Eye Didn't Know!

Happy Birthday, Joaquin Rodrigo! (1901-1999)

Did you know? Famed Spanish composer Joaquin Rodrigo was born on this day in 1901. He is best known for his guitar concertos, which helped introduce the guitar into the classical repertory. 

Rodrigo was blinded at age 3 from diphtheria, according to his biography. Diphtheria, while exceeding rare today, was common before the diphtheria vaccine was invented. Diphtheria causes a thick membrane to form over the mucous membranes, typically in the airways, which can cause death. It also can cause scarring of the conjunctiva (the membrane over the white part of the eye) and ulceration of the cornea. 

Did you also know? Beginning in 1939 (until ?) Rodrigo was the head of the artistic section of ONCE, the Spanish foundation for the blind. ONCE remains today a powerful global force helping the blind integrate into society.

 

image courtesy Wikimedia Commons

Izon® Eyeglasses, by Ophthonix

Did you know? For a number of years, San Diego–based Ophthonix has produced customized eyeglasses as well as an aberrometer/autorefractor to measure the eye's wavefront characteristics and refraction. It is only recently, however, that a large-scale, well-designed, rigorous, double-masked study has been presented to show the effectiveness of these eyeglasses as well as the process by which they are made.

This paper is available on their website, here. It's not light reading, but would be of interest to an ophthalmologist, optometrist, or optician. It's small print, too, so I recommend downloading the pdf file and using your pdf viewer to enlarge the text.

The study was performed at the prestigious University of Illinois Eye and Ear Infirmary, and published in the Review of Optometry, October 2008 (not a peer-reviewed publication). 

The study consisted of two phases. The first phase tested 83 subjects with their old glasses, new glasses prescribed by a regular refraction, and glasses made by Ophthonix (wavefront-guided iZon® lenses). Subjects wore each of the new glasses for two weeks, and neither subject nor experimenter knew which lenses were being tested.

A battery of visual function tests was administered. The iZon lenses performed the best on seven of nine parameters, and the difference was statistically significant on four of them.

A second phase consisted of testing 52 subjects. Each was given four sets of lenses: lenses made with a traditional refraction made elsewhere, a traditional refraction made at the Ophthonix lab, glasses made with a refraction from the Ophthonix autorefraction, and glasses made with the Ophthonix autorefraction with wavefront-guidance and their proprietary 3-layer lenses.

The results of the second phase can be summarized by "there is an ordered progression of visual benefits derived from the components of the lenses... the best overall visual performance was gained by coupling Z-view® refraction with a 3-layer lens iZon® lens design."

It is notable that many of the visual tests in which the iZon® lenses excelled were ones which have real-world consequences, such as low-contrast situations (like driving at night), glare situations (like driving into headlights or playing golf on a sunny day), and tests called the Environmental Visual Acuity Test, which measured how much farther away subjects could read signs they encountered (the iZon® lenses provided a 20% improvement compared to a conventional lens), and the Low-Luminance Acuity Test (viewing dark letters against a dark background-- like driving on a dark road at night--the iZon® lenses provided a 20% improvement vs. all other lenses.)

The study is also notable for it provides the first somewhat clear description of just what occurs in the production of iZon® lenses. Rather than correcting for wavefront aberrations, (which custom-Lasik surgery attempts), the iZon® lenses are said to optimize vision in this way:

iZon®Lens Structure (3-Layer) 

The wavefront-guided iZon®Lens is a unique design, with a three 

layer structure. The mid-layer iZonikTMmaterial is a photo-polymer that 

is sandwiched between separate back and front lenses. All three lay- 

ers are 1.6 index material. The correction for the iZon®Lens is derived 

from all 2nd to 6th order aberrations of the eye as measured by the 

Z-View®Aberrometer. The aberrations are analyzed and manipulated 

by a proprietary algorithm—the second of two used in the iZon®Lens 

process—to determine the best sphere-cylindrical fit for the back 

surface. The iZon®Lens is wavefront-guided, as opposed to wave- 

front-corrected. Wavefront-guided refers to the use of wavefront tech- 

nology to incorporate all 2nd to 6th order aberrations in determining the 

best sphere-cylindrical fit, as opposed to wavefront-corrected that 

implies correcting individual aberrations. By utilizing a wavefront- 

guided approach,  the iZon®Lens is optimized and unaffected by gaze 

angle shifts that could result with the programming required in a 

wavefront-corrected design. 

The key point of this paragraph is that "the aberrations are analyzed and manipulated by a proprietary algorithm to determine the best sphere-cylindrical fit for the back surface."  

It's not clear to me if the front surface of the lens or the thin iZonik (tm) layer sandwiched between have refractive properties, but this does indicate that the higher-order aberrations are not being precisely corrected for, but rather are being used to give a better sphere/cylinder correction. 

It apparently works (for those 65% of the population who are candidates for the lenses) to provide crisper "high-definition" vision with gains in many visual measurements.

One finding lacking in this study was a subjective evaluation of the lenses by the subjects. Previous studies showed a very large preference for the iZon® lenses vs. conventional lenses.

As a final note, I have had a pair of iZon® glasses for over a year. My impression is that they provide exceptionally crisp vision, but I don't have a conventional pair made at the same time to compare them to.

I can say that the autorefraction obtained of my eyes by the Ophthonix Z-View® autorefractor/aberrometer is the most accurate autorefraction I have ever had. It wasn't necessary to change a thing! 

Also of note is that I have a small financial interest in the Ophthonix corporation.

Did you also know? Other companies are using other technologies to customize eyeglass lenses. One company promises "changeable-focus" lenses with no moving parts. Time will tell if this becomes a reality.