HISTORY

History of Prisms

and Hemianopia

 

Several factors have led to the evolution of the use of prisms for hemianopia.  There are more stroke and head injury survivors than ever before, and our society demands that people be more mobile.  Our ability to manufacture optical devices and prisms has become more cost effective and research is beginning to show them to be more effective for people with hemianopia.

 

Fresnel press-on prisms were introduced in the early 1970’s.  These inexpensive static cling prisms could be easily applied to eyeglass lenses for trial.  This gave eye doctors the opportunity for experimentation on the possible uses for prisms at a low cost.  This flurry of experimentation included many attempts to resolve visual field loss (VFL) issues using these temporary press-on prisms.

 

Various trials using the press-on prisms included applying the prisms to half of both lenses on the blind side, applying them across the whole face of both lenses toward the blind side,  applying them over half of one lens toward the blind side and applying them over the whole face of one lens toward the blind side, etc.    Although expectations were initially high, most results were disappointing.

 

These methods either did not result in visual field expansion or caused extreme double vision and disorientation for the user.  Prisms applied in these ways did not work in the manner intended, but actually increased the discomfort and disorientation of the user.

 

Applying the prism to half of one lens on the blind side did show limited promise and in the late 1980’s and early 1990’s  the InWave™ and the VFAS types of lenses were introduced using this principle.  In experienced hands, they could be effective, but very few professionals were successful in developing the level of expertise required to fit them. 

 

These disappointing results led to the prevailing opinion that “prisms don’t work” which exists today among most professionals dealing with VFL.  This opinion has been confirmed by research addressing these early prism configurations causing resistance to the use of all prisms by VFL professionals .

 

A new approach backed by clinical trials has led to a prism configuration that does work. This is the Peli Lens™ configuration which initially offered 20º of field expansion at a modest price and is backed by clinical trials, and a 74% patient acceptance rate.  The Peli Lens now can be constructed to offer up to 30º of field expansion.

 

 

A Brief History of Prisms and Hemianopia

A Brief History of Dr. Peli and Hemianopia

 

 

Dr. Peli, Senior Scientist at the world renowned Schepens Eye Research Institute, Boston, MA has been sought after for consultation on visual issues from patients and doctors all over the world. He witnessed the flurry of experimentation with  press-on prisms in the ‘80’s and ‘90’s and pondered how he could use them to offer his hemianopic patients some help.

 

a photo of Eli

Peli

In 1999, he conceived the novel idea of prism placement now known as the Peli Lens.  He then recruited 12 hemianopic patients from the Boston area and constructed a small trial to verify that his idea had promise.  The results were published in 2000.  Dr. Peli was so encouraged by the results that he partnered with Chadwick Optical, Inc. to attempt to manufacture a cosmetically acceptable and reasonably priced lens based on his concept.  Both Dr. Peli and Chadwick quickly ran out of funds to do this, so in 2002, Chadwick Optical applied for and received a grant from the NEI-NIH (National Eye Institute of Health) to pursue production and clinical trials.  These ended in 2005 at which time 40Δ Horizontal  Peli Lens, with 20º field expansion was introduced for sale.  The results of the clinical trials were published in 2008.

 

 

In 2006, Chadwick and Dr. Peli again partnered on an NEI-NIH grant to improve the Peli Lens design using more powerful prisms which resulted in about 30º expansion of the visual field.  Another design studied in the clinical trials is an Oblique design patented by Dr. Peli which shifts images into the mid-line plane by tilting the more powerful prisms at an Oblique angle.

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