Speckle board

The newly developed method only requires the detection of movement directions of light patterns (speckles) for the determination of refractive error of the human eye. The subjective evaluation of the effect of the corrective lenses by the patient can thus be reduced to a simple question (e.g. right/left). Hereby it combines basically an objective measuring method (since no interpretable visual signs are observed) with a subjective method (since feedback from the patient is required).

Challenge

Determining the visual defect of the human eye when fitting eyeglasses or preparing for surgical procedures is a time-consuming process for many patients. The aim of this process, called refraction, is to determine the refractive value of the eye at which the image is sharply focused on the retina when looking at the distance. The corresponding correction is made up of the three values of a sphere, a cylinder and a preferred direction of the cylinder (axial position), which are also frequently listed in eyeglass prescriptions as sphere and astigmatism. Especially in patients with complex visual defects and resulting low visual acuity ("low-vision patients"), there are sometimes significant discrepancies between the results of automated measuring devices (autorefractors) and manually performed examinations by qualified persons. In general, low-vision patients find it difficult and time consuming to evaluate small changes in the amount of vision correction.

Our solution

The optimized method presented here for testing the visual defect in patients is based on the use of dispersive effects of the eye and the movement of patterns, but does not require the detection of sharp images. Here, the best possible correction is determined solely by deciding on a motion direction or the change of it. This makes refraction processes much more efficient and speeds up the decision-making process for patients, thereby also avoiding fatigue effects. By reducing the process to the assessment of a motion direction, it is also possible to carry out self-measurements as the process itself is simplified considerably and mobile systems can also be used in in fields of outpatient and inpatient care. The measurement setup contains two coherent laser sources of different wavelengths in the visible spectral range (green and red). In addition, relative motion between a rough surface and the surfaces illuminated by the lasers is necessary to generate the moving speckle pattern. The procedure represents a novelty in this respect, since only the detection of movement directions of light patterns (speckles) is required for the determination of refractive error. The subjective evaluation of the effect of the corrective lenses by the patient can thus be reduced to a simple question (e.g. right/left). If the speckle pattern moves in a known direction, the position of the focal point reverses the direction of motion for a nearsighted eye, while it remains the same for a farsighted eye. An ideal eye would not detect any movement of the pattern. By using two lasers with different wavelengths, the dispersion of the eye can also be taken into account.

Experimental setup with two laser diodes (532nm and 635 nm) projected on a rotary cylinder and observed in reflection through a beam splitter (left). Scheme of the beam propagation of a moving speckle pattern into the near- and farsighted eye. (right) (source: Laser Zentrum Hannover e.V.)

Advantages

• Simple setup
• Only requires the detection of movement directions of light patterns (speckles) for the determination of refractive error of the human eye
• Speeds up the decision process (better/worse) and therefore avoiding fatigue effects of the eye
• Combines objective measuring method with a subjective method of the patient
• Takes dispersion of the eye into account by using two different laser wavelengths

Applications

• Determining the visual defect of the human eye
• Eyeglasses
• Surgical procedures

Development Status

Determination of refractive errors of the human eye successfully tested

Patent Status

Laser Zentrum Hannover e.V.
DE102017123301A1 (disclosed)
EP3691515A1 (disclosed)
US2020245861A1 (disclosed)

References

Contact

Dr. Markus Muchow
Patent Manager Physics & Technology
E-Mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Tel.: +49 551 30724 159
Reference: MM-2260-LZH

Tags: Measurement and analysis technology, Laser physics and optics, Physics and Technology & Software