Compensating for Polarization Changes Introduced by Components with Retardation in Polarization Sensitive Retinal Scanning Systems

Unmet Need
The most sensitive part of the human retina, the fovea, changes the polarization state of light when scanned with a low-power polarized beam of light. This produces a particular pattern which can be used for eye tracking or monitoring central fixation. The latter is useful in diagnosing strabismus (cross-sightedness) and amblyopia (“lazy eye”), as is done by several existing vision screening devices. Unfortunately, some optical components of these instruments interfere with the polarization measurements by introducing unwanted retardance which alters the polarization state of the light entering the eye and of the light reaching the detection system after reflection from the ocular fundus. Similarly, the cornea also affects polarization, further reducing precision and reliability.

Technology Overview
Researchers at Johns Hopkins have developed a suite of tools to perform retinal birefringence scans while automatically compensating for unwanted retardance within the instrument and in the cornea. The invention relates to compensating for polarization changes introduced by components with retardation in polarization-sensitive retinal scanning systems. Compensating retarders are provided to nullify the effect of unwanted retardance in the forward and return light paths, so that the polarization states of the light entering the eye and the light reaching the detection system are not contaminated by the effects of the unwanted retardance. Mueller matrices are also used to mathematically calculate the parameters for the compensating retarders. A variable retarder system has also been described, to compensate for the corneal birefringence of the patient’s eye via feedback control. This process is capable of automatically removing false positive decisions. This could save both time and money, while limiting room for human error.

Stage of Development
Functional prototype, late stage testing

Publications
B. Gramatikov. “A method of calculating compensators in polarization-sensitive optical systems.” Optik. Vol. 201 (Jan. 2020).
 

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