatment based on its results yields significantly higher contrast sensitivity and lower spherical aberrations. Once the wavefront analysis is obtained in the seated position preoperatively using the iDesign system, it gets automatically transferred to the VISX Star S4 Excimer laser for treatment to remove a predetermined amount of tissue from the inner corneal layer.
The VISX Star S4 Excimer laser that Dr Khouri uses also has the Iris Registration feature in addition to the 3D Active Trak technology. The shape and contour of the iris in your eye is unique. This is measured during the preoperative evaluation in a seated position. Another set of measurements is taken when you lie down on the laser bed prior to the beginning of the laser treatment. These two measurements are used as cross reference points to allow the laser to deliver the treatment as planned with a high degree of accuracy and precision by ensuring accurate alignment. This is especially critical when astigmatism is being treated as the position of the eye changes in 3 dimensional space from a standing to a lying position due to small movements of the eye muscles called cyclotorsion.