Patent Application: US-201214114354-A

Abstract:
the present invention relates to a method for measuring ocular scattering , comprising the steps of : sequentially projecting images from an extensive light source , corresponding to different visual angles , onto the retina ; recording the output light in a camera or detector once it has passed through the eye twice ; calculating the intensity at the center of each recorded image ; calculating the psf for each angle from the previous intensities ; and calculating the average of the value of the psf between the angles . the invention also relates to a system for carrying out said method . the invention can be used to measure the intensity of the scattered light in an objective manner .

Description:
fig2 a shows the psf of an eye with intraocular scattering . fig2 b shows the image of a uniformly illuminated disc , such as a particular case of a ring with inner radius 0 , through this system . it is verified that if the ratio of energy in a circle having radius r with respect to the total energy of the psf is i c ( where 0 & lt ; i c & lt ; 1 ), therefore the fraction of the intensity at the center of a disc having radius r with respect to the intensity of an infinite disc is also equal to i c . this ratio is equal to : i c = ∫ 0 ⁢ 2 ⁢ πφ · p ⁢ ⁢ s ⁢ ⁢ f ⁡ ( φ ) ⁢ ⅆ φ ( equation ⁢ ⁢ 1 ) where psf ( φ ) is the psf of the system ( including scattering ) and θ is the radius of the circle in fig2 a , or of the disc in fig2 b . in both cases , it is assumed that the psf is normalized ( ∫ 0 π / 2 ⁢ 2 ⁢ πφ · p ⁢ ⁢ s ⁢ ⁢ f ⁡ ( φ ) ⁢ ⅆ φ = 1 ) , i . e ., the central intensity of a complete disc is equal to 1 . fig3 shows a possible implementation of the double - pass system of the invention , in which images are projected sequentially , subtending different visual angles corresponding to different eccentricities of the retina . the extensive object would be a ring having inner radius r 0 and outer radius r illuminated by a source s , or a circle like in the example , which is not more than a ring with inner radius r 0 = 0 . the light projected by this object can be collimated by the optic c to subsequently be propagated through the scatterer d and filters f . the dimension of the disc can be controlled by the aperture a . the image of this extensive object is projected onto the retina of the eye using lenses l 1 , l 2 and l 3 . the diaphragm d 1 is conjugated with the pupil of the eye ( by means of lenses l 2 and l 3 ) to enable thus controlling the portion of the pupil through which the object is projected towards the fundus of the eye . the image of the circle projected onto the retina can then be recorded using a beam splitter ( bs ) and lenses l 4 , l 5 and l 6 . the diaphragm d 2 is conjugated with the pupil plane ( by means of lenses l 4 and l 5 ) to enable thus controlling the portion of the pupil area through which the output light of the eye is recorded . diaphragms d 1 and d 2 can be arranged such that the projection of the object and the recording are done in different zones of the pupil area , such that light reflected on ocular surfaces is prevented from contributing to the intensity of the image recorded on the camera or the detector . estimating scattered light is thus not affected by the contribution of back - scatter , “ backwardly ” scattered light , in the inlet path of the light in the eye , which enables restricting the analysis to forward - scatter , or “ forwardly ” scattered light , which is the scattered light component directly related to visual quality loss ( de waard , et al . 1992 ). fig4 shows how the illumination and the recording can be done through different portions of the pupil of the eye . the diaphragms do not necessarily have to be circular : the same effect can be achieved with other shapes , such as a ring - shaped mask at the inlet and a central circular shape at the outlet , provided that the diaphragms are different and do not overlap when projected onto the pupil . fig5 shows two different methods for separating the pupil area into two different portions for the illumination and the recording of the object projected onto the retina . fig5 a shows two semicircular apertures , whereas fig5 b shows a circular sub - aperture and a concentric ring . in reference to the embodiment of fig3 , the extensive object can be generated by a liquid crystal modulator illuminated by a halogen lamp having a broad spectral range , and where the light generated by the source is collimated and homogenized by means of the collimator c and the scatterers d . the spectral filter f allows selecting the spectral profile of the light that will strike the eye . the selected wavelength is preferably 400 nm to 700 nm , with a bandwidth of 5 to 50 nm . the use of a source having a broad spectral range , combined with the use of filters or other elements capable of selecting a specific section of the spectral range , allows estimating intraocular scattering with different wavelengths of the incident light ( from red to blue ). this characteristic is especially relevant for diagnosing potential pathologies responsible for a specific level of intraocular scattering because analysis of the relationship between the scattered light profile and the incident wavelength allows establishing hypotheses as to the type of scattering centers responsible for intraocular scattering in each case ( coppens , et al . 2005 ). the dimensions of the disc are controlled by means of a computerized spatial modulator . an image of the object is projected onto the retina of the eye through lenses l 1 , l 2 and l 3 . the diaphragm d 1 is conjugated with the pupil of the eye ( by means of lenses l 2 and l 3 ) to enable thus controlling the portion of the pupil through which the object is projected towards the fundus of the eye . the image of the disc projected onto the retina can then be recorded using a beam splitter ( bs ) and lenses l 4 , l 5 and l 6 . the diaphragm d 2 is conjugated with the pupil plane ( by means of lenses l 4 and l 5 ) to enable thus controlling the portion of the pupil area through which the output light of the eye is recorded . the diaphragms d 1 and d 2 can be arranged such that the projection of the object and the recording are done in different zones of the pupil area , such that light reflected on ocular surfaces is prevented from contributing to the intensity of the image recorded on the camera or the detector . a series of discs corresponding to visual angles ranging from 0 . 01 to 10 degrees are projected onto the retina sequentially . the intensity at the center of each disc is recorded . the derivative of this intensity with respect to the radius of the disc is numerically estimated by the finite difference method . the derivative divided by 2π times the angle of each disc is equal to the psf of the double - pass at the corresponding angle . this can be explained by taking the derivative of equation 1 ( where the psf is the autocorrelation of the psf of the system , characteristic of the double - pass ), resulting in equation 2 : p ⁢ ⁢ s ⁢ ⁢ f ⁡ ( n ) = 1 2 ⁢ π ⁢ n ⁢ i c ⁢ ( i + 1 ) - i c ⁡ ( i ) i + 1 - i ( equation ⁢ ⁢ 3 ) where i is the radius of consecutive discs and n =( i + 1 + i )/ 2 . the average of the value of the psf between angles from 0 . 5 to around 10 ° is a magnitude that characterizes intraocular scattering ( cie 135 - 1999 ). if necessary , the psf corresponding to the single - pass through the ocular media can be numerically calculated from that corresponding to the double - pass and using fourier treatment - based deconvolution techniques . in another embodiment , the extensive object is a translucent film backlit by leds as shown in fig6 . the intensity of the light can be homogenized by scatterers d and suitable spacing between diodes . the dimension of the generated disc can be controlled by means of the number of diodes concentrically illuminated . an image of the object is projected onto the retina of the eye through lenses l 1 , l 2 and l 3 . the diaphragm d 1 is conjugated with the pupil of the eye ( by means of lenses l 2 and l 3 ) to enable thus controlling the portion of the pupil through which the object is projected towards the fundus of the eye . the image of the disc projected onto the retina can be recorded by means such as a ccd camera or a photodetector using a beam splitter ( bs ) and lenses l 4 , l 5 and l 6 . the diaphragm d 2 is conjugated with the pupil plane ( by means of lenses l 4 and l 5 ) to enable thus controlling the portion of the pupil area through which the output light of the eye is recorded . the diaphragms d 1 and d 2 can be arranged such that the projection of the object and the recording are done in different zones of the pupil area , such that light reflected on ocular surfaces is prevented from contributing to the intensity of the image recorded on the camera or the detector . by illuminating different concentric distributions of leds in a controlled manner , a series of discs corresponding to visual angles preferably ranging from 0 . 01 to 10 degrees are projected onto the retina . the intensity at the center of the recorded image of each disc is recorded in the camera or the detector . each concentric disc of leds is modulated at a specific frequency to be able to discriminate its effect in the subsequent analysis of frequencies . the isolated contribution of each ring on the central area recorded is extracted by means of the spectral analysis of the recorded signal . the device of the invention preferably has means for assuring correct alignment of the eye with respect to the optics of the system and means for synchronizing the source and the detector or camera to prevent unnecessary exposures of the retina . p . m . prieto , f . vargas - 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