High Precision Wavefront Sensor for Ophthalmological Applications

Laser eye surgery or laser vision correction commonly as referred to as LASIK (1), has become very popular in recent years. Worldwide, 28 million LASIK procedures have been performed since 2009 (2) 11 million of which have been performed in the United States alone since 2011 (3). With the increase of LASIK popularity, there has been considerable discussion concerning the visual impact of correcting the higher order monochromatic aberrations of the eye pupil (e.g. astigmatism, spherical aberration, and coma). For correcting the high order aberrations, the demand for high precision sophisticated instrumentation for the clinical evaluation has increased. Currently, there are a few instruments that measure aberrations and are referred to as aberrometers or wavefront sensors. The aberrometer devices typically represent the aberrations as an ocular wavefront-error map at the corneal or pupil plane. Among these aberrometers are the Tscherning aberrometer (4), Spatially Resolved Refractometer (SRR) (5,6) Retinal ray-tracing (7) and the Shack-Hartmann sensor aberrometer (8). The Shack-Hartmann sensor aberrometer is currently the most commonly used.

Lartec Inc. proposes high precision wavefront sensors with performance projected to exceed that of the Shack-Hartmann aberrometer. Lartec Inc’s proposed wavefront sensor should give high accuracy in measuring high order monochromatic aberrations. This will help opthamologists gain higher rate success in LASIK procedures as well as aid manufacturers and optometrists in designing more accurate customer made RGP contact lenses, intraocular lenses (IOLs), and eye glasses.

The Shack-Hartmann wavefront (13) sensor has originally been used in astronomical applications (14,15,16,17), but its applications have been extended further for lens design (18).

In astronomy, wavefront sensors are used to measure the wave front distortion results from atmosphere turbulence (14-17); the measured distortion is used to correct the images. In ophthalmic applications, wavefront sensors are used to test the eye's pupil. If the eye’s retina reflection through the pupil is flat, then the eye is a perfect optical system; if the reflected light out of the retina through the pupil is not a flat plane and consists of irregular curved shapes, then the eye is not a perfect optical system. The wavefront measurements are used to design the appropriate eye glasses.

Our new wavefront sensor is based on deflection sensors used in nondestructive testing instruments such as atomic force (19-21) and laser-ultrasonic microscopes (23).

The use of deflection sensors with the appropriate tips enables these microscopes to measure variations, within a few nanometers, of topology variations. The deflection sensors are basically a partial block of a modulated surface probe beam followed by phase sensitive detection.

Here we used the same basic principles, but we are extending it into two dimensions using a novel design of a heterodyne receiver and simple Fourier techniques to enhance the sensitivity. In this proposal we emphasize the application toward ophthalmology applications, but in principle, the proposed instrument with a slight modification can be utilized for rapid nondestructive testing (NDT) in metrological applications.