Aberrometers—Marketing Hype or Worth Waiting For?

If you are considering refractive surgery and have been keeping up on the latest, you have heard of aberration technology. Current laser surgery changes the shape of the cornea to correct for refractive errors such as myopia, hyperopia and astigmatism. Since the eye is not a perfect sphere, after the cornea is altered, light continues to be bent by the surface of the cornea, elements within the cornea, elements within the media of the eye and ends up focusing on a non-spherical retina. All of these elements differ per individual. Aberration technology involves using near infrared light from an "aberrometer" to determine where your individual aberrations occur. Near infrared is used because it has advantages over visible illumination: it is more comfortable for the subject, pupil dilation is not essential, and light exposure can be lower due to the higher reflectance of the eye fundus and the better sensitivity of most of the photodetectors at this wavelength. The aberrometer sends the data to the "wavefront guided" laser and you receive a "custom" ablation of your cornea which supposedly yields better refractive results. The problem is that the eye is in a dynamic state - it is constantly changing. Today's aberrations will differ tomorrow, next week, next month and years from now. In quantum physics, one principle states that the actual act of measuring something affects the measurement. Ever notice that in certain situations you blink and things blur and then clear again on the next blink? Every blink you make changes the tears - tears are created, break-up and are washed away all within the space of a blink and this changes the aberrations of your eye significantly. The act of measuring the aberrations of the eye can affect the aberrations of the eye - with your head in an enclosed space your focus mechanism goes into action, changing the wavefront of the eye. Also the near-infrared light the aberrometer uses may affect the accuracy of the measurement and the eye may also focus near-infrared light differently than it focuses everyday light, flourescent light, etc. While doctors achieve 20/20 or better vision with non-aberration technologies and the same results with scanning or spot lasers, what are the real benefits of this procedure in the short term and do you get what you pay for?

Study #1 - found that in myopes (nearsighted people) aberrometer measurements were similar to techniques your doctor uses to measure your vision, including accuracy and repeatability (autorefractor) (OVS, Vol. 80, No 1, January, 2003)

Study #2 - different aberrometers measure differently - no two aberration measurements are the same. Often the ability to measure and correct aberrations exceeds the eye and brains ability to discriminate between them.

Study #3 - Images captured using different lights showed noticeable differences. The largest variations may increase as an eye ages. Different wavelengths, however, provide aberration estimates within the experimental error.

Study #4 - Laser numbers (your prescription) can be predicted from teh eye's optics alone and predicted better with computed methods such as infrared aberrometry.

Study #5 - little if any variability in the magnitude of aberrations of the eye is correlated with refractive error.