Grinding It Out: Wavefront Spectacle Lens in Clinical Practice

Abstract

This is the first literature report of a series of Zeiss iScription^© process wave guided spectacles (glasses) compared with conventional non-wave guided glasses. We designed a prospective pilot study of our initial clinical experience. Fifty patients with wavefront and fifty non-wavefront glasses were compared for lens changes made for comfort or visual clarity after initial manufacture and fitting. Minimum follow up was 90 days. Forty-six (92%) of the wavefront glasses required no modifications after initial delivery compared to 42 (86%) of non-wavefront glasses. There was a trend for conventional glasses to be returned more often than wavefront glasses but the difference was not statistically significant.

Introduction

In its most simple form, a prescription for a lens to correct a refractive error of the human eye specifies these essential variables: “sphere”, “cylinder” and “axis”. Determining these three numbers to maximize visual acuity, comfort and satisfaction to the person wearing and paying for their glasses has been a challenge for many generations of ophthalmologists, optometrists and opticians. Conventional glasses often fail to correct higher order and off-visual axis optical aberrations. This creates sub-optimal visual acuity and reduced contrast sensitivity across varying pupil sizes and ambient light situations.

i.Scription^© by Zeiss Optical¹ is among a new generation^{2, 3} of customized, wavefront guided refractive lens systems currently being introduced in the United States. Wavefront glasses combine state of the art technology to individually determine and precision grind lenses that correct lower and higher order optical aberrations thus providing each eye with its best possible vision under all viewing situations.

This pilot study examines our clinical experience with the i.Scription wavefront glasses and is a first literature report.

Methods

Discover Vision Centers (DVC) is a large, multi-location ophthalmologist owned eyecare practice located in the Greater Metropolitan Kansas City area. Practitioners include ophthalmologists, optometrists and opticians. A wide variety of clinical eye related studies First Literature Report are on-going at the DVC practice. In July 2010, the Northland office of DVC was one of eight centers in North America to first receive the Zeiss i.Scription^© wavefront refraction-lens fabrication system.

We prospectively compared i.Scription^© technology with advanced—but not wavefront guided spectacle prescription generating and lens manufacturing techniques. We used a consecutive series of the first 50 i.Scription^© multi-focal glasses purchased and worn by DVC patients. A minimum follow up of 90 days was required. The control group came from the same time interval and optical shop beginning July 2010 when i.Scription^© became available at DVC-Northland. Only progressive multifocal presbyopia correcting lens were studied, i.e. we did not include single vision lenses. The control group of progressive non-wavefront glasses was ground at Carl Zeiss Vision Kansas City and the progressive wavefront glasses at Carl Zeiss Vision Kentucky, Hebron, Kentucky.

We tabulated for i.Scription^© and the control group of progressive glasses:

1. near segment height raised or lowered;

2. no-charge lens regrinds for clarity;

3. lens that were changed from progressive multifocal to single vision lenses;

4. switch to or from i.Scription© lens; and

5. refunds on glasses.

The new lens warranty of both groups was 60 days. We assumed any dissatisfied patients wishing a no-charge change in either group of glasses would present within the first 90 days of wear. Subjective refractions were performed mostly by ophthalmic technicians and assistants but the final refraction was approved by a DVC ophthalmologist or optometrist. i.Scription^© measurements were all obtained using the Zeiss i.Profiler^plus® an instrument that combines an autorefractor, Shack-Hartman wavefront aberrometer and a Atlas 9000 corneal topographer (See Figure 1). The iProfiler^plus data was obtained by ophthalmic technicians and assistants of varying experience. Statistical analysis was performed. Waveform custom fit for each patient using the frames they intended to purchase was done by experienced DVC opticians using the proprietary Zeiss i.Terminal. (See Figure 2) There was no charge made to the patient for the i.Profiler^Plus or i.Terminal measurements.

Figure 1.

The Zeiss iProfilerPlus is a combination auto-refractor, aberrometer and corneal topographer.

Figure 2.

The Zeiss iTerminal is used to customize the wavefront lens to the spectacle frames the patient plans to purchase and the way they fit the person’s face.

Results

Fifty conventional non-wavefront progressive glasses

• Segment height raised or lowered	1 (2%)
• Prescription change	6 (12%)
• Switch to single vision lens	0
• Glasses returned for refund	0
• Change to i.Scription© lens	0
• No changes made after glasses delivery	43 (86%)

Fifty Zeiss i.Scription© wavefront progressive glasses

• Segment height raised or lowered	2 (4%)
• Prescription change	1 (2%)
• Switch to single vision lens	1 (2%)
• Glasses returned for refund	0
• Change to conventional progressives	0
• No changes made after glasses delivery	46 (92%)

The data were analyzed with 2 × 2 contingency tables and Fisher’s exact tests. The glasses return rate was not statistically significant between conventional and wavefront lenses (p = 0.5246). When reasons for return were categorized as “prescription change” or “other”, the analysis revealed a trend for conventional glasses to be returned for prescription change more frequently than Zeiss glasses (p = 0.0879).

Discussion

Crude magnifiers called “reading stones” were used by scripture copying monks about 1000 A.D.^4,5 Italian glass artisans produced paired convex lens that were initially balanced on the nose (eyeglasses) and later combined with sidebars to form spectacles sometime between 1268 and 1289. Paintings by Tomasso da Modena in 1352 first depicted monks reading and copying with eyeglasses perched on their noses.⁴ These converging lenses would help hyperopia (farsightedness) and presbyopia. Concave diverging lens to correct myopia (nearsightedness) appeared in the 16^th century and astigmatism not until 1825.⁵ Benjamin Franklin is credited with inventing the bifocal. Not to be outdone London optician John Isaac Hawkins patented trifocals in 1827.⁵ The first modern progressive or no-line bifocals (Varilux^©) appeared in 1959. In the United States about 160 million people, or just over 50%, wear glasses some or all the time.⁶ As every ophthalmologist, optometrist and optician will attest, most of these glasses wearers want perfect vision with their glasses.

Obstacles to the ‘perfect’ pair of glasses include aberrations inherent in any optical system, bio-diversity caused by the organic structure of the eye, the presence or absence of many ophthalmic and/or systemic diseases, variances in the ability of humans to cooperate in subjective refractive techniques, the skill and experience of the refractionist, the craftsmanship of lens fabrication and glasses construction including fitting them to the face and head. An intangible, but very important factor, to the person wearing them is how glasses affect their perceived physical appearance, attractiveness and age to others.

As with any optical system both the eye and any form of glasses create optical aberrations which degrade the image of objects. A discussion of the many forms of optical aberrations is beyond the scope of this paper. Basically aberrations scatter point source incoming light rays blurring their image into a non-point focus on the human retina and macula. Lower order aberrations in the eye are called refractive errors: myopia, hyperopia, astigmatism and presbyopia. Conventional contemporary glasses do an adequate job of correcting these lower order aberrations. Higher order aberrations (spherical and chromatic aberrations, trefoil, coma, etc.) have in recent years been recognized as causing as much as 20% of total optical aberration.⁷

One of the newest and most effective ways of reducing and/or eliminating lower and higher order optical aberrations is wavefront guided technology. Wavefront assumes each eye is unique and projects a single reference laser beam in the center of the macula. As this beam bounces off the macula and is scattered as it emergences from the cornea, the wavefront instrument analyzes the diffracted light pattern. Deviations from the reference beam are a measure of total optical aberration. This technology has been used with great success in lasik (laser assisted in-situ keratomileusis) surgery⁸ on the cornea and the manufacturing of intra-ocular implants.⁹

iZon^© lens (Ophthonix Inc., Vista CA) were the first commercial wavefront-guided lens. Binder and Dreher^{10, 11} reported a small series of 30 patients, ages 19 to 60 years, tested on two occasions with iZon wavefront glasses and conventional non-wavefront lens. Neither the refractionist tester nor the patient was aware of which spectacles were/were not wave guided. Comparisons were made between uncorrected visual acuity, best corrected visual acuity and low contrast visual acuity. The investigators found the iZon glasses were statistically significantly better than the control regular glasses for: best corrected Snellen visual acuity, low contrast acuity and mid-frequency contrast acuity. Comparison of the results for each testing session was not statistically different. Subsequent studies^{12, 13, 14} have reported good results with wavefront glasses.

Zeiss Optical has recently introduced the Zeiss i.Scription© system.¹ It has four components:

1. wavefront objective refraction;

2. conventional subjective refraction;

3. proprietary calculation of suggested final i.Scription© prescription; and

4. ultra-precise free lens production and fitting.

Step one begins with measurements obtained with the iProfiler^Plus (See Figure 1). This includes objective refraction, cornea topography and Shack-Hartman wavefront aberrometry. A proprietary process integrates and analyses this composite data into a wave form glasses prescription. The ophthalmologist or optometrist examines the data, current glasses prescription, and compares the subjective refraction and the iProfiler^Plus suggested glasses prescription. Modifications can be made but in most cases the iProfiler^Plus calculation was not modified. The patient is also given their subjective refraction, possibly modified by their DVC ophthalmologist or optometrist, to use for purchase of conventionally ground glasses. This latter prescription can be filled at a DVC optical shop or elsewhere as the patient chooses. At the time of writing, in the Greater Kansas City area i.Scription© glasses can only be obtained at a DVC optical shop. The technology will be available in other non-DVC locations in the near future. Wavefront glasses are more expensive than regular glasses.

The highly individualized wavefront lens fabrication is further customized by the Zeiss i.Terminal^© dispensary system.¹⁵ (See Figure 2) The patient wears the glasses frame they plan to purchase. Measurements include: monocular inter-pupillary distance, fitting heights, pantoscopic angle, vertex distance and frame wrap. The wavefront information must be sent to a Zeiss wavefront lens manufacturing facility for fabrication. This can be done electronically or by a complex paper i.Scription© formula.

Forty-six (92%) of the wavefront glasses required no modifications after initial delivery compared to 43 (86%) of non-wavefront glasses. Our pilot study suffers from underpowering due to the relatively small number of individuals followed. There was a trend for conventional glasses to be returned more often than wavefront glasses but the difference was not significantly statistically different. However, if this observed trend persisted over a larger group of 250 individuals in each study group the difference between wavefront and non-wavefront glasses would rise to statistical significance (P=0.05 or <).

The authors have found wavefront glasses especially effective for a variety of common clinical situations: initial adjustment to progressive glasses or a history of single vision or progressive glasses adjustment failure, history of multiple lens re-grinds, individuals with professions or personalities requiring maximum corrected visual acuity, pseudophakic (IOL) patients bothered by dysphotopsia or glare, night vision problems, dissatisfied lasik patients and for prolonged near work for monovision patients.

Spectacles have been evolving for over a 1000 years; wavefront glasses are the current state of the art in 2011. We anticipate that the number of people wearing wavefront glasses will continue to steadily increase.

Biography

John C. Hagan, III, MD, FACS, FAAO, MSMA member since 1977, Melissa M. Cable, MD, MSMA member since 1999, and John F. Doane, MD, MSMA member since 1997, practice ophthalmology at Discover Vision Centers in Kansas City.

Contact: jhagan@bizkc.rr.com