What is Wavefront? The Most Advanced Wavefront Technology of Israen in Eye Examination

Wavefront technology developed for custom LASIK may soon be regularly used by ophthalmologists to better diagnose vision problems in eye exams, potentially rendering the familiar eye chart obsolete.

With this conventional approach, the information you provide to the ophthalmologist is very subjective, relying more on what you think you see rather than what you actually see. But wavefront measurements are objective, as vision errors can be automatically determined by the way light waves travel through the eye.

One day, these detailed wavefront measurements could replace conventional eyeglass or contact lens prescriptions, which only describe vision problems in terms of myopia, hyperopia, and astigmatism of the eye.

Just as custom LASIK (or "wavefront-guided") has the potential to provide sharper vision compared to conventional LASIK, glasses and contact lenses produced with this advanced technology may also provide clearer vision than standard lenses.

What is Wavefront Eye Examination?

So what does "wavefront" actually mean?

The types of distortions that this wavefront captures as it travels through the eye provide valuable information about vision errors and how to correct them.

What is Wavefront Technology (Aberrometry)?

Wavefront and High-Order Aberrations

Previously, with conventional eye testing methods, only low-order vision errors could be diagnosed and treated. High-order aberrations such as coma, trefoil, and spherical aberration were largely overlooked by eye care professionals because their impact on vision was thought to be insignificant at the time and because there were no feasible means to accurately identify or correct them.

Now, as high-order aberrations can be accurately identified using wavefront technology and corrected with new types of glasses, contact lenses, intraocular lenses, and refractive surgery, they have become more important factors in eye exams.

High-order aberrations are beginning to receive more attention as they have been identified as sources of visual side effects after LASIK surgery and other types of refractive surgery — causing phenomena like halos, ghost images, and other visual symptoms.

New wavefront-guided laser beams used in vision correction surgery can reduce some high-order aberrations, thereby improving visual performance, especially for low-light activities like driving at night.

How is Wavefront Measurement Performed?

With most aberrometers, you rest your chin on a chin rest. Next, you are asked to look into the device and focus your eyes on a light point. After a few seconds of silence (no feedback required), the wavefront measurement is complete, and a wavefront map of your eye will be printed out for your eye care professional.

In general, aberrometers use a three-step process:

1. Since the wavefront passes through the opening at the front of the eye (the pupil), your pupil diameter is measured. This measurement is used to infer the shape of the reference wavefront representing a theoretically perfect eye with the same pupil size as yours.

2. A beam of light is projected into your eye and reflected back by the retina. The wavefront of this reflected light is captured by the aberrometer. Since no eye is optically perfect, all such wavefronts will contain at least some distortion.

3. A map of the aberration of the eye is created by comparing the shape of the obtained wavefront with a pre-programmed reference wavefront, measuring all the differences between the two wavefronts. Then, your eye's wavefront map, sometimes referred to as an "optical fingerprint" because no two eyes produce the same exact map, is created.

Traditional eye exams using technology with trial lenses can be time-consuming and rely on subjective feedback from the patient.

Wavefront eye exams are automated and objective, measuring vision errors in just seconds and in much greater detail.

What Does Your Eye's Wavefront Map Mean?

When you start interpreting the results of your eye's wavefront map, remember that the reference shape used for comparison is flat or two-dimensional.

Although no eye is perfect, the theoretically perfect wavefront map of an eye is a flat plane. Note how this three-dimensional shape represents vision errors changing to nearly flat after the eye is corrected with wavefront-guided LASIK.

The actual three-dimensional wavefront map of your eye is created by comparing it with this theoretically perfect flat wavefront map. The three-dimensional distortion occurring in the actual wavefront map is based on how individual light rays are altered as they pass through the eye.

Defects in the cornea and lens can alter the path of light rays by causing them to speed up, slow down, or bend incorrectly (refraction).

Based on the various patterns that can appear on the wavefront, over 60 different aberration shapes have been identified and classified as vision errors.

Wavefront Measurement

Defined by Dutch physicist Fritz Zernike in 1934, this polynomial is well-suited for this task because it is designed to meet the requirements of a circle.

This finding is presented in the form of a Zernike prescription and a topographic map, a detailed drawing of the shape of the aberration wavefront. Together, they create an aberration map or unique "optical fingerprint" that details the vision errors of the eye.

How Your Wavefront Map is Used

The wavefront map is a complete, accurate description of every aberration affecting your eye. The ophthalmologist uses your wavefront map as a blueprint to custom design your vision correction method, whether it is refractive surgery like LASIK, intraocular lenses, contact lenses, or eyeglasses.

Remember that you can never achieve a perfect wavefront, as no eye is perfect. Even if you are diagnosed with certain high-order aberrations, this is not necessarily a cause for concern unless the level of aberration causes significant vision problems such as difficulty seeing at night.

The visual performance of the patient's optical system (eye) is based on the measured aberration indices, divided into corneal and internal components.

References

1. Maeda, N., 2009. "Clinical Applications of Wavefront Aberrometry - A Summary." Clinical and Experimental Ophthalmology, 37(1): pp.118-129.

2. Salés, C. and E. Manche (2015). "Comparison of Eye Aberrations Measured by Fourier-Based Hartmann-Shack Aberrometer and Zernike-Based Tscherning Aberrometer Before and After Laser In Situ Keratomileusis Surgery." J Cataract Refract Surg 41(1): 1820-1825.

3. Ohlendorf, A., et al., 2020. "Enhancing Digital Workflow for Measuring Refractive Errors." Clinical Medicine Journal, 9(1): pp. 2205.

4. Jinabhai, A. (2019). "Custom Aberration Control Measures for Patients with Keratoconus Using Contact Lenses." Clin Exp Optom 103(1): 31-43.

5. Kumar, P., et al. (2019). "Is There a Difference in Visual Performance and Optical Quality Between Different Contact Lens Correction Methods in Patients with Keratoconus?" Contact Lens and Anterior Eye, S1367-0484(20):30052-30057.

6. Hoy, L., 2019. "Decoding the Corneal Reshaping Process with Ortho-K." Lecture for CCLSA Victoria.