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Holograms test for astigmatism

15 Aug 2007

Optometrists could soon be asking their patients to look through a hologram to help diagnose astigmatism.

A one-step holographic technique is helping researchers in Australia to test for errors in the human eye. The researchers say that holography is a simple, high speed and low cost way to diagnose astigmatism and could aid our understanding of human vision. (Optics Letters 32 1926)

"The aim of the research was to offer a simpler and faster way of finding the focusing errors of the eye," Kodikullam Avudainayagam, a researcher at the University of New South Wales, told optics.org. "This research could open the door for potential applications of holography in optometry."

Currently, optometrists measure astigmatic error by sequentially changing the lenses viewed by the subject until clearest vision is attained. Avudainayagam and his colleagues have designed a simple, one-step method using a holographic target consisting of sunburst patterns arranged at various distances.

The hologram is made from high-resolution photographic emulsion on a glass plate. The team used standard procedures to record the hologram with wavefronts emanating from a specially-designed 3D object containing several staggered sunburst patterns.

The patterns are arranged in such a way that when a 20 D lens is placed in front of these patterns, their image vergences after the lens range from -2.0 to +2.0 D in steps of 0.5 D.

"When an astigmatic subject looks through the hologram, they will see the images of various sunburst patterns located at different distances from their eye," explained Avudainayagam. "The subject will be asked to identify the sunburst patterns that appear to have all the lines uniformly blurred and two other patterns where one of the lines appears darkest/ sharpest than the other lines. From the location of these patterns in the array and from the orientation of the darkest lines seen, the astigmatism of the subject can be worked out very simply."

The hologram resembles a transparent glass in appearance, which means that the subject has a lens-free view of targets placed at different distances from the eyes. According to Avudainayagam, this method overcomes proximal accommodation - a phenomenon that occurs when a lens is placed in front of the eye. "When we use a magnifier or a microscope, we know that the object is close to us," he explained. "This knowledge makes us increase the focusing power of our eyes automatically."

The next step for Avudainayagam and his colleagues is to refine the procedure. "The method still needs to be tested on real eyes especially on young subjects with astigmatism," concluded Avudainayagam.

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