Cellview Imaging Inc.

L&r Medical Inc.

Rishard Weitz

Mark Hathaway

Channel separation in ophthalmologic systems is achieved by introducing a small angle between each beam incident on the scanner. The multiple channels are emitted from multiple emitters positioned such that their respective beams reach an X-Y scanner with small angular separations between the beams. This removes the need for dichroic components to combine the multiple channels into a single beam. This also allows the emitters to use the same wavelength if desired, such as in a combined SLO and OCT system in which it may be desirable to use the same light source in order to reduce the cost and complexity of the system.

Angular separation of scan channels

A method is provided for determining the thickness of a retina. A single beam is used to illuminate the retina of a patient. Interference between reflections off different layers within the retina cause autocorrelation in the returned signal. An FFT applied to the autocorrelation signal reveals the strongest autocorrelation, which indicates the distance between the nerve fiber layer (NFL) and the layers between the inner segment/outer segment (IS/OS) and the retinal pigment epithelium (RPE), the dominant scatterers. By analyzing autocorrelation, a single beam can be used. This avoids the problem of movement of the patient, arising in the use of a standard OCT interferometer, resulting in a simpler and less expensive technique of measuring retinal thickness.

Retinal Thickness

A method is provided for determining the thickness of a retina. A single beam is used to illuminate the retina of a patient. Interference between reflections off different layers within the retina cause autocorrelation in the returned signal. A spectrometer produces a frequency spectrum of the beam reflected by the retina, and an FFT applied to the frequency spectrum produces a spatial domain signal (SDS). Autocorrelation within the reflected beam results in edges within the spatial domain signal, and the spatial coordinate of the SDS at which the power of the SDS drops precipitously indicates the distance between the nerve fiber layer (NFL) and the layers between the inner segment/outer segment (IS/OS) and the retinal pigment epithelium (RPE), the dominant scatterers. By analyzing autocorrelation, a single beam can be used. This avoids the problem of movement of the patient, arising in the use of a standard OCT interferometer, resulting in a simpler and less expensive technique of measuring retinal thickness.

Retinal thickness

In line-scan scanning laser ophthalmoscopy (SLO) a narrowband of wavelengths is required. For greater flexibility the frequencies of this narrowband should be selectable. This is possible using a broadband tunable single mode source, but such a solution is expensive. A system is provided in which an extended broadband source is used. Light from the extended source passes to a diffraction grating, which introduces a wavelength dependent angular separation when reflecting the light. By rotating the diffraction grating, only light of a selectable narrowband passes through a fixed output slit for use by the line-scan SLO system. Alternatively, the diffraction grating can be fixed and a rotatable mirror lying between the diffraction grating and the output slit can be used to select the wavelengths reaching the line-scan SLO system.

Diffraction grating for wavelength selection in line-scan SLO

In a OCT interferometer it is necessary to balance dispersion within the reference arm with dispersion within the object arm. This is normally done by replicating within the reference arm the components found in the object arm. This adds to the complexity and cost of the OCT interferometer. A method is provided for determining the design of and designing a simplified OCT interferometer, in which the reference arm contains only a single piece of glass of a single glass type. This reduces the cost and complexity of the OCT interferometer, and reduces power loss and undesired reflections within the reference arm.

Dispersion compensation

In an OCT system, the autocorrelation signal depends only on the strength of the signal in the object arm scattered back from a patient's retina and is a result of different reflections from different layers of the retina interfering with each other. The strength of the autocorrelation signal depends on how well focused the system is. Normally the autocorrelation signal is treated as noise. However by removing the reference path signal, the autocorrelation signal is easily measured and analyzed. The optimal focus can the then be found by adjusting the focus value until the autocorrelation signal is maximized.

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Toronto, Canada

Rishard Weitz