WaveForm

Which is better “1 or 2”

This familiar phase has been used for over a century when conducting a subjective eye exam. The subjective exam is conducted by placing lenses of varying power in front of the patient’s eyes and asking the patient to subjectively identify the lens that provides the best vision, lens “1 or 2”. The same subjective method has been used for decades without any significant advances in the testing procedure. Although ophthalmic physicians are experts in the art of subjective refraction this method often leaves the patient confused on what response to provide. This can even result in the patient’s final Rx not providing the best visual correction.

Pictured Right: Subjective eye exam using the outdated Which is Better “1 or 2” methodology

It is now possible eliminate most of the confusion of the “1 or 2” eye exam.

Advances in technology over the past decade have brought significant improvements that allow the subjective eye exam to be revolutionized. One advancement involves the use of the Huvitz WaveFront Aberometer.  Similar in design to an autorefractor, it uses a wavefront of light to objectively measure the overall refractive power error of the eye. This is done by by mapping how light rays travel through the eye and by providing maps using color gradients to represent magnitudes of the refractive errors, which enables ophthalmic phycisian to locate and possibly correct even obscure imperfections that cause vision defects.

Pictured Left: Huvitz HRK-8000A WaveFront Aberrometer

High and low order optical aberrations

Conventional subjective eye exams measure low order (2nd order) optical aberration?sphere, cylinder and axis and, in the case of a presbyope, the addition power. Through advancements in LASIK surgery, wavefront aberrometry was developed to optimize the visual outcome. Huvitz Wavefront Aberrometry is an advanced 21st century optical measuring technology that measures high order aberrations within the human eye, called Zernike coefficients. Only one of these levels?2nd order aberrations?are measured in conventional subjective refractions today. An aberrometer is capable of taking advanced, objective and complex optical measurements of the human eye in seconds, compared to the typical 15 minute subjective eye exam.

Optical aberrations are defined as anything that causes light to bend and can change significantly as the pupil dilates under low light conditions, such as at night. This is why many people are happy with their vision during daylight hours and then are uncomfortable and complain about their vision at night. The important optical aberrations that affect vision are:

The figure to the right shows Zernike radial orders n=0 through n= 5. Each radial point is called a Zernike polynomial. Every eye, just like your fingerprint has a unique set of Zernike polynomials known as the “optical fingerprint” of the eye. Only 2nd order polynomials are currently measured in an eye exam.

2nd Order optical aberrations ? currently measured in all eye exams providing sphere, cylinder and axis corrections

3rd and 4th Order optical aberrations ? high order aberrations currently not measured in today’s eye exams but can account for up to 20% of the eye’s refractive error.

5th and 6th Order optical aberrations ?also high order aberrations not currently measured in today’s eye exam. These aberrations are of less significance clinically, however they manifest in reduced vision for a small percentage of eyes.

Uncorrected high order aberrations (HOA’s) can lead to poor nighttime vision, a reduction in depth of focus for reading, glare around lights at night and reduced color perception. All of these HOA’s manifest in varying degrees for each individual patient. Pupil size is a significant contributor to the manifestation of high order aberrations. As the pupil increases in size, more peripheral light enters the eye. As a result, a blur circle is created instead of a point focus on the retina. As the blur circle increases in size and shape, visual clarity is diminished. This is why even some patients with 20/20 vision can complain of visual discomfort.

The WaveForm printout show potential improvement to visual acuity with the higher order aberrations corrected.

Wavefront aberrometery has been commercially available for over 10 years. Its primary use, when originally introduced into the optical industry, was to provide optical measurements that could aid the refractive surgeon improve the vision outcome for LASIK. The aberrometer shines a perfectly shaped wave of light into the eye and captures reflections distorted based on the eye’s surface contours. Thus, it generates a map of the optical system of the eye, which can be used to prescribe a solution, correcting the patient’s specific vision problem.

The figure left demonstrates the manifestation of uncorrected high order aberrations on patients with 20/20 vision.

This technology has greatly improved optometrists and ophthalmologists’ ability to develop more precise and specific prescriptions. By using the Huvitz Wavefront Aberrometer, it is possible for many patients achieve a much higher standard of vision.

Veatch Ophthalmic Instruments has partnered with Waveform to bring the best possible technology to advance the subjective eye exam. WaveForm specializes in non-surgical vision optimization an advanced objective eye exam process and utilizing WaveForm custom designed spectacle lenses and highly customized contact lens technology. Founded in 2004 as an intellectual property management company to license and develop non-surgical vision optimization applications, WaveForm is now an industry leader in developing refractive (wavefront) technology to optimize vision through improved spectacle and contact lens technology. WaveForm's extensive experience has led to a strong relationship with Veatch Ophthalmic Instruments, enabling us to serve eye care providers state-of-the-art optical solutions that greatly enhance patient care.

WaveForm has also developed a patented fitting process enabling eyecare providers to uniquely provide and exactly position highly accurate wavefront-guided contact lenses on eyes by aligning the contact lens optics to each individuals visual axis. The result is improved and consistent visual acuity under all lighting conditions.

Optimized WaveFront Refraction (OWR)

Optimized Wavefront Refraction (OWR) is based on WaveForm's proprietary software, incorporating a set of Zernike coefficients that convert the low-and high-order data set into an optimized low-order prescription. This is achieved through a very simple turn-key process where the eye doctor or technician uses an aberrometer to measure the Zernike data set. This data set is seamlessly transmitted to WaveForm's website. Within seconds the website sends the Zernike dataset to WaveForm's secure server; then the code is processed into the OWR prescription and immediately returned via the website back to the eye doctor's computer. While the patient is still in the chair, the eye doctor has an opportunity to evaluate the OWR prescription and refine it if necessary.

There are instances where a refinement of the sphere power is necessary, as in the case of young eyes when accommodation needs to be eliminated, so as not to over-minus the patient or, for example when the patient has other medical related conditions such as cataracts. Based on USA clinical research, WaveForm's OWR system provides an accurate end point prescription in 90% of all eyes tested.

Once the eye doctor assesses the OWR, the frame information and eyeglass lens material is recorded into the waveformlenses.com order entry screen. With the press of a button the order is sent to WaveForm's free-form eyeglass lens manufacturing lab. All of this may happen within about 5 minutes from start to finish. This leaves the eye care practitioner more time to provide medical diagnosis and treatment, see more patients, and increase practice profitability. The average USA optometrist currently sees two patients per hour with conventional eye exams—under the OWR process an optometrist could see as many as 6 patients per hour.

Contact Lens Case Study

This High Astigmatism Case Study is of a patient that had been searching for a contact lens solution for 30 years without success. The WaveForm medical lens solution provided the desired results.

• 5 diopters of against the rule astigmatism
• Patient had been searching for a solution for 30 years
• Patients was informed he would never be able to wear soft toric lenses
• Resultant BVA = 20/15 OU

Read the full study here: High Astigmatism Case Study

100 Eye Comparative Study

A 100 Eye Comparative Study was completed by WaveForm designed to compare the patients' visual acuity obtained from a standard subjective refraction wth the visual acuity obtained with the OWR objective refraction. The objective refraction was completed by taking a wavefront acquisition using he Huvitz HRK-7000AW aberrometer and calculating the best sphero-cylindrical refraction using WaveForm's OWR (Optimized Wavefront refraction) software algorithm.

The results revealed:

• 61.2% of the patients tested achieved visual acuity using the OWR process that was equal to the subjective refraction
• 25.5% of the patients tested achieved visual acuity that was better than the subjective refraction.

The benefits of the OWR process are many, but speeding up the exam process is a major one. With the OWR you will have more time to use as desired. See more patients and increase revenues or reduce your work load. The choice is yours to make.

Read the full study here: 100 Eye Comparative Study.

WaveForm offers two state-of-the-art technologies that help greatly improve refraction experience and Rx results:

Optimized WaveFront Refraction (OWR) for eyeglass lenses

• Single Vision
• Bifocal Progressive

WaveFront-Guided Contact Lenses (WFGCL)
(Expected to be commercially available early 2012)

WaveForm’s wavefront-guided contact lens technology, the individual optical fingerprint is generated on the surface of the soft contact lenses and placed directly on the eye’s surface, thereby fully correcting this unique optical fingerprint.

Reproduces complex optical surfaces on our soft contact lenses Generates free-form eyeglass lens prescriptions to exacting standards With the Optimized Wavefront Refraction (OWR) system, eye care professionals and their patients enjoy a frustration-free eye exam process—while saving time and cost, satisfying patients and boosting profit.

What is a WaveFront?

A wavefront is a physical representation of the optical quality of a light beam's optical quality. The quality of a light beam can be degraded by any imperfect optical element, a lens, a piece of glass, and in the eye, a cornea for example. When the light beam is "perfect" in terms of optical quality, the wavefront is plane (flat). When light is degraded by an optical element, the corresponding wavefront is not plane anymore, but has a disrupted shape. A representation of this shape, by way of its variations and amplitude, gives a precise knowledge of the amount of perturbation that was introduced by the optical elements.

Some ophthalmic physicians have described a wavefront in recent years as a measure of the total refractive errors of the eye, including myopia, hypermetropia, astigmatism, and other refractive errors that cannot be corrected with glasses or contacts.

How is the WaveFront measured?

The Huvitz HRK-7000AW is an aberrometer used to measure the WaveFront. An aberrometer uses the wavefront to objectively measure the overall refractive power error of the eye. This is done by mapping how light rays travel through the eye and by providing maps using color gradients to represent magnitudes of the refractive errors, which enables ophthalmologists to locate and possibly correct even obscure imperfections that cause vision defects.

The Huvitz HRK-7000AW measures aberrations, and an aberration is a vision defect that occurs when light rays are improperly bent (refracted) in the eye. An aberration may occur because of a flaw in the structure of the eye. There are lower order aberrations, sphere and cylinder, and there are higher order aberrations such as coma, trefoil and spherical aberration. Patients who complain of glare, halos, starbursts and poor night driving often have increased higher-order aberrations.

What is Hartmann-Shack? How does wavefront aberrometry differ from other wavefront measurement techniques?

Hartmann-Shack is the wavefront measuring technology utilized in the Huvitz WaveFron Aberrometer. A Hartmann-Shack-based system measures a wavefront in one shot, which makes it quicker compared to other technologies that use consecutive measurements. This gives it a high repeatability, because the longer the measurement takes, the more negative effect eye movements will have on the repeatability. Hartmann-Shack can have a very high resolution, which is directly related to the number of measuring points.

Ray tracing is the main alternative technique. This is a fine method to measure wavefront but it needs more time to measure since it is not a one-shot but a consecutive measurement. It has also fewer measuring points, thus reducing the precision. But most damaging is the fact that ray tracing incurs the aberrations twice because it passes light through the eye to create a wavefront and then retrieves it from the retina to measure it. This fundamentally hampers both the repeatability and precision. The Marco OPD is an example of an aberrometer that utilizes this technology.

Is this Adaptive Optics?

No the Huvitz HRK-7000AW uses the first two elements of Adaptive Optics, but not the third.

Adaptive Optics consists of 3 elements:

• Wavefront sensor
• Algorithms
• Deformable mirror

How do aberrometers differ from auto-refractometers? How do aberrometers differ from corneal topographers?

Aberrometers differ from auto refractometers because they measure more optical parameters than auto-refractometers do.

Auto refractometers measure the average optical quality of the eye. Aberrometers measure this same average quality and also detailed local differences in optical quality. This is important because the optical quality in an eye is not homogeneous.

Auto refractometers measure sphere and astigmatism. Aberrometers measure sphere, astigmatism, and also what is known as irregular astigmatism. Irregular astigmatism is a group name for those optical defects that were near impossible to measure before the introduction of the aberrometer.

The optics of the eye are mostly determined by 2 elements: the cornea and the crystalline lens. Aberrometers differ from corneal topographers in that corneal topographers are only able to measure the optical quality of the eye linked to the cornea. Aberrometers measure the global optical quality of the eye, due to both cornea and crystalline lens.

What are higher order aberrations? Is this the same as irregular astigmatism? How do they influence the quality of my patients’ vision?

Lower order aberrations (LOAs):

• 1st Order Aberration - tilt (prism) 2nd Order Aberration - defocus (sphere) and cylinder (astigmatism)

Some of the most important higher order aberrations (HOAs):

• 3rd Order Aberration - coma and trefoil
• 4th Order Aberration - spherical aberration and quadrefoil
• 5th Order and higher – pentafoil etc.

Approximately 90% of the eye’s optical imperfections are due to lower order aberrations with the rest being made up of higher order aberrations.

Everyone has a certain degree of higher order aberration in their visual system that may affect the way they see. People with significant higher order aberrations may not see perfectly, even with the best glasses or contact lenses possible. Two common and potentially disruptive higher order aberrations are spherical aberration and coma. Spherical aberration creates halos around points of light while coma makes points of light appear comet-like with a blurry tail-like smudge to them.

Irregular astigmatism was a term used before the aberrometer arrived to better identify unknown causes for lack of visual acuity due to the optical quality of the eye. The aberrometer has now opened our eyes to much higher detail.

Another example to show the influence of higher order aberrations is sphere. Sphere can be seen on a wavefront as a spherical shape all along the pupil of the eye, that means that the optical defect, myopia for example, is the same in all parts of the pupil of the eye. If only sphere is considered, the myopia will be the same for any pupil size of the patient. When looking at higher order aberrations, it is possible to identify wavefront shapes that vary in the pupil area. For example spherical aberration is a higher order aberration, which is characterized by a variable power over the pupil. This means that if also this higher order aberration is taken into account , the myopia of the patient will vary with his pupil size. This could explain why someone with high spherical aberration can see halos at low light conditions, when the pupil is big.

What is Zernike and how do I use it?

Fritz Zernike was a Nobel Prize winning physicist who developed a set of mathematical functions (polynomials) to very precisely describe very complex shapes like wavefronts. He introduced that a set of pre-determined known shapes, of growing complexity, can be combined to precisely describe a surface that fits as well as possible to a measured wavefront.

Zernike analysis describes the wavefront mathematically as the weighted sum of Zernike basis functions or modes. The weight which must be applied to each mode when computing the sum is called an Zernike coefficient and is usually expressed in microns.

Each mode describes a certain three-dimensional surface and corresponds with ocular aberrations. For instance, second-order Zernike polynomials represent the conventional aberrations such as defocus and astigmatism. Zernike polynomials above the second order represent the higher-order aberrations that are suspected of causing night glare and halos.

Zernike polynomials help to simplify the wavefront technology by combining all aberrations into one single map. This is called a wavefront map and is usually a two-dimensional map using colour gradients representing powers of the aberrations. These Zernike polynomials can also be displayed as a pyramid starting from 0 (no aberrations or piston) to, theoretically, as high as you want to go.

What is RMS? What is the RMS of a "normal, healthy" eye?

RMS stands for Root Mean Square, a term that is used in relation with Zernike polynomials. It is a quadratic sum of the Zernike coefficients that give the power of the aberrations for the terms that have been summed. For example higher order RMS is the total of all the higher order aberrations. You can also come across “Total RMS”, which is the overall magnitude of all the eye’s refractive errors (sphere, cylinder and HOAs)

In a Zernike polynomial, the correct way to combine the aberration coefficients is to take the root mean square of them. Aberrometers use the RMS to record and measure optical aberrations as detailed as 0.01 microns.

Thanks to this kind of accuracy, aberrometers can express lower and higher order aberrations in terms far more accurate than ever seen in clinical eye care. With the RMS system, we can reconstruct the mathematical calculations of an aberration into Zernike polynomials.

How are WaveFronts used to measure accommodation? Why is this important? 

The way to measure accommodation with an aberrometer is to make the internal fixation target start from the far point of a subject and then make the target approach over a custom defined distance and in a custom defined number of steps. At each step a wavefront measurement will be taken and by measuring the defocus, we get also a measure of the patient’s ability to accommodate.  It is then possible to analyse the evolution of all the components of the optical quality of the eye with accommodation: sphere (with a direct link to presbyopia), cylinder and also higher-order aberrations.

With a rapidly aging population in the West, presbyopia is a problem for more and more people. Having a tool that can measure this is an important step forward in eye care. Having a tool that also allows to measure any related aberrations to accommodation can provide valuable insight into a patient’s evolution of visual quality.

Is Hartmann-Shack WaveFront aberrometry a difficult technique to learn? How long will it take to get up and running?

Hartmann-Shark wavefront aberrometry is not difficult to learn because the measurements are very easy to do (comparable to that of an auto-refractometer), and because there is more and more literature available and an increasing number of practitioners with experience. Doing a measurement can be learnt in minutes and having a good working knowledge of exploiting the information is a question of practice and can take some weeks, depending on the intended application and previous experience of the user.

Why is wavefront aberrometry an essential part of modern ophthalmic practice?

Eye care has known a number of major technological innovations in recent years. Aberrometers have made it possible for the first time to measure higher order aberrations in the clinic. This breakthrough has been a runaway success with refractive surgeons from the outset, and now there is a growing realisation in the market that the type of precision and detail offered by aberrometers is increasingly needed in the general practice as well.

There is a growing number of new correcting elements based on information coming from aberrometry. Best known are Lasik and IOLs; aberrometers can help making a sharper prescription.

Contact and spectacle lens manufacturers are under tremendous pressure to offer custom correction solutions. Aberrometers have been the key enablers for this trend. It is clear that aberrometers are an essential part of the forward-looking ophthalmic practice.